Bruce M. Bell, Senior Scientist

The University of the Stete of New York ALBANY , N.Y. 12224 The Stete Educetion Depertm,nt e.. FEBRUARY 1916

New York State Museum & Science Service

A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA

A Study of North American Edrioasteroidea

by Bruce M. Bell

Memoir 21 New York State Museum and Science Service

The University of the State of New York The State Education Department Albany, New York 12234, 1974 THE UNIVERSITY OF THE STATE OF NEW YORK

Regents of The University (with years when terms expire) 1981 THEODORE M. BLACK, A.B., Litt.D., LL.D., Pd.D., D.C.L. Chancellor Sands Point

1987 CARL H. PFORZHEIMER, JR., A.B., M.B.A., D.C.S., H.H.D. Vice Chancellor Purchase

1978 ALEXANDER J. ALLAN, JR., LL.D., LitLD. Troy 1980 JOSEPH T. KING, LL.B. Shelter Island 1981 JOSEPH C. INDELICATO, M.D. Brooklyn 1979 FRANCIS W. MCGINLEY, B.S., J.D., LL.D. Glens Falls

1986 KENNETH B. CLARK, A.B., M.S., Ph.D., LL.D., L.H.D., D.Sc. ____ Hastings on Hudson 1983 HAROLD E. NEWCOMB, B.A. Owego

1988 WILLARD A. GENRICH, LL.B., L.H.D., LL.D. _ Buffalo 1982 EMLYN I. GRIFFITH, A.B., J.D. _ Rome 1977 GENEVIEVE S. KLEIN, B.S., M.A. _ Bayside 1981 WILLIAM JOVANOVICH, A.B., LL.D., LitLD., L.H.D. Briarcliff Manor 1976 MARY ALICE KENDALL, B.S. Irondequoit 1984 JORGE L. BATISTA, B.A., J.D. Bronx 1982 LOUIS E. YAVNER, LL.B. New York

President of The University and Commissioner of Education EWALD B. NYQUIST

Executive Deputy Commillioner of Education GORDON M. AMBACH

Associate Commissioner for Cultural Education JOHN G. BROUGHTON

Assistant Commissioner for State Museum and Science Service NOEL C. FRITZINGER

Director, State Science Service HUGO JAMNBACK

State Geologist JAMES F. DAVIS

State Paleontologist DONALD W. FISHER Contents

Abstract...... 1 Acknowledgments...... 2 Abbreviations ...... 2 Introduction 3 Previous Investigation...... 4 Morphology ...... 9 Terminology as Applied to Edrioasteroidea ...... 9 Orientation 13 Morphology of the Isorophida ...... 13 Thecal shape 13 Oral area...... 14 Oral covering plates ...... 14 Oral frame and central lumen 17 Hydropore structure ...... 18 Stone canal passageway ...... 19 Ambulacra 20 Coverplates ...... 20 Coverplate passageways ...... 21 Floorplates 22 Interambulacra ...... 22 Anal structure...... 22 Peripheral rim 23 Morphology of the Edrioasterida 24 Thecal shape 24 Oral area...... 24 Oral covering plates ...... 24 Oral frame and central lumen 24 Hydropore structure ...... 26 Stone canal passageway ., ...... 26 Ambulacra 26 Coverplates ...... 27 Floorplates 27 Floorplate passageways 27 Interambulacra ...... 28 Anal structure...... 28 Margin of the oral surface 28 Preservation ...... 29 Attachment 30 Symmetry and Phylogenetic Implications...... Symmetry and Phylogenetic Implications (continued) Organ Systems 36 Digestive tract 36 Hydrovascular system...... 36 Respiration...... 38 Ontogeny...... 39 Diagnostic Summary of Edrioasteroid Taxa Included 41 Systematic Paleontology 49 Class Edrioasteroidea Billings, 1858 ...... 49 Order Isorophida Bell, ord. nov. 50 Suborder Lebetodiscina Bell, subord. nov. 51 Family Lebetodiscidae Bell, jam. nov. 53 Genus Lebetodiscus Bather, 1908 54 L. dicksoni (Billings), 1857 55 Genus Foerstediscus Bassler, 1935 ...... 65 F. grandis Bassler, 1935 ...... 66 F. splendens Bassler, 1936 71 F. solitarius Bell, sp . nov. 74 Genus Belochthus Bell, gen. nov...... 77 B. orthokolus Bell, sp. nov. 77 Genus Streptaster Hall, 1872 82 S. vorticellatus (Hall), 1866 ...... 83 Genus Cystaster Hall, 1871 ...... 91 C. granulatus Hall, 1871 ...... 94 C. stellatus (Hall), 1866...... 100 Family Cameyellidae Bell,fam. nov. 108 Genus Carneyella Foerste, 1917 ...... 110 C. pilea (Hall), 1866 112 C. faberi (Miller), 1894 ...... 124 C. ulrichi Bassler and Shideler, 1936 ...... 127 C. valcourensis Clark, 1920 ...... 129 Genus Cryptogoleus Bell, gen. nov. 129 C. chapmani (Raymond), 1915 131 C. reticulatus Bell, sp. nov...... 138 C. multibrachiatus (Raymond), 1915 ...... 140 C. youngi (Raymond), 1915...... 143 C. platys (Raymond), 1915 144 C. billingsi (Chapman),1860 146 Suborder Isorophina Bell, subord. nov...... 146 Family IsorophidaeBell,fam. nov 147 Genus Isorophus Foerste, 1917 ...... 148 I. cincinnatiensis (Roemer), 1851 152 I. austini (Foerste), 1914...... 167 I. warrenensis (James), 1883 171 Systematic Paleontology (continued) Class Edrioasteroidea Billings, 1858 (continued) Order Isorophida Bell, ord. nov. (continued) Suborder Isorophina Bell, subord. nov. (continued) Family Isorophidae Bell,fam. nov. (continued) Genus Isorophusella Bassler, 1935 ...... 174 I. incondita (Raymond), 1915 176 I. trentonensis (Bassler), 1936 190 I. pleiadae (Sinclair and Bolton), 1965 ...... 191 Genus Hemicystites Hall, 1852 ...... 194 H. parasiticus Hall, 1852...... 196 Genus Rectitriordo Bell, gen. nov. 200 R. kirkfieldensis Bell, sp. nov. 200 Genus Curvitriordo Bell, gen. nov. 204 C. kentuckyensis (Bassler), 1936 204 C. shideleri (Bassler), 1936 ...... 206 Family Agelacrinitidae Chapman, 1860 208 Genus Agelacrinites Vanuxern, 1842...... 210 A. hamiltonensis Vanuxem, 1842 212 Genus Krama Bell, gen. nov. 219 K. devonicum (Bassler), 1936 219 Genus Postibulla Bell, gen. nov. 232 P. legrandensis (Miller and Gurley), 1894 234 P. keslingi Bell, sp. nov. 237 P. jasperensis (Harker), 1953 ...... 241 P. alpenensis (Bassler), 1936 ...... 243 Genus Discocystis Gregory, 1897 243 D. kaskaskiensis (Hall), 1858...... 244 Genus Lepidodiscus Meek and Worthen, 1868 ...... 251 L. squamosus Meek and Worthen, 1868 ...... 253 L. laudoni (Bassler), 1936 ...... 257 L. sampsoni (Miller), 1891 ...... 267 Genus Ulrichidiscus Bassler, 1935 271 U. pulaskiensis (Miller and Gurley), 1894...... 271 Genus Cooperidiscus Bassler, 1935 ...... 277 C. alleganius (Clarke), 1901 277 Genus and species indeterminate 280 Family Uncertain 281 Genus Hadrochthus Bell, gen. nov. 281 H. commensalus Bell, sp. nov...... 281 Suborder and Family Uncertain...... 284 (?) Hemicystues carbonarius Bassler, ...... 284 Systematic Paleontology (continued) Class Edrioasteroidea Billings, 1858 (continued) Order Edrioasterida Bell, ord. nov...... 287 Family Edrioasteridae Bather, 1898 290 Genus Edrioaster Billings, 1858 ...... 290 E. bigsbyi (Billings), 1857...... 292 E. priscus (Miller and Gurley), 1894 ...... 302 Genus Edriophus Bell, gen. nov. 303 E. levis (Bather), 1914 ...... 304 E. saratogensis (Huedemann), 1912 310 Bibliography...... 315 Plates...... 321

Text Figures 1. Isorophida . 15-16 2. Edrioasterida . 25 3. Lebetodiscus dicksoni (Billings), 1857 . 57 4. Lebetodiscus dicksoni (Billings), 1857 . 59 5. Foerstediscus grandis Bassler, 1935 . 69 6. Foerstediscus splendens Bassler, 1936 . 72 7. Foerstediscus solitarius Bell, sp. nov. . . 75 8. Belochthus orthokolus Bell, sp. nov. . . 78 9. Streptaster vorticellatus (Hall), 1866 . 84 10. Cystaster granulatus Hall, 1871 . 96 11. Cystaster stellatus (Hall), 1866 . 101 12. Cystaster stellatus (Hall), 1866 . 103 13. Carneyella pilea (Halt), 1866 . 115 14. Carneyella pilea (Hall), 1866 . 119 15. Carneyella faberi (Miller), 1894 . 125 16. Carneyella ulrichi Bassler and Shideler, 1936 . 128 17. Cryptogoleus chapmani (Raymond), 1915 . 133 18. Cryptogoleus chapmani (Raymond), 1915 . 135 19. Cryptogoleus reticulatus Bell, sp. nOl!o . 139 20. Cryptogoleus multibrachiatus (Raymond), 1915 . 141 21. Cryptogoleus youngi (Raymond), 1915 . 22. Cryptogoleus platys (Raymond), 1915 . 145 23. Isorophus cincinnatiensis (Roemer), 1851 . 155 24. Isorophus cincinnatiensis (Roemer), 1851 . 156 25. Isorophus cincinnatiensis (Roemer), 1851 ...... 1.57 26. Isorophus austini (Foerste), 1914 ...... 169 27. Isorophus warrenensis (James), 1883 173 28. Isorophusella incondita (Raymond), 191.5...... 177 29. Isorophusella incondita (Raymond), 1915...... 179 30. Isorophusella incondita (Raymond), 1915, growth series...... 183 31. Isorophusella incondita (Raymond), 1915, growth series...... 187 32. Isorophusella incondita (Raymond), 1915, growth series...... 189 33. Isorophusella trentonensis (Bassler), 1936 191 34. Isorophusella pleiadae (Sinclair and Bolton), 196.5 193 35. Hemicystites parasiticus Hall, 1852 197 36. Rectitriordo kirkfieldensis Bell, sp. nov. 201 37. Rectitriordo kirkfieldensis Bell, sp. nov. 203 38. Curvitriordo kentuckyensis (Bassler), 1936 ...... 20.5 39. Curvitriordo shideleri (Bassler), 1936 ...... 207 40. Agelacrinites hamiltonensis Vanuxem, 1842...... 213 41. Agelacrinites hamiltonensis Vanuxem, 1842...... 21.5 42. Krama devonicum (Bassler), 1936 . .. 221 43. Krama devonicum (Bassler), 1936 223 44. Krama devonicum (Bassler), 1936 22.5 45. Krama devonicum (Bassler), 1936 227 46. Postibulla legrandensis (Miller and Gurley), 1894...... 23.5 47. Postibulla keslingi Bell, sp. nov. 239 48. Postibulla jasperensis (Harker), 1953 ...... 242 49. Discocystis kaskaskiensis (Hall), 1858...... 247 50. Discocystis kaskaskiensis (Hall), 1858...... 249 51. Lepidodiscus squamosus Meek and Worthen, 1868 2.5.5 52. Lepidodiscus laudoni (Bassler), 1936 ...... 2.59 53. Lepidodiscus laudoni (Bassler), 1936 ...... 261 54. Lepidodiscus laudoni (Bassler), 1936 ...... 263 55. Lepidodiscus sampsoni (Miller), 1891 ...... 268 56. Ulrichidiscus pulaskiensis (Miller and Gurley), 1894 ...... 273 57. Ulrichidiscus pulaskiensis (Miller and Gurley), 1894 , 274 58. Ulrichidiscus pulaskiensis (Miller and Gurley), 1894 ...... 275 59. Cooperidiscus alleganius (Clarke), 1901...... 279 60. Hadrochthus commensalus Bell, sp. nov. 283 61. Hemicystites carbonarius Bassler, 1936; Agelacrinites hanoveri Thomas, 1924 ...... 285 62. Edrioaster bigsbyi (Billings), 1857 ...... 293 63. Edrioaster bigsbyi (Billings), 1857 , 295 64. Edriophus levis (Bather), 1914 ., ...... 305 65. Edriophus saratogensis (Ruedemann), 1912 " 311

A Study of North American Edrioasteroidea1 by Bruce M. Bell, Senior Scientist

ABSTRACT

Sixty-five described species, formerly grouped into the the exterior of the theca. (II-A) Suborder Lebetodiscina three major, commonly recognized families of the Class Bell, subord. nov., with a single alternating biseries of Edrioasteroidea Billings (1858) have been restudied. ambulacral coverplates with a passageway system; ambu- Forty of these are recognized here (13 only with reserva- lacral floorplates imbricate; anal structure a periproct. tions), whereas the remaining 25 are here synonymized. (II-A-I) Family Lebetodiscidae Bell, jam. nov., with oral Eight new genera iBelochthus, Curvitriordo, Cryptogo- area including two pairs of lateral shared coverplates and Zeus, Edriophus, Hadrochthus, Krama, Postibulla, Recti- commonly secondary orals; hydropore structure along the triordo) and six new species (Belochthus orthokolus, proximal posterior side of ambulacrum V, near the oral Cryptogoleus reticulatus, Foerstediscus solitarius, Had- area; ambulacral coverplates massive, ambulacral tunnel rochthus commensalus, Postibulla keslingi, Rectitriordo high and narrow, coverplate passageways nearly vertical; kirkfieldensis) are described. peripheral rim plates squamose, not geniculate. (II-A-2) The 46 edrioasteroid species here described are grouped Family Carneyellidae Bell, jam. nov., with oral area in- into the following nine subdivisions of the class. (I) Order cluding one large hydropore oral and no shared cover- Edrioasterida Bell, ord. nov., with a subgloboid theca; plates or secondary orals; hydropore in the right posterior oral frame formed by 10 compound plates; hydropore part of the oral area; ambulacral coverplates of moderate penetrates two posterior plates of the oral area and is elon- thickness, ambulacral tunnel low and wide, coverplate pas- gate normal to the suture line; amhulacra formed by bi- sageways oblique; peripheral rim plates geniculate. (II-B) serial floorplates with floorplate passageways connecting Suborder Isorophina Bell, subord. nov., with four large the amhulacral tunnel to the thecal cavity, and biserial central primary orals or numerous small undifferentiated coverplates without intra-ambulacral o-r intrathecal exten- central orals; ambulacral coverplates form multiple alter- sions; the margin of the oral surface is on the lower side nating biseries or cyclic series of two to seven sets of of the theca, reflexed up toward the center of the theca, plates; coverplate passageways absent; anal structure with a distal membrane which extended down to the sub- valvular. (II-B-l) Family Isorophidae Bell, jam. nov., strate. (I-A) Family Edrioasteridae Bather (1898) with with four large primary orals, two pairs of lateral shared the characters of the order. (II) Order Isorophida Bell, coverplates, (me large hydropore oral, and secondary ord. nov., with domal, discoidal or clavate theca; oral frame formed by the five proximal amhulacral floorplates orals; hydropore structure formed by few plates, inte- and commonly by primary oral plate intrathecal exten- grated with the central oral rise; ambulacral coverplates sions; hydropore structure in or near the posterior oral form multiple alternating biseries of two or three sets of area, opening between plates along sutures; amhulacra plates. (II-B-2) Family Agelacrinitidae Chapman (1860), formed by uniserial floorplates without and with numerous oral plates, primaries commonly undiffer- by biserial or multiple series of coverplates with intra- entiated; hydropore structure commonly includes many thecal and/or intra-ambulacral extensions, with or without plates which form a large separate protuberance; ambu- coverplate passageways which connect the thecal cavity to lacral coverplates form cyclic sets of two to seven plates.

1 Manuscript submitted for publication January 26, 1973.

1 Acknowledgments

Sincere thanks are extended to the following: Kenneth York), John Monteith (Royal Ontario Museum), Norman E. Caster (University of Cincinnati), who spent an ex- D. Newell (American Museum of Natural History), orbitant amount of time and energy as principal advisor, Eugene S. Richardson (Field Museum of Natural His- research associate, and editor of the manuscript which tory), and Harrell 1. Strimple (University of Iowa), for constitutes my doctoral dissertation; William H. White, lending study specimens. Jr. (Milford, Ohio), who revealed many edrioasteroid The Department of Geology, University of Cincinnati collecting sites, aided in collecting, and donated numerous provided research facilities, financial support, and Mu- specimens for study; Elizabeth R. Dalve (Cincinnati, seum of Paleontology specimens for this study. Research Ohio) , who drafted many of the text illustrations; Thomas and manuscript preparation costs were supported in part E. Bolton (Geological Survey of Canada), John 1. Carter by grants from the Nevin M. Fenneman Fund, and the (University of Illinois), May D. Dash (Peabody Museum Walter H. Bucher Fund of the University of Cincinnati, of Natural History, Yale University), Alan S. Horowitz and by the award of the Fenneman Fellowship during my (Indiana University), Robert V. Kesling (University of terminal year of residence at the University of Cincinnati. Michigan), Porter M. Kier (Smithsonian Institution), The manuscript was prepared during my term as the cura- Bernhard H. Kummel (Museum of Comparative Zoology, tor of paleontology at the New York State Museum and Harvard University), George C. McIntosh (Buffalo, New Science Service.

ABBREVIATIONS

Specimens are listed by catalog numbers with the NYSM New York State Museum, Albany, New York repository names abbreviated as follows: ROM Royal Ontario Museum, Toronto, Ontario AMNH American Museum of Natural History, New SUIC University of Iowa, Department of Geology, York, New York Paleontology Collection, Iowa City, Iowa CFM Field Museum of Natural History, Chicago, UCMP Museum of Paleontology, Department of Illinois Geology, University of Cincinnati, Cincin- nati, Ohio CFMP Field Museum Paleontology Collection CFMPE UCLAPC University of California, Los Angeles, De' partment of Geology, Paleontology Collec- CFMUC University of Chicago Walker Museum de- tion, Los Angeles, California posited at the Field Museum UIPC University of Illinois, Department of Ceol- GSC Geological Survey of Canada, Ottawa, On- ogy, Paleontology Collection, Urbana, Illi- tario nois IUPC Indiana University, Department of Geology, UMMP University of Michigan, Museum of Paleon- Paleontology Collection, Bloomington, In- tology, Ann Arbor, Michigan diana USNM United States National Museum, Washington, ISGS Illinois State Geological Survey, Urbana, D.C. Illinois USNMS United States National Museum, Springer ISM Illinois State Museum, Springfield, Illinois Collection MCZ Museum of Comparative Zoology, at Harvard YPM Peabody Museum of Natural History, Yale College, Cambridge, Massachusetts University, New Haven, Connecticut

2 Introduction

Edrioasteroids are not common fossils. When an ama- Bell, subord. nov., with two families, the Isorophidae Bell, teur paleontologist, W. H. White, Jr., revealed an excep- lam. nou., and the Agelacrinitidae Chapman (1860). tionally prolific occurrence of these echinoderms in the Largely for want of material a few species, mostly Euro- Upper Ordovician near Cincinnati, Ohio in 1964, an at- pean, are excluded from this study, although they prob- tempt was made to gather specimens for a population ably belong to the Isorophida. These are Anglidiscus study. Preliminary attempts to classify the specimens fistulosus Anderson (1939), Argodiscus hornyi Prokop soon demonstrated inconsistencies in the existing taxon- (1965), Thresherodiscus ramosus Foerste (1914), four omy, and suggested that a major review of the class was in species assigned to Lepidodiscus Meek and Worthen order. The ensuing investigation has included the type (1868), seven species assigned to Agelacrinites Vanuxem specimens of 65 of the approximately 115 described edrio- (1842), and eight species assigned to Hemicystites Hall asteroid species, supplemented by numerous additional (1852) . undescribed specimens. Also omitted are four small, distinct groups of species. Of the 65 described species that were examined, only A family has been proposed for each of these by earlier 40 are recognized here, and 13 0.£ these only with reserva- workers. 1) The Cyathocystidae Bather (1899a) includes tions. The remaining 25 species are here placed in syn- two genera, Cyathocystis Schmidt (1879) with the type onymy. Six new species are described. and three other assigned species, and Cyathotheca Jaekel The original 65 species included types for 18 of the ap- (1927) with the type and one other species. 2) The proximately 29 commonly recognized genera of edrio- Stromatocystitidae Bassler (1935) includes Stromato- asteroids. Fourteen of these genera are recognized here; cystites Pompeckj (1896) with the type and three assigned the other four are junior synonyms. Eight new genera are species, Walcottidiscus Bassler (1935) with the type and introduced, three based on new, and five on previously one other species, and Xenocystites carteri Bassler (1936)_ described, species. 3) The Pyrgocystidae Kesling (1967) includes only the The 22 genera and 46 species of edrioasteroids de- type genus, Pyrgocystis Bather (1915) with the type scribed here represent most of the species which have for- species and 12 others, described primarily on the arrange- merly been included in three families, the Edrioasteridae, ment of pedunculate zone plates, a feature of questionable Hemicystitidae, and Agelacrinitidae as defined by Bassler taxonomic significance. 4) The Lispidecodidae Kesling (1935,1936) and Regnell (1966). These species are here (1967) includes only one species, Lispidecodus plinthotus thought to represent two maj or groupings, the order Ed- Kesling (1967). rioasterida Bell, ord. nov., with one family, the Edrioaster- At this stage it appears that the Cyathocystidae is a idae Bather (1898), and the order Isorophida Bell, ord. valid family grouping. The family probably belongs to nov. The first order includes few species, whereas the the order Isorophida. The striking morphology of the Isorophida includes many. It has been subdivided into Stromatocystitidae suggests that they probably represent the suborder Lebetodiscina Bell, subord. nov., with two a new order. The Pyrgocystidae and Lispidecodidae have families, the Lebetodiscidae Bell, lam. nov., and the Car- unusual thecal shapes, but both belong to the Isorophida, neyellidae Bell, lam. nov., and the suborder Isorophina and probably to the suborder Isorophina,

3 Previous Investigation

Numerous papers dealing with edrioasteroids are listed from the Echini via Palaechinus. Moreover, he erro- in the bibliography of this work, but only a handful have neously interpreted nearby echinoderm columnals as de- made major contributions. Most are brief descriptions tached parts of his edrioasteroid, and thereby suggested of new taxa, commonlybased on a few isolated specimens. relationship to the crinoids. Moreover, because of the scarcity of specimens in most During the 1850's, several new edrioasteroids were de- collections, new descriptions have usually included little scribed as cystoids, e.g., Roemer (1851), Agelacrinus comparative data and those are often based only on pub. [sic] cincinnatiensis, A. rhenanus ; Hall (1852), Hemi- lished descriptions. The result has been the gradual ac- cystites parasiticus; Hall (1858), Agelacrinites [now cumulation of ill-defined species, not uncommonly based Discocystis] kaskaskiensis. on inadequate type material. E. Billings (1854, 1857) suggested that the edrioaster- The first described edrioasteroid was found by J. J. oids were not true cystoids. He pointed out that the" rays Bigsby in 1822 (Trenton Limestone, Middle Ordovician, supposed to be grooves for the reception of arms are in Ottawa, Ontario). It was described by Sowerby (1825) fact true ambulacra ... It is scarcely necessary to add as a new fossil belonging to the "Class Radiaria," a that it [A. buchianus] is not a cystidea, and that in all Cuvier subdivision of the animal kingdom embracing all probability neither Agelacrinites of Vanuxem, nor Hemi- animals with "radial" symmetry. Sowerby (1825, p. cystites of Hall, should be placed in that order. They are 319) noted that the fossil resembles the arms of an low forms of Asteriadae" (Billings, 1857, p. 293). Bill. Asterias lying on an Echinus. Although he included it ings' 1857 paper also described two new species, Cyclaster among the genera ofthe " Asteridae " owing to " the want bigsbyi and Agelacrinites [now Lebetodiscus] dicksoni. of ambulacra," Sowerby (1825, p. 319) suggested it might He noted the passage of " pores" through the arnbulacral be " considered as a connecting link to be placed between floorplates of C. bigsbyi. In 1858 Billings proposed the the two families of Crinoidea and Blastoidea." substitute Edrioaster for the preoccupied Cyclaster. More- The second edrioasteroid to appear in the literature was over, considering all edrioasteroids " Asteriadae," he con- a section of the" turret" or peduncular zone of what was cluded: "None of the Cystidae have ambulacra whose later to be described as Pyrgocystis sulcatum. (Middle pores penetrate through the covering of the body, and Silurian, Gotland). Figured by Hisinger (1841), it was therefore all such genera as Edrioaster, Agelacrinites, and described as a fragment of a " crinoid" stem. By" crin- Hemicystites belong to a very different division of the oid " Hisinger implied only that it was a sessile echino- Echinodermata. When we know more of their structure, it derm, as opposed to the mobile" Asteridae." Vanuxem is probable that they will be arranged as a sub-order, for (1842) applied the first binomial to an edrioasteroid, which the name Edrioasteridae would be appropriate, as Agelacrinites hamiltonensis (Middle Devonian, New it would suggest their sessile condition on the one hand, York). His specimen included six individuals, all occur- and on the other their affinity to the Asteriadae" (Bill. ring on a fragment of a large pelecypod valve. Mistaking ings, 1858b, p. 85) . the smooth pelecypod as a "connecting surface" between E. J. Chapman (1860) agreed with Billings' forecast the individual edrioasteroids, he suggested (1842, p. 158) for separation 0.£ the edrioasteroids. However, he thought that it demonstrated a unique organization, being the only them closest to the cystoids, as evidenced by their" pyra· known "crinoid . . . found clustered together so as to midal orifice" (anal structure). The imbricate thecal form one system," hence the name Agelacrinites, meaning plates of some edrioasteroids suggested to Chapman rela- " a herd of crinoids" (New Latin from Greek agel« herd, tionship to the" Ophiurians," as did the ambulacral struc- krinon lily) . ture. However, the position of the mouth (which Chapman 1. von Buch (1845) assigned Agelacrinites to the cys- believed to be in the center of what is now considered the toids. The genus was reported from the Cheirurus claviger aboral side of the body) suggested they were as close to beds at Wesela, Bohemia, by Beyrich (1843, 1846). In the" Echinida " as to the" Ophiurians." Chapman re- 1848 Forbes described Agelacrinites [now Edriophus jected Billings' term Edrioasteridae, because: 1) the sup- ( ?)] buchianus from the Caradoc beds, Denbighshire, posed sessile or parasitic condition of the group was by Great Britain, based on an internal mold. He thought no means established, and 2) the relation to the starfish Agelacrinites to be a connecting link between the cystoids implied by that name was also not certain. Thus Chapman Pseudocrinites and Sphaeronites, but not far removed coined the substitute term Thyroida, which refers to the

4 PREVIOUS INVESTIGATION 5 presence of the "valved aperture." The Thyroida con- Steinmann (1890) proposed the Gruppe Cystasteroidea sisted of the monotypic Agelacrinitidae with all described (third group of the class Cystoidea) for the edrioasteroids. edrioasteroid species included in the genus Agelacrinites. He replaced this name with Edrioasteroidea in 1903,. [Reg- Many new edrioasteroid species were described in the nell (1966) reports that the term Cystostellaroidea was last half of the 19th century. Most were brief descriptions also proposed by Steinmann (1903) in his" Einfiihrung which covered only thecal form, ambulacral position, anal in die Palaontologie," but examination of this text failed structure, and occasionally, generalized descriptions of to reveal that name.] Bernard (1893) gallicized Stein- ambulacral and oral plates. Species were commonly as- mann's 1890 term to " Cystoasteroides," indicating that to signed to the" Cystidea," or merely referred to as new his mind the group represented a transition series from echinoderms. Among these are three important papers by the" Cystides " to the" Asteroides." Hall (1866, 1871, 1872) which introduced three of the Haeckel (1896a), attempting to produce a phylogenetic more common Upper Ordovician edrioasteroids and re- diagram of the echinoderms, introduced for the edrio- viewed several other species. Barrande (1887) described asteroids the term Agelacystida (order Agelacrinida), a suite of seven new species from the Ordovician of and listed it as the third" family" under the Cystoidea. Bohemia. He defined the family (1896a, p. 404, here translated from S. A. Miller (1877) listed the order Agelacrinidea under German) as: the" Class Echinodermata," but did not define the taxon. Cystoids with very numerous small plates, or scales, In 1882 he modified his ordinal name to Agelacrinoidea which often exhibit very different form and arrange- with one family, Agelacrinidea (derived from his arbi- ment on the oral and aboral parts of the capsule. Five ambulacra, very elongate, and regularly divided, the trary change in the spelling of Agelacrinites to Agela- long ambulacral groove each with two rows of cover crinus) . He defined the order and family as follows plates. Between the central mouth and the eccentric (1882, p. 221) : valve-pyramid of the anus no third opening is discern- ible. Body thin, circular and parasitic upon other objects. The lower side consists of a thin, smooth, attaching Haeckel's (1896b, p. 107) expanded diagnosis of the membrane or plate. The upper side is more or less con- family Agelacystida included the following additions: vex, and composed of thin, squamiform or imbricating "Cystoids with a pentaradial, usually regular but occa- plates, usually much smaller at the periphery than to- sionally bilateral theca . . . [thecal plates] usually have ward the center. Ambulacra constituting part of the convex surface furrowed on the interior, and composed pores, ... the theca has a vertical main axis, it is some- of a double series of transverse alternating plates, some- times disk-shaped or semispheroidal, and tapered under- times having smaller. middle, intercalated ones. Two neath into a short stem, . . . [central] pentagonal mouth, or more rows of ambulacral pores connect the exterio-r ... [ambulacra with] pinnules." Haeckel (1896b, P: with the interior of each ambulacrum. The so-called 110·111) divided the Agelacystida into two subfamilies. ovarian or anal aperture is situated in one of the inter- ambulacral areas, and is usually surrounded by cunei- (1) Subfamily Hemicystida, with "theca flexible, with a form plates forming a depressed circular prominence. flexible squamous skeleton. Plates rounded (rarely poly- The genera belonging to this order and family are gonal) imbricate, usually (or always?) without double Agelacrinus, Edrioaster, and Hemicystites. pores." The genera listed with their supposed type species are: "Hemicystis (granulata) , Agelacrinus (vorticella- By 1889, enough additional species had been described tus), Lepidodiscus (cincinnatiensis), Agelacystis (hamil- to encourage Miller to divide his order Agelacrinoidea tonensis}:" (2) Subfamily Asterocystida, with "theca into two families, Agelacrinidae and Hemicystidae. stiff, with an immovable plated skeleton. Plates polygonal, Neither family was formally defined, but it must be as- connected firmly by fibers, not imbricate; usually (or sumed that with the genus Hemicystites remo'ved from the always?) with double pores." The genera listed with their Agelacrinidae a new family having the attributes of the supposed type species are: "Cyathocystis (plautinae), genus would be required. Gomphocystis (tenax), Asterocystis (tuberculata), Aster- Many texts and synthetic taxonomic works on Paleontol- oblastus (stellatus), Edriocystis (bigsbyi), Mesites ogy appeared in the last quarter of the 19th century. Most (pusireDskyi)." Haeckel's summation of the morphology treated the edrioasteroids quite summarily, often using of the Agelacystida is confusing owing to the inclusion of their own terms for the group. Among these were Zittel's four true cystoids along with the edrioasteroids, hence the "Handbuch der Palaeontologie" (1879) and "Grund- description of pinnules, etc. His descriptions of edrio- ziige der Palaeontologie" (1895) [translated and modi- asteroid species were based largely upon interpretation of fied by Eastman (1896) as " Textbook of Paleontology"], earlier publications, thus adding little new information. in which the family Agelacrinidae was placed with the Moreover, he assigned different type species to described cystoids, genera and altered spelling, commonly replacing generic 6 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21 endings with "-cystis" to reflect his phylogenetic inter- Family AGELACRINIDAE pretation. Body cup-shaped or cap-shaped; upper side convex Commenting upon this procedure which violated then in the middle, depressed at the periphery, underside accepted, and now formalized, rules of nomenclature, level, attached by the entire surface. Theca, apart from the coverplates of the ambulacra, composed of squa- Bather (1914a, p. 115) exclaimed" Neither the nomen- mose, overlapping plates which diminish in size toward clatoral nor the taxonomic vagaries of Professor Haeckel the periphery, where they are solidly fused together. won any favour, and it is needless to allude further to him Ambulacra straight or curved spirally, in doing so V or to other writers who shared his ignorance of the facts and also IV can be curved contrasolarly. Anus closed but not his imagination." by irregularly placed plates, coverplates large, finger- shaped, subambulacral plates present. O. Jaekel (1895) introduced the term Thecoidea for the edrioasteroids. In 1899 he published a lengthy treatment Genera: Hemieystites, Agelacrinites. of the group, the first to systematically relate thecal con- struction to soft part morphology and function. His dis- Jaekel differentiated his new order from other Pelma- cussion included analysis of the thecal shape and mode tozoa on die basis of the unique combination of fivetraits: of attachment, oral area and frame, amhulacral system of (1) the structure of the ambulacra, i.e., five fixed amhu- coverplates and floorplates, mode of ambulacral curva- lacra with differentiated coverplates; (2) lack of other ture, interamhulacral plating, anal structure, hydrovascu- subvective appendages; (3) position and manner of clo- lar system, intestinal system, musculature system, nervous sure of the anus; (4) the lack of a stem; (5) the lack of system, genital system, ontogeny, phylogeny, mode of life, thecal pores. The families were differentiated on the basis and geological distribution. Jaekel's work was largely a of four characters: (1) thecal shape; (2) size of attach- synthesis of earlier description, salted with speculation ment area; (3) length and disposition of the amhulacra; about phylogenetic and ontogenetic relationships and (4) degree of differentiation of ambulacral coverplates. functional morphology. It provided a much needed sum- It is apparent that most of his conclusions on morphology mary of the class. Jaekel subdivided the Thecoidea into were derived from species of the family Agelacrinidae as two families, summarized below (translated from Ger- defined by Bather. Jaekel doubted the presence of pores man). in the arnbulacra of Edrioaster as described by Bather, and further defined the ambulacra of all edrioasteroids as hav- Order THECOIDEA ing a uniseries of floorplates. Thecoidea are Pelmatozoa, whose five radiating Bather (1898-1915) published a series of papers deal- ambulacra have no side branches or free arms; but are ing with the edrioasteroids. Included were the first de- fixed through their total length to the body, and are tailed analyses of several species, with the new taxa: Di- closed by differentiated thecal plates. The body is nocystis barroisi (1898), Edrioaster levis (1914), Lebeto- spheroidal, sack-, cup- or disc-like, free or with the discus (1908) for Agelacrinites dicksoni Billings (1857), underside attached to the sea floor or foreign object, without a stem. The theca is occasionally leathery Pyrgocystis sardesoni (1915), P. grayae (1915); and P. with a weakly developed skeleton. The elements of the anstice (1915). Bather also covered Edrioaster buchianus latter are irregularly arranged, interrupted by the (Forbes) (1848) and Edrioaster bigsbyi (Billings) ambulacral pentamer, and at times also equipped with (1857). Bather's specimens included several large, well- respiratory grooves, but without thecal pores. The gut preserved specimens of Edrioaster bigsbyi and Edrioaster was turned solarly. The anus is on the upper side in interradial position, and is closed with either small, [now Edriophus] levis. His extensive analysis of these two irregularly arranged plates or by larger ones that are species included explanation of formerly misrepresented arranged radially. The parietal pores and primary stone- ambulacral structure and floorplatepassageways, the canal pore may be absent from the theca. The sex oral area and underlying frame, and the hydropore open- organs lie entirely within the theca. ing. This information, combined with analysis of internal molds of Edrioaster buchianus, dictated his conclusions Family THECOCYSTIDAE regarding edrioasteroid morphology and their systematic Body pentagonal or spheroidal, sack- or cup-shaped, position within the echinoderms. The importance placed free or with a part of the undersurface coherent. Theca on the well-defined structure of the species he assigned to leathery, with small, weakly calcified to thick polygonal Edrioaster is exemplified by his misrepresentation of the plates directly abutting or partly fused. Ambulacra short, and straight or spirally elongated; coverplates coverplate passageways of Lebetodiscus dicksoni as floor- often little differentiated. plate passageways. Bather's reconstruction of the oral sur- face of Edrioaster (1914a, fig. 1) has been commonly re- Genera: Stromatocystites, Cyathocystis, Thecocystis, produced in both papers and texts and used to exemplify Cystaster, Edrioaster, Dinocystis. the important morphological features of the "typical" PREVIOUS INVESTIGATION 7

edrioasteroid. A summary of Bather's classification of the differentia when dealing with edrioasteroids. Only a few edrioasteroids (1900) is presented below. His family speculated about possible interrelationships within the Steganoblastidae [for Astrocystites Whiteaves (1897) = group and the phylogenetic implications of the group as Steganoblastus Whiteaves (1898)] and Cyclocystoides a whole. Owing to the limited knowledge of the morpho- Billings and Salter (1853) need not be considered, since logic spectrum within the group, the classification and its these two genera are now placed in the class Edrioblastoi- implications remained on a rather superficial level. dea Fay (1962) and Cyclocystoidea Miller and Gurley In connection with description of several new species, (1895), respectively. Bather's classification raised the J. M. Clarke (1901) gave a much needed review of the edrioasteroids to the class level, defined two new families species belonging to Bather's Agelacrinidae, in order to and redefined the Agelacrinidae: " provide the means to unsnarl the tangle of names into which American Paleontologists with the aid of their Brit- Class EDRJOASTEROIDEA ish and German brethren have plunged these organisms." Pelmatozoa in which the theca is composed of an in- Summarizing the morphology of Agelacrinidae, Clarke definite number of irregular plates, some of which are (1901, p. 192-193) concluded that of the taxobases of the variously differentiated in different genera; with no sub- lower taxa of the group: vective skeletal appendages, but with central mouth, from which there radiate through the theca five un- It appears from the foregoing that we may leave out branched ambulacra, composed of a double series of of consideration as a generic character of the agela- alternating plates (covering-plates) , sometimes sup- crinites the variation in the direction of the rays and ported by an outer series of larger alternating plates may consider as structures of convenient generic (side-plates or flooring-plates}. Pores between (not value 1) the character of the thecal plates, whether through) the ambulacral elements, or between them and a) squamous or b) mosaic, and if the latter, whether the thecal plates, permitted the passage of extensions 1) polygonal and smooth or, 2) irregular and sculp- from the perradial water-vessels. Anus in tured; 2) the character of the rays, whether a) long interradius, on oral surface, closed by valvular pyramid. and whiplash shaped, with narrow, arched cover Hydropore (usually, if not always, present) between plates or b) shorter and broader, with broad and mouth and anus. long cover plates; 3) the presence and structure of a peripheral band either a) composed of few large Family 1. AGELACRINJDAE plates with very fine ones on the outer edge or b) Edrioasteroidea with a theca composed mostly of broad with a great number of small plates. thin plates, flexible, attached temporarily or perma- nently by the greater part of the aboral surface; with Although it is manifest that Clarke used several thecal the ambulacra confined to the oral surface. features no longer considered to be of generic value, he Genera: Stromatocystis, Cystaster (Thecocystis of made a great contribution by using a systematic approach Jaekel), Hemicystis, Agelacrinus, Streptaster, Lepido- to the group. discus, Discocystis, Echinodiscus, (Haplocystis). Numerous other works on the edrioasteroids appeared from 1900-1936. Among the notables of this period are Family 2. CYATHOCYSTJDAE Spencer (1904), who first sectioned an edrioasteroid (Car- Edrioasteroidea with the theca composed on the oral neyella pilea); Foerste (1914), who presented a major surface of five deltoids surrounded by marginals, but summary of morphology, discussed evolutionary develop- below of a fused solid mass of stereom, with irregular longitudinal sutures; permanently attached by the ab- ment, and gave comparative descriptions of many species; oral surface as by an encrusting root; ambulacra con- Raymond (1915,1921), who contributed several new Mid- fined to oral surface. dle Ordovician species; Williams (1918), who reviewed Genus: Cyathocystis Agelacrinites, including an ontogenetic series for one spe- cies; and, finally, Bassler (1935, 1936), who published Family 3. EDRIOASTERJDAE two papers which between them listed all the known spe- Edrioasteroidea with flexible theca composed of thin cies of edrioasteroids, and attempted to group these spe- plates; attached, if at all, by a small central portion of cies into a supposedly unified classification scheme. the excavated aboral surface; ambulacra pass on to aboral surface. Bassler had the great advantage over all previous work- Genera: Aesiocystis, Edrioaster, Dinocystis. ers of being able to study literally hundreds of specimens of Cincinnatian edrioasteroids in the United States Na- The publication of Jaekel's (1899) and Bather's (1900) tional Museum collections, where there were also repre- papers, along with Bather's subsequent publications of sentatives of nearly every known genus. This sample was the detailed morphological work on which he had based still too small, however, and especially the employed tech- his classification, marked a new era. Previously, paleon- niques were too inadequate to allow proper analysis of all tologists had mostly concerned themselves with specific the structural features of the group. However, Bassler did 8 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21 correctly evaluate as useless several of the features that Family EDRIOASTERIDAE Bather (1899) had been previously used as generic traits. He listed seven Theca flexible, depressed, usually globular, attached features that were commonly used as generic taxobases: by the small central excavated part of the aboral sur. face; ambulacra strongly curved and passing onto Variable within a genus: aboral surface; floorplates arranged in two series, one on each side of the ray, and alternating along the me- 1. amount of imbrication of interambulacral plates dian line. [Bassler notes that the only actually diag- 2. width of peripheral border of plates nostic feature of the family is the presence of the hi- 3. number of ambulacra. series of floorplates.] Genera: Edrioaster Billings (1858) ; Dinocystis Bather Constant within a genus: (1908). 1. plate structure of the ambulacra 2. plate structure of the oral area Family CYATHOCYSTIDAE Bather (1899) 3. direction of the curvature of the amhulacra Edrioasteroidea in which the aboral portion consists 4. extent of curvature of the ambulacra. of a fused solid mass of plates attached permanently to some foreign object. Bassler divided the class Edrioasteroidea into five fam- Genera: Cyathocystis Schmidt (1880); Cyathotheca ilies which included 24 genera and 92 species. Seven of Jaekel (1927). these genera and 30 of the species were proposed in these two papers. A combination of the two papers results in Position Uncertain: the following summary of Bassler's classification: Astrocystites Whiteaves (1897). [Now Class Edrlo. blastoidea Fay (1962).]

Class EDRIOASTEROIDEA Billings (1858) [not 1854·58, as Bassler gave]. [No diagnosis given.] Bassler concluded his contributions to the edrioaster- oids in a joint work with Moodey (1943), in which they Family STROMATOCYSTITIDEA Bassler (1936) compiled the stratigraphic occurrence of the group and a Theca with a basal layer of plates (in contrast with bibliographic index of genera and species (in which they all other edrioasteroids with basal areas of attachment recognized 23 genera and 92 species). Bassler's (1935, without plates). 1936, 1943) works represent a most significant contrihu- Genera: Stromatocystites Pompeckj (18%); Wakat· tion. Disagreement has since arisen over many of Bass- tidiscus Bassler (1935); Xenooystises Bassler (1936). ler's observations and conclusions, as is expected when new material and techniques appear, but the value of Bass- Family HEMICYSTITIDAE Bassler (1936) ler's synoptic and bibliographic work has not been dimin- ished. Theca composed of thin plates with an oral surface of five ambulacra separated by interambulacrals and attached by the greater part of the aboral surface per· Several outstanding morphologic studies on edrioaster- manently or temporarily to some outside object. Oral oids have been published in recent years. Anderson covering plates three; one large plate next to the anal (1939) described Lepidodiscus fistulosus and gave a com- area with two smaller adjacent ones. parative morphological evaluation of this and other edrio- Genera: Cystaster Hall (1872) ; Cincinnatidiscus Bass- asteroid species. Regnell (1945) offered extensive rede- ler (1935); CarneyeUa Foerste (1917); Streptaster scription of species included in Stromatocystites, Cyatho- Hall (1872); Lebetodiscus Bather (1908); Foerstedis- theca, Pyrgocystis, and (1950) gave an analysis of Age. cus Bassler (1935); Pyrgocystis Bather (1915); Hemi- cystites Hall (1852) . lacrinites ephraemovianus (Bogolubov) and Lepidodiscus fistulosus Anderson. Ehlers and Kesling (1958) described cyclic coverplates in Discocystis laudoni and considered Family AGELACRINITIDAE Chapman (1860) [not Bass- ler (1935) or Clarke (1901)] their taxonomic implications. Kesling and Ehlers (1958) interpreted the cyclic coverplates and other morphologic Theca as in the Hemicystitidae except that the plates covering the oral area are small, numerous, and with- features of Lepidodiscus squamosus. Kesling and Mintz out any definite order. A single row of ambulacral (1960) extensively described both internal and external floorplates overlapping proximally. morphology of Isorophus cincinnatiensis and Carneyella pilea from specimens exposing the inner and external sur- Genera: Thresherodiscus Foerste (1914); Agelacrin- faces and also from ground, serial views of two specimens. ites Vanuxem (1842); Isorophus Foerste (1917); lso- orphusella Bassler (1935); Lepidodiscus Meek and Kesling (1960) revealed hydropore structures in 20 spe' Worthen (1868); Discocystis Gregory (1897); Ulrich- cies of edrioasteroids, and most recently (1967) he de· idiscus Bassler (1935); Cooperidiscus Bassler (1935). scribed two new families; Lispidecodidae for the new TERMINOLOGY 9

Lispidecodus plinthotus, and Pyrgocystidae for Pyrgo- zation of his groupings. However, all of the major types cystis. of hydropore structures recognized here were reported by Kesling's (1960) paper on the hydropore structures of Kesling. a broad cross section of edrioasteroid species is perhaps Hegnell (1966) published the only recent summary of the most significant recent morphologic paper. This struc- of the Edrioasteroidea. This work is largely a literature ture had been overlooked by most earlier workers except compilation, owing to the unfortunate unavailability of in Edrioaster bigsbyi and related species. Kesling's care- many type specimens (Regnell, 1969, personal communi- ful analysis of the hydropore structure in 20 species dem- cation). However, RegneII's complete review of morphol- onstrates the taxonomic significance of the structure. ogy, ontogeny, evolutionary trends, ecology, and distribu- Moreover, his splendid reconstructions of 13 species sug- tion is flavored with his own extensive knowledge of Brit- gested the importance of many other thecal details com- ish and European edrioasteroids, adding insight to former monly scantily considered. Kesling recognized six basic interpretations. He accepted Bassler's five-family subdi- types of hydropore structures based on plate structure and vision of the class, although he expanded Bassler's abbre- position. Consideration of additional species has allowed viated family diagnoses. Regnell lists 27 described gen- refinement of Kesling's scheme, including some reorgani- era.

Morphology

TERMINOLOGY AS APPLIED TO EDRIOASTEROIDEA aboral pole - point of intersection of the oral-aboral axis ambulacral radius - thecal radius defined by the mid- with the aboral surface of the theca; marks the center line of an ambulacrum; in curved ambulacra the radius of the aboral surface. is defined by the midline of the proximal end of the aboral surface - morphologically related unit of the ambulacrum, which is extended directly toward the edge theca distal to the oral surface plates; commonly forms of the theca. only part of the lower side of the individual. ambulacral tunnel- space enclosed between the amhu- adradial - direction toward the adradial suture. lacral floorplates and overlying coverplates ; the ambu- adradial suture - zone of contact between the oral-am- lacral food groove extends along the floor of this space. bulacral series plates and interambulacral plates; ad- ambulacrum - morphologically and functionally unified radial suture line marks the intersection of the adradial group of structures which form each of the endothecal suture with the thecal surface. subvective system radii, including coverplates, floor- adult stage - mature theca with fully developed struc- plates, tunnel, and, in life, food groove organs. Identi- tures; ephebic, sexually mature. fied by the Lovenian system: I·V numbered clockwise, ambitus - theoretical line encircling the exterior of the I along the left side of the 'posterior inter ambulacrum. theca which marks the greatest thecal circumference per- anal area - anal structure and the enclosed anus. pendicular to the oral-aboral axis; separates the lower anal structure - morphologically related group of plates from the upper side of theca; commonly the greatest surrounding the anal opening. horizontal circumference of the theca. ambulacral bifurcation plates - see bifurcation plates. anterior - direction toward the anterior pole of theca; along or parallel to the axial plane. ambulacral coverplates - plates which cover the ambu- lacral groove and roof the ambulacral tunnel; may be a anterior oral midline - perradial line between opposing single or multiple biseries, or a cyclic series of plates. oral plates; extends anteriorly from the oral pole. ambulacral floorplates - plates which underlie the anterior pole - intersection of the anterior-posterior axis ambulacral groove and floor the ambulacral tunnel; with the anterior tip of the theca (opposite interamhu- may be a uniseries or a single biseries of plates. lacrum 5). 10 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21 anterior-posterior axis - axis which extends through the cyclic - referring to serially repeated arrangement of center of the theca; aligned with the center of the oral plates. area, the anterior primary ambulacral radius, and the cyclic eoverplate series - coverplates along each side of center of posterior interambulacrum; perpendicular to the ambulacral perradial line which form serially transverse axis. repeated sets of plates, each set a cycle; cycles on one anterior primary ambulacral radius - primary radius side of the ambulacrum a mirror image of those on the opposite inter ambulacrum 5, the anus, and the hydro- opposing side of perradial line; opposing cycles alter- pore region; defined by the anterior oral midline and nate, offset by half a cycle. ambulacrum III. distal- relative direction or position away from the oral anus - terminal exit of digestive tract. pole, toward the aboral pole of the theca, defined by axial diameter - anterior-posterior thecal diameter. moving along the structure to which the term is applied. axial plane - plane passing through the theca along the E.g., for the ambulacra, the distal tip is the end furthest anterior-posterior axis; perpendicular to upper side of from the oral area. In forms with curved ambulacra theca. the distal part is located by proceeding along the length bifurcation plates - two large, unpaired plates, one of the ambulacrum, even though in straight-line distance lying at the junction of each lateral pair of ambulacra the distal tip may be closer to the oral pole than another (l·II and IV-V) ; the perradial tip of each bifurcation part of the same ambulacrum. See discussion under plate lies at the junction of the two ambulacral perradial Orientation for differing definition of proximal and lines with each other and with one end of the transverse distal as applied to other echinoderms. oral midline. (Bifurcation plates are classified as ambu- lacrals, although they could as easily be considered domal- thecal shape in which the oral surface is convex orals, as done by many authors.) upward and is confined to the upper side of the theca; the distal edge of the oral surface forms the thecal hiseries - double row of alternating plates. ambitus. The nonplated aboral surface forms the entire central lumen - opening which extends from the proxi- lower side of the theca. Lateral view: concave-convex mal ends of the ambulacral tunnels down through the or planoconvex; plan view: circular or subcircular. oral frame into the underlying thecal cavity. clavate - club-shaped thecal form in which the oral sur- double biseries - two distinct sets of coverplates with face plates form three regions: an upper gibbous each forming an alternating biseries of pairs of plates, "head," a lower, constricted pedunculate zone, and an the pairs of one set alternating with those of the other outward flaring peripheral rim; the nonplated aboral to form an integrated system. surface is restricted to the area underlying (distal to) " echinoidal " - thecal shape in which the oral surface the peripheral rim, and conforms to shape of underlying extends past the ambitus onto the lower side of the substrate. theca and is divided into five areas: 1) the upper oral contrasolar - counterclockwise or sinistral direction of surface, convex upward, extending from the oral region curvature. down to the ambitus; 2) the subambital zone, constrict- coverplate height - elevation of a coverplate above the ing downward, sides sloping inward toward the oral- interambulacra, measured normal to thecal surface. aboral axis; 3) the resting zone, a narrow area with coverplate length - external dimension of a coverplate plate exteriors parallel to the underlying substrate; measured normal to the length of the ambulacrum, i.e., 4) the incurved zone, with plates flexed upward and distance from adradial suture to perradial line. inward toward the thecal cavity to form a central, basal, coverplate passageways - tubular canals which extend convex upward invagination in the lower side of the along lateral sutural faces of contiguous ambulacral and theca; and 5) the flexible membrane, which extends oral coverplates: they connect the exterior to the in- from the distal edge of the incurved zone downward to terior of the theca (not in direct communication with the underlying substrate. The amhulacra extend past the ambulacral tunnel). the ambitus onto the subamhital zone but end or curve coverplate thickness - dimension from the exterior before reaching the resting zone; the aboral surface is extremity of a plate to the internal extremity, perpen- restricted to a small region surrounded by the distal dicular to the external surface of the plate. edge of the membrane. In lateral view, oblate spheroid; plan view, circular or subcircular, coverplate width - external dimension measured par- allel to the length of an ambulacrum, i.e., proximal- endothecal- amhulacra between thecal plates, in contact distal dimension. with both the interior and the exterior of the theca. TERMINOLOGY 11 exterior side of theca (external; outer side) - thecal lower side of theca - part of the theca distal to the surface in contact with the external environment, the ambitus; composed of the aboral surface of the theca outside of the theca; opposite of inner side. and commonly the distal parts of the oral surface. tloorplate passageways (floorplate "pores") - tubular marginal area - morphologically unified part of the canals which extend along lateral sutural faces of con- theca which forms the distal sector of the oral surface; tiguous ambulacral floorplates; they connect the ambu- usually a peripheral rim. lacral tunnel to the interior of the theca. multiple biseries - two or more sets of coverplates, each food groove - trough which extends along the base of of which forms an alternating biseries of pairs of plates, the ambulacral tunnel (upper side of floorplates); the pairs of each set alternate with those of the other proximally empties into the central lumen. sets to form an integrated system. gerontic stage - old age, normally represented by an oral-aboral axis - axis which passes through the center unusually large theca and perhaps by modification of of oral area perpendicular to the upper side of the theca. some thecal structures. oral area (oral region) - morphologically related struc- hydropore - external opening through the theca which tures which surround the stomial opening, including links the hydrovascular system with the external en- oral covering plates, oral frame, and related soft part vironment; delimited by plates of the hydropore structures. structure. oral frame - structure underlying the external oral area, hydropore oral - unpaired oral plate in right posterior formed by proximal ambulacral floorplates and com- part of the oral region; commonly forms the posterior monly other elements; surrounds the central lumen or edge of the hydropore. stomial chamber. hydropore structure - group of plates which externally oral plates (orals, oral covering plates) - elements surround the hydropore. which form the external covering of the oral area and inner side of oral surface - side of the oral surface roof the central lumen; distally continuous with the plates in contact with the thecal cavity; the inside of the ambulacral coverplate series. theca; opposite the exterior side. (Commonly referred oral pole - point of intersection of the oral-aboral axis to as the aboral side of the theca by earlier authors.) with the oral surface of the theca; marks the center of interambulacrum - sector of theca between two ambu- the oral region. lacra, distal to oral area plates, proximal to peripheral oral surface - morphologically related unit of the theca rim; an interradius, that includes the oral area, ambulacra, interambulacra, intra-ambulacral extension - part of an ambulacral anal area, and marginal area; (not necessarily equal coverplate or oral plate which is produced inward into to the upper side of the theca); always composed of the ambulacral tunnel. calcareous plates. intrathecal extension - part of an external thecal plate peripheral rim - quasi.regularized series of plates which which is produced inward into the interior of the theca. form the margin of the oral surface; includes several juvenile stage - immature stage of growth; thecal struc- circlets of plates which diminish in size distally. tures incompletely formed. peripheral rim transition plates - plates in the periph- lateral depression series - groups of small, basinlike eral rim which separate plates externally elongate con- depressions on the exterior lateral edges of the cover- centric with the thecal margin from those externally plates; they flank the suture lines between contiguous elongate radially. ambulacral coverplates ; associated with the external periproct - loosely united anal structure composed of foramina of the coverplate passageways. several circlets of plates, each circlet irregular; struc- lateral shared coverplate pair (shared coverplate) - ture was probably conical in life. pair of oral plates which flank the transverse oral mid- peristome - thecal elements surrounding mouth. line; proximal to the lateral ambulacral bifurcation perradial- direction toward the perradial line. plate, distal to the central primary orals. left lateral primary ambulacral radius - primary perradialline - junction between closed opposing memo ambulacral radius which extends from the oral pole out bers of coverplate pairs or series; extends approxi- to the left ambulacral bifurcation plate along the trans- matelyalong the midline of each ambulacrum. verse midline of the theca; this radius bifurcates at the primary ambulacral radii -three radii: anterior, right left lateral bifurcation plate and forms two lateral lateral, and left lateral; they extend out from the center ambulacral radii, i.e., ambulacra I and II. of the oral area and are marked by the anterior and 12 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21

transverse oral midlines. The two lateral radii bifurcate suture - plane formed by the junction of connected to form the two lateral pairs of ambulacra, 1·11 and plates. IV·V; the anterior radius continues as ambulacrum III. suture line - surficial line on the theca formed by the primary orals -large oral plates with intrathecal exten- intersection of sutures with the thecal surface. sions which participate in the formation of the under- tessellate - plating arrangement in which sutures be- lying oral frame and have a fixed position in the theca tween contiguous elements are vertical or nearly so; relative to ambulacral and other oral plates. adjacent plates abut one another and form a mosaic, as proximal- relative direction or position toward the oral tiles in a floor. pole, away from the aboral pole of the theca; defined test - sum of all the mesodermal skeletal plates. by moving along the structure to which the term is theca - enclosing body surface structures consisting of applied; opposite of distal. the body wall with mesodermal skeleton of discrete right lateral primary ambulacral radius - primary plates, and the nonplated body wall of the aboral ambulacral radius which extends from the oral pole out surface. to the right amhulacral bifurcation plate along the thecal cavity - space surrounded by the theca; con- transverse midline of theca; this radius bifurcates at the tained soft parts during life. right lateral bifurcation plate and forms two lateral thecal diameter-length of a line extending through the amhulacral radii, i.e., ambulacra IV and V. theca in a plane perpendicular to the oral-aboral axis secondary orals - small to large oral plates without and through the ambitus. intrathecal extensions, commonly with a fixed position transition plate - see peripheral rim transition plates. relative to the primary orals; frequently only surficial elements. transverse axis of theca - axis which extends through the oral-aboral axis perpendicular to the anterior-pos- shared coverplate - see lateral shared coverplate pair. terior thecal axis; location commonly expressed sur- single biseries - one set of biserially arranged plates. ficially by the position of the transverse oral midline. solar - clockwise, or dextral direction of amhulacral transverse diameter - thecal diameter perpendicular to curvature. axial diameter. stone canal- tubular connection hetween the hydropore transverse oral midline- perradial line which extends and the circumesophageal ring canal. across the exterior of the oral region between opposing stone canal passageway - opening through which the anterior and posterior orals perpendicular to the an- stone canal extended; leads from the hydropore to the terior primary ambulacral radius; extends from the interior of the theca; formed by the inner parts of the proximal tip of one lateral ambulacral bifurcation plate hydropore structure plates in combination with addi- to the other. tional elements, commonly the adjacent amhulacral floorplates. upper side of theca - part of the theca proximal to the ambitus; composed of plates of the oral surface, but stroma canals - passageways in the plates filled with does not necessarily contain all of the oral surface stroma during life; secondarily filled with calcite, plates. pyrite, etc. in the fossil state. valvular anal structure - anal structure commonly submarginal ambulacral suture- zone of contact be- formed by an inner and an outer circlet of large, sub- tween the ambulacral coverplates and floorplates in the triangular plates; outer circlet elements alternate with Edrioasterida. and overlap the plates of the inner circlet along beveled, submarginal suture line - intersection of the sub- tightly fitting margins. marginal ambulacral suture with the thecal surface; young adult stage - ontogenetic stage of transition from extends along the line of contact of the adradial ends juvenile to full-sized mature adult, in which the propor· of the coverplates and the externally exposed parts of tional sizes of the structures are transitional from the floorplates in the Edrioasterida. juvenile to adult forms. subvective system - Grgan system that gathers and transports food to the mouth; the ambulacral system. MORPHOLOGY OF THE ISOROPHIDA 13

ORIENTATION

The orientation of the edrioasteroid theca is based upon asteroids, are used differently than in some other echino- thecal symmetry. Following Bather (l900a) , specimens derm groups. Proximal, as defined in standard diction- are placed in their "natural" or life position; the side aries, means toward or closest to the origin or point of of the theca containing the oral region is directed upward attachment of a limb or organ; distal the opposite of prox- and the ambitus is horizontal. The interambulacrum with imal. Therefore, the term has frequently been applied to the anal structure is placed closest to the observer; the pelmatozoan echinoderms in relation to the point of attach- ambulacrum opposite the anal interambulacrum is di- ment of the stem. For example, the proximal parts of the rected away from the observer. The axial plane of bilateral ambulacra of a blastoid, as designated by Beaver (1967, symmetry is parallel to the line of observation and bisects p. 5347) in the" Treatise on Invertebrate Paleontology," the specimen into right and left halves, corresponding to are the parts of these structures closest to the point of right and left of the viewer. A plane passing through the attachment of the stem, and thus furthest from the oral theca at right angles to the axial plane, referred to as the opening which lies at the summit of the calyx. In edrio- transverse plane, bisects the theca into anterior and pos- asteroids, proximal is used to indicate direction toward terior halves. the oral area along the course of any particular structure; The upper side of the theca lies above the ambitus, the distal indicates away from the oral area. This usage was lower side below. The upper and lower sides are not to be ingrained, if not originated, by Bather in his many works confused with the oral and aboral surfaces which are dealing with edrioasteroids and has been followed since morphologic terms which define related groupings of the- by most authors. The distal parts of edrioasteroid ambu- cal structures that are independent of the thecal shape. The lacra are those furthest from the oral region. oral surface includes the oral region, hydropore structure, The directions defined by proximal and distal fOT a ambulacra, interambulacra, anal structure, and the mar- given ambulacrum are determined by following the course ginal area. The aboral surface is that part of the theca of the structure. The distal tip of a curved ambulacrum distal to the marginal area, apparently a nonplated memo which extends back toward the oral area lies closer to the brane, oral pole in straight line distance than a more proximal The oral surface of domal edrioasteroids is equal to the part of that same ambulacrum. upper side of the theca; the distal edge of the marginal area marks the ambitus of the theca. Thus the entire Extending the definition of proximal and distal to their lower side of the theca is formed by the nonplated aboral most useful limits, the terms are applied to any feature of surface. However, in clavate or " echinoidal " thecae, the the edrioasteroid theca and always signify toward or away oral surface extends past the ambitus onto the lower side from the center of the oral area, along the course of the of the theca, and the lower side includes both the distal structure. For example, the most distal point on the parts of the oral surface and the nonplated aboral surface. external thecal surface is the center of the aboral surface, The terms proximal and distal, as applied to the edrio- i.e., the aboral pole.

MORPHOLOGY OF THE ISOROPHIDA Text fig. 1, pl. 1-57.

Thecal shape The Isorophida are small to moderate-sized edrioaster- the ambitus of the theca. The oral surface appears to have aids, thecal diameters commonly ranging from 8 to been at least semiflexible during life, capable of moderate 30 mm. A few larger species are known. The theca in- expansion and contraction. The aboral surface forms the cludes a plated oral and nonplated aboral surface, the entire lower side of the theca, distal to the ambitus. This latter presumably covered by a soft membrane. surface was probably covered by a soft membrane which The most common thecal shape is domal with the oral apparently conformed to the shape of the underlying surface limited to the upper side of the theca. It is cen- substrate. trally convex or domed upward, with the marginal periph- Most " nondomal " Isorophida are clavate, with a gih- eral rim flared outward distally, parallel to the underlying bous upper area, a downwardly constricting pedunculate substrate. Thus the distal edge of the marginal zone forms zone below the ambitus, and a basal, marginal, peripheral 14 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21

tim that flares outward against the underlying substrate. anterior oral midline; that between the single posterior Here the oral surface extends past the ambitus to form oral and the two anteriors forms the transverse oral mid. part of the lower side of the theca. The ambulacra are line. The posterior plate is the largest, often equal to the usually confined to the convex Upper oral surface, above combined widths of the two anterior primary orals. the ambitus. Occasionally they extend a short distance Adradially the three primary orals are in contact with the onto the lower part of the gibbous region. Clavate thecae adj acent interamhulacral areas and form the adradial may have been extensible in life, thus increasing and suture lines of the oral area. decreasing thecal height. The nonplated aboral surface is In the Carneyellidae the oral plates include only the confined to the basal section of the theca, and extends three primary orals plus a large, right posterior hydropore distally underneath the peripheral rim. It apparently con- oral (text fig. lA). These orals are flanked distally by the forms in shape to the underlying substrate. proximal ambulacral coverplates and the two lateral ambn. Discoidal and cylindrical thecae occasionally occur. lacral bifurcation plates. In the Lebetodiscidae the three Individual specimens of many species may display appar· primary orals are flanked by pairs of lateral shared cover- ently irregular or unusual, complexthecal forms. These plates, one on each side of the central orals along the are modifications of one of the basicthecal shapes, appar· transverse oral midline (text fig. lD). Additional second- ently correlated with an irregular or restricted resting ary oral plates may also be present along both oral area surface. An extreme example of such modification is seen midlines. Hydropore orals are absent in this family. The in a well-preserved Carneyella pilearesting upon a section of crinoid stem (pl. 17, fig. 1-4). Postmortem thecal col- lapse commonly modifies original thecal shapes.

Text figure 1. ISOROPHIDA

Oral area A. Carneyella pilea (Hall) , 1866, UCMP 40465, (x 5), pl. 17, fig. 7.* The Isorophida oral region is composed of sets of exter- *Unless otherwise noted, all text figures are tracings of plate out- nal covering plates, or orals, which form a solid roof over lines from an enlargement of the photograph illustrated in the the underlying oral frame structure (text fig. lA, D, F, G, plate figure cited. H). The oral area is elevated above the interambulacra B. Reconstruction of a segment of an ambulacrum of Carneyella with the highest part of this central oral rise at the oral pilea (Hall), oblique view with proximal coverplates removed to expose the floorplates and the ambulacral trough (approxi- pole. mately x 20).

(x ORAL COVERING PLATES C. Lebetodiscus dicksoni (Billings), 1857, GSC 437, 3), pI. 1, fig. 10. The external orals are classifiedas 1) primary orals with intrathecal extensions which participate in the forma- D. Foerstediscus splendens Bassler, 1936, USNM 4079, oral area, (x 10), pl. 5, fig. 4. CP, ambulacral coverplate; HCP, hydro- tion of the oral frame; 2) secondaryorals, which are more pore ambulacral coverplate; HI, hydropore interamhulacral surficial in nature and lack frame-forming extensions; and plate; LAO, left anterior primary oral plate; LBP, left lateral 3) lateral shared coverplate pairs which resemble normal bifurcation plate; 0', secondary oral plate; PO, posterior pri- ambulacral coverplates in shape, hut lie proximal to the mary oral plate; RAO, right anterior primary oral plate; RBP, point of bifurcation of the two lateral primary radii right lateral bifurcation plate; SC, lateral shared coverplate. (text fig. ID, F). The two lateral arnbulacral bifurcation E. l sorophus cincinnatiensis (Roemer), 1851, UCMP 40470, (x 3), plates are arbitrarily considered ambulacrals rather than pl. 28, fig. 8. orals for descriptive purposes. The ambulacra merge F. Reconstruction of the oral area of lsorophus cincinnatiensis proximally with the oral region, thus no sharp boundary (Roemer) (approximately x 10). BP, lateral bifurcation separates these structures, and the identification of ele- plate; HO, hydro pore oral plate; LAO, left anterior primary ments as orals vs, ambulacrals is somewhat artificial. oral plate; LASCP, left anterior lateral shared coverplate; Most, if not all, oral elements wereprobably derived from LPO, left posterior primary oral plate; LPSCP, left posterior ambulacral plates. lateral shared coverplate; 0', secondary oral plate; RAO, right anterior primary oral plate; RASCP, right anterior lateral The number and arrangement ofthe external oral plates shared coverplate; RPO, right posterior primary oral plate; is variable and of taxonomic importance. Lebetodiscina RPSCP, right posterior lateral shared coverplate; 1, primary have the simplest oral plate arrangement (text fig. lA, D). ambulacral coverplate; 2, secondary ambulacral coverplate. All have three large primary oral plates, two anterior and G. lsorophusella pleiadae (Sinclair and Bolton), 1965, GSC 14680·1, one larger posterior element, whichform the center of the (x 12), pl. 36, fig. 1. Inner side of the oral surface. oral region. All three plates are incontact centrally. The H. Agelacrinites hamiltonensis Vanuxem, 1842, NYSM 362·A, suture line between the anterior two plates forms the (x 2.5), pl. 40, fig. 1. MORPHOLOGY OF THE ISOROPHIDA 15

ambulacral coverplates

coverplotes

II

coverplate intra-ambulacral extension passageways A

I 5 periproct

adrodial suture

cover plate passageways anterior oral midline transverse oral midline

D 16 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21

...... ------...... //

/ ,- / / / /- / / " / " I' / I I I I \ \ \ \ \ \ -, -, -, <, <, '-

valvular

intra- thecal extensions of coverplotes / floorplate component / of oral frame

central oral lumen

ambulacral floorplates valvular anal structure

intra-thecal extension of posterior primary oral

ridges on basal surfaceof proximal circlet of geniculate plates of peripheral rim

cyclic series (two-plate sets) of coverplates

valvular anal structure MORPHOLOGY OF THE ISOROPHIDA 17 lateral shared coverplates of the Lebetodiscidae oral region than any other oral surface structure, and supports the extend the transverse oral midline from the primary orals outer orals even after thecal collapse has occurred. This out to the bifurcation plates. The adradial ends of the accounts for the pronounced elevation of the external oral shared coverplates are commonly in contact with the adja- area in most specimens. cent interambulacral areas, whereas the secondary oral The central lumen, bounded by the oral frame, directly plates are more commonly confined to the perradial part underlies the center of the "external oral region. It is oval of the oral region along the midlines. in plan view, transversely elongate, and extends from the The external oral plates of the Isorophina are com- proximal ends of the ambulacral tunnels downward monly more numerous than those of the Lebetodiscina through the oral frame into the thecal cavity beneath. A (text fig. IF, H). Moreover, when externally differen- conspicuous gap commonly occurs in the posterior side of tiated, four large primary orals form the center of the the frame, and permits direct access from the central oral region, in contrast with the three primaries of the lumen into the thecal cavity area under interambu- Lebetodiscina. lacrum 5. This gap may be modified by bladelike exten- In the Isorophidae the oral area includes four central sions that divide it into right and left halves, or into a primary orals, two pairs of lateral shared coverplates, one small subchamber between the central lumen and the pos- large hydropore oral, and secondary orals (text fig. IF). terior part of the thecal cavity. Externally the large primaries extend proximally from the The transversely elongate oral frame is subovate in plan interambulacra and meet centrally along the transverse view. Distally the radial extremities are continuous with and anterior oral midlines. One pair of lateral shared the ambulacral structures, which imparts a pentagonal out- coverplates flanks each side of the central orals along the line to the distal margin. The anterior part of the frame transverse oral midline. These are somewhat smaller than is nearly semicircular in plan view, except for outwardly the primaries. Their distal perradial edges are commonly flaring lateral extremities. These form a wide zone of con- in contact with the proximal, perradial end of the two tact with the posterior section of the frame. The posterior lateral bifurcation plates. Variable numbers of small sec- unit is broadly arcuate, the flared lateral extremities being ondary orals are inserted along the transverse and anterior a continuation of the arc of the entire posterior side. Thus oral midlines and lie between the four central orals and the frame is transversely elongate with the unequally the proximal ambulacral coverplates. The large single curved anterior and posterior halves joining at attenuated hydropore oral abuts the right margin of the right pos- lateral regions. terior primary oral; it forms an asymmetrical posterior The oral frame comprises the expanded proximal floor- bulge in the oral area outline. This bulge extends distally plates of the five ambulacra, commonly combined with along the proximal part of the posterior side of ambu- intrathecal extensions from the primary oral plates. The lacrum V. anterior half of the frame is formed by the proximal floor- The oral plates of the Agelacrinitidae may be similar to plates of ambulacra II, III, IV, and the intrathecal exten- those of the Isorophidae and include four large, central sions of the two anterior primary oral plates. The three primary orals, several sets of secondary orals, and one or floorplates are expanded proximally, both inward and more right posterior hydropore orals. More commonly, laterally, each in contact with the adjacent floorplates the area is covered by numerous small orals, the primaries along the innermost edges of the frame. The contact zone not being differentiated from other plates. These numer- between the floorplate of ambulacrum III and the two ous orals commonly reflect the ambulacral coverplate pat- adj acent lateral floorplates is small, because the intrathecal tern and thus appear to grade distally into the proximal extensions of the two anterior primary oral plates reach ambulacral coverplate sequence without a distinct break. inward to form the interradial parts of the frame. These Thus it is difficult to determine the total number of orals lie between the upper parts of the floorplates, and each for most of these species. Several to many specialized wedge-shaped extension decreases in size inward, ending hydropore structure plates lie along the posterior margin above the base of the frame. The posterior sides of the and make up part of the oral area. floorplates of ambulacra II and IV flare outward to form a wide contact zone with the adjacent floorplates of amhu- ORAL FRAME AND CENTRAL LUMEN lacra I and V. The inner part of the oral region structure of the Iso- The posterior side of the frame is composed of the prox- rophida is hidden under the roof of oral covering plates. imal floorplates of ambulacra I and V, and the intrathecal It consists of a massive rim of plates which surrounds a extensions of the posterior primary orals. Extensions central lumen (text fig. IG). This rim constitutes the oral from hydropore orals, or perhaps occasionally other plates frame. It is a rigid structure composed of tightly sutured associated with the hydropore structure, may possibly be plates. The rim penetrates further into the thecal cavity included also. The two floorplates are expanded inward 18 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21 and laterally. Their anterior edges flare outward laterally D). The first of these is more common. It is found in all and form the wide contact zone with expanded pos- Carneyellidae, Isorophidae, and Agelacrinitidae. The terior sides of the two lateral anterior floorplates. The shape and size of the structure is variable. It may be ele- two posterior floorplates commonly do not make contact vated above the level of adj acent oral and ambulacral across the posterior interradius. Thus this section is plates to form a rounded, elongate, or circular protuber- formed entirely by the intrathecal extensions of the pos- ance, or it may be integrated into the central oral rise and terior primary oral (or orals), and occasionally also by thus show no separate relief. In intermediate, semi-inte- hydropore plates. These intrathecal extensions end far grated types the structure forms a small but distinct rise above the innermost edges of adjacent floorplates and along the posterior part of the central oral rise. thereby leave a large posterior interradial gap. The dis- Within this first type considerable variation occurs in position of the intrathecal extensions of the posterior pri- size, location, and type of plates involved. The simplest mary oral and associated elements is variable and depends condition is found in the Carneyellidae and the Isorophi- upon the family. Usually the extensions are complex and dae, in which the structure is integrated into the central consist of at least two inner blades on each side of the gap, oral rise; the hydropore structure is of approximately the one directed obliquely anterior, and one obliquely pos- same elevation as the proximal part of ambulacrum V. terior. These blades delimit a shallow chamher between The structure is composed of the hydropore oral, com- the central lumen and the posterior part of the thecal monly the adjacent edge of the right posterior primary cavity. Additional bladelike extensions from the cover- oral, and two or three opposing proximal plates of the plates extending down into the center of the posterior gap oral-ambulacral series. have been observed in some forms and these subdivide In the Carneyellidae the posterior edge of the opening the gap into right and left halves. The intrathecal exten- is bounded by the anterior edge of the hydropore oral sions of hydropore plates and the associated plates of the (text fig. IA). The anterior side is commonly formed by stone canal passageway may modify the right posterior the two proximal, posterior coverplates of ambulacrum V. region, depending upon the type of hydropore structure. However, the opening may extend proximally between the In some species of Agelacrinitidae the oral frame, hydropore oral and the adj acent edge of the right Jros- although similar in shape to the above type, appears to be terior primary oral. In this case, the left anterior edge of formed only by the five enlarged proximal f1.oorplates, the opening is bounded by the primary oral. In some without intrathecal extensions of the orals. This type of forms in the family the opening may extend further dis- frame may also lack a posterior gap, the two posterior tally along the anterior edge of the hydropore oral and the floorplates being in contact across the posterior inter- third posterior coverplate 0.£ ambulacrum V thereby forms radius. This frame type has been observed only in the distal part of the anterior side of the opening. agelacrinitid species in which the external oral area is The hydropore structure in the Isorophidae is quite sim- formed exclusively by numerous small orals. ilar to that of the Carneyellidae, but the plates of the an- terior side differ due to the increased number of plates in the Isorophidae oral region (text fig. IF). The anterior Hydropore structure edge of the hydropore oral forms the entire posterior mar- In the Isorophida an opening presumed to be a hydro- gin of the opening. The anterior side is bounded by the pore is located between the oral pole and the anus, com- adradial ends of the right posterior lateral shared cover- monly offset to the right of the axial thecal plane (text plate and the proximal posterior primary coverplate of fig. lA, C, D, F, H). It lies near the proximal posterior ambulacrum V. In Isorophidae with larger openings, the edge of ambulacrum V. It is a slitlike opening along the right side of the right posterior primary oral forms the contact zone between two or more plates. Commonly the proximal part of the anterior edge of the opening. When direction of elongation is either parallel to the proximal the opening is distally extended, the adradial margin of the midline 0.£ ambulacrum V, or is nearly parallel to the second posterior primary coverplate of ambulacrum V transverse thecal axis. forms its distal anterior side. Two basic types of hydropore structures occur in the In both families the slitlike opening is commonly paral- Isorophida, Variations within these allow recognition of lel to the proximal part of the midline of ambulacrum V. several subtypes. In one type the structure is located However, the large hydropore oral may extend into the within the right posterior asymmetrical bulge of the oral adjacent proximal posterior edge of ambulacrum V. When area and is formed by oral and amhulacral plates (text this penetration is pronounced, the hydropore is elongate fig. IA, F, H). The other type lies distal to the oral area, nearly parallel to the transverse thecal axis. The adradial along the posterior side of ambulacrum V, and is formed ends of the plates of the oral-amhulacral series which by ambulacral and interamhulacral plates (text fig. IC, bound the hydropore are often enlarged, their width being MORPHOLOGY OF THE ISOROPHIDA 19 greater thanthat of adj acent orals and ambulacrals. This lacral plates. These differ in size and shape from the allows identification of these plates even in specimens in adjacent" typical" squamose interambulacral plates. At which the structure is disrupted. Moreover, the bounding least one of these modified interambulacrals is large. The edges of all plates of the hydropore structure may be thick- structure rises above the level of the adjacent interambu- ened to form a small raised rim which surrounds the open- lacral plates to form a distinct bulge along the proximal ing. posterior side of ambulacrum V. The orientation of the In the Carneyellidae and Isorophidae, the plates sur- slitlike opening in this type of hydropore structure is vari- rounding those in contact with the hydropore are fre- able and ranges from nearly parallel to the midline of am- quently modified in shape and size. These are considered bulacrum V to parallel to the transverse axis of the theca. " peripheral" hydropore structure plates even though they " Peripheral" hydropore structure plates in the Lebeto- are not in direct contact with the opening. The most com- discidae may be ambulacral coverplates which are short- mon " peripheral" is the ambulacral coverplate adjacent ened to accommodate the intrusion of hydropore inter- to the distal end of the hydropore oral. It is commonly ambulacrals into the edge of the ambulacrum, or oc- shortened (adradial-perradially}, owing to the intrusion casionally they may be additional modified interambu- of the hydropore oral into the edge of ambulacrum V. lacrals. The number, arrangement, shape, and size of The length of the opening, the number of ambulacral these supplementary plates are constant at the generic or coverplates in contact with it, the number of " peripheral" specific level. plates, and the size, shape, and orientation of the large hydropore oral are constant at either the generic or spe- cific level within the Carneyellidae and Isorophidae. Stone canal passageway The Agelacrinitidae have the same basic type of hydro- The stone canal passageway leads inward from the slit- pore structure as the Carneyellidae and Isorophidae (text like hydropore into the thecal cavity (text fig. 1G). The fig. IH). It lies along the posterior margin o·f the oral inner end lies distal to the inner rim of the oral frame, area and comprises ambulacral and oral elements. How- near or adjacent to the proximal posterior side of ambu- ever, the structure may include either several plates form- lacrum V. The passageway is conical and expands inward ing a small protuberance which is semi-integrated with the rapidly. It ranges from subcircular to subtriangular in central oral rise, or it may contain numerous plates which cross section. The inner end is many times the size of the form a large, elongate protuberance posterior to the oral hydropore. In some forms the axis of the passageway is rise. The anterior side of the protuberance is formed by essentially perpendicular to the thecal surface; in others plates of the oral-ambulacral series, the anterior ends of the axis is oblique, with the hydropore distal to the center which may perradially reach the transverse oral midline of the large inner opening of the passageway. or may lie distal to other posterior orals which form the The stone canal passageway is formed by the intra- transverse midline. The posterior margin of the structure thecal parts of the plates of the hydropore structure, one is formed by few to many plates. These may be considered or two underlying ambulacral floorplates, and occasion- either multiple hydropore orals or modified interambula- ally, additional elements. The upper end of the passage· crals that have been incorporated into the oral series. The way, immediately beneath the hydropore, is formed by the elongate opening extends along the summit of the pro- inner sections of all the plates which bound the hydro- tuberance and lies along the contact line between the an- pore. In those species with few hydropore structure plates, terior and posterior plates of the structure. the cross section of at least the upper part of the passage- The second basic type of hydropore structure found in way is angular. Where many plates are involved, the pas- the Isorophida is limited to the Lebetodiscidae. It lies sageway is nearly terete. The inner part of the passage- distal to the oral area along the proximal posterior part of way is formed by the posterior adradial sides of the prox- ambulacrum V and extends into the adjacent proximal imal one or two floorplates of ambulacrum V, and intra- region of interambulacrum 5 (text fig. lC, D). It in- thecal extensions from one or more posterior hydropore corporates only ambulacral coverplates and modified inter- structure plates. ambulacrals. The ambulacral components are usually the The structure of the stone canal passageway is ade- first and second proximal coverplates of the posterior side quately known in only a few species, because of its in- of ambulacrum V. Occasionally the third coverplate is in- ternal location. The details of its construction appear to cluded. The adradial edge of the proximal ambulacral be quite variable. Moreover, since the passageway is coverplate is enlarged and produced outward into inter- formed only in part by the hydropore structure plates, it ambulacrum 5. The posterior adradial margin of this plate may vary independently from the hydropore structure. bounds the anterior edge of the hydropore. The posterior Thus some species with nearly identical hydropore struc- side of the opening is bounded by one or more interambu- tures appear to have characteristically different stone 20 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21

canal passaGeway Th b s, e stone canal passageway structure cally. Lebetodiscina have a single alternating biseries of may eventually furnish the basis for further refinement of coverplates which form a zigzag perradial line (text fig. edrioasteroid classl·ficat'Ion. lA, B, C, D). Coverplate shape, size, and angle of inclina- tion are generic or specific taxobases, The Isorophidae have alternating multiple biseries in which individual Ambulacra pairs of two or more coverplate sets alternate along the The five ambulacra are commonly slightly elevated ex. ambulacrum. Double biseries, formed by two sets of ternally and form low, rounded ridges above the inter- plates, are the most common (text fig. IE, F, G). The ambu.lacra. Occasionally they rise more abruptly as Agelacrinitidae coverplate sequence is commonly cyclic, promment, steep-sided ridges. Proximally the ambulacra with two to seven serially repeated sets of plates forming reflect the triradiate character of the oral area, being dis. the cycles (text fig. IH). Opposing cycles alternate, offset posed as a single anterior ambulacrum which extends out by half a cycle length, and form a prominent undulating from anterior oral midline, and two lateral pairs, one perradial line. Other Agelacrinitidae may have complex extendmg from each end 0.£ the transverse oral midline. alternating biserial sets of coverplates or a combination of The junction of the perradial lines of each two lateral am- both cyclic and biserial sets. The number of sets of cover- bulacra with one end of the transverse oral midline occurs plates, the order of occurrence, and individual plate at the perradial tip of an unpaired lateral bifurcation shapes are generic and specific level taxobases. plate. The two lateral bifurcation plates are usually larger Bladelike intra-ambulacral extensions commonly extend than adj acent proximal ambulacral coverplates. The am. from the inner, ambulacral tunnel surfaces of the cover- bulacra may be straight, or they may curve. Direction of plates (text fig. 1B, G). They are largest under the per- curvature is variable and includes all solar, all contra- radial tips 01 the coverplates, and decrease ad radially to solar, or various cornbinations of the two directions. Am- merge with the inner sides of the coverplates before reach- bulacral disposition is a generic taxobasis. Additional ing the floor of the ambulacral tunnel. variations in the shape of the ambulacra include rate of In the Lebetodiscina and the Isorophidae, the inner ex- curvature, width, amount of distal taper, height of maxi- tremities of these blades flex proximally so as to underlap mum elevation, and proportional length. The level of tax- the proximally adj acent coverplate. They also extend per· onomic significance of these features is variable within radially under the tips of opposing plates. Thus the intra- the order. ambulacral extensions firmly interlock adjacent and oppos- Occasionally the number of ambulacra varies. One or ing coverplates when closed. This interlocking required more of the five primary ambulacra may bifurcate. These sequential (or peristaltic) operation of the coverplates, may be equally developed, or one may be a small side- the individual plates being movable only in conjunction shoot off the main ambulacral course. One specimen of with surrounding coverplates. Each entire half of a cover- Cystaster stellatus has four such ambulacral bifurcations; plate series was probably imbedded in continuous flesh. the resultant nine arnhulacra are the most that have been This would have appeared in life as a long ribbon which observed. Occasionally one 0.£ the five primary ambu- extended the length of the ambulacrum. During opening. lacra may not develop. Neither addition nor subtraction the two opposing ribbons progressively separated along of ambulacra appears to be of taxonomic importance, the perradialline with movement initiated at the distal tip They would seem to- be ontogenetic "accidents." The of the ambulacrum. The perradial edge of the opposing unique specimen of T'hresherodiscus ramosus Foerste ribbons rotated slowly upward and outward, and two op- (1914, Kesling, 1960) is reported to have only three pri- posing, broad undulations swept proximally in a wave- mary ambulacra, one anterior and two lateral, but these like motion. Coverplate closure reversed the process. Cov- split repeatedly to form nineteen distinct 'branches. If erplate intra-ambulacral extensions are thought to occur this species belongs Ito the Isorophida, it is unique. in most Agelacrinitidae. However, these may not interlock The ambulacra of the Isorophida are formed by a uni- adjacent or opposing elements. This being so, the cover- series of floo'rpJ:ates overlain by sets of coverplates (text plate movement in agelacrinitids may have differed from fig. IB). The arnbulacral tunnel is enclosed between these that in other Isorophida, The intra-ambulacral extensions two sets of plates. of the coverplates in the Lebetodiscina participate in the formation of the upper parts of coverplate passageways COVERI>LATES and thus are enlarged. The coverplates are disposed as alternating biseries or Adradially, intrathecal extensions of the coverplates cyclic sets of plates along each ambulacrum. Opposing commonly pass between the lateral edges of the floorplates coverplates, when cIo,sed, meet centrally along the per· and adjacent interambulacrals into the thecal cavity (text radial line. Coverplate pattern is important taxonomi- fig. IB, G). In the Lebetodiscina, those extensions form MORPHOLOGY OF THE ISOROPHIDA 21 the inner ends of the coverplate passageways. The intra- passageway is circular in cross section and is shared sub- thecal extensions interlock the coverplates into the theca equally by two contiguous coverplates, They are formed and may be an important part of the articulating appa- by opposed hemicylindrical grooves in the lateral faces of ratus for movement of the coverplates. In the Isorophidae, the coverplates. The axis of the passageway thus parallels only coverplates of the primary set appear to develop large the exterior surface of the coverplates. intrathecal extensions which interlock the coverplates into In species with thick ambulacral coverplates oriented the theca, and probably also participate in the articulatory almost vertical to the thecal surface, the axes of the pas- apparatus (text fig. IG). Most, and perhaps all Agela- sageways are also vertical (e.g., Lebetodiscus). In those crinitidae lack intrathecal extensions and the coverplates with thinner coverplates, oriented almost parallel to the end above the lateral margins of the floorplates. Thus the thecal surface, the passageway axes are almost horizontal coverplates adradially abut the upper edges of the (e.g., Cryptogoleus). adjacent interambulacrals. The external foramen of each passageway opens along The coverplate intrathecal extensions may have been the suture line between the adj acent plates. attachment sites for muscles used to open the coverplates. The plane of the opening is nearly parallel to the outer Alternatively, the upper surfaces of the extensions may surface of the coverplates and is thus oblique to the axis merely have abutted the inner sides of the overlying inter- of the passageway. External openings are therefore ellip- ambulacrals, plate movement being due to pressure ex- tical. They are elongate normal to the ambulacral axis, erted on the ambulacral tunnel surfaces of the coverplates. and flanked by the upper, lateral edges of the two serially This would have forced the perradial ends of the plates adjacent coverplates. The upper end of each passageway, upward while the adradial ends were held in place by the which is visible through the external foramen, is formed extensions. entirely by the outer surface of the curved, bladelike, The coverplates of the Isorophida were sutured to the intra-ambulacral extension of the distal plate. underlying floorplates along their zone of articulation, the The width and shape of the external foramen are vari- adradial suture. In contrast with the common echinoderm able. In some species with large, thick coverplates which plan, the coverplates were also sutured to one another are oriented almost normal to the thecal surface, the laterally. This strengthened the coverplate series in forms foramina are wide, almost circular (e.g., Lebetodiscus). with intra-ambulacral extensions that interlocked adjacent In other species with similar coverplates, the foramina coverplates (Lebetodiscina, some Isorophidae). In those may be very elongate. In forms with thin coverplates without extensions (Agelacrinitidae, some Isorophidae) which externally almost parallel the thecal surface, the the suturing alone held adjacent coverplates together. The foramina are narrow and slitlike (e.g., Cryptogoleus). smaller medial coverplates, such as plates of the tertiary The inner foramina of the passageways are bounded by set in multiple biseries and the plates of the fourth, fifth, the edges of the intrathecal extensions of adj acent cover- etc. sets in cyclic series, end before they reach the adradial plates. The inner sides of these extensions are nearly articulation zone. These coverplates were suspended over parallel to the interior thecal surface, and thus are oblique the ambulacral tunnel, held by their tight suturing to the to the passageways. The inner foramina are thus also laterally adjacent, larger coverplates which were in contact elliptical and elongate normal to the ambulacral axis. adradially with the underlying floorplates. The lateral These openings are shared subequallyby serially adjacent suturing has resulted in the common preservation of the plates. coverplate series intact, even in thecae which have col- At least two genera, Lebetodiscus and Foerstediscus, lapsed during preservation. In the Isorophina, where more have accessory structures, called "lateral depression se· than one set of coverplates constitute the series, cover- ries," associated with the external foramina of the pas- plates of the secondary, tertiary, etc. sets are intercalated sageways (text fig. ID). These are rows of external basin- between existing primary coverplates. These intercalates like depressions, one along each lateral margin of the are generated by the flesh which laterally connects the primary coverplates. coverplate, close to the contact line between contiguous coverplates. The coverplates in genera so endowed are axially convex outward. The small basins are incised into COVERPLATE PASSAGEWAYS the flanks of the axial convexity. Thus the basins are In the Lebetodiscina there is a system of ambulacral deepest toward the axis of the coverplate, The sutural passageways along the lateral sutural faces of the serially sides of the basins are confluent with the deep lateral adjacent coverplates (text fig. lA-D). These extend from groove formed along the suture line between the adjacent the exterior of the theca into the thecal cavity, one row convex coverplates, There are commonly eight or nine along each side of the ambulacrum. Passageways also ex- depressions to a row. Perradially the depressions flank tend between the larger oral covering plates. Each tubular the external foramen of the coverplate pass'ageway. In the 22 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR21 opposite direction they extend almost to the adradial Both squamose-imbricate and polygonal-tessellate inter. suture line. Depressions on contiguous coverplates do not ambulacrals may occur within the same genus, but are of necessarily correspond in number or position. Those on specific significance, one side of the suture may lie opposite to, or alternate Commonly domal thecae have squamose, imbTicate with, the opposing row; occasionally both conditions are interambulacrals. In clavate forms the interambulacrals found along a single suture line. are polygonal and tessellate on the upper surface, but be- In the Lebetodiscina the coverplate passageway system low the ambitus, where they are continuous with the appears to have housed tubular branches from the internal pedunculate zone plates, they are in some forms squamose, radial canals. These branches probably extended beyond proximally imbricate, and irregularly arranged, whereas the outer foramina and probably functioned as respira- in others they are very thin, elongate, imbricate plates tory structures. The lateral depression series would sug- which are arranged in numerous vertical columns. The gest that at least in some species the external parts of the transition from polygonal interambulacrals to squamose lateral branches were further branched and sent exten- or rectangular peduncular zone plates may be abrupt or sions into each of the depressions. gradual. When gradational, the distal interambulacrals become progressively thinner and more elongate. FLOORPLATES The pedunculate zone of clavate forms appears to have The ambulacral floorplates 0'£ all Isorophida are a been extensible, with the imbricate plates able to telescope tightly sutured uniseries which forms a solid ambulacral together. When fully contracted, the theca would be more floor, without passageways into the thecal cavity (text fig. stable in turbulent water. When extended, the upper oral lB, G). Floorplates are commonly trough-shaped with surface would be elevated far above the substrate, prob- concave upper sides which form the broad axial ambu- ably for feeding. Minor extensions and contractions may lacral groove. Adradially the upper margins of the floor- be related to the pumping mode of respiration believed to plates are nearly planate and form articulation sites for have been employed by clavate species. the overlying coverplates. The inner surfaces of the floor- plates vary from evenly convex inward to more angular forms with large lateral nodes. Contiguous floorplates may Anal structure imbricate, their proximal margins overlapping adjacent The Isorophida anal area lies in the posterior inter- plates along oblique sutures (e.g., Lebetodiscina and some ambulacrum, commonly near its center. Two basic anal Agelacrinitidae) . In the Isorophidae and most Agela- organizations occur. In the Lebetodiscina the anal struc- crinitidae the floorplates are commonly quite thick and ture is a periproct, formed by numerous plates grouped abut along vertical sutures. In the Isorophida all flOOT- into several irregular circlets (text fig. lA, C). Plate size plates are completely hidden from external view by the commonly decreases toward the center, and at least the overlying coverplates, except in disrupted or weathered more central plates are elongated toward the central anal specimens. opening. The structure may be elevated into a subconical mound. The periproct was merely a flexible zone around Interambulacra the anus. In the Isorophina there is a radial, valvular anal struc- The interambulacra of the Isorophida are polyplated; ture (text fig. IE, G, H). Commonly it is formed by two plates are variable in number and are distributed without imbricating circlets of triangular OT subtriangular plates. apparent order. The largest elements' are central and The plates of the outer circlet alternate with and overlap distal. Smallest plates lie along the adradial suture lines, those of the inner one. Both sets are beveled along this adjacent to the ambulacra. Commonly small interamhu- zone of imbrication and fit snugly together. The zone of lacrals also surround the anal structure in interambu- overlap is commonly wide so that all but a narrow axial lacrum 5. strip of each inner element is hidden from external view Interambulacrals are commonly squamose and imbri- when the structure is closed. The distal ends of the anals cate and form highly flexible thecal areas. The direction abut the surrounding interambulacrals; their contact zone of imbrication is basically proximal, but near the ambu- is commonly modified by ridges, grooves, or flanges on Iacra the plates overlap adradially irrespective of the both sets of plates. Occasionally three circlets of plates direction the ambulacra assume. The adanal interambu- appear to be included in the valvular structure, whereas lacrals radially imbricate toward the anus. a few forms appear to have only one circlet of anals. In some Isorophida the interambulacrals are thick, When closed, the valvular anal structure appears to polygonal, and abut along vertical sutures. Such tessellate have been nearly level with the surrounding interambu- areas appear to have been only slightly, if at all, flexible. lacral surface or perhaps elevated into a very low, MORPHOLOGY OF THE ISOROPHIDA 23 rounded mound in some. To open, the anals rotated numerous small plates, in which circlet organization is less against the surrounding interambulacrals, centrally lifting apparent. up and out, thereby opening the central anus. The large, In the center of the rim the circlets are transitional lateral overlap of adjacent anals would permit the struc- between the concentrically elongate proximal plates and ture to open widely without these anals losing contact the distal, radially elongate plates. In some, these are with each other. merely irregular squamose plates. In others, they are The valvular anal structure is believed to have been ovoid and elongate radially, but the externally exposed part of an anal pumping system involved in respiration. parts are sagittate. In such plates the exposed zone is It is found only in the Isorophina, which lack the made up of a proximally convex, semicircular "head" apparently respiratory coverplate passageways found in which forms the anterior third of the plate. An elongate the Lebetodiscina. crest or shaft extends distally from the center of the straight distal edge of the "head." The lateral mar- gins of the distal two-thirds of the plate, which flank the shaft, are depressed and overlain by small, radially elon- Peripheral rim gate plates of the next distal circlet. The anterior" heads" A peripheral rim forms the margin of the oral surface appear to form a circlet of small plates elongate concentric in the Isorophida (text fig. lA, C, E, G, H). It is formed with the thecal margin. The distal shaft also appears to by several circlets of proximally overlapping and distally he a discrete plate and to form alternate, radially elongate diminishing plates. There are one to three proximal cir- plates in the adjacent distal circlet. The straight distal clets of larger plates which are externally elongate, con- edges of the anterior "heads" are aligned so as to form centric with the thecal margin. Distal circlets of varying a distinct circle around the rim. number are formed by radially elongate elements. The larger plates of the peripheral rim in all Isorophina The large plates of the proximal rim circlet commonly and Carneyellidae are geniculate. The upper, externally alternate proximally and distally, forming two subcirclets, exposed parts extend down to the underlying substrate The lateral edges of plates in the distal sub circlet overlap where they flex distally outward to form a broad basal the lateral edges 0'£ the two adj acent proximal subcirclet zone parallel to the substrate. This extends distally out members. Thus although plates of both subcirclets are under the adjacent, more distal rim plates. These genicu- subequal in size, the externally exposed part of the distal late bases support the rim plates during thecal collapse, ones is much larger than that of adjacent, proximal sub- the upper ends of the plates remaining nearly in life posi- circlet plates. Commonly the distal subcirclet elements tion. In collapsed specimens the adj acent distal inter- are externally squamose, the proximal plates subtrape- ambulacrals are depressed, and leave the upper ends of zoidal. the proximal rim plates elevated far above the interambu- The plates of the second rim circlet are much smaller lacrals. This pronounced elevation of the rim in collapsed than the proximals and commonly are from five to seven specimens led many earlier workers to suggest that it was times as numerous. Proximally they overlap the distal a fused structure. edges of the proximal circlet. Second circlet plates that Small vertical ridges of varying development may be overlap lateral sutures between proximal elements lie in formed on the lower sides of the bases of the rim plates part proximal to those that overlap the centers of proximal (text fig. IG). The ridges are elongate normal to the circlet plates. This produces a scalloped line of distally thecal margin and commonly are sharp crests which are convex arcs 'at the contact of the two circlets. In forms in contact with the underlying substrate. Seven to 10 with proximal-distal subcirclets, five to seven second cir- ridges per plate have been observed on the large plates of clet plates overlap each distal plate, whereas only three the proximal circlet of the rim. These ridges appear to or four overlap the externally narrower plates of the have been related to thecal attachment. proximal subcirclet. Thus the scallops of the line adjacent The rim plates of the Lebetodiscidae, and perhaps of a to distal subcirclet plates are much wider than, and alter- few other Isorophida, are squamose rather than genicu- nate with, those adjacent to proximal subcirclet plates. late. Thus thecal collapse affects equally both distal inter- This produces a series of larger convex arcs regularly ambulacral and proximal rim plates, so that the division alternating with much smaller ones. The line between the between the two regions has no marked relief and is often second and third circlets may also be scalloped, but be- difficult to locate. This difference in rim plate structure cause of common irregularities of the third circlet the arcs may signify a different mode of attachment for the Lebeto- are less distinct. Outer circlets of the rim are formed by discidae. 24 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21

MORPHOLOGY OF THE EDRIOASTERIDA Text fig. 2, pI. 58-63.

Thecal shape the transverse midline at the central oral pole. The orals are distally continuous with the ambulacral coverplate The Edrioasterida have semigloboid thecae which reo series and there is no distinct boundary between plates of semble the test of some regular echinoids and thus are the two sets. Thus the total number of orals is not apparent informally called "echinoidaI." The upper oral surface in most species. Three or four central o-rals may be some- is convex upward. Commonly the center of this area is what larger than the others. However, oral plate divisions nearlyplanate, the rate of curvature increasing distally. comparable to the primaries, secondaries, or lateral shared The distal margin of the upper oral surface is vertical and coverplates found in most Isorophida are not found in the forms the ambitus of the theca. Below the ambitus the Edrioasterida. Adradially the orals meet the exposed theca constricts gradually. This subambital zone com- parts of the interradial oral frame plates along a sub- monly forms about one-third of the total thecal height. marginal suture line which is continuous with the adjacent Distal to this zone the theca constricts rapidly, the exterior proximal ends of the ambulacral submarginal suture lines. parallel to the substrate, forming the resting zone. Beyond this area the thecal plates flex upward and inward toward ORAL FRAME AND CENTRAL LUMEN the center of the theca to form the ineurved zone. A flex- ible membrane apparently extended from the distal edge A massive oral frame, surrounding a central lumen, of the incurved zone back down to the substrate. Numer- forms the inner part of the oral region (pI. 61, fig. 2, 5, ous minute plates were imbedded in this membrane, each 7-9). It lies in part under the roof of oral covering plates. squamose and elongate concentric with the thecal periph- The frame is formed by five large radial and five large ery. The distal margin of this membrane was apparently interradial plates. All are compound. The proximal edge attached to the substrate and surrounds a small circular of the frame is subovate and transversely elongate. It ex- ( ?) area comparable to the nonplated aboral surface of tends down into the thecal cavity further than any other the Isorophida. The Edrioasterida are commonly large structure. The distal margin of the frame is subpentag- edrioasteroids, adult thecal diameters ranging from 30 to onal, the radial extremities continuous with the five over 50 mm, although a few smaller species occur. ambulacra. The oral area lies in the center of the upper oral surface. The central lumen lies directly under the central oral The five radiating ambulacra extend past the ambitus into covering plates. It is transversely elongate and ovoid to the subambital thecal zone, but end or curve before reach- subpentagonal in cross section. The lumen extends from ing the resting zone. The hydropore structure, which is the proximal ends of the ambulacral tunnels downward associated with the posterior edge of the oral area, and through the frame and opens directly into the center of the anal structure are both on the upper oral surface. the thecal cavity below. " Echinoidal " thecae appear to have been only slightly, Each radial element of the frame is formed by the fusion if at all, flexible in life. of several proximal pairs of the biserial floorplates from one ambulacrum. Passageways which penetrate the frame Oral area plates mark the position of the fused sutures and allow The oral area includes external oral coverplates which form a solid roof over the proximal edge of the under- Text figure 2. EDRIOASTERIDA lying oral frame and over the central lumen (text fig. 2A). A. Edrioplius levis (Bathed. 1914. UCMP -lO-l79; (x pl. 62. Both oral covering plates and parts of the interradial fig. 1. frame elements are visible externally. The o-ral area is 13. Edrioaster bigsbyi (Billings) , 1857. GSC 1407-E. (x 8l. seg- slightly elevated above the interambulacral areas to form ment of one ambulacrum which exposes the upper surface of a low central oral rise. the floorplates, C. Edrioaster bigsbyi (Billings), 1857. GSC 1407-E. (x 8), cross ORAL COVERING PLATES section of the ambulacrum seen in fig. B. The left floorplate The center of the oral area is formed by seven or more shows its proximal sutural face with the coverplate passageway, oral .coverinp; plates which abut perradially along the sutural groove. and pits. TIlt' right floorplatc (diagonally antenor and the transverse oral midline (text fig. 2A). lined) is a section through the center of the alternate opposing floorplate. Parts of the hydrovasculur system presumed present The proximal end of the anterior oral midline intersects in life and one open coverplate have been reconstructed. MORPHOLOGY OF THE EDRIOASTERIDA 25

externally exposed adradial perradialline parts of interradial elements of oral frame sub-marginal suture

adradial suture

lateral bifurcation plates oral plates

coverplates

externally exposed interambu10 cro], plates adradial ends of floorplates

area of periproct in complete specimens sutural grooves floorplate passageway

branch canol swelling for movement extending down of cover plate sutural groove

B cross-section of opposing floorplate upper pits radial conal perradial trough lateral branch

lateral sutural face of floorplate

ampulla coverplate articulation site

branch canol in floorplate passageway externally exposed adradial end of floorplate 26 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21 determination of the number of floorplate pairs included Hydropore structure in each compound plate. The proximal edge of the com- The Edrioasterida opening presumed to be the hydro. pound radials are enlarged and extend inward and later- pore is located between the oral pole and the anus, offset any to form at least the five radial segments of the inner to the right of the axial thecal plane (text fig. 2A). It lies rim of the frame. In some forms these elements may in the right posterior part of the oral area, adj acent to the extend laterally so as to meet under the interradial ele- proximal, posterior edge of ambulacrum V. The opening ments, and thereby form all of the inner edge of the frame is a small, elliptical slit which extends across the suture rim. The distal ends of the radials extend out under the between two plates. The long axis of the opening is com- proximal three or four pairs of floorplates of each ambu- monly almost parallel to the proximal part of the midline lacrum. The paired elements of two or three adoral pairs of ambulacrum V. of ambulacral floorplates are separated from one another The anterior end of the opening is housed in the right along the perradial suture. Consequently, part of the posterior edge of the interambulacral part of the posterior upper face of the distal part of each radial is exposed interradial plate of the oral frame. The posterior half of between these separated proximal floorplates. the slit lies in the posterior hydropore plate, which is a The five compound interradial plates of the oral frame modified proximal interamhulacral that has been incor- are wedged between the radials. Each is formed by two porated into the oral-ambulacral series. The left anterior or more individual proximal floorplates from adj acent edge of this plate abuts the right posterior edge of the pos- ambulacra, and the proximal interambulacral plates of terior frame interradial. The right side of the posterior the adjacent interambulacrum. Opposing pair members plate abuts, or is fused to, the adradial end of one or more of two or more proximal floorplate pairs of each ambu- proximal posterior floorplates of ambulacrum V. Its pos- lacrum apparently have separated perradially and mi- terior margin abuts the proximal interambulacrals, The grated away from each other to become incorporated into posterior hydropore plate seems to be an element of the different interradial frame plates. The adjacent floor- oral-ambulacral series because it either intrudes into the plates from each ambulacrum fuse together and are also posterior side of ambulacrum V, or is fused to a proximal fused laterally to the proximal floorplates from the ambu- floorplate. Both hydropore plates have a thickened raised lacrum on the other side of that interradius, thereby form- rim around the pore opening. ing the proximal edge of each interradial. Passageways penetrating the proximal edge of the interradial elements mark the fused sutures between the constituent ambulacral Stone canal passageway floorplates. Adradially, the ankylosed floorplates are fused to the proximal plate of the adjacent interamhu- The stone canal passageway leads downward from the lacrum, and thereby incorporate this plate also into the hydropore to the thecal cavity (pl. 61, fig. 5). It pene- oral structure. Although the interradials include fewer trates both plates which bound the hydropore. Apparently floorplates than the radials, the addition of the proximal the passageway is oval in cross section and expands in interambulacral plates makes them considerably larger diameter inward. The inner end of the passageway appears than the radials. The proximal margins of the interradial to be formed by the inner parts of the two hydropore plates of the frame are enlarged and extend downward plates. The inner opening lies adj acent to the distal edge into the thecal cavity between the radials. In some in- of the right posterior margin of the oral frame rim. stances the inner ends of the interradials apparently extend as far inward as the radials and thus form an inner rim of alternating elements. In others they may end before Ambulacra reaching the frame rim, being underlapped by the lateral The five ambulacra are broad and extend past the edges of the radials. ambitus into the subamhital zone. They are elevated The adradial ends of the oral covering plates rest on the above the adjacent interambulacra and form low, wide, upper surface of the fused floorplate parts of the inter- rounded ridges on the thecal surface. Proximally they radial frame plates. The interradial frame plates are in merge with the central oral rise. The ambulacra originate part exposed externally. This exposed zone proximally as a single anterior ambulacrum, which extends from the includes the upper adradial ends of the fused floorplates anterior oral midline, and two lateral pairs - one pair and distally the entire upper side of the fused interamhu- arising from each end of the transverse oral midline. The lacral constituents of the interradials. The upper ends of two perradiallines of each lateral pair of ambulacra meet the fused floorplate parts of each interradial laterally abut the transverse oral midline at the perradial tip of the the proximal, lateral edge of the first normal floorplate lateral bifurcation plate. However, in contrast to the of each adj acent ambulacrum. Isorophida, this plate is not larger than the adj acent cover- MORPHOLOGY OF THE EDRIOASTERIDA 27 plates in the Edrioasterida. It is distinguished only by its FLOORPLATES position. The ambulacral floorplates are an alternating biseries The ambulacra are variously curved in all known spe- (text fig. 2B). The perradially opposing alternate floor- cies of the Edrioasterida; they may be all solar, all con- plates slope steeply downward to form a deep, central trasolar, or I-IV contrasolar and V solar. Curvature is ambulacral trough. Along the floor of the trough, the commonly pronounced only in the subambital zone where angular perradial tips of the floorplates form a medial the ambulacra become concentric with the thecal ambitus. suture line of right-angled zigzags. The ambulacra may distally curve hack toward the oral The thick adradial ends of the floorplates abut adjacent area and even extend their tips up onto the upper oral interambulacrals along vertical or slightly oblique su- surface. Ambulacral disposition appears to be constant tures, the latter sloping inward toward the ambulacral within each edrioasterid genus. axis. Adjacent floorplates may vary in length and thus Edrioasterida ambulacra are formed by the two alter- the adradial suture lines between the interambulacrals nating biseries of coverplates and floorplates (text fig. 2B, and the floorplates may be somewhat irregular, particu- C). The coverplates roof the axial ambulacral trough larly along the proximal parts of the ambulacra. The which is formed by the centrally depressed floorplates. upper surfaces of the floorplates are externally exposed The ambulacral tunnel, enclosed between the two sets of between the adradial and the submarginal suture lines. plates, is commonly large and transversely elongate in These areas slope upward toward the ambulacrum and cross section. The coverplate biseries exactly matches the form its elevated lateral margin. floorplate with each coverplate centered over a floorplate. Perradial to the submarginal suture line, the upper sur- However, the floorplates are longer and extend adradially face of each floorplate forms the rather narrow articula- beyond the coverplates. tion zone for the coverplates. This flat zone flanks the upper edge of the deep ambulacral trough and is slightly

COVERPLATES inclined toward the adjacent trough. The ambulacral coverplates form a single alternating biseries of plates which meet perradially along a zigzag FLOORPLATE PASSAGEWAYS or sinuous line (text fig. 2A, C). The adradial ends of the A system of passageways connects the ambulacral tun- coverplates are straight or slightly curved outward adra- nel with the thecal cavity (text fig. 2B, C). The passage- dially. The lateral (proximal, distal) edges of each plate ways extend inward along the lateral sutures between adja- are straight, parallel, and normal to the ambulacral mid- cent floorplates, one row along each side of the ambulacral line. Perradially the coverplates may be pointed or trough. The upper ends of the passageways open into sinuous. small, subcircular pits centered over the sutures between The adradial ends of the coverplates meet the externally adjacent floorplates. The pits lie along the upper margins exposed parts of the floorplates along submarginal suture of the trough, along the inner edge of the articulation zone lines. These lines extend along each side of the ambu- for the coverplates. The pits are thus in part roofed by the inner surfaces of the overlying coverplates. The inner lacra, perradial to and concentric with the adradial suture ends of the passageways open as elongate depressions lines. Adradially, the coverplates rest on the upper sur- which extend along the inner lateral suture lines between faces of the floorplates. The inner or lower adradial edges the floorplates. Each is elongate normal to the ambulacral of the coverplates are beveled and fit tightly against the axis. Hoorplates when closed. Except for the beveled zone, each In at least some Edrioasterida, each floorplate pit which coverpIate is uniform in thickness. Neither intrathecal nor leads downward to a passageway also opens perradially intra-ambulacral extensions are present. Thus in the into a deep groove (text fig. 2B, C). The groove extends Edrioasterida individual coverplates are not interlocked along the lateral floorplate suture down the slope of the with adjacent elements as in the Isorophida. Opening and ambulacral trough. The perradial end of each groove closing of the coverplates could have been random, with opens into a lower subcircular pit at the edge of the floor individual plates moving independently of adjacent ele- of the ambulacral trough. Lower pits form a single row ments. Moreover, plate movement could have been initi- along each side of the trough floor, but do not lead to ated in any sector of an ambulacrum and progressed in passageways. Shallow lateral grooves may flank both either direction, or, all coverplates could have been moved sides of each deep sutural groove with a small ridge sepa- at once. The tissue investiture of the coverplates may, rating the grooves. The zigzag perradial suture line of of course, have imposed restrictions on the movement the floorplate series may also be depressed and form a patterns. shallow zigzag axial groove. 28 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21

The floorplate passageway system of the Edrioasterida the surrounding interambulacrals. The structure appears probably housed lateral branches of the axial radial canal to have acted only as a loose, flexible covering for the which lay beneath each ambulacrum (text fig. 2C). In anal area and was capable of moderate expansion. those forms with deep sutural grooves, the branches prob- ably extended from the passageways down the groove into Margin of the oral surface the lower pits which served as podial seats. The part of the branch canal housed in the upper, lateral pits may Small plates, proximally continuous with the distal have participated hydrostatically in coverplate opening. large interambulacrals, form the resting and the proximal Expansion would have exerted pressure on the inner sides part of the incurved thecal zones. These are commonly of the overlying coverplates, thereby opening them. polygonal abutting plates, but have been reported to be squamose and imbricate in Dinocystis barroisi Bather. The resting zone is formed by plates with external surfaces Interambulacra parallel to the underlying substrate. Commonly it is very narrow, only one or two plates wide. Distal to the resting The interambulacral areas of the Edrioasterida theca zone the thecal plates are flexed upward and inward, are formed by large, polygonal plates which abut laterally away from the substrate and toward the center of the along vertical sutures. Commonly the largest plates are thecal cavity. The plates of the most distal circlet of the central, with smaller ones lying along the ambulacral su- incurved zone are commonly larger than the proximally tures. The tessellation of the interambulacral areas sug- adjacent plates. Their distal margin may taper to a thin gests relative rigidity. Distally the interambulacra extend edge directed toward the center of the lower surface. into the subambital zone between the distal parts of the A thick basal membranous ring was apparently attached ambulacra. to the distal edge of the incurved zone, as the presence of numerous minute platelets would seem to indicate. These platelets are squamose, imbricate, and elongate concentric Anal structure with the thecal margin. The membrane apparently ex- The anal structure is located in interambulacrum 5, tended downward and distally attached to the underlying commonly near the center of the distal edge of the upper substrate. It surrounds a small, nonplated basal area oral surface sector. It is a periproct formed by what seem which is the aboral surface of the theca. This may have to be three irregular circlets of plates. The central plates been the actual area of adhesion. The distal membrane may be elongated toward the central anus. Distal anal appears to have been the only flexible part of the edrio- elements are irregularly polygonal and much smaller than asterid test. Preservation

Edrioasteroid thecae have been subjected to several rigid than other types, for the plates are commonly dis- modifications during preservation. These affect the theca rupted in an irregular manner. in important but often subtle ways that obscure original Lateral compression and other stresses, perhaps related features and suggest erroneous alternatives. to the gradual decay of soft parts, commonly cause com- Nearly all specimens have undergone thec-al collapse in plete disruption of part or all of the thecal plates. Domal which the upper oral surface is depressed against the forms not uncommonly preserve only the peripheral rim underlying substrate or lower surface plates. In the com- intact, with all of the central thecal plates totally jumbled. mon domal theca, collapse accentuates the imbrication of Clavate forms may preserve a regularly collapsed pedun- the interambulacrals and depresses their inner faces culate zone with the plates telescoped together, but with against the substrate. Distal interambulacrals are com- the upper oral surface elements completely disrupted. monly jumbled or pushed in under the proximal plates of Sediment reworkers (burrowers) also disrupt individ- the peripheral rim. The orals and ambulacral coverplates uals. Commonly edrioasteroids are preserved on the sur- are held above the substrate by the underlying thick oral face of a firm, calcareous layer, buried by an overlying frame and ambulacral floorplates. Thus the apparent ele- shale. Reworker trails have been traced from overlying vation of the oral-ambulacral structures is often greatly shales through specimens. All plates adj acent to the bur- exaggerated by thecal collapse. The differential downward rows are disarranged. This destruction is most often movement of the interambulacrals which flank the amhu- found when the burying mud is quite thin. If the overly- lacra and oral area, tends to cause slight lateral shifting ing shale is thicker (six to eight inches or more after com- of the ambulacral eoverplates and orals. Therefore, pression), most reworkers were not able to penetrate to although the basic coverplate arrangement is maintained, the firm, calcareous layer on which the edrioasteroids the sporadic and irregular slippage often alters plate lived. When the overlying shale is thin (five inches or shapes and sutural features. The central elevation of the less), most specimens are partially or completely disrupt- anal structure may be either increased or decreased dur- ed by sediment reworkers. ing collapse. In those forms with geniculate rim plates, the The most subtle preservational modification of edrio- upper ends of the proximal rim plates remain elevated asteroids is surficial etching of the thecal plates. Most of above the substrate, nearly in life position, and the rim this seems to be due to etching by ground water moving stands in marked relief above the adj acent, depressed along the limestone-shale interface, where the edrioaster- interambulacrals. oids occur. All exposed plate surfaces are affected, on Clavate edrioasteroids are commonly preserved with both the inner and outer surfaces of the theca. Small the lower pedunculate zone completely collapsed, the plates and the thin edges of larger plates are most severely imbricate plates being telescoped together. Only slight etched. The results can be quite misleading if not prop- plate disruption occurs when the upper circlets are pre- erly appreciated. served inside the lower areas, in spite of the somewhat Etched specimens expose subsurficial section views of larger diameter of the upper circlets. From this it appears the theoa, The exposed " surface" outline of plates with that the lower circlet plates were flexibly united laterally differing inner and outer shapes may be extensively alter- and that the pedunculate region was contractile in life. ed by etching. The most significant alteration is on the Occasionally, when clavate forms toppled sideways before taxonomically important coverplates. The external sur- burial, the pedunculate zone is later-ally compressed but faces are removed, exposing the upperperradial ends- of preserved in a distended condition. intra-ambulacral extensions. This modifies the cover- In depressed clavate forms, the upper oral surface is plate outline and may replace a simple zigzag perradial pressed down onto the collapsed pedunculate zone. Col- line with a complexly interdigitating one. lapse affects this surface as in dornal forms and leaves the There may be differential etching of the skeletal stereom interambulacra depressed and the ambulacra and oral and the calcite filling of stroma canals. This commonly ac- area elevation exaggerated because they are supported by counts for delicate pitting on etched plate surfaces. inner floorplates; ambulacral coverplates and orals com- Edrioasteroids appear to be unusually susceptible to monly have shifted irregularly in these forms also. surficial etching. Severely etched specimens are CQm· " Echinoidal " thecae are commonly depressed, with the monly associated with a variety of other calcareous fossils, subambital, resting, and incurved zones flattened under including other echinoderms, which show littleor no evi- the upper oral surface. These thecae appear to be more dence of etching.

29 Attachment

Edrioasteroids are found resting directly upon firm rim maintains its original position on the substrate. At carbonate substrates or upon the hard parts of other in- least one species (H adrochthus commensalus) lived at. vertebrates. Commonly the resting site is smooth or only tached to the thecae of then living cystoids. In order to slightly irregular. Occasionally individuals rested on rela- cling to these bobbing cystoids, the edrioasteroids must tively small objects and the theca was contorted to main- have been firmly attached. tain contact of the peripheral rim with the object (e.g., Some Isorophida may have been capable of very limited Carneyella pilea resting on a segment of crinoid stem, movement, whereas others appear to have been immobile pl. 17, fig. 1-4). and thus firmly anchored. Young specimens of certain In the Isorophida the lower side of the peripheral rim species are commonly found attached to the sloping lateral is in contact with the substrate. The aboral surface of the margins of brachiopods, whereas large adults of these theca, presumably a soft membrane, may also have lain species are found centered on the upper surface of similar on the substrate surface, surrounded by the rim. Their brachiopods. This would suggest that during growth the method of adherence to the substrate is unknown. No young edrioasteroids were able to migrate to the centers suggestion of calcareous cement has been found. Possibly of the brachiopod valve. the aboral basal membrane maintained a constant suction Evidence suggesting that some species were entirely im- for fixation. In forms with geniculate rim plates (the mobile after larval settling is more convincing. Young in- Carneyellidae and Isorophina), small vertical ridges dividuals have been found with adjacent large specimens which project down to the substrate surface are often " overgrowing" part or all of the small theca (pl. 55, developed on the basal surfaces of the geniculate plates. fig. 15). If movement were possible, the smaller individ- These may have been sites of attachment for muscular or uals would surely have moved laterally to avoid being ligamentous tissue which distally connected to the sub- overgrown and hence "suffocated" by the larger speci- strate. If suction created by the basal membrane was the men. Thus at least some, and perhaps all, Isorophida were fixative force, these ridges may have acted as nonskid incapable of movement, which suggests some sort of per· runners (Caster, personal communication, 1971). manent mode of attachment. Some Isorophida appear to have been rigidly fixed. Large clavate species are commonly attached by a very In the Edrioasterida, the "echinoidal " theca appears small,basal, peripheral rim. If these were not firmly fixed to have been attached by the fleshy, aboral surface memo the high theca would appear to have been unstable, and brane or perhaps by the surrounding basal edge of the would have toppled sideways with only slight water agio distal polyplated membranous ring of the oral surface. tation. Moreover, occasionally specimens with a variety Inadequate preservation precludes further analysis, but the of thecal shapes are found obliquely compressed, disrupt. central basal zone seems to have been the only available ing the upper parts of the theca, whereas the peripheral site of fixation.

30 Symmetry and Phylogenetic Implications

Echino-derm symmetry is complex. Fundamentally the toward one side of the posterior interambulacrum. The Echinodermata are bilateral, as demonstrated by the hydropore commonly lies to the right of the axial plane, ontogeny of extant members of the phylum (Hyman, in or near the posterior part of the oral region; it is al- 1955, Ubaghs, 1967, Fell, 1967, etc.). This fundamental ways posterior to the midline of ambulacrum V. Thus the bilateral symmetry is masked by various secondary sym- edrioasteroid axial plane is essentially equivalent to the metries superimposed upon the bilaterality. Although this crinoidal plane of Cuenot (1948), if one allows the slight secondary symmetry is most commonly pentamerous or offsetting of the hydropore to the right of the plane, and pentaradiate, other types not uncommonly may be substi- the occasional lateral displacement of the anal s-tructure. tuted, or actually superimposed, upon a preceding second- Edrioasteroid bilaterality is also reflected by the con- ary symmetry. Thus echinoderm symmetry is best de- figuration of the oral region and proximal parts of the scribed as palimpsestic (Caster, 1967). ambulacra. The oral area commonly has a marked trans- Adult edrioasteroid thecae commonly have prominent verse elongation, symmetrically developed on each side of pentaradiate symmetry, the five ambulacra alternating the axial plane except for the right lateral hydropore orals, with the five interambulacral regions. The adult pentara- The anterior ambulacrum, bisected by the axial plane, is diate symmetry is imperfect, altered by bilateral sym- distinctly set off from the four lateral ambulacra which metry and a subtle triradiate plan which is evident in originate as pairs from the lateral extremities of the trans- juveniles. versely elongate oral area; I-II proximally unite at the Edrioasteroid symmetry is complicated by the common left edge of the oral area; IV-Vat the right edge. Thus occurrence of ambulacral curvature which distorts the the transverse elongation of the oral region and the devel- symmetry of the distal parts of the ambulacral-interambu- opment of a single anterior and two lateral pairs of ambu- lacral regions. In species with all ambulacra curved in the lacra are also bilaterally symmetrical with respect to the same direction, the result is to add a spiral aspect. How- axial plane. ever, commonly only the more distal parts are curved so The five ambulacra stem from a triradiate, rather than that the spiral component is irregular and apparently not a pentaradiate origin. This has been suggested by some homologous to the spirality of such forms as the Helico- earlier workers, particularly Foerste (1914, p. 412) and placoidea. Moreo-ver, most forms have one or more ambu- more recently by Caster (1967) in a general application lacra curved in a direction opposite to the others, which to all pentaradiates. This triradiate pattern is reflected by destroys the spiral aspect. The ontogeny of species with the oral area midlines. An anterior midline is formed by curved ambulacra suggests curvature in a late develop- the perradial suture line between the anterior orals. It ment in the class since all their juveniles have straight extends along the proximal, anterior part of the axial ambulacra. Thus the irregular spirality appears to have plane of symmetry, and terminates proximally at the oral been superimposed on the basic bilateral, triradiate, and pole, perpendicular to the transverse oral midline. The pentaradiate symmetries. To facilitate discussion, the fol- transverse midline is formed by the junction between the lowing description of edrioasteroid symmetry ignores anterior and posterior orals, It originates at the oral pole ambulacral curvature. Each type described may be com- and extends laterally out to the proximal tips of the two plicated by curvature. lateral bifurcation plates. Both midlines may be serrate, The bilateral aspect of edrioasteroid symmetry is de- a zigzag pattern imposed upon them by perradial angu- fined by the antero-posterior, or axial plane of symmetry larity of the oral plates. However, the major direction which passes through the oral pole, the center of the pos- and "averaged" position of the midlines remains con- terior interambulacrum, and the primary axis or midline stant. The midlines thus form a triradiate pattern from of ambulacrum III. The plane of adult bilateral symmetry the oral pole, one anterior primary radius along the axial being discussed here must not be confused with the funda- plane, and two lateral primary radii, one right, one left, mental plane of bilaterality of larvae and the ancestral each normal to the axial plane. echinoderms, which is thought to be oriented differently. The triradiate nature of the oral region is also reflected The axial plane commonly passes through the center of in the structure of the oral frame, although less distinctly the anus, although occasionally this structure is offset than in the external oral area. All five ambulacral tunnels

31 32 A STUDY OF NORTH AMERICA:'> EDRIOASTEROIDEA MEMOIR 21 empty directly into the central lumen, However, the inter- within the phylum beyond establishment of the" dipleu- ambulacral I interradial) distance between the two tunnels rula "-like, bilateral ancestor. Fell convincingly supports of each lateral pair of ambulacra (I-II and IV-V) is small. his conclusion by contrasting phylogenetic inferences from The interambulacral space between the anterior member the extant larval types with the contradictory phylogenies of each lateral pair (II and IV) and the anterior ambu- suggested by the morphology of postlarval echinoderms, laerum (Ill) is larger, and distinctly separates the an- both extant and fossil. That extant echinoderm larvae are terior ambulacrum from the lateral pairs. The interamhu- totally irrelevant to the phylogeny of the phylum is in lacral distance between the posterior members of the direct contradiction to views expressed by many notable lateral pairs (I and V) across the posterior interradius is workers, such as Hyman (1955). very large, clearly setting apart the two lateral pairs. Fell and Moore (1966), Moore and Fell (1966), and The pentaradiate aspect of the edrioasteroid thecal sym- Fell (1967) suggest the most significant aspect of post- metry thus develops distal to the oral area. The midline of larval echinoderms is symmetry and related growth gradi- ambulacrum III, which marks the anterior ambulacral ents. The" standard" pelmatozoan-eleutherozoan division radius, is a straight-line continuation of the anterior pri- of the echinoderms so forcefully promulgated by Bather mary radius. In contrast the two lateral primary radii (1900) is rejected by these authors because it is founded bifurcate at the edge of the oral area to form four second- upon ecologic adaptation. A new four-part division of the ary ambulacral radii, marked by the midlines of ambu- phylum is proposed in the" Treatise" based upon sym- lacrum I and II, IV and V. metry and growth gradients. The subphyla Homalozoa, Correlations between the symmetry found in adult Crinozoa, Asterozoa, and Echinozoa are briefly charac- edrioasteroids and other echinoderms is speculative. How- terized as follows: ever, because such correlations may suggest homologies and aid in interpretation of phylogenetic relationships, a Subphylum HOMALOZOA Whitehouse, 1941: asym- few alternatives are discussed here. metrical or with some degree of bilateral symmetry. Recent discussions of echinoderm symmetry are found Subphylum CRINOZOA Matsumoto, 1929: globose in the" Treatise on Invertebrate Paleontology," parts S forms with partial " radiate" meridional symmetry, and U. Ubaghs (1967) summarized the subject, drawing all with exothecal ambulacral feeding appendages of upon the ontogeny of extant classes to demonstrate that some type. the symmetry found in adult echinoderms is secondary, Subphylum ASTEROZOA HAEcKEL (in Zittel), 1895: superimposed upon the basic or fundamental bilaterality commonly star-shaped forms with radially divergent of the class. During ontogeny, in extant echinoderms, a axes of symmetry formed by extensions of the body. secondary pentaradial symmetry is imposed upon the developing bilateral organism. Moreover, a secondary Subphylum ECHINOZOA Haeckel tin Zittel), 1895: bilateral plane of symmetry is developed. This does not commonly globoid, cylindroid, or domal forms with necessarily correlate with the primary plane of bilaterality. meridional symmetry, ambulacra confined to body which cannot (or only with greatest difficulty) be identi- surface, lacking any type of exothecal appendages fied in adult or "postmetamorphic individuals" (Ubaghs, like those of Crinozoa, or divergent body extensions 1967, p. Sl1). The adult plane of bilateral symmetry is like those of the Asterozoa. based on features such as the anus, hydropore, madre- porite, etc., and not on the features which define the The differing symmetry patterns exemplified by the bilateral symmetry of the larvae. Ubaghs concludes (1967, Crinozoa, Asterozoa, and Echinozoa, are discussed by Fell p. SIl) that homologies based on the adult bilateral plane and Moore (1966). Homology of the symmetries for the of symmetry are "not ... proven." Nevertheless, al- subphyla and also within the classes assigned to the though not proved, suggested correlations of adult bilat- Echinozoa are given by Moore and FeU (1966). A more eral and pentameral symmetries between echinoderm extensive treatment of the significance of the growth gradi- classes are important phylogenetic indicators. ents in the three subphyla is presented by Fell (1967). Fell (1967) presents a rigorous treatment of eehino- These authors contend the four basic symmetry patterns derm ontogeny and concludes, in agreement with Ubaghs, represented by the four proposed subphyla are indepen- that the larvae of extant Echinodermata demonstrate the dent of mode of life. and represent the most significant presence of a fundamental bilateral symmetry in the anees- characteristic of members of the phylum. Thus the symme- try of the phylum, suggesting a "dipleurula "·like ances- try patterns are the fundamental basis for division of the tor for the phylum. However, larval evolution has subse- Echinodermata at the subphylum level. quently modified these stages to such a great extent that Acceptance of this proposed echinoderm division based extant larvae are of no help in interpreting phylogenies upon symmetry depends upon acceptance of Moore's and SYMMETRY AND PHYLOGENETIC 33

Fell's interpretations of homologies of symmetry types and oped in echinoderms after the fundamental bilateral sym- their related growth gradients. metry of the ancestor is lost; (21 the Homalozoa, as far as A comprehensive analysis of echinoderm symmetry is can be interpreted from the fossil record, fit neither of the beyond the scope of this work. However, evidence pro- above growth gradient patterns, and are thus basically vided by the Edrioasteroidea, which Moore and Fell asymmetrical organisms with a secondary bilaterality include in the Echinozoa, appears to contradict some of later developed in some. their conclusions. In contrast with Fell's suppositions, the carpoid Homa- Basic to the four-part division of the echinoderms are lozoa may have a primary triradiate symmetry (Caster, the following assumptions and interpretations: (1) only 1967) which is differentially developed among the mem- two types of growth gradients exist in echinoderms, bers of that group; in some carpoids a bilateral aspect is (2) the Homalozoa fit neither growth pattern and thus are superimposed upon the triradiate pattern. Other echino- far removed from other echinoderms, (3) a homologous derms, including the edrioastercids, have a trimerous pat- primary plane of adult bilateral symmetry is found in most tern and these likewise suggest that some pentarneral pat- classes of echinoderms, (4) the ambulacra of most groups, terns may be modified from a triradiate symmetry devel- except the Homalozoa, can be specifically identified and oped early in the evolution of at least one major segment therefore homologized from one group to another, (5) a of the echinoderms. Thus both of Fell's basic assumptions primary pentameral symmetry was developed in the may be questioned. Before discussing pentameral vs. echinoderms immediately after the original bilaterality triradiate as the basic symmetry, the homology of the was lost, and only the Homalozoa lack this fundamental plane of bilateral symmetry found in adult echinoderms pentamerism. must be considered. Fell (1967, p. 583) defines two major growth gradients Moore and Fell (1966) contend that if properly identi- which are found in the development of postmetamorphic fied, the plane of bilateral symmetry of postlarval echino- echinoderms: (1) a meridional pattern, in which the derms (not the fundamental bilateral symmetry of larvae hydrocoel sends out five meridional water tubes and the and the ancestral stock) is homologous in most classes of entire "skeleton and nervous system thereafter differen- echinoderms, including all Crinoidea and most other tiates under the same meridional gradients"; (2) a Crinozoa, Echinozoa, and probably Asterozoa. This plane " radial" pattern of gradients, in which the five water is the primary anterior-posterior plane of the adult, i.e., tubes extend from the hydrocoel " radially outward in the the crinoidal plane (Cuenot, 1948) or axial plane. It ex- horizontal plane, carrying body wall and coelom with tends through the anterior ambulacrum (Ill), the oral them, and thus they produce the divergent, radiating arms. pole, and the posterior interambulacrum (5). Identifica- The whole skeleton and nervous system differentiates tion of the plane in Crinozoa is simple, but in other groups thereafter under the control of such dominant radial gr.adi- it is less obvious, partly due to the method of correlating ents, with the calyx alone retaining the ancient meridional Lovenian numbers with Carpenter letters. If done im- system." (Fell's usage of" radial" can be confusing when properly, the anterior ambulacrum is incorrectly identified used with standard terms such as pentaradial, etc., which and the plane of bilaterality likewise incorrectly placed. he would probably term "pentameridional" for echi- Moore and Fell (1966) reevaluated the methods of noids; therefore when used in Fell's sense of radiating out- ambulacral identification in the Crinozoa, Asterozoa, and ward on a horizontal plane, away from the body, " radial" Echinozoa to allow the consistent and accurate identifica- is placed in quotation marks.) This dual system of growth tion of the antero-posterior plane. Their reevaluation pro- gradients is viewed by Fell as the only framework in which duced a significant change in ray identification for the the larvae of extant echinoderms can be interpreted. echinoids, as well as the Asterozoa. Others remain con- Echinozoa (Echinoidea, Holothuroidea) follow the first sistent with those of previous workers. pattern, while both Asterozoa and Crinoidea (the only The proposed changes in ambulacral identifications are living members of the Crinozoa) are dominated by the based on two features considered to be of fundamental second type. Thus the growth gradients of larvae which importance: (1) modification of thecal shape; (2) the yield the symmetry of the adult members of these three patterns of ambulacral development or distribution which subphyla, support the phylum division as proposed by indicate the location of the anterior ambulacrum. Rejected Fell and Moore (1966). Moreover, a close relationship is is the contention that the hydropore (or madreporite] suggested for the Crinozoa and Asterozoa, a contention location is of prime importance in identifying the pos- supported by fossil evidence presented by Fell in a number terior interambulacrum. Thus according to, Moore and of works. Fell, the location of the madreporite in echinoids is in Fell's conclusions about growth gradients rely on two interamhulacrum 2, which correlates to the A·E inter- basic assumptions: (1) a pentamerous symmetry is devel- radius of the Carpenter system and not to the CD inter- 34 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21

radius. The madreporite of the Asterozoa is placed in the ration is suggested here for some of the edrioasteroids, D-E interradius, on the oral side in the Ophiuroidea, the the suggestion that the " third opening" is not a hydro. aboral side in the Asteroidea; it is not in the CoD inter- pore but rather a gonopo-re is here rejected. radius, as commonly defined. Support for the proposed The last, and perhaps most important of the five changes is discussed at length by Moore and Fell (1966). assumptions noted here as inherent in the four-part Their conclusion rests not only upon a declaration that division of the echinoderms found in the "Treatise," is thecal shape and ambulacral disposition should be used as the derivation of five-part symmetry. Fell and Moore the primary basis of ray identification, but also upon inter- (1966) contend that as the ancestral echinoderm stock pretation of a variety of other thecal features previously lost its fundamental bilateral symmetry, a basic penta- not co-nsidered \apical system, anal migration, etc.). radial symmetry was developed, with a moore or less ap- Moore' and Fell (1966) present a convincing argument parent component of bilaterality always formed as an for homology of the basic adult plane of bilaterality found integral part of the new radial symmetry. Fell (1967) sug- in most Crinozoa. Asterozoa, and Echinozoa - all of gests that the development of the five-part radiating sym- which is dependent upon acceptance of their interpretation metry apparently was related to a common unknown of ray homologies. However, acceptance of their work is " globoid " progenito-r of the Echinosoa, Asterozoa, and far from universal, as witnessed by Ubaghs' (1967, Crinozoa. Thus the Homalozoa are to be considered either p, Sl1) contention in the" Treatise" that" the selection early offshoots, before the radial symmetry developed, or of anyone plane as a plane of reference for orientation of as highly degenerate. all the classes [of echinoderms J is more or less arbitrary, The edrioasteroids display a marked triradiate sym- and homologies based on such comparisons are judged metry as described above. The triradiate aspect of thecal as not being proven." Moreover, as noted above, the symmetry defined by the oral area is generally accom- Homalozoa are excluded from consideration in the dis- panied by a pentaradiate pattern defined by the distal cussion of ray homology and bilateral symmetry owing to parts of the ambulacra. However, in at least one prob- their lack of an apparent five-part form, which thereby lematic genus, Thresherodiscus Foerste, only three pri- deletes one of the four major subdivisions of the phylum. mary ambulacra are formed. All three repeatedly bifur- An interesting observation arises when the Moore and cate distally, and thus a five-part plan is never developed. Fell primary plane of adult bilateral symmetry is identi- Thresherodiscus, represented by a single specimen, may fied in the edrioasteroids. It passes through ambulacrum be considered a specialized offshoot rather than a repre· III, the oral pole, and the anus. Thus the hydro pore lies sentative reflecting the basic symmetry of the group. How- in the CoD interradius (interambulacrum 5) near the bi- ever, Foerste (1914, p. 412) concludes that Threshero- lateral plane but slightly offset to the right. In the Cri- discus " offers a striking confirmation" that a triradiate nozoa and holothurians, the hydropore lies along the pattern is the basic edrioasteroid symmetry. bilateral plane of symmetry (in the CoD interradius}, The ontogenetic development o-f edrioasteroid species although it may be slightly offset from this plane in some, may support the contention that triradiate symmetry is as in the edrioasteroids. In contrast, the hydro pore (or basic in the class and that the pentaradiate form is sec- madreporite) does not lie in the bilateral plane in other ondarily derived. In all species for which juveniles- have groups; rather it is found in the D-E interradius of the been found, a pronounced three-part symmetry of the oral- Asterozoa and the A-E interradius in the Echinoidea. One ambulacral structure occurs in the earliest stages. Devel- can accept Fell's conclusion that the hydropore should not opment proceeds by the extension of three primary radii be used to define the primary plane of bilateral symmetry - one anterior, two transverse - radiating outward from because the opening has migrated in some groups. How- the central oral pole. The five-part symmetry of adults is ever, identical migration routes may very well be impor- developed by the bifurcation of both lateral primary radii, tant indicators of phylogenetic relationships., Thus the thereby producing four lateral ambulacra and a single location of the hydropore in the CoD interradius, either anterior ambulacrum. Thus at least in ontogeny, the along or near the plane of bilaterality, suggests relation- pentaradiate symmetry is a later development, superim- ships between the Crinozoa and two groups included in posed upon a basic triradiate plan. the Echinozoa by Moore and Fell, namely the holothurians If edrioasteroids are basically triradiate, what of other and the edrioasteroids. How much weight should be groups? As noted above, Caster suggests that the carpoid applied to this correlation of hydropore position is uncer- Homalozoa (Stylophora, Cornuta, and Soluta) which Fell tain; Moore and Fell (1966, p. U125·U126) suggested the and Moore (1966) dismiss as being asymmetrical, are edrioasteroids respired anally, as do the holothurians, and basically triradiate. Moreover, a triradiate pattern is seen thus the supposed hydropore (" third opening" of Reg. in some crinoids. Among these are the examples selected nell, 1966) was more likely a gonopo-re. While anal respi- by Moore and Fell (1966) to demonstrate symmetry. Not- SYMMETRY AND PHYLOGENETIC IMPLICATIONS 35 ing this obvious pattern, they suggest it correlates with the group of echinoderms does prove to be basically triradi- development of the trivium and bivium found in echinoids ate, a revision of the four-part" Treatise" division of the and holothurians, phylum is suggested. However, the members of a bivium are closely associ- Moore and Fell 119661 conclude that a basic difference ated with each other, as are the three members of the stemming from the symmetry of echinoderms is repre- trivium, and the two groups are distinctly set apart from sented by the pattern of growth gradients, and this allows one another by wide interradial spaces. In contrast, the the distinction of three basic groups in the phylum: (L) pattern of ambulacral disposition and related oral plate forms with exothecal ambulacral appendages, (2) forms arrangement in the crinoids illustrated by Moore and Fell with "radial" (directed outward) extensions of the (1966) follows that described for the edrioasteroids. The body, and (3) forms with meridional ambulacra, lacking anterior ambulacrum is distinctly set off from two pairs 0.£ any exothecal ambulacra or body extensions. A fourth lateral ambulacra, each two lateral amhulacra converging group, as defined by Moore and Fell, rests largely on neg- to form a single axis before reaching the oral pole. Thus ative evidence, as the members apparently lack any con- the two lateral ambulacra on each side of the theca are sistent pattern of symmetry. Within this framework the grouped as a pair, both lateral pairs distinctly set apart edrioasteroids, without exothecal appendages or body ex- from the single anterior ambulacrum. Moreover, each tensions, must be placed in the Echinozoa. lateral pair is widely set apart from the other by the very The inclusion of the Edrioasteroidea under the sub- wide posterior interamhulacrum. Therefore, the supposed phylum Echinozoa is questioned. The apparently basic members of the hivium as interpreted by Moore and Fell, triradiate symmetry of the edrioasteroids suggests closer i.e., ambulacra I and V (or D and C), have the greatest ties to the crinoids and cystoids, some of which seem to interradial distance between them of any of the five ambu- be triradiate. Moreover, the position of the hydropore in lacra. The triradiate nature of these crinoids hardly seems interambulacrum 5, and the adult plane of bilateral sym- comparable to the trivium-bivium groupings of echinoids metry, are comparable in most crinoids, cystoids, and and holothurians. edrioasteroids. In contrast, the hydropore (madreporite) Evidence of a basic triradiate symmetry in the edrio- asteroids is not definitive, but certainly suggests the penta- is found in a quite different position in the Asterozoa and radial pattern is secondary, superimposed upon the earlier the echinoids. triradiate form. Combined with the triradiate pattern seen Thus the phylogenetic relationships of the edrioaster- in many crinoids, and perhaps also in the carpoid Homa- oids to other echinoderms remains in question, and their lozoa, this evidence casts doubt on the supposition that placement within either the " Crinozoa" or " Echinozoa " pentamerism is basic to all echinoderms except for the is still uncertain. Moreover, the usefulness of these two supposedly" asymmetrical" homalozoans. If one major supposedly systematic categories is questionable. Organ Systems

DIGESTIVE TRACT

The ambulacra, central lumen, and anal structure estab- discina and the Edrioasterida, by a valvular structure in lish the location of the tissue systems involved in the the Isorophina, Little is known about the rest of the tract. ambulacral food grooves, stomial cavity, and anus, Both Jaekel (1899) and Bather (1915) reasoned that respectively, in edrioasteroids. Judging from crinoids, a the edrioasteroid gut looped solarly around the thecal cav- presumably ciliated groove extended along the floor of ity, based on homology with other echinoderms. Bather each ambulacral trough, conducting food to the central (1900) suggested that a specimen of Edrioaster buchianus " mouth" or stomial cavity which lay below the roof of (Forbes] implied this solar gut curvature because a slight permanently closed oral plates. This is an organization elevation of the posterior interambulacrum to the right of well suited to suspension feeding. The proximal end of the the anus probably reflected the path of the rectum. Wil· gut passed down through the central lumen of the oral Iiams (1918) also thought that the presence of a coiled frame into the thecal cavity. In those forms with a prom- gut was suggested by two crushed juvenile specimens of inent posterior frame gap, it seems likely that the gut ex- Isorophus austini (Foerste) , in which he thought he saw tended posteriorly through the gap into the thecal cavity traces of a looped internal organ impressed into the lower beneath interambulacrum 5. side of the oral surface plates. A spiral, solarly looped The anus lies in interambulacrum 5, commonly almost gut is a distinct possibility for edrioasteroids inasmuch as centrally. It is surrounded by a periproct in the Lebeto- many other echinoderms show such a condition.

HYDROVASCULAR SYSTEM

The hydrovascular system in edrioasteroids is presumed supposed hydropore in a variety of species, ranging to have included a hydropore, a stone canal, a circum- through all the major taxonomic groups of the class. esophageal ring canal, and five radial canals which in Hegnell (1966) maintained a neutral position concern- some instances seem to have had multiple lateral branches. ing the hydropore, referring to it as the" third opening," Such features as polian vesicles, Tiedemann's bodies, or in the only recent major review of the class. He notes that accessory organs could possibly have been part of the sys- the opening may have been the hydropore, a genital open- tem without leaving a trace in the skeleton. ing, or a combination of the two. The double function as An opening into the theca, thought to be the hydropore, both a hydropore and a gonopore is quite possible, but lies between the oral pole and the anal area, commonly its primary function would seem to have been that of a offset slightly to the right of the axial plane. This is com- hydropore, parable to the hydropores found in many cystoids, cri- A stone canal presumably led from the hydropore into noids, and other primitive pelmatozoan echinoderms. The the thecal cavity. What is judged to be the passageway for structure is composed of orals and/or modified inter- this canal is formed by the inner parts of the plates of the ambulacral plates combined with the proximal coverplates hydropore structure, and commonly also by the underlying of the posterior side of ambulacrum V. Construction and exact location are taxonomically important. proximal floorplates of ambulacrum V. The passageway As noted by Kesling (1960, p. 141), " Bather's detailed is funnel-shaped, and expands inward to open along the work (1900b) on Edrioaster buchianus (Forbes) leaves right posterior, distal margin of the oral frame. scarcely any room for doubt that the species had a water The stone canal is presumed to have led to a circumeso- vascular system that opened through a hydropore." Kes- phageal ring, probably circumambient to the oral frame. ling (1960) identified the location and structure of the However, direct evidence of this structure is lacking.

36 ORGAN SYSTEMS 37

Kesling and Mintz (1960) postulated that the ring canal beneath the floorplates (see below). In these groups the of Isorophus cincinnatiensis was inside the oral lumen. circumesophageal ring canal most likely encircled the Noting that the inner end of the stone canal passageway oral frame. In the Isorophina there appears to be no evi- lies outside the oral frame, they reasoned that the ring dence as to the position of either the circumesophageal canal was primarily confined to the area of the central ring or the radial canals, but by analogy they, too, prob- lumen in the center of the oral frame, and presumably ably lay outside the lumen and beneath the floorplates, encircled the esophagus or anterior part of the gut. The respectively. posterior part of the canal was supposedly squeezed The floorplate passageways of the Edrioasterida sug- through the large posterior gap in the oral frame to make gest that the radial canals were under the ambulacra. contact with the inner end of the stone canal. Moreover, Along each ambulacrum, alternate lateral branches ex- the radial water canal of ambulacrum V supposedly tended from the radial canal and passed up through the branched off this distal part of the ring canal near its con- two rows of floorplate passageways into the ambulacral nection to the stone canal, and entered ambulacrum V tunnel, where they entered the two lateral upper rows of through a supposed passageway between the second and pits at the upper ends of the passageways. At least in third floorplate of ambulacrum V. The presence of this Edrioaster bigsby, these lateral branches appear to have passageway is questionable (see I. cincinnatiensis). The extended from the pits toward the floor of the ambulacral remaining four radial canals presumably branched from trough along the deep grooves which follow the lateral the part of the ring canal located within the central lumen sutures between floorplates. These open into lower basin- of the oral frame and extended directly into- the proximal like depressions which perhaps housed podia. The parts ends of ambulacra tunnels via their openings into the of these branch canals housed in the upper pits were prob- upper part of the central lumen. ably swollen, and may have aided in the opening of over- Kesling and Mintz (1960, p. 32'1) reasoned that the lying coverplates by hydrostatic pressure. The lower amhu- ring canal could not have extended around the outside of lacral trough parts of the extensions, perhaps developed as the oral frame because it would have to pass- under the podia, may have aided in food gathering or perhaps were frame twice, at ambulacrum I and V, and therefore" any entirely respiratory structures. compression of the flexible theca would pinch the ring Bather (l900b, p. 196-197, 1915, p. 263) suggested a canal between the frame and the obj ect to which the edrio- much different hydrovascular anatomy for Edrioasterida asteroid was attached." However, the inner edge of the species. He thought that the radial canals extended ex- oral frame rim extends further into the thecal cavity than ternally along the floor of the ambulacral trough with any other structure, and therefore the canal could have lateral branches extending alternately up the lateral extended around the outside of this region, free from any sutural grooves to form podia in the upper pits. The floo-r- "pinching." Moreover, there is no indication that during plate passageways, he thought, housed tubes connecting life the theca would be so depressed that the base of the the podia to internal ampullae. This configuration does oral frame would come into contact with the underlying not explain the function of the lower basinlike depressions substrate. Thus the problem of pinching the ring canal or which flank the floor of the ambulacral trough. Moreover, any of the other organs in the region probably never the coverplates abut the floorplates along the zone housing arose. the upper lateral pits and partially roof them over. This The only supposedly direct evidence of the ring canal's would seem to make it unlikely that they accommodated presence was reported by Bather (l900b, p. 198) in the podia. type specimen of Edrioaster buchianus (Forbes), an in- In the Lebetodiscina, coverplate passageways connect ternal mold of the theca: "The mouth was central and the thecal cavity with the exterior of the theca. These roughly five-lobed, widest on the posterior side, and ... passageways lack direct communication with the amhu- was surrounded by a stout ring of stereom, .over which the lacral tunnel and therefore the radial canal for each ambu- food groove passed . . . The proximal or aboral pores lacrum must have extended axially beneath the floor- [floorplate passageways] were connected with one another plates. Alternate lateral branches extended from each above this stereom ring, but below the outer theca [oral side of the radial canal and passed up through the passage- covering plates] , so as to form a closed ring-canal (hydro- ways to the external sides of the coverplates. The distal circus) around the mouth." The illustrations accompany- parts of the lateral branches apparently were respiratory ing this description suggest a slight depression extending structures. In Lebetodiscus and Foerstediscus, a series of around the inner edge of the oral frame, the supposed loca- lateral basinlike depressions is developed along the lateral tion of the ring canal. edges of the coverplates, near and along the external fo- The structure of the ambulacra in the Edrioasterida and ramina of the passageways. These may reflect further the Lebetodiscina suggest that the radial canals extend branching of the lateral branch canals. 38 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21

Ambulacral passageways are not developed in the plates. No evidence of canals or podial structures has been Isorophina. Thus radial canals, if present, may have observed in this group. Obviously respiration, if that is extended either along the floor of the amhulacral trough, the function of external hydrovascular podia in other or more likely, may have been housed within the thecal edrioasteroids, must have been otherwise achieved in the cavity and extended along the ambulacra under the floor- Isorophina.

RESPIRATION

As seen above, two fundamentally different metho-ds 01 water into a cloacal chamber. There may have developed respiration appear to have been employed by edrioaster- some sort of anal respiratory tree analogous to- that found oids. The Edrioasterida and the Lebetodiscina are in recent holothurians. thought to have respired via external extensions of the In support of this interpretation, it is found that the hydrovascular system. In the Edrioasterida, this system valvular anal structure of the Isorophina contrasts with includes lateral branches of the radial canals which lie the periproct of loose, irregular circlets of plates found in within the ambulacral tunnels. The ends of the branches the Edrioasterida and Lebetodiscina. With ambulacral apparently formed podia which were exposed to the sur- hydrovascular extensions capable of carrying out respira- rounding sea water when the ambulacral coverplates were tion, these forms did not rely on anal pumping. The lack open. As in many extant echinoderms, respiration most of an ambulacral passageway system in all Isorophina thus likely occurred by gaseous exchange through the mem- appears to correlate with the development of a valvular branous surfaces of these podia. anal structure as part of an anal respiratory apparatus. In the Lebetodiscina, the lateral branches of the radial Fell and Moore (1966, p. UU8) compared edrioaster- canals extended through sutural passageways between the oids to the dendrochirote holothurians and suggested that, ambulacral coverplates, and thereby effected direct com- like psolid holothurians, edrioasteroids probably had in- munication with the external environment. ternal respiratory trees for respiration. Their conclusion In contrast to the above groups, the Isorophina appear thus concurs with the suggested mode of respiration pro- to have respired by anal pumping, like most extant holo- posed here for the Isorophina, but not for the Edrioaster- thurians, The Isorophina lack ambulacral passageway ida or Lebetodiscina. In addition, G. W. Sinclair (personal systems. Moreover, no evidence has been found to suggest communication, 1968) has long held that the Isorophid the development of any sort of hydrovascular extensions anal structure was a valve used in thecal pumping. How- housed in the ambulacral tunnels. However, these organ- ever, he doubts that the structure functioned as an anus. isms do have a valvular anal structure. It is formed by an inner and an outer circlet of large triangular plates, the Williams (1918, p. 76) also suggested anal respiration outer circlet plates alternating and overlapping inner for the edrioasteroids. He compared the edrioasteroids plates along tightly fitting, beveled edges. Because of this with Antedon, the extant crinoid, and reports, " the rectum zone of overlap, the beveled edges of adjacent plates would projects as the tubular papilla and the rectal tube is- in the remain in contact during opening and closing and thereby living animal seen to undergo frequent movements of con- maintain the structural unity of the apparatus. It is sug- traction and dilation by means of which water is drawn gested that this structure reflects the development of a res- into and expelled from the rectum. There is thus intestinal piratory anal pumping system. The flexible theca of the respiration." Citing the valvular anal structure of " Agela- Isorophina would permit expansion and contraction, and crinites," Williams suggested respiration was via anal thereby allow the alternate intake and expulsion of sea pumping, as in Antedon. Ontogeny

Ontogenetic development has been observed in a few After the earliest observed stage, development varies edrioasteroid species. The most complete series of speci- depending upon the family. In the Carneyellidae, proxi- mens included here is for lsorophusella incondita (Ray- mal ambulacral coverplates are the next external oral- mond), a member of the family Isorophidae. Less com- ambulacral series plates to develop (or become manifest). plete growth series are also described for species which In the Lebetodiscidae and Isorophina, lateral shared cover- represent the other three families of the Isorophida. plates and/or secondary orals are formed next. They are Unfortunately, juveniles are unknown among species of inserted along the transverse oral midline between the the Edrioasterida. primary orals and lateral bifurcation plates. The earliest observed stage of development is found in Concurrent with the oral-ambulacral plate development, tiny specimens, approximately 0.5 mm in diameter, which the peripheral rim slowly adds new circlets of plates and represent species in which average adult thecal diameters also inserts new plates into the existing circlets, thereby are 15 to 18 mm. The theca of these smallest forms is enlarging the circumference of the rim. Hydropore plates dominated by the peripheral rim which forms approxi- and anals appear suddenly in specimens approximately mately two-thirds of the total oral surface area. The rim 1 mm in diameter. When first observed these plates are appears to be made of two or three circlets of plates, the quite large in propo-rtion to thecal diameter, which sug- proximal elements quite large in proportion to thecal gests they were present in smaller specimens, perhaps even diameter. The central third of the oral surface includes in those 0.5 mm in diameter. Perhaps these plates were the plates of the oral-ambulacral series which form a tri- hidden under the peripheral rim in the smaller collapsed lobed structure with one anterior and two lateral radii. specimens. Interambulacrals are also observed at approxi- Primary orals form the center of the area, flanked laterally mately the same stage, usually two or three in interamhu- by two lateral bifurcation plates. Two anterior primary lacra 1-4, but with four or five in the larger posterior orals farm an anterior hump; the anterior oral midline interradius, extends between these plates and marks the anterio-r pri- Development proceeds by the addition of new plates mary radius. In Lebetodiscina one, and in Isorophidae and the progressive increase in size of previously formed two, posterior primary orals fo-rm the straight posterior elements, although not all at the same rate. side of the area which centrally abuts the anterior pri- The oral-ambulacral series adds plates along each pri- maries along the transverse oral midline. The transverse mary radius. The two lateral radii bifurcate and form midline extends laterally out to the tip of each lateral four lateral ambulacra, whereas the anterior radius con- bifurcation plate and defines the right lateral and left tinues as a single extension. The lateral bifurcations are lateral primary radii. The two distal bifurcation plates initiated by the insertion of coverplates on both sides of extend the lateral radii moore than twice the distance fro-m each lateral bifurcation plate. After two to four cover- the center of the area than does the short anterior radius. plates have been inserted in each of the four secondary At this stage the central triradiate oral-ambulacral area radii, the outline of the oral-ambulacral area begins to is separated from the proximal margin of the rim by small assume a five-part shape. This commonly occurs when the " interambulacral" spaces, but plates have not been thecal diameter is between 2.5 and 3 mm. By the 3 to observed in these areas. The posterior interradius is the 3.5 mm stage, all five ambulacral radii are distinct. Inser- largest. tion of coverplates continues through the addition of Proximal ambulacral floorplates may be inferred in coverplates at the distal tip of each ambulacrum. These these earliest known growth stages because the center of are added singly at the center of the distal tip, and then the oral region is arched upward in the collapsed thecae, shift alternately right and left to form pairs. In species suggesting the presence of underlying floorplates. How- with two or more sets of coverplates, secondary plates are ever, the inner side of the oral surface has not been inserted between primaries. The initial plate of the second- observed in young specimens included in this study. Wil· ary set appears at the proximal end of the ambulacrum, Iiams (1918) reported that in juvenile lsorophus austini adj acent to the first formed plate of the primary set, usu- (Foorste), 1.3 mm in diameter, only the five proximal ally after four to six primaries have formed. Commonly floorplates which form the oral frame are seen. He did the theca is around 3 mm in diameter at this stage. The not describe smaller individuals. insertion zone of the secondaries then migrates distally,

39 40 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21 but lags behind that of the primaries and remains about enlarge slowly while new plates are occasionally inserted three to five primary plate pairs from the distal tip of the in the structure. However, the relative areal extent of the ambulacrum. Species with additional sets of coverplates structure decreases throughout ontogeny, and the adult continue to insert new sets as the ambulacra lengthen and anal area is nearly always a relatively small part of the the thecal diameter increases. Apparently the time of first total oral surface. appearance of each new set is quite variable from one spe- The peripheral rim, which dominates the early growth cies to another. Individual ambulacra of a specimen may stages, slowly adds new circlets and intercalates new develop at different rates, the number of coverplates per plates in the existing circlets until the thecal diameter ambulacrum being quite variable. reaches approximately 5 mm, Thereafter, although new The ambulacra continue to lengthen as floorplates and plates are inserted into the circlets, which increases the coverplates are added at their distal tips, and through circumference of the rim, only rarely are new circlets enlargement of previously formed plates. In forms with developed. The rim increases in size slowly, and gradually curved amhulacra, curvature is usually initiated when becomes proportionally smaller throughout ontogeny. the thecal diameter reaches 4 or 5 mm, Prior to this, the Commonly specimens less than 5 mm in diameter are ambulacra are straight. The distal parts of the ambulacra dominated by juvenile features. The ambulacra-Inter- commonly become concentric with the thecal margin by ambulacra become the spatially dominant parts of the the stage when the thecal diameter is between 5 and 7 mm. theca beyond this stage. In species with curved ambu- The ambulacra thus increase in proportional size rapidly lacra, the direction of curvature is usually apparent by and become one of the major features, in area, in the this stage. Beyond the 5 mm stage, adult thecal characters adult theca. dominate. The transition from juvenile to adult is graduaL The oral plates continue to enlarge in size, and in those but in species of 15 to 20 mm adult diameter, the 7 to forms with shared coverplates and secondary orals, new 8 mm stage appears to be almost identical in thecal pro- plates are added from the 1 mrn stage up to forms 6 to portions to the large adults. Individuals of 5 to 8 mm are 7 mm in diameter. Commonly most orals are present by generally referred to as young adults. the 5 to 6 mm stage, although some species, particularly Even in species where the average adult diameter is in the Agelacrinitidae, continue to add orals for a much only 10 to 12 mm, the transition from juvenile to young longer time period, perhaps throughout adulthood. Al- adult appears to fall around the 5 mm stage. This is also though the plates of the oral area enlarge and increase in the case for those with adult diameters exceeding 20 mm. number, the proportional size of the area decreases Exceptions are found among the Agelacrinitidae, in which throughout ontogeny. In adults this area is usually a rela- species with several sets of ambulacral coverplates may tively small part of the total oral surface area, in contrast continue to add new series and thus change the coverplate with the youngest known juveniles, in which it occupies pattern well into, and perhaps in some instances through- nearly a third of the total oral surface. out, adulthood. The interambulacra increase rapidly in areal extent as What might be called gerontic edrioasteroids have been the ambulacra lengthen, and commonly form the largest observed in only a few species. These are characterized part of the adult theca. New plates are apparently in- by exceptionally large thecal diameters. In at least one serted along the proximal and lateral margins of the inter- species iLsorophus cincinnatiensisi , geronticism is also radii along the adradial suture lines. suggested by the distal tips of the ambulacra curving back The anal structure, when first observed, is proportion- toward the oral region, whereas in average-sized adults ally quite large and fills much of the posterior interradius. the ambulacra are merely distally concentric with the The plates are large when first observed and continue to thecal margin. Diagnostic Summary of Edrioasteroid Taxa Included

CLASS EDRIOASTEROIDEA BILLINGS, 1858

Polyplated, thecate, sedentary Echinodermata with: A-I. Suborder LEBETODISCINA Bell, subord. nov. - anal structure in posterior interambulacrum (5) Isorophida with: - triradiate or (? secondary) pentaradial symmetry 1) three central primary oral plates - endothecal ambulacral-oral system composed of two 2) ambulacral coverplates forming single, alternat- distinct sets of thecal elements: ing biseries; with intra-ambulacral and intra- a) coverplates thecal extensions b) floorplates 3) sutural passageways developed between cover- forming five (±) ambulacra and a central oral struc- plates, extending directly from thecal cavity to ture exterior of theca - hydropore structure located in or near right posterior 4) ambulacral floorplates imbricate, each floorplate side of oral area proximally overlapping distal end of adj acent - accessory hydrovascular sutural passageway systems floorplate commonly present 5) anal structure a periproct - interamhulacral areas polyplated, without regular order - anal structure in posterior interambulacrum (5) A-I-a. Family LEBETODISCIDAE Bell, lam. nov. Lebetodiscina with: A. Order IsoRoPHIDA Bell, ord. nov. Edrioasteroidea with: 1) theca domal, discoidal, or clavate 1) theca domal, discoidal, or clavate; aboral surface 2) oral area including two pairs of lateral shared nonplated coverplates; secondary orals commonly pres- ent 2) oral frame formed by five proximal, ambulacral f1oorplates, (±) intrathecal extensions from oral 3) hydropore structure distal to oral area, open- covering plates ing along adradial suture line of proximal pos- terior part of ambulacrum V; composed of 3) hydropore structure located in or near right poste- interambulacral plates and ambulacral cover- rior part of oral area, adjacent to proximal, poste- plates rior edge of ambulacrum V; structure composed of ambulacral and oral or interambulacral ele- 4) ambulacra forming high, pronounced ridges ments; hydropore opening along junctions between on thecal surface edges of plates and elongate parallel to plate mar- 5) ambulacral coverplates massive gins 6) ambulacral tunnel high and narrow 4) ambulacra composed of: 7) coverplate passageways commonly nearly ver- a) uniserial floorplates without sutural passage- tical ways 8) peripheral rim plates squamose, not geniculate b) biserial or multiple series of coverplates with intrathecal and/or intra-amhulacral extensions with or without sutural passageways which ex- A.I.a(l) Genus Lebetodiscus Bather, 1908 tend from interior to exterior of theca 1 ) theca domal, oral surface highly convex 5) margin of oral surface a peripheral rim, flaring 2) oral area includes two sizes of secondary outward parallel to substrate oral plates

41 42 A STUDY OF NORTH AMER1CAN EDRIOASTEROlDEA MEMOIR 21

3) hydropore formed by expanded adradial A·I.a(3) Genus Belochthus Bell, gen. nov. end of second ambulacral coverplate of 1) theca domal, (?) moderately convex posterior side of ambulacrum Y and ad- 2) oral area includes at least three large, sec. jacent two or three interambulacral plates ondary oral plates; primary orals and bi- 4) ambulacra curved, I-Y contrasolar furcation plates sagittate in external appear. 5) coverplate passageways large ance 6) lateral depression series present 3) hydropore structure formed by proximal 7) interambulacral plates large, a few distal to two coverplates of posterior side of amhu. ambulacra lacrum Y and at least one large interamhu, 8) thecal plates smooth lacral element 4) ambulacra straight OJ) L. dicksoni (Billings), 1857 5) coverplate passageways somewhat oblique Type species to thecal surface Character of genus 6) lateral depression series unknown 7) interambulacral plates extend distal to A·I.a(2) Genus Foerstediscus Bassler, 1935 amhulaera and form wide zone of imhri. 1) theca domal, oral surface highly convex eating plates proximal to peripheral rim 2) oral area commonly includes two sizes of (3.1) B. orthokolus Bell, sp, nov. secondary oral plates Type species 3) hydropore structure as in Lebetodiscus, per· Characters of genus haps more complex in some species 4) ambulacra curved, I·Y solar A.I.a(4) Genus Streptaster Hall, 1872 5) coverplate passageways large 1) theca domal; convex oral surface dominated 6) lateral depression series present by extremely high ambulacra 7) few interambulacral plates distal to amhu- 2) oral area includes secondary oral plates lacra 3) hydropore structure composed of three 8) thecal plates smooth or nodose plates - second and third proximal cover- (2.1) F. grandis Bassler, 1935 plates of ambulacrum V, and one large, Type species bulbous interambulacral 1) secondary oral plate arrangement unique 4) ambulacra curved, I·Y contrasolar 2) hydropore structure includes four major 5) coverplate passageways vertical, open ex- plates ternally along most of length 0.£ coverplates 3) anal structure near center of interambu- 6) lateral depression series absent lacrum (5) 7) interambulacral plates few in number 4) pro50pon of prominent nodes covers interambulacral and marginal plates 8) large spines set in basins along summit of columnar ambulacral plates; interambu- (2.2) F. splendens Bassler, 1936 lacral and rim plates with large nodes

1) secondary oral plate arrangement unique (4.1) S. vorticellatus (Hall), 1866 2) hydropore structure formed by several Type species plates Characters of genus 3) anal structure near center of interambu- lacrum (5) 4) thecal plates smooth A.I.a(S) Genus Cystaster Hall, 1871 (2.3) F. solitarius Bell, sp. nov. 1) theca discoidal to clavate 1) secondary orals poorly known 2) secondary oral plates absent 2) hydropore structure formed by four plates .1) hydropore structure formed by four plates 3) anal structure in proximal part of inter. -- two proximal coverplates of posterior ambulacrum (5) ; near oral area side of ambulacrum Y, and two large inter- 4) thecal plates probably smooth ambulacrals DIAGNOSTIC SUMMARY OF TAXA 43

4) ambulacra straight; draped down thecal (1.1) C. pika !Hall), 1866 surface in clavate forms Type species 5) coverplate passageways' external foramina 1) prosopon of small, irregular tubercles very elongate and small, perra dial coverplate ridges 6) lateral depression series absent (1.2) C. [aberi (Miller), 1894 7) interambulacral plates small, squamose; 1) prosopon of numerous large, clavate form narrow zone distal to ambulacra in tubercles with distal tips rounded, com- discoidal forms, extensive pedunculate zone monly three or more per ambulacral in clavate forms; large nodes on inter- coverplate; also large ambulacral cover- ambulacral and rim plates, which com- plate ridges and small lateral coverplate monly obscure squamose shape of plates; ridges spines present on summit of ambulacral coverplates in some (1.3) C. ulrichi Bassler and Shideler, 1936 1) prosopon of numerous, large, clavate (5.1) C. granulatus Hall, 1871 tubercles with distal tips acuminate, com- Type species monly one per ambulacral coverplate; 1) theca clavate also large perradial coverplate ridges 2) external ridge on larger interambulacral and small lateral coverplate ridges hydropore plate may be larger or more prominent than in other species (1.4) (?) C. valcourensis Clark, 1920 (5.2) C. stellatus (Hall), 1866 Characters obscure 1) theca discoidal 2) external ridge on larger interambulacral A-I·b (2) Genus Cryptogoleus Bell, gen. nov. hydropore plate may be smaller or less 1) ambulacra straight prominent than in other species 2) ambulacral terminations commonly pene- trate proximal circlet of peripheral rim A-l·b. Family CARNEYELLIDAE Bell, fam. nov. 3) coverplate passageways' external foramina sIitIike, difficult to detect Lebetodiscina with: 4) anal area may be transitional from normal 1) thecal domal periproct to more complex valvular type 2) oral area including one large hydropore oral; no secondary orals or shared coverplates (2.1) C. chapmani (Raymond), 1915 present Type species 3) hydropore structure in right posterior part of 1) theca large oral region, composed of orals and ambulacral 2) ambulacra taper moderately, termina- coverplates tions blunt 4) ambulacra forming low, rounded ridges 3) ambulacral coverplates nearly horizontal externally 5) ambulacral coverplates of moderate thickness 4) interambulacral plates large 6) ambulacral tunnel low and wide 5) thecal plates smooth to foveolate; pitting 7) coverplate passageways oblique subdued, most prominent on proximal 8) peripheral rim plates geniculate rim plates

(2.2) C. reticulatus Bell, sp. nov. A.I.bO) Genus Carneyella Foerste, 1917 1) theca of mo·derate size 2) ambulacra not tapered, terminations very 1) amhulacra curved, I-IV contrasolar, V solar blunt 2) ambulacral terminations confined to inter- 3) ambulacral coverplates moderately con- ambulacral areas vex externally 3) coverplate passageways' external foramina 4) interambulacral plate size moderate elliptical to slitlike 5) all thecal plates covered by prominent, 4) anal structure a periproct coarse pitting 44 A STUDY OF NORTH AMERICA!" EDRIOASTEROIDEA MEMOIR 21

(2.3) C. multibrachiatus (Raymond), 1915 3) ambulacra of moderate width in proportion 1) theca moderate to small to thecal diameter, with gradual distal taper 2) ambulacra taper slightly, terminations 4) interambulacrals of moderate size; squa- blunt mose and imbricate 3) ambulacral coverplates moderately con- vex externally (1.1) I. cincinnatiensis (Roemer), 1851 4) interambulacral plates small, externally Type species convex, appear bulbous Of knobby 1) theca moderate to large 5) thecal plates smooth or with subdued 2) five or more secondary orals pitting, occasional large nodes present 3) primary ambulacral coverplates dis- tinctly larger externally than secondar- (2.4) C. youngi (Raymond), 1915 ies; secondaries rarely reach adradial Characters uncertain suture line externally (2.5) C. platys IRaymond) , 1915 4) interambulacrals moderate in size Characters uncertain (1.2) I. austini (Foerste}, 1914 (2.6) C. billingsi (Chapman), 1860 1) theca small Characters uncertain 2) five or more secondary orals 3) proximal secondary ambulacral cover- A-II. Suborder IsoRoPHINA Bell, subord. nov. plates nearly as large externally as pri- maries, reach adradial suture line Isorophida with: externally 1) four large, central primary orals, or numerous 4) interambulacrals moderate in size small, undifferentiated central orals 2) amhulaoral coverplates forming multiple, alter- (1.3) I. ioarrenensis (James), 1883 nating biseries or cyclic series of two to seven 1) theca small to moderate sets of plates; coverplates with intra-ambulacral 2) secondary orals present and/or intrathecal extensions 3) secondary ambulacral coverplates large, 3) coverplate passageways absent commonly reach adradial suture line 4) ambulacral floorplates commonly abutting along externally vertical sutures, rarely imbricate 4) interambulacral plates very large 5) anal structure valvular

A-lI-a. Family IsoRoPHIDAE Bell, [am, nov. A-lI-a (2) Genus Isorophusella Bassler, 1935 Isorophina with: 1) ambulacra straight or slightly curved 2) ambulacral coverplates form a regular, 1) theoal domal alternating, double biseries 2) oral area with four large, primary orals, two 3) ambulacra of moderate to broad width. pairs of lateral shared coverplates, one large with gradual distal taper hydropore oral, and secondary orals 4) interambulacrals squamose. imbricate 3) hydropore structure with few plates; inte- grated with central oral rise (2.1) I. incondita (Raymond), 1915 4) ambulacral coverplates forming simple alter- Type species nating, multiple biseries of two or three sets of plates 1) theca of moderate size 5) interambulacrals commonly squamose and 2) one right lateral secondary oral imbricate 3) large primary ambulacral coverplates alternate regularly with small secondary coverplates A-II-aO) Genus Isorophus Foerste, 1917 4) thecal plates smooth 1) ambulacra curved, I-IV contrasolar, V solar (2.2) I. trentononsis (Bassler), 1936 2) ambulacral coverplates form double alter- 1) theca small nating biseries 2) one right lateral secondary oral DIAGNOSTIC SUMMARY OF TAXA 45

.)) secondary ambulacral coverplates exter- (5.1) C. kentuckyensis (Bassler}, 1936 nally nearly as large as primaries in Type species proximal part of ambulacra 1) Triple biseries of ambulacral coverplates 4) thecal plates bear scattered, irregular formed by regularly alternating pairs of nodes three sets of plates; opposing pair mem- (2.3) I. pleiadae (Sinclair and Bolton), 1965 bers in contact perradially 1) theca small (5.2) C. shideleri (Bassler), 1936 2) external oral surface not observed 1) Triple biseries of ambulacral coverplates formed by alternating pairs of three sets A-I1-a (3 Genus Hemicystites Hall, 1852 of plates; opposing pair members of pri- 1) ambulacra straight mary and secondary sets separated per- 2) ambulacral coverplates form double alter- radially by pairs of tertiary coverplates nating biseries 3) ambulacra wide 4) interambulacrals squamose, imbricate A-I1·b. Family ACELACRINITIDAE Chapman, 1860 (3.1) H. parasiticus Hall, 1852 Isorophina with: Type species 1) theca domal or clavate 2) oral plates either numerous with primaries 1) theca small undifferentiated, or occasionally with four pri- 2) one or more secondary orals maries flanked by numerous secondary orals 3) hydropore opening on top of small pro- 3) hydropore structure commonly with many tuberance formed by four or five of the plates forming large, isolated OT semi-inte- six hydropore structure plates grated protuberance along posterior oral rise 4) secondary ambulacral coverplates com- 4) ambulacral coverplates forming complex monly large, some approaching size of multiple biseries or cyclic sets primaries 5) interambulacrals squamose-imbricate or poly- 5) coverplates perradially arched, form per- gonal-tessellate radial ridge 6) interambulacrals of moderate size 7) valvular anal structure large A-I1-b (l) Genus Agelacrinites Vanuxem, 1842 1) theca domal A-I1-a (4) Genus Rectitriordo Bell, gen. nov. 2) fifteen or more oral plates which include 1) ambulacra straight two or more apparently differentiated pri- 2) ambulacral coverplates form regular triple mary orals and one large hydro pore oral biseries 3) hydropore structure semi-integrated, 3) ambulacra of moderate width formed by few plates 4) interambulacrals squamose, imbricate 4) ambulacra curved, I·IlI contrasolar, IV·V (4.1) R. kirkfieldensis Bell, sp, nov. solar; of moderate width 5) ambulacral coverplates form alternating Type species two-plate cycles 1) oral surface highly convex 6) interambulacrals large, subpolygonal, 2) oral area includes approximately 13 sec- slightly imbricate ondary orals 7) valvular anal structure with two circlets of 3) interambulacrals relatively large alternating plates 4) distal rim plates subtriangular in ex- ternal outline (1.1) A. hamiltonensis Vanuxem, 1842 Type species A·II.a(5) Genus Curoitriordo Bell, gen. nov. 1) theca large 1) ambulacra curved, I·IV contrasolar, V solar 2) oral plate arrangement variable 2) ambulacral coverplates form triple biseries 3) hydropore structure formed by one large 3) ambulacra of moderate width hydropore oral and two to five oral- 4) interambulacrals squamose, imbricate ambulacral series eoverplates 46 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21

4) two sets of ambulacral coverplates form 2) posterior part of posterior oral protuber- regular to irregular two-plate cycles ance formed by three plates 5) interambulacrals large 3) hydropore structure formed by four or 6) thecal plates with prominent to subdued more plates, which include two posterior ridge and node prosopon elements (3.2) P. keslingi Bell, sp, nov. A.II-b(2) Genus Krama Bell, gen. nov. 1) theca of moderate size 1) theca dornal 2) posterior part of posterior oral protuber. 2) sixteen or more oral plates which include ance formed by two large plates four large primary orals, one hydropore 3) hydropore structure formed by four oral, and lateral secondary orals which re- plates, which include one large posterior semble ambulacral coverplate sequence element 3) hydropore structure semi-integrated (3.3) ( ?) P. jasperensis (Harker), 1953 4) amhulacra curved, I-III contrasolar, IV·V 1) theca small solar; of moderate width 2) posterior oral protuberance formed by 5) ambulacral coverplate sequence a mix- two plates ture of cyclic sets and biserial pairs 3) hydropore structure formed by two,plates 6) interambulacrals squamose, imbricate 4) only one alternating set of coverplates 7) valvular anal structure formed by two cir- developed clets of alternating plates (3.4) (?) P. alpenensis (Bassler), 1936 (2.1) K. devonicum (Bassler), 1936 Characters unknown Type species 1) theca of moderate size A-II·h(4) Genus Discocystis Gregory, 1897 2) hydropore structure formed by three or more plates 1) theca clavate 3) ambulacral coverplate series which in- 2) numerous small orals, primaries undiffer- cludes three-plate cycles and one late- entiated developing fourth set added as biserial 3) large hydropore protuberance separate pairs from oral rise 4) interambulacrals relatively large 4) ambulacra curved, I-IV contrasolar, V 5) anal plates centrally elevated to fo-rm solar; long and narrow small central protuberance 5) ambulacral coverplates form three- or four-plate cycles 6) interamhulacrals large, polygonal, tessel- A-I1-b(3) Genus Postibulla Bell, gen. nov. late 1) theca domal 7) valvular anal structure formed by two cir- 2) many oral plates, primaries not differenti- clets ated; large posterior oral protuberance (4.1) D. kaskaskiensis (Hall), 1858 present Type species 3) hydropore structure semi-integrated 4) ambulacra curved, I-III contrasolar, IV- 1) theca large V solar; narrow 2) hydropore structure formed by at least .5) ambulacral coverplates form two- or three- three large posterior plates plate irregular cycles, coverplates steeply inclined A·I1·h(5) Genus Lepidodiscus Meek and Worthen, 6) interambulacrals squamose, imbricate 1868 7) valvular anal structure formed by three 1) theca highly convex, domal, or clavate circlets which form highly elevated cone 2) numerous small orals, primaries undiffer- entiated (3.1) P. legrurulensis (Miller and Gurley), 1894 3) large, elongate hydropore structure sepa- Type species rate from central oral rise, posterior side I) theca small formed by many plates DIAGNOSTIC SUMMARY OF TAXA 47

4) .ambulacra curved, 1-IY contrasolar, Y (6.1) U. pulaskiensis (Miller and Gurley), 1894 solar; long Type species 5) ambulacral coverplates form six-plate 1) theca large cycles 2) anterior hydropore structure orals do not 6) interambulacrals squamose, imbricate, or reach transverse oral midline perradially polygonal, tessellate 3) thecal plates smooth or finely pustulose 7) valvular anal structure formed by two cir- clets (5.l) L. squamosus Meek and Worthen, 1868 A-II-b (7) Genus Cooperidiscus Bassler, 1935 Type species 1) theca clavate (?) 1) theca large, highly convex, domal 2) numerous orals (?) 2) ambulacral coverplates smooth perrad- 3) hydropore structure large, separate from ially central oral rise (?) 3) ambulacral floorplates imbricate 4) ambulacra curved, I·Y solar; long, ex- 4) interambulacrals squamose, imbricate tremely narrow 5) ambulacral coverplate series includes two (5.2) L. laudoni (Bassler), 1936 or more sets of elements 1) theca large, clavate; pedunculate zone 6) interambulacrals numerous, squamose, im- plates numerous, imbricate, suhrectan- bricate gular, very thin, and in vertical columns 7) valvular anal structure formed by two cir- 2) ambulacral coverplates perradially clets of plates raised, form small perradial ridge (7.1) C. alleganius (Clarke), 1901 3) ambulacral floorplates abutting; each with two lower-surface, lateral protuber- Type species ances 1) theca large, upper oral surface convex 4) central interambulacrals polygonal, tes- upward, lower surface uncertain sellate 2) hydropore structure apparently formed by numerous plates (5.3) L. sampsoni (Miller), 1891 3) ambulacra remain widely separated from 1) theca clavate or subclavate, pedunculate each other distally zone plates squamose, imbricate, without 4) thecal plates apparently smooth or nearly regular order so 2) amb ulacral coverplates perradially raised, form a perradial ridge 3) ambulacral floorplates abutting; each A-II-b (8) Genus and species indeterminate with four or more inner surface, lateral Pennsylvanian fragments protuberances 4) interambulacrals large, polygonal, tes- sellate A·II-c. Family Uncertain

A-II·b (6) Genus Ulrichidiscus Bassler, 1935 1) theca highly convex, domal, or clavate A-II-c (I) Genus Hadrochthus Bell, gen. nov. 2) numerous oral plates; primaries undiffer- 1) theca domal entiated 2) oral area with few plates, primary orals 3) large, elongate hydropore structure sepa- differentiated rate from central oral rise 3) hydropore structure semi-integrated, small 4) ambulacra curved, I-Y contrasolar; long 4) ambulacra straight, wide 5) ambulacral coverplates form seven-plate 5) ambulacral coverplates form single alter- cycles nating biseries 6) interambulacrals polygonal to squamose; 6) interambulacrals large, thick, polygonal, tessellate to slightly imbricate tessellate 7) valvular anal structure formed by two cir- 7) valvular anal structure formed by one cir- clets of plates clet 48 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21

(1.1) H. commensalus Bell, sp, nov. B-I·a. Family EDRIOASTERIDAE Bather, 1898 1) theca small to mo-derate in size Characters of the order 2) fourteen oral plates which include three primary orals, two pairs of lateral shared coverplates, four secondary orals, one B·I·a(l) Genus Edrioaster Billings, 1858 small hydropore oral 1) ambulacra curved, I·IV contrasolar, V solar 3) small hydropore protuberance formed by 2) ambulacral coverplates perradially angular, two plates form right-angle, zigzag, perradiallines 4) ambulacral coverplates large 3) right posterior hydropore plate abuts adra- 5) interambulacrals large, few in number dial ends of proximal posterior floorplates 6) thecal plates may have large nodes of ambulacrum V (Ll) E. bigsbyi (Billings), 1857 A-III. Suborder and Family Uncertain Type species (?) Hemicystites carbonarius Bassler, 1936 1) theca large 1) theca small, domal 2) thecal plates with large, rounded nodes 2) characters not interpretable 3) ambulacral curvature initiated above ambitus B. Order EDRIOASTERIDA Bell, ord. nov. (1.2) E. priscus (Miller and Gurley), 1894 Edrioasteroidea with: 1) theca small 1) thecal shape "echinoidal," oral surface plates ex- 2) thecal plates smooth tending below ambitus onto lower side of theca 3) ambulacral curvature initiated below 2) oral frame formed by 10 compound plates which in- ambitus clude numerous floorplates and five modified proxi- mal interambulacrals B.I.a(2) Genus Edriophus Bell, gen. nov. 3) hydropore structure located in posterior part of oral 1) ambulacra curved, I·V solar area, formed by two plates; hydropore opening 2) ambulacral coverplates perradially sinuous elongate perpendicular to suture line and penetrat- and elevated, form sinuous perradial ridge ing both plates 3) right posterior hydropore plate fused to 4) amhulacra composed of: adradial ends of proximal posterior floor- a) biserial floorplates with sutural passageways plates of ambulacrum V which extend from ambulacral tunnel into thecal cavity (2.1) E. levis (Bather), 1914 b) biserial coverplates without intrathecal or intra- Type species ambulacral extensions; without sutural passage· 1) theca large ways 2) thecal plates smooth 5) margin of oral surface on lower side of theca, reo flexed upward toward center of theca with distal (2.2) (?) E. saratogensis (Ruedemann), 1912 membrane; imbedded with minute plates; attached 1) theca small to substrate; peripheral rim not present 2) thecal plates finely pustulose Systematic Paleontology

Class EDRIOASTEROIDEA Billings, 1858

Diagnosis The largest interambulacral plates are in the central Polyplated, thecate, sedentary Echinodermata with: and distal parts of each interambulacrum. initially triradiate and subsequently pentaradiate symme- try; five (±) endothecal ambulacra radiating from cen- Discussion tral oral structure of covering orals and underlying oral The present study includes most species formerly plaoed frame; ambulacral system formed by two sets of thecal ele- in three of the seven commonly recognized families of the ments - coverplates and floorplates ; sutural passageways class Edrioasteroidea - the Agelacrinitidae, Hemicysti- present or absent, associated with ambulacra; hydropore tidae, and Edrioasteridae [sensu Bassler (1935, 1936) opening in or near right posterior part of oral area, pos- and Regnell (1966) ]. Here two orders, two suborders, and terior to midline of ambulacrum V; interambulacra ir- five families are recognized (see Diagnostic Summary of regularly polyplated; anal structure on upper oral surface Taxa Included). in posterior interambulacrum, periproctal or valvular; theca domal, clavate or globose (without stalk). Range and occurrence of edrioasteroids including de- Description scribed taxa not covered in this study Edrioasteroids are small to moderate sized echino- Class EDRIOASTEROIDEA Billings, 1858 derms; adult thecal diameters range from 9 to approxi- Lower Cambrian - Pennsylvanian. Australia, Belgium, mately 50 mm, 20 mm being the average. The theca is Canada, Czechoslovakia, England, France, Germany, commonly formed by a polypIated oral surface (which Scotland, Sweden, United States, U.S.S.R. may extend below the ambitus) and nonplated central aboral surface, without a stem or stalk. Order ISOROPHIDA Bell The ambulacra are formed by outer coverplates and underlying floorplates. Edrioasteroids lack exothecal Suborder LEBETODISCINA Bell appendages. The central covering orals are distally con- Family LEBETODISCIDAE Bell tinuous with the ambulacral coverplate series. The oral Black River Group, Mohawkian Series, Middle Ordo- frame is formed by enlarged proximal ambulacral floor- vician - Keyser Group, Cayugan Series, Upper plates and commonly, also' by intrathecal extensions from Silurian. Australia, Canada (Ontario), Czechoslo- the overlying orals. In certain species (Edrioasterida) , vakia, United States (Indiana, Kentucky, Minnesota, the oral frame includes 10 large compound plates. Ambu- Ohio, Pennsylvania). lacral coverplate passageways (in Lebetodiscina) or floor- plate passageways (in Edrioasterida) may be present. Family CARNEYELLIDAE Bell The oral-ambulacral series reflects a triradiate thecal Chazy Group, Mohawkian Series, Middle Ordovician symmetry, but the five ambulacra - one anterior and two - Richmond Group, Cincinnatian Series, Upper lateral pairs - impose a dominant pentaradiate form on Ordovician. Canada (Ontario), United States (Illi- the theca, apparently superimposed on the primary tri- nois, Indiana, Kentucky, Minnesota, New York, Ohio, radiate pattern. Tennessee) . The hydropore commonly is formed by the right pos- terior plates of the oral area. In certain forms (Leheto- discidae) it is distal to the oral area, along the proximal, posterior, adradial edge of ambulacrum V, flanked by proximal plates of interambulacrum 5. The underlying stone canal passageway opens into the thecal cavity along the distal, right posterior margin of the oral frame.

49 50 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21

Suborder IsoRoPHINA Bell Others: Family IsoRoPHIDAE Bell Family STROMATOCYSTITIDAE Bassler, 1936 Chazy Group, Mohawkian Series, Middle Ordovician [Stromatocystites Pompeckj, 1896; Walcottidiscus, - Clinton Group, Niagaran Series, Middle Silurian. Bassler, 1935] Lower Cambrian (" Olenellus beds ") Canada (Ontario, Quebec) ?Czechoslovakia, United - Middle Cambrian. Canada (British Columbia, States (Indiana, Kentucky, Minnesota, New York, Newfoundland), Czechoslovakia, France, Germany, Ohio, Tennessee, Virginia). Sweden, U.S.S.R. Family AGELACRINITIDAE Chapman, 1860 Family CYATHOCYSTIDAE Bather, 1899 Helderberg Group, Helderbergian Series, Lower De- [Cyathocystis Schmidt, 1879; Cyathotheca Jaekel, vonian - Magdalena Group, Virgilian Series, Penn- 1918] ? Lower Ordovician; Chazy Group, Mo- sylvanian. Canada (Alberta, Ontario), England, hawkian Series, Middle Ordovician. United States Germany, United States (Alabama, Illinois, Indiana, (Oklahoma, Tennessee), U.S.S.R. (Estonia). Upper Iowa, Kentucky, Michigan, New Mexico, New York, Ordovician or Lower Silurian. Sweden. Pennsylvania, West Virginia), U.S.S.R. Family PYRGOCYSTII}AE Kesling, 1967 Order EDRIOASTERIDA Bell [Pyrgocystis Bather, 1915] Family EDRIOASTERIDAE Bather ? Lower Ordovician; Chazy Group, Mohawkian Ser- Trenton Group, Mohawkian Series, Middle Ordo- ies, Middle Ordovician - Middle Devonian. Czecho- vician. Canada (Ontario, Quebec), United States slovakia, England, Germany, Scotland, Sweden (Got- (Kentucky, Michigan, Minnesota, New York). (?) land), United States (Minnesota, New York), "Psammites du Controz," Upper Devonian. Belgium. U.S.S.R.

Order IsoRoPHIDA Bell, ord. nov.

Diagnosis plate pairs, and hydropore orals, all distinctly set apart Edrioasteroidea with: domal or clavate theca, ambu- from adjacent proximal amhulacral coverplates. In other lacra commonly limited to upper oral surface; oral frame forms the orals are numerous small plates which resemble formed by five enlarged, proximal ambulacral floorplates, the ambulacral eoverplate series; distally they appear to with or without intrathecal extensions from primary grade into the proximal ambulacral series without an orals; hydropore structure in or posterior to right pos- obvious break. Opposing orals meet perradially along the terior margin of oral area, opening along junctions anterior and transverse oral midlines. hetween plates, elongate parallel to plate margins; ambu- The transversely elongate oral frame underlies the lacra formed by biserial or cyclic sets of coverplates, with external orals and surrounds a large central lumen. The intra-ambulacral and/or intrathecal extensions, and uni- proximal rim of the frame, which extends down into, the serial floorplates; amhulacral coverplate passageways thecal cavity, is ovate. Distally the frame is continuous present in some; margin of oral surface a peripheral rim. with the floorplate series of each ambulacrum, which imparts a pentagonal outline to the frame. Description The hydropore structure is commonly formed by several The thecae of adult Isorophida range from approxi- plates, as many as twenty in some forms. It may be inte- mately 10 to 50 mm in diameter with domal forms 15 to grated into the central oral rise, semi-integrated (i.e., 25 mm the most common. forming a small but distinctly elevated area on the sloping The oral area is elevated ahove the interambulacra and posterior side of the rise), or it may he a separate large forms the central oral rise which is distally continuous protuberance posterior to the oral rise. with the elevated amhulacral ridges. The stone canal passageway leads into the thecal cavity The external orals may be large specialized plates, from the hydropore. The upper part of the inwardly classified as primaries, secondaries, lateral shared cover- expanding, funnel-shaped passageway is formed by the ORDER ISOROPHIDA 51 plates of the hydropore structure. The inner parts may be plate overlapping the distal margin of the adjacent proxi- formed by both intrathecal extensions from the hydropore mal plate. plates and also the adj acent parts of one or two proximal The interambulacra are covered either by squamose floorplates of ambulacrum V. imbricate plates or by polygonal tessellate ones. Inter- Externally, the ambulacra are commonly elevated above ambulacrals lack apparent order, except that the largest the interambulacra and form low, rounded ridges which plates are found in the central and distal parts of an inter- radiate outward from the central oral rise. Occasionally ambulacrum. the ambulacra form large. high ridges. They are confined The peripheral rim is formed by several circlets of to the upper oral surface in all but a few species. The plates, the plates diminishing in size distally. The large ambulacra may be straight or curved. The curvature pat- proximal plates may be grouped into alternating proximal tern is constant at the generic level. and distal subcirclet members. Rim plates are commonly Ambulacral coverplates form single alternating biseries, geniculate, their basal surfaces resting on the underlying multiple biseries, or cyclic series which include two to substrate. In domal thecae the distal margin of the rim seven sets of coverplates. Coverplates in most species have forms the thecal ambitus. In clavate forms it is located at intra-ambulacral extensions, and in many they extend the base of the pedunculate zone. adradially past the floorplate margins into the thecal cavity as intrathecal extensions. Coverplate passageways are Discussion sometimes developed; these extend between coverplates The order Isorophida embraces most of the species from the thecal cavity to the exterior of the theca. included in this study. Numerically, these are the com- The uniserial ambulacral floorplates are commonly mon edrioasteroids. It is divided into two suborders, each trough-shaped with the upper surface centrally concave with two families. inward. forming a deep axial trough. The lateral margins Taxonomically important structural differences between of the upper surface form narrow, nearly horizontal artic- the Isorophida and Edrioasterida are summarized under ulation zones, one flanking each side of the trough, on the discussion of the Edrioasterida and in the Diagnostic which rest the adradial parts of the overlying coverplates. Summary of Taxa Included, in the Introduction. The inner surfaces of the floorplates are commonly convex inward. In some forms the floorplates are thick and the inner surface shape is modified. Large lateral protuber- RANGE AND OCCURRENCE: Middle Ordovician through ances may occur on the inner floorplate surfaces. Upper Pennsylvanian of North America, Europe, Asia, Contiguous floorplates may abut along vertical sutures, and Australia. or they may he imbricate with the proximal end of each

Suborder LEBETODISCINA Bell, subord. nov.

Diagnosis lateral shared coverplates and secondary orals. The oral frame includes both proximal floorplates and intrathecal Isorophida with: center of oral area farmed by three extensions from at least the primary orals. primary orals; ambulacral coverplates forming single, The hydropore structure is formed by oral-ambulacral alternating biseries, coverplates with both intra-ambu- series plates, and in some species by modified posterior lacral and intrathecal extensions; ambulacral coverplate interambulacrals. passageways present; ambulacral floorplates imbricate; The ambulacral coverplates form a single alternating anal area a periproct. biseries of plates, opposing plates meeting along zigzag perradial lines. The coverplates have both intra-amhu- Description lacral and intrathecal extensions. Large sutural passage· Lebetodiscina commonly have domal thecae. In Cys- ways extend from the thecal cavity to the exterior of the taster stellatus the theca approaches a discoidal form, and theca, each formed along the lateral suture between adja- in C. granulatus it is clavate. cent coverplates, The external foramina of the passage- The oral area includes the three large, central primary ways vary from large, subcircular openings to elongate orals and either a single large hydropore oral or sets (}f slits. 52 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21

The uniserial ambulacral floorplates are imbricate, with Bather (1908) redescribed the ambulacral structure and the proximal margin of each overlapping the distal edge passageways of Lebetodiscus dicksoni (Billings). He real- of the next proximal floorplate. ized that the passageways penetrated into the thecal cavity, Interambulacral plates are squamose and imbricate. but thought they were homologous to the passageways The anal periproct is formed by several irregular cir- which extend between the ambulacral floorplates of Edric- clets. At least the more central elements are elongate to- aster bigsbyi, and thereby misidentified coverplates as ward the central anus. The structure commonly lies near floorplates. the center of interambulacrum 5. Raymond (1915, 1921) contradicted Bather by descrih- The peripheral rim may be formed by either geniculate ing the passageways of Lebetodiscus dicksoni as being or squamose plates. located along the sutures between ambulacral coverplates. However, he attributed little importance to the passageway Discussion system and suggested that its presence was a specific, or perhaps generic, taxobasis. In the same work Raymond The species within the Isorophida include most forms described other species here placed in the Lebetodiseina, placed by Bassler (1935, 1936) in his family Hemicysti- but failed to observe their passageway systems. tidae. Regnell (1966) followed Bassler's classification in the only subsequent comprehensive summary of the edrio- Wilson (1946) reported multiple" pores" between the asteroids. Kesling (1960, 1967) suggested the removal of ambulacral coverplates of Lepidoconia lorijormis (Ray. several species included by Bassler in the Hemicystitidae, mond) , here recognized as a junior synonym for Lebeto- although he did not undertake a major revision of the discus dicksoni. Based on a single specimen with a well- family. A complete discussion 0.£ Bassler's Hemicystitidae preserved lateral depression series, she reported that five is included under the discussion of the family Carneyel- " pores" lie along the lateral edges of each ambulacral Iidae, coverplate. Apparently she believed the basinlike lateral depressions led to passageways which extended into the The coverplate passageway system found in all Lebeto- ambulacral tunnel. It is unclear why she reported only discina is unique and separates this suborder from the five " pores" per coverplate edge, for the specimen she Isorophina (the other suborder of the Isorophida). More- described has seven to nine depressions in each lateral over, the Lehetodiscina have a single alternating biseries depression series (pl. 2, fig. 1-5). Wilson did not mention of coverplates, in contrast with the multiple biseries or the large, elliptical external foramen along each of these cyclic sets of eoverplates found in the Isorophina. Further, lateral suture lines of the coverplates. However, she did the Lebetodiscina anal structure is a periproct 0.£ loose, report the presence of a single large "pore" along the irregular circlets of plates, whereas the Isorophina have a sutures between the coverplates in another specimen of valvular anal structure formed by large, regularly ar- Lebetodiscus dicksoni. ranged, triangular plates. Regnell (1966) summarized published reports of the The existence of a coverplate passageway system passageways in Lebetodiscus dicksoni. He also reported throughout the Lebetodiscina is recognized here for the Wilson's multiple "pore" system for Lepidoconia loti- first time. However, the passageways were first reported [ormis. Regnell's interpretation of the functional role of by Billings (1857). He observed that a series of depres- the passageways was thus based in part upon erroneous sions was present along the ambulacral coverplates (or data. "marginals") of Lebetodiscus dicksoni (Billings). Un- sure whether or not they penetrated the theca, he noted The suborder Lebetodiscina includes two families which their similarity to the "pores" in Edrioaster bigsbyi appear simultaneously in the Middle Ordovician. The (Billings), which he had already demonstrated to extend nature of their prior phyletic relations is still obscure. into the thecal cavity. However, as Billings reported, the That they are related and presumably, therefore, had a " pores" of E. bigsbyi are formed between the amhulacral common ancestry is suggested by the occurrence in both floorplates, whereas those of Lebetodiscus dicksoni are families of three primary orals. a single biseries of cover- between the coverplates. plates, the coverplate passageway system. the imbricate floorplates, and a periproctal type of anal structure. The The passageways' were also reported by Hall (1871) Carneyellidae appear to be the simpler forms, the oral area in a plate explanation of Carneyella pilea (Hall). He having only four plates and the hydropore structure inte- recorded "minute pores passing between the plates" grated with the oral region. However, simplicity is not along the perradial part of the ambulacral coverplates. necessarily to be equated with primitiveness. Hall apparently did not know the extent or the location of the inner parts of these structures. Interestingly, this nota- RANGE AND OCCURRENCE: Middle Ordovician througho tion has been disregarded in subsequent literature. Upper Silurian of North America, Europe, and Australia. FAMILY LEBETODISCIDAE 53

Family LEBETODISCIDAE Bell, [am, nov. occur at the bottom of deep troughs. The external fora- men of each passageway opens between two adjacent cov- Type genus: Lebetodiscus Bather, 1908 erplates at the perradial end of the sutural trough. The pitlike lateral depressions, when present, are incised into Diagnosis the lateral slope of each coverplate and open laterally into Lebetodiscina with: oral area including at least two the trough. pairs of shared coverplates, secondary orals frequently Interambulacral plates are squamose and imbricate. present; hydropore structure distal to oral area, opening They may be small and numerous, or relatively large and along adradial suture line of proximal, posterior part of few in number. ambulacrum V, composed of ambulacral coverplates and The periproct, which is commonly near the center of interambulacral elements; ambulacra forming high, pro- interambulacrum 5, is formed by several irregular circlets nounced ridges on thecal surface, amhulacral coverplates of elongate plates, all equal to, or smaller than, the sur- large, extremely thick (perpendicular to the thecal sur- rounding interambulacrals. face) and wide (perpendicular to ambulacral axis); The peripheral rim is formed by squamose plates. Dur- ambulacral tunnel narrow and high; coverplate passage- ing collapse, the proximal rim plates and distal Interam- ways nearly vertical; peripheral rim plates squamose. bulacrals are equally depressed, obscuring the boundary between the two zones. This contrasts with the common Description high elevation of the proximal rim plates above the inter- ambulacrals in forms with genioulate plates. Lebetodiscidae have small to moderate-sized dornal External plate surfaces are commonly smooth, but nodes thecae which average from 10-20 mm adult diameter. and ridges are found in a few species. Commonly the oral surface appears to have been nearly hemispherical with the marginal plates almost vertical in many specimens. The oral area includes three large central primary orals, Discussion two pairs of lateral shared coverplates, one on each side The family Lehetodiscidae embraces five genera and of the central orals along the transverse oral midline, and eight species. Three genera are monotypic; one genus a variable number of secondary orals. includes two species, and one has three. Except for one The hydropore structure comprises the adradial ends new genus and species, this group has been included pre· of one or two modified ambulacral coverplates and a vari- viously in the family Hemicystitidae Bassler (1936). This able number of interambulacral plates, at least one of was one of five families recognized by Bassler in 1936, which is commonly enlarged. the first work to subdivide isorophid species into more The five ambulacra rise abruptly above the interamhu- than one family. Earlier workers had included all the lacra as high ridges. This elevation results from the mas- Isorophida in a single family, the Agelacrinitidae. siveness of the coverplates, each being extremely thick Bassler (1936) and subsequent authors included in the normal to the thecal surface. Moreover, these coverplates Hemicystitidae several other species which are excluded are thick perpendicular to the arnhulacral axis, thereby from the Lebetodiscidae. Most of these are included here restricting the ambulacral tunnel to a very narrow, high in the Carneyellidae. Analysis of Bassler's Hemicystiti- structure. dae, which is rejected here, is presented under the discus- The coverplate passageways extend along the lateral sion of the Carneyellidae. sutural surfaces between adjacent coverplates and are Kesling (1967) suggested that one species here consid- parallel to the long axis of the coverplates (text fig. 3). ered to be a Lebetodiscidae, the clavate Cystaster granu- Therefore, they extend normal to the thecal surface and latus Hall, be removed from Bassler's Hemicystitidae and are nearly vertical. Passageways in this family are large placed in his new family Pyrgocystidae. As described by and open through conspicuous foramina. Series of de- Kesling, the primary diagnostic character of Pyrgocystis pressions or pits may be associated with the external for- Bather (1915) is the highly elevated" turret-like" theca. amen of each passageway, one row flanking each side of Pyrgocystis is not included in the present study and thus the lateral suture line between adjacent coverplates. These cannot be adequately discussed here. However, the fam- rows of depressions are called lateral depression series. ily Pyrgocystidae is tentatively recognized, but seems best The external appearance of the thick coverplates in the restricted to the type genus. Thecal shape alone seems to Lebetodiscidae is distinctive. Each plate is highly con- be generally a poor basis for family recognition since vex and this forms a prominent median ridge which ex- both high and low forms occur in most families. In de- tends from the adradial suture to the perradialline. There- tailed morphology Cystaster is clearly a member of the fore, the lateral suture lines between adj acent coverplates Lebetodiscidae. However, the combination of thecal shape MEMOIR 21 54 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA with other possible distinctive features of Pyrgocystis aeterized by: 1) oral area with shared coverplates and may warrant the separation of that genus at the family secondary orals; 2) hydropore structure located along level, as Kesling proposed. the right proximal posterior edge of ambulacrum V, Clearly there is much yet to be discovered about the formed by ambulacral coverplates and interambulacral el- evolution of the Lebetodiscidae, since three of the five ements; 3) ambulacral coverplates very thick, thereby genera are monotypic and all five seem to be soundly con- forming high ambulacral ridges and a high, narrow am- ceived. Generic taxobases include: 1) thecal shape and bulacral tunnel and orienting the large coverplate passage- size; 2) number, arrangement, and size of secondary or- ways almost normal to the thecal surface; 4) squamose als; 3) hydropore construction; 4) ambulacral disposi- peripheral rim plates. The Carneyellidae are character- tion; 5) ambulacral coverplate size and shape; and 6) ized by: 1) oral area with only the three primary orals structures associated with the coverplate passageways. and one hydropore oral (no shared coverplates or second- At least one published description of a specimen not ary orals); 2) hydropore structure located in the right included in this study suggests relationship to the Lebeto- posterior part of the oral region, formed by ambulacral discina. Phillip (1965) described the only Southern coverplates and orals (rather than interambulacrals) ; 3) Hemisphere edrioasteroid, a small specimen from Aus- ambulacral coverplates of moderate thickness, thereby tralia, preserved only as a mold in coarse sandstone. forming low, rounded ambulacral ridges and low, wide Phillip's brief description and illustration strongly sug- ambulacral tunnels, thus making the coverplate passage- gest that the specimen belongs to the genus Cystaster, and ways nearly parallel to the thecal surface; 4) peripheral may even belong in the North American species C. stella- rim plates geniculate. tus. In contrasting the differences between the Lebetodis- RANGE AND OCCURRENCE: Middle Ordovician through Up. cidae and the CarneyeIlidae, the Lebetodiscidae are char- per Silurian of eastern North America and Australia.

Genus Lebetodiscus Bather, 1908 1938 Lebetodiscus Bather, Bassler, R. S., Fossilium Catalogus I: Animalia, pars 83, Cravenhage, Holland; 122. 1842 [non] Agelacrinites Vanuxem, L., Nat. Hist. New York, pt. 1943 Lebetodiscus Bather, Bassler, R. S. and Moodey, M. W., IV, Geology, 3:158, fig. 80. GeoI. Soc. America, Spec. Pap. 45: 206. 1857 Agelacrinites Vanuxem, Billings, E., GeoI. Surv, Canada, 1946 Lebetodiscus Bather, Wilson, A. E., GeoI. Surv. Canada Rept. Prog. 1853-1856: 294-295. Bull. 4: 19; Lepidoconia Wilson, ibid.: 21, pl. 4, fig. 2. 1858b Agelacrinites Vanuxem, Billings, E., GeoI. Surv. Canada, 1966 Lebetodiscus Bather, Regnell, G., in Treatise Invert. Fig. and Descriptions of Canadian Organic Remains, dec. Paleont., R. C. Moore (ed.) , Lawrence, pt. D, Echinoder- 3: 84, pl. 8, fig. 3, 3a, 4, 4a. mata 3, 1: D165, text fig. 127.4; Lepidoconia Wilson, idem, 1881 Agelacrinites Vanuxem, Grant, J. A., Ottawa Field Natural- ibid.: Ul65, text fig. 127-1. ists' Club, Trans. 2: pl. 1, fig. 9. 1887 Agelacrinites Vanuxem, Barrande, J. [partim], Systeme TYPE SPECIES: Agelacrinites dicksoni Billings, 1857 Silurien du centre de la Boheme, Prague, pt. 1, 7(1): 55,83. 1896b Agelacrinus Vanuxem, Haeckel, E., Die Amphorideen und Cystoideen, Leipzig, 1: pl. 3, fig. 29. Diagnosis 1899 Agelacrinites Vanuxem, Jaekel, O. [partim], Starnmes- Lehetodiscidae with: domal theca, oral surface highly geschichte der Pelmatozoen, Bd. 1, Thecoidea und Cys- convex; oral region with secondary oral plates; hydropmre toidea, Berlin: SO, pl. 2, fig. 2. structure formed by enlarged adradial end of second prox· 1901 Agelacrinites Vanuxem, Clarke, J. M., New York State Mus. imal posterior coverplate of ambulacrum V and two or Bull. 49(2) : 191, text fig. 3. three modified interambulacrals; amhulacra curve con- 1908 Lebetodiscus Bather, F. A., GeoI. Mag. (n.s.) , dec. 5, 5: 543·550, pl. 25, fig. 1. trasolarly; eoverplate passageways large, lateral depres- 1915 Lebetodiscus Bather, Raymond, P. E. [partimJ, Ottawa sion series present. Naturalist, 29 (5.6): 53·56, pl. 1, fig. 6. 1921 Lebetodiscus Bather, Raymond, P. E. [partim], GeoI. Surv, Description Canada, Mus. Bull. 31 (Geol. Series 38): 4.7, pl. 1, pl. 2, The genus Lebetodiscus is monotypic. Therefore, sepa· fig. 9, pl. 3, fig. 1, 2. ration of generic and specific taxohases is uncertain. 1935 Lebetodiscus Bather, Bassler, R. S., Smithsonian Misc. ColI. 93(8): 6. Features outlined in the above diagnosis are in part in- 1936 Lebetodiscus Bather, Bassler, R. S., Smithsonian Misc. ColI. ferred to be of generic rank from taxobases established 95 (6) ; 9, pl. 3, fig. 10. for related Lebetodiscidae. LEBETODISCUS 55

Lebetodiscus dicksoni (Billings), 1857 V and three (two r ) modified interambulacral plates; interambulacral plates large, thick, and bearing one or two Text fig. 3.4; plate 1-2 rows of depressions along distal extremity of external part 1825 "A Fossil Belonging to the Class Radiaria ", Sowerby, G. B., of plates. Zoo!. Jour., London, 2 (7 art. 37): 318·320, pl. 11, fig. 5. 1848 "A remarkable American fossil ", Forbes, E., Geol. Surv. Description Great Britain and Mus. Practical Geology, London, Mem. 2 (2) : 519·520. The domal theca of Lebetodiscus dicksoni is highly con- 1857 Agelacrinites dicksoni Billing" E., Geol. Surv. Canada, vex. The rim is commonly inclined at a high angle to the Rept. Prog. 1853-1856:294·295. substrate, and its distal edge is occasionally reflexed under 1858b Agelacrinites dicksoni Billings, E., Geol. Surv, Canada, Fig. the upper side of the theca. The amhulacra and central and Descriptions of Canadian Organic Remains, dec. 3: 84. oral region are highly elevated above the interamhulacra pl. 8, fig. 3, 3a, 4, 4a. and form conspicuous ridges on the thecal surface. Adults 1881 Agelacrinites dicksoni Billings, Grant, J. A., Ottawa Field are commonly 20 to 24 mm in diameter, 24.2 mm the Naturalists' Club, Trans. 2: pl. 1, fig. 9. greatest known diameter. 1887 Agelacrinites dicksoni Billings, Barrande, J., Systerne Si- The oral region includes three primary orals, two pairs lurien du centre de la Boheme, Prague, pt. I, 7(1): 55, 83. of lateral shared coverplates, and four secondary orals 18%b Agelacrinus dicksoni Billings, Haeckel, E., Die Arnphori- (text fig. 3A, pI. 1, fig. 9.11). The two anterior primary deen und Cystoideen, Leipzig, 1: pl. 3, fig. 29. orals abut each other laterally, along the anterior oral mid- 1899 Agelacrinites dicksoni Billings, Jaekel, 0., Stammesge- schichte der Pelmatozoen, Bd. I, Thecoidea und Cystoidea, line. The single large, central posterior oral meets the an- Berlin: 50, pl. 2, fig. 2. terior primaries along the slightly anteriorly arcuate, 1901 Agelacrinites dicksoni Billings, Clarke, J. M., New York transverse oral midline. One pair of lateral shared cover- State Mus. Bull. 49(2): 191, text fig. 3. plates flank each side of the central primary orals. These 1908 Lebetodiscus dicksoni (Billings), Bather, F. A., Geol. Mag. are similar in shape and size to the amhulacral coverplates. (n.s. ), dec. 5, 5: 543-550, pl. 25, fig. 1. Four small secondary oral plates lie along the transverse 1915 Agelacrinites dicksoni Billings, Bassler, R. S., United States oral midline, inserted between the perradial ends of the Nat. Mus. Bull. 92. 1: 20. primary orals and the adjacent shared coverplates. Two 1915 Lebetodiscus dicksoni (Billings l , Raymond, P. E., Ottawa are anterior to the midline and lie distal to the opposing Naturalist 29 (5-6): 53·56; Lebetodiscus lorijormis Ray. mond, ibid.: 56, pl. 1, fig. 6. posterior secondaries. The secondary orals are surficial 1921 Lebetodiscus dicksoni (Billings), Raymond, P. E., Geol. and end a short distance below the surface of the theca, in Surv. Canada, Mus. Bull. 31 (Geol. Series 38): 4-6, pl. I, contrast with the primary orals and shared coverplates, pl. 3, fig. 1; Lebetodiscus lorijormis Raymond, ibid.: 7, pl. both of which extend into the interior of the theca. The 2, fig. 9, pl. 3, fig. 2. transverse oral midline appears finely serrate in partially 1935 Lebetodiscus dicksoni

o

(( \ \ \\ \ 1

\ \

E

G 58 A STUDY OF NORTH AMERICAN EDRIOASTEROIDEA MEMOIR 21

Large, bladelike intra-ambulacral extensions are pro- side of the coverplate. The upper end of each passageway duced from the proximal edge of the ambulacral tunnel and the external foramen are unequally shared by the two side of each coverplate (text fig. 3D, G). They extend in- adjacent coverplates, the more distal plate forming a ward toward the ambulacral tunnel and flex proximally larger part than the proximal one. This disparity results toward the oral region. The distal part of each extension from the large size of the intra-ambulacral extension on curves upward and the distal edge of the extension abuts the proximal inner edge o-f each coverplate. The outer sur- the inner side of the adjacent, next proximal coverplate. face 01 this extension forms most of the perradial side 01 Thus these intra-ambulacral extensions are trough-shaped the upper part of the passageway and foramen, and thus (text fig. 3C, D). The perradial end of each extension is restricts the participation of the proximal coverplate. The produced furthest toward the oral region. The lower, or width of the proximal intra-ambulacral extension rapidly adradial part of the extension progressively decreases in diminishes inward so that shortly below the surface of the size downward and merges with the side of the coverplate ambulacrum the passageways are equally formed by the approximately halfway down to the floorplates. The out- two adjacent coverplates, each half being formed by the wardly curved proximal tip of the trough-shaped extension hemicylindrical groove in the sides of adjacent cover- fits into a shallow groove on the inner surface of the next plates. The passageways lead from the thecal cavity to the proximal coverplate. Thus the adj acent coverplates are exterior. Thus the passageways lack direct communication tightly locked together when closed. Apparently this inter- with the ambulacral tunnel. locking was maintained even when the coverplates were A row of obovate, basinlike depressions is incised into rotated open, with essentially no differential movement oc- both external lateral edges of each coverplate so that one curring between the laterally sutured adjacent coverplates. row flanks each side of the lateral suture line between The outer distal edge of each coverplate is slightly extend- adj acent coverplates (text fig. 3C, H, 4D; pl. 1, fig. 5; ed distally so as to abut the proximal outer edge of the pl. 2, fig. 4, 5). Perradially these depressions flank the adj acent posterior coverplate. Thus a space is formed edges of the passageway external foramina. In the opposite between this outer edge and the underlying intra-ambu- direction they extend down almost to the adradial suture lacral extension of the adjacent distal coverplate. This line. Each depression 01 the series is subcircular and space is the upper part of the sutural passageway, de- deeply incised into the external surface of the coverplate. scribed below. The floor of the basin remains at nearly the same level. The basal adradial ends of the coverplates extend be- Thus owing to the convexity of the external coverplate tween adjacent interarnhulacrals and the underlying surface, each basin becomes progressively deeper toward amhulacral floorplates into the interior of the theca and the center of the plate. The walls of the basin are nearly form the intrathecal extensions of the coverplates. These vertical. Each basin opens directly into the suture line are as thick as the external parts of the coverplates, in con- trough between adj acent coverplates through a narrow trast with most intrathecal extensions, which are consider- channel. ably thinner than the external parts of the plates. The relationship of the two opposing rows of basins Large passageways extend from the thecal cavity to the along each lateral suture line appears to be random. The exterior of the theca along the lateral sutures of adj acent basins have been observed opposite one another, altemat- coverplates. Each passageway is formed suhequally by the ing, or even changing their relative position along the adjacent edges of two contiguous coverplates, The great length of a single sutural trough. thickness of the coverplates permits the passageways to extend vertically into the interior of the theca. Each cov- erplate has a hemicylindrical groove incised into each lat- Text figure 4. Lebetodiscus dicksoni (Billings), 1857 eral sutural face (text fig. 3E, F, H). The two opposing grooves of adj acent coverplates unite to form a terete, A. ROM 161-t-a (x 4), pl. 2, fig. 8. Ambulacral floorplates are shaded. tubular passageway. The inner end or inner foramen of B-D. GSC 1414. each passageway opens into the thecal cavity. It is formed B. Oral surface, (x 4), pl. 2, fig. 2. Ambulacral floorplates are by the intrathecal extensions of adj acent plates, each form- shaded. ing half of the elliptical opening. The aperture is elliptical C. Peripheral rim segment, (x 5), pl. 2, fig. 6. rather than circular because the inner surfaces of the cov- D. Ambulacrum II, (x 11), pl. 2, fig. 4. Coverplate intra-amhu- erplate extensions lie at a slight angle to the vertical cylin- lacral extensions and lateral basins are stippled; floorplates drical passageway. Thus the internal foramen is elongate are shaded. normal to the amhulacral axis. The external foramina are E·F. Segment of ambulacrum IV, GSC 1412, (x 12). also elliptical, elongate normal to the amhulacral axis in E. Interior side, pl. 2, fig. 12. correlation with the downward curvature of the exterior F. Exterior side, pl. 2, fig. 13. Ambulacral tunnel zone stippled. LEBETODISCUS 59

E

F

B 60 A STUDY OF NORTH AMERICA'" EDRIOASTEROIDEA MEMOIR 21

Commonly eight or nine basins occur in each row. it. The structure appears to have been elevated to form Those near the center of the plate are largest and deepest, a low, conical protuberance. those near the adradial suture line are much shallower. The peripheral rim comprises seven or eight circlets of Basins near the perradial line are also shallow, and open squamose plates. During coIlapse these are equally de- broadly into the adjacent passageway foramen. pressed with the adjacent distal interambulacrals, which The ambulacral floorplates are uniserial and thick, sub- obscures the boundary between the two areas. The proxi. rectangular in plan view, the width being nearly as great mal four circlets of large plates are externally elongate con- as the length. Sutures between consecutive floorplates are centric with the thecal margin. The next circlet outward oblique, the proximal end of each plate overlapping the is formed by a transition series of plates which are ex- distal end of the next plate. However, the degree of over- ternally sagittate. The depressed distal lateral flanks of lap appears to be less than in Streptaster vorticellatus or each transition plate are overlapped by radially elongate Carneyella pilea, where overlap approaches half the floor- plates of the circlet. The distal two circlets of small plates plate length. The lower or inner surface of each floor- are radially elongate. plate is evenly convex inward. The upper surface is convex The peripheral rim appears to have been steeply in- upward, but a small axial trough is incised into the center clined to the substrate in most specimens, suggesting that of each, which extends the length of the floorplate. The the proximal circlet plates did not internally intersect the lateral zones of the upper surface, which flank the axial underlying surface. trough, slope downward toward the adradial suture. Small External plate surfaces appear smooth, except for a fine concavities are excavated into this sloping surface, each pitting which reflects the microstructure of the plates with a small raised rim along the adradial edge. The basal where stroma canals intersected the plate surface. part of the inner ambulacral tunnel edge of an overlying coverplate fits into each of the excavations. Only the Specimens inner edge of the coverplate rests on the floorplate; the GSC 1407.B. Fragment of the holotype of Lebetodiscus remaining basal part extends laterally past the floorplate dicksoni (Billings) (1857, p. 294-295, 1858, pl. 8, fig. 3, margin and forms the intrathecal extension of the cover- 3a). "Trenton Limestone," Trenton Group, Mohawkian plate. Series, Middle Ordovician. Ottawa, Ontario. 13.1 mm In the proximal parts of the ambulacra each floorplate long by 5.3 mm wide. underlies slightly more than two pairs of coverplates, Dis- Text fig. 3B, pI. 1, fig. 1, 2. tally the floorplates decrease in proximal-distal length This specimen is believed to be a fragment of the holo- more rapidly than do the coverplates, so the relationship type which apparently includes the distal tip of ambu- between the two sets of elements approaches one-to-one, lacrum II and the adjacent parts of interambulacra 1 and The ambulacral coverplates rise vertically from the edges 5, together with a bit of the adj acent peripheral rim. The of the narrow axial trough for most of their height. Only fragment has been sawed from the holotype (some time the uppermost part of each is flexed inward (perradially) since the original description) by a vertical cut through to meet the opposing coverplate along the perradial line. the specimen and the matrix. A second cut was also made The ambulacral tunnel is thus quite narrow and exception- adj acent and nearly parallel to the first. It extends only ally high. part way through the theca and leaves both a vertical and The interambulacrals are imbricate, subpolygonal to a horizontal section visible, as seen in pI. 1, fig. 1, 2 and squamose plates. Each is relatively large }n proportion to text fig. 3B. Unfortunately, the remainder of the holotype thecal diameter, compared to the interambulacral plates of is apparently lost. most edrioasteroids, Sutures between the imbricated In the collection of the Geological Survey of Canada, plates are oblique and each plate proximally overlaps the this specimen had been included with the type material of distal edge of the adjacent element. One or two rows of Edrioaster bigsbyi. Although it is only a fragment, it is elongate depressions occur near the distal edge of the obvious from the structure of the ambulacra that it per- upper surface of each interambulacral. Usually, they are tains to Lebetodiscus dicksoni. Fortunately, owing to the in part covered by the overlapping part of the next distal scarcity of L. dicksoni, Raymond (1915, 1921) described plate. Thus the depressions falsely appear to be sutural in detail the holdings of the Geological Survey of Canada. openings into the theca. All of the specimens which he saw have been accounted The periproctal anal structure lies slightly proximal to for except the type, and it is therefore quite likely that this center of the posterior interambulacrum. It includes a is a fragment of the missing specimen. Moreover, corn- large number of plates which form several irregular cir- parison of this fragment with Billings' (1858) original clets. The periproct plates are elongate toward the anal figure of the holotype shows a close similarity between the orifice but become progressively smaller as they appro-ach specimen and the drawing. It should be noted, as Bather LEBETODISCUS 61

(1908) had previously, that Billings' illustration of the This specimen (referred to by authors as the " Fitzpat- type specimen is much more complete than his written ric specimen") has been deeply etched. The interambu- description. Bather evidently saw the type specimen before lacral elements are reduced to merest films, and the it was sawed, and indicated that the drawing was accu- thicker ambulacral and oral plates have been greatly re- rate. The specimen included the proximal parts of all five duced. The smaller secondary orals are lost entirely. The ambulacra, the distal part of three of these, and the two major thecal structures can be recognized, however. A intervening interambulacral areas. This contrasts with fragment of the proximal part of ambulacrum IV was the original description which reported only one "per- broken from the specimen at some previous time and was feet" ambulacrum and the adjacent interambulacra. glued back in place. This fragment was removed again and is illustrated here, showing its outer and inner side (text fig. 4E, F, pI. 2, fig. 12, 13). Both the exterior and GSC 437. Illustrated Specimen of L. dieksoni by Grant interior surfaces of the plates have been etched. The cov- (18811 and others. "Cobourg beds, Trenton Limestone," erplates were disproportionately reduced by solution, thus Trenton Group, Mohawkian Series, Middle Ordovician. the floorplates appear to be much larger relative to the Steamboat landing, foot of Sussex Street, Ottawa, Ontario. coverplates than in nonetched specimens. Apparently over 23.6 mm axial by 22.5 mm transverse diameter. half the thickness of the coverplates has been removed. PI. 1, fig. 9-11. The "Grant specimen" (of authors) is an extremely well preserved individual with little plate disruption. A ROM 161-t-a. A Lebetodiscus dicksoni described by few peripheral rim plates are not visible. However, the Raymond (1915, 1921) and by Wilson (1946) as " GSC surface of the theca has been deeply etched, particularly 1415." "Trenton Limestone," Trenton Group, Mohawk- the high ambulacral and oral regions. Thus almost all of ian Series, Middle Ordovician. Ottawa, Ontario. 22.7 mm the lateral depression series of the coverplates are missing, axial by 20.9 rom transverse diameter. along with other surficial features. Text fig. 4A, pI. 2, fig. 7-9. The specimen has collapsed, disrupting some plates, and has also been crushed after lithification. All five GSC 1414. Holotype of Lepidoconia loriformis (Hay- ambulacra are preserved, but most other thecal structures mond) 0915, p. 56). Cobourg beds of Trenton Lime- are difficult to interpret. One section of the peripheral rim stone, probably the" Cystid beds," about 180 feet below is well preserved. Sections of ambulacra II and III had the top of the Trenton, Trenton Group, Mohawkian Se- been previously ground away to expose a vertical cut ries, Middle Ordovician. Ottawa, Ontario. 24.2 mm axial through ambulacrum II and an oblique cut through ambu- by 22.8 mm transverse diameter. lacrum III, thereby revealing sectional views of the struc- Text fig. 4B, C, 0, pI. 2, fig. 1-6. ture of the ambulacra. This individual has collapsed and the interambulacra The specimen was found in the Royal Ontario Museum and ambulacra I, IV, and V are disrupted and in part under the number 161·t·a. There can be little doubt about crushed. Only ambulacra II and III and part of the per- the identity of this specimen as the old GSC 1415, for the ipheral rim remain intact. Fortunately, the specimen has specimen compares well with Raymond's 1915 descrip- undergone little etching so that the rim and the two well- tion, including the ground sections through ambulacra II preserved ambulacra retain their surficial features, includ- and III. Wilson (1946) noted that GSC 1415 was missing ing the lateral depression series of the ambulacral cover- from the Geological Survey collections and erroneously plates. The partial disruption of the theca exposes lateral considered the specimen to be the holotype of the species, views of the floorplates and also parts of some of the cov- which it clearly is not, as noted by Raymond (1915). erplates that are generally hidden from external view. Dr. Thomas E. Bolton of the Geological Survey of Canada The specimen was long considered an example of advises: "The loan of fossil specimens, types and non- Lebetodiscus dicksoni, but Raymond (1915) proposed for types, was very extensive in the late 1800's and early it the species L. loriformis and Wilson (1946) created the 1900's, and it is very possible that type 1415 was included genus Lepidoconia for Raymond's species. in a shipment to Parks by Billings-W. R. Billings, or even Whiteaves. Records are nil of such movements" GSC 1412. Illustrated Specimen of Lebetodiscus dicksoni (personal communication, 1969). by Raymond (1921, pI. 3, fig. 1). "Trenton Limestone," Trenton Group, Mohawkian Series, Middle Ordovician. ROM 18848-A. Trenton Limestone, Trenton Group, Peterborough, Ontario. 21 mm axial by 23.7 mm trans- Mohawkian Series, Middle Ordovician. Ottawa, Ontario. verse diameter. 17 mm axial by 20.5 mm transverse diameter. Text fig. 4E, F, pI. 2, fig. lOB. PI. I, fig. 12, 13. 62 A STUDY OF NORTH AMER1CAN EDRIOASTEROIDEA MEMOIR 21

This specimen is missing a section of the right posterior scribed, a specimen from the Trenton Limestone (Ottawa) part of the theca and most of the rim plates. The specimen from the collection of Professor Frech at Breslau. The has been etched, leaving only remnants of the coverplate second individual, the first edrioasteroid ever reported, lateral depression series and enlarging the external fora- was illustrated and briefly described by Sowerby (1825), mina of the coverplate passageway system. Happily, the mentioned by Forbes (1848), illustrated by Billings etching exposes the interdigitation across the perradial (1858), and illustrated and described in detail by Bather line of the inner perradial ridges of the ambulacral cover- (1908) . It is from the Lower Trenton Group, Middle plates, a feature clearly seen only in this specimen. Ordovician, Table Rock at Chaudiere Falls of the Ottawa River at Ottawa, Ontario, Canada. The third is a speci- ROM 18855 (A.C). Three specimens of L. dicksoni. men listed by Ami (1905) as belonging to this species, Trenton Limestone, Trenton Group, Mohawkian Series, from the collection of Sheriff Dickson. It is from the Middle Ordovician. Hull, Quebec. Trenton Limestone at Pakenham, Ontario.

ROM 18855·A. 10.5 mm axial by 10.3 nun transverse Discussion of previous investigations diameter. The designation of the holotype of Lebetodiscus dick- PI. 1, fig. 6. soni (Billings), (represented here by specimen GSC A small, poorly preserved individual that has suffered 1407-B, which is considered to be a fragment of the orig- extensive etching and has collapsed into an underlying inal specimen), requires explanation for some earlier depression in the substrate. workers have been confused as to its identity. The first illustration and brief description of a speci- ROM 18855·B. 22.8 nun axial by 25 mm transverse men of L. dicksoni was by Sowerby (1825), but no name diameter. was assigned to the species. This same specimen was PI. 1, fig. 3-5. again referred to by Forbes (1848), but remained with- A large specimen which is centrally disrupted; a zone out a hinomen, In 1857 Billings proposed the name of less disrupted plates surrounds the jumbled central Agelacrinites dicksoni for a different specimen, then in region. The distal tips of all five ambulacra are nearly the collection of the Geological Survey of Canada. Billings intact. Fortunately, the specimen has undergone but little had only one specimen in his possession, but noted he had etching, and therefore surface detail of the plates is well seen others. Because his specimen was incomplete, he preserved. Moreover, the disrupted central plates expose based part of his original description on an unspecified views of all sides of the ambulacral coverplates and those number of other specimens which he did not cite. The fol- normally hidden parts of these plates are revealed. lowing year, Billings revised his definition of A. dicksoni, and figured two specimens - the fragmentary individual YPM 28451 (old 2361). A specimen of L. dicksoni in the collection of the Geological Survey of Canada (the which was one of ten specimens labeled Edrioaster. Lower one specifically mentioned in the original description), Trenton, Trenton Group, Mohawkian Series, Middle Ord- and a second one, the Bigsby specimen. It is entirely pOSe ovician. Curd's farm, Mercer County, Kentucky. 18.6 mm sihle that the Bigsby specimen played a part in the orig- axial by 15.1 mm transverse diameter. inal description (i.e., one of his" other specimens" of the PI. 1, fig. 7, 8. species), but this cannot be established. Thus the frag- This individual has been replaced by beekite, which mentary specimen specifically identified by Billings in the obscures most sutures. The main structural features of the original description (1857) and figured by him in plate theca are preserved, although the left anterior quarter of 8, fig. 3, 3a (1858) must be considered the holotype by the specimen is missing. It is noteworthy in that it is the monotypy. The Bigsby specimen is considered to be only only example of the species known from outside the an Illustrated Specimen. Bather (1908) evidently arrived Ottawa, Ontario region. Moreover, ambulacrum II has a at the same conclusion and referred to the specimen of small side branch just proximal to the point at which the plate 8, fig. 3, 3a as the holotype of Lebetodiscus dicksoni. main extension of the ambulacrum is broken. This is the GSC 1407·B is believed to be a fragment of that specimen. only representative of this species in which an additional Billings' (1857) original description of Agelacrinites ambulacrum is known. The specimen also appears to be dicksoni was brief, citing thecal size and shape, amhu- essentially uncollapsed, preserving the original convexity lacral shape and direction of curvature, and the double of the oral surface. The center of the theca is 7.7 nun row of "marginals" [coverplates]. The two earlier de- above the most distal preserved part. scriptions of the Bigsby specimen (Sowerby 1825, Forbes Three other representatives of L. dicksoni have been reo 1848), published without a hinomen, also noted only gen- ported. Jaekel (1899) illustrated, but only briefly de- eral thecal features. Billings' (l858, p. 84) redescription LEBETODlSCUS 63 of the species compared "two rows of small circular in- Raymond noted that Bather has misinterpreted the ambu- dentations on each side of the rays" with the ambulacral lacral coverplates as floorplates, and pointed out that the floorplate " pores" of Edrioaster bigsbyi. However, Bill- true floorplates were uniserial, but hidden from view in ings was unsure whether or not the A. dicksoni depres- Bather's specimen, However, Raymond did not deny the sions actually penetrated into the theca. This paper in- existence of the small median plates which Bather re- cluded the first illustration of the holotype (plate 8, fig. 3, ported; rather he ascribed them to an additional series of 3a) and also reillustrated the Bigsby specimen (plate 8, coverplates such as had been referred to by Foerste fig. 4, 4a). (1914) as median coverplates in Isorophina. Bather (1908) redescribed A. dicksoni, and proposed In addition to redescribing L. dicksoni, Raymond pro- the genus Lebetodiscus for it. Bather's detailed descrip- posed Lebetodiscus Iorijormis, based on one large speci- tion was based on the Bigsby specimen, and differs sig- men long considered to belong to L. dicksoni. Although nificantly from that presented here in relation to the ambu- Raymond acknowledged the close resemblance of this lacral structure. Bather reported the arnbulacra were specimen to L. dicksoni, his diagnosis was more evolution- formed by large, convex-upward, biserial floorplates ary than morphologic. He thought his new species" forms [actually the coverplates] with a small, median food one of the' connecting links' with the species of later for- groove trough roofed by tiny irregular covering plates. mations" (Raymond, 1915, p. 56). The only feature He recognized the large sutural passageways, but since he actually noted by Raymond as differing from the average interpreted the coverplates as floorplates, he described specimens of L. dicksoni was that the arnbulacra were so the passageways as homologous to those in the floorplates long that they nearly touched one another. This supposed of Edrioaster bigsbyi. Bather presented four drawings of trait is due principally to preservation and to the large ambulacra exteriors. Two of these (1908, text fig. 1, 2) size and advanced age of the specimen. Wilson (1946) are regularized and appear as he described them. The proposed the genus Lepidoconia for Raymond's" species." other two (1908, text fig. 3, 4) were prepared from mag- She admitted its similarity to Lebetodiscus, but dis- nifications. It appears that Bather's irregular, tiny, me- tinguished her genus by the presence of a unique" pore" dian "coverplates" are probably fragments of plates. system consisting of five" pores " on each lateral margin This explains why he thought only a few "coverplates" of each ambulacral coverplate. She reported the" pores" were present in the specimen and that all that could be on the two sides of each plate as opposite. while the said about them was that they were tiny and had no reg- " pores" of adjacent plates were alternate. ular arrangement. It now appears that Bather's specimen The specimen upon which Lepidoconia lorijormis is is a typical example of L. dicksoni. Unfortunately, it was based is a typical Lebetodiscus dicksoni. It has undergone not available for reexamination during this study. little etching. Thus surficial features are well preserved. Bather's misinterpretation of arnbulacral coverplates in including the lateral depression series of the ambulacral L. dicksoni as Hoorplates probably stemmed from his coverplates which Wilson described as a multiple" pore" definitive work on Edrioaster bigsbyi. The plates of the system. The lateral depressions, seven to nine per row latter are unusually large, and Bather studied excellently (not five), are surficial features, limited to the exterior prepared specimens. This work first established the of the plates. The only other criterion noted by Wilson morphology of the ambulacra of E. bigsbyi, including the for separating her new genus from Lebetodiscus was the structure of the floorplate passageways. Bather considered presence of a well-developed peripheral rim. Although E. bigsbyi to be a "typical" edrioasteroid. Thus he ex- the peripheral rim is not well preserved in most individ- pected to see similar characters in Lebetodiscus dicksoni. uals, remnants are present in many specimens of L. Noting the large coverplate passageways, he assumed these dicksoni. to be between floorplates, as in E. bigsbyi. Wilson (1946) also briefly redescribed Lebetodiscus Raymond (1915, 1921) described all specimens of L. dicksoni. She noted the presence of" pores" in the arnbu- dicksoni in the collections of the Geological Survey of lacra, but suggested that they lie between "side plates" Canada. He noted that Bather had misinterpreted the which were larger than another set of plates "on top of arnbulacral structure. Raymond also suggested that two the ambulacral groove." It appears that Wilson was in of the three features Bather used to distinguish L. dicksoni part using Bather's terminology and in part that of Ray- from the other edrioasteroids were in fact preservational, mond, without actually attempting to reconcile their i.e., the supposed absence of a peripheral rim and the differences. thecal shape, which Bather described as being more con- Subsequent references to Lebetodiscus dicksoni have vex and less sessile than that of related species. The third been cursory. Bassler's brief mention of Lebetodiscus is feature used by Bather to distinguish his new genus was noteworthy only because he erroneously described the the supposed biseries of ambulacral floorplates with pores. interarnbulacral plates as mosaic (tessellate), at least in