194 .-\ S1TDY OF NORTH .HIERICAN EDRIOASTEROIDEA 'tlEMOIR 21 Text fig. :34. pl. 36, fig. 1·3. GSC 14680-5. Paratype of Isorophusella pleiadae (Sir;. The holotype is well preserved. Floorplates have been clair and Bolton) (1965, pl, 11, fig. 5, 6 J. 7 mm axial lost from ambulacrum III. which exposes the inner side of by 7.2 mm transverse diameter. the coverplates. A few floorplates are crushed in the other PI. :36, fig. 8. ambulacra. The oral frame is slightly abraded but not This specimen is only slightly disrupted, but lacks the disrupted. The anal structure lies to the right of center of floorplates of ambulacra II and IV. The theca has been interambulacrum 5 (left from the inner surface view J. more deeply etched than the others, and details are 01.. Etching has removed some surficial features, especially the scure. The oral frame and the hydropore structures an' smaller basal ridges of the distal rim plates. relatively well preserved, as is the anal area. GSC 14680-2. Paratype of lsorophusella pleiadae (Sin- clair and BoltonI (1965, pl. 11. fig. 4.5,6). 5.7 mm axial GSC 14680·6. Paratype of Isorophusella pleiadae (Sin .. by 6 mm transverse diameter. clair and Bolton) (1965, pI. 11, fig. 3, 5. 61. 6.1 mm axial PI. 36, fig. 5. by 6.2 mm transverse diameter. This individual, considerably smaller than the holotype, PI. 36. fig. 9. appears to retain thecal proportions characteristic of a In this specimen, ambulacra II and IV are missing sev- young adult. The ambulacral-interambulacral areas are eral f1oorplates, and those of I and III are poorly pre. proportionately smaller, and the oral area and the rim served. The oral frame and stone canal passageway are proportionately larger than is common in adults. Plate both intact. Etching has again removed most of the distal boundaries are less clear in this specimen, but the thecal rim plate basal ridges. structures appear identical to those of the holotype. The anal structure is very close to the left side of ambulacrum GSC 14680-7. Paratype of lsorophusella pleiadae (Sin- V. Etching has removed most of the basal ridges from clair and Bolton) (1965, pI. 11. fig. 3.6). 5.7 mm axial the distal plates of the rim. by 5.7 mm transverse diameter. GSC 14680-3. Paratype of Isorophusella pleiadae (Sin- PI. 36, fig. 10. clair and Bolton) (1965, pl. 11, fig. 5, 6). 8.4 mm axial This individual, like paratype 14680-2. appears to be by 8.8 rnrn transverse diameter. less fully developed than the others. It is a young adult. PI. 36, fig. 6. The specimen is not in good condition. for many of the This specimen is the largest of the type series, but has plates are partially crushed and etched. The anal structure been disrupted. Only ambulacrum I, parts of interam- is well preserved. bulacra 1 and 5, the anal structure, and one segment of the rim are intact. Discussion GSC 14680-4. Paratype of Isorophusella pleiadae (Sin- The seven type specimens appear to represent a distinct clair and Bolton) (1965, pI. 11, fig. 5, 6). 5.5 mm axial species, as suggested by the small thecal diameters and by 5.6 mm transverse diameter. adult thecal proportions. PI. 36, fig. 7. The species is referable to lsorophusella on the basis of: This is a well-preserved specimen with all of the am- the slight ambulacral curvature with I. II. III contrasolar bulacral floorplates preserved. The oral frame and stone IV, V solar; the shorter length of ambulacrum IV; and the canal passageway are very well preserved. A small sec- regularity of the double biseries of amhulacral coverplates. tion of the left posterior rim has been lost. Etching has RANGE AND OCCURENCE: Richmond Group. Cincinnatian removed all but the larger basal ridges of the proximal Series, Upper Ordovician of Anticosti Island. Quebec. rim plates. Genus Hemicystites Hall, 1852 1855 Agelacrinus Vanuxern. Roemer. F. [partim]. in Lethal'a Ceognostica, H. G. Bronn. 3rd edition. Stuttgart. Bd. I. pl. 1842 [non] Agelacrinites Vanuxem, L.. Nat. Hist. New York. pt. 2, Palueo-Lethaeu, 2: 277. IV, Geology 3: 158. fig. 80. 1857 Hemin-stites Hall. Pictet, F.·J .. Traite de Paleontologic on 1852 Hemicystites Hall. J.. Nat. Hist. New York, pt. VI. Palaeon· Naturelle des Animaux Fossils. 2nd edition. Pari" tology 2: 245·246. 335. pl. 51, fig. 18·20. 4: 305·306 [11011 pl. 99. fig. 25]. 1854 Hemicystites Hall, Billings. E.. Canadian Jour. Industry. 1860 Agelacrinites Vanuxern, Chapman. E. J. [partim 1. Canadian Sci. and Art: 273. .Jour. Industry. Sci. and Arts (n.s.) , 5: 360·365. HEM/CYST/TES 195 1862 Agelacrinus Vanuxem, Dujardin, F. and Hupe, H. [partim], right lateral secondary oral, arranged as in other Iso- Histoire Naturelle des Zoophytes Echinodermes, Paris: 84 rophidae. [non pl. 5, fig. 8). The ambulacra are short, wide, and straight. The am- 1866 Hemicystites Hall, J., New York State Mus., 20th Ann. Rept. (adv. pub.) : 8. bulacral coverplates form a double biseries of alternating pairs of large primary and smaller secondary plates. The 1871 Hemicystites Hall, J. [partim], New York State Mus., 24th Ann. Rept. (adv, pub.) : explanation of pl. 2. perradial parts of the coverplates may be flexed upward to 1872 Hemicystites Hall, J. [partim), New York State Mus., 24th form a rounded axial ridge which extends the length of Ann. Rept.: 216. the ambulacra along the perradial lines. The ambulacral 1873 Hemicystites Hall, Meek, F. B. [partimJ, Geol. Surv, Ohio, floorplates are uniserial and trough-shaped. Y. I, Geology and Palaeontology, pt. 2, Palaeontology, sect. Interambulacral areas are restricted in size by the broad I: 53·54. ambulacra, are covered with squamose, imbricate plates 1889 Hemicystites Hall, Miller, S. A. [partim], North American and are small to moderate in size in proportion to thecal Geology and Palaeontology, Cincinnati: 252. diameter. 1894 Hemicystites Hall, Miller, S. A. and Gurley, F. E., Illinois The prominent valvular anal structure is formed by State Mus. Bull. 5: 13. regularly alternating inner and outer circlet plates. 1896b Hemicystis Hall, Haeckel, E. [partim], Die Amphorideen und Cystoideen, Leipzig, 1: 111·112 [non pl. 3, fig. 27·28). The peripheral rim is typical of the family. 1899 Hemicystites Jaekel, O. [partim] , Stammesgeschichte der Pelmatozoen, Bd. I, Thecoidea und Cystoidea, Berlin: 49. Discussion 1900a Hemicystis Hall, Bather, F. A., in A Treatise on Zoology, Hall's (1852) original description of the genus and the E. R. Lankester (ed.) , London, pt. III, Echinoderma: 207. type species, H. parasiticus, summarized only major thecal 1903 Hemicystis Hall, Delage, Y. and Herouard, E. Traite de Zoologie Concrete, T. 3, Echinodermes, Paris: 415. characters that separated the new taxa from other maj or 1915 Hemicystites Hall, Bassler, R. S. [partim], United States echinoderm groups. A very generalized drawing of H. Nat. Mus. Bull. 92, 1: 605·606. parasiticus accompanied the text. Under additions and 1935 Hemicystites Hall, Bassler, R. S. [partim), Smithsonian corrections in the same volume' (p, 355), Hall explains Misc. ColI. 93 (8) : 7. that Hemicystites "is apparently identical with Agelacri- 1936 Hemicystites Hall, Bassler, R. S. [partim), Smithsonian nites of Vanuxem [1842], the description and figure of Misc. ColI. 95 (6): 10-11, pl. 4, fig. 5·6. which I had overlooked at the time this volume was 1938 Hemicystites Hall, Bassler, R. S. [partim), Fossilium Cat· written." alogus I: Animalia, pars 83, Gravenhage, Holland: 110. E. Billings (1854), F. Roemer (1855), F. 1. Pictet 1943 Hemicystites Hall, Bassler, R. S. and Moodey, M. W. (1857), and Dujardin and Hupe (1862) concurred with [partim), Geol. Soc. America, Spec. Pap. 45: 202, 204. Hall and recognized Hall's species as an Agelacrinites. As 1946 Hemicystites Hall, Wilson, A. E. [partim], Geol. Surv. Can- ada Bull. 4: 20. was pointed out by Meek (I873), the subsequent equating 1958a Hemicystites Hall, Ehlers, G. M. and Kesling, R. V. of the two genera may in part be explained by the errone- [partim], Jour. Paleont. 32 (5): 933·934. ous illustration of an 1sorophus cincinnaiiensis (then 1965 Hemicystites Hall, Sinclair, G. W. and. Bolton, T. E. placed in Agelacrinites) as an example of Hemicystites [partim], Geol. Surv. Canada Bull. 134 (3): 38·39. parasiticus by Pictet (1857) and by Dujardin and Hupe 1966 Hemicystites Hall, Regnell, G. [partim], in Treatise Invert. (1862) . Paleont., R. C. Moore (ed.) , Lawrence, pt. U, Echinoder- By 1866 Hall was disposed to consider Hemicystites as mata 3, 1: Ul62 [non) text fig. 118·3, 120·5a, 125·7, 126·11. a distinct genus. He also described Agelacrinus (Hemi- cystites) stellatus in 1866. In Hall's (1871) publication TYPE SPECIES: Hemicystites parasiticus Hall, 1852. of the plate of illustrations for that work, he lists Hemi- cystites stellatus and also a new species, Hemicystites (s.g, Diagnosis Cystaster) granulatus. Detailed drawings of both species Isorophidae with: ambulacra straight, wide; ambulacral were presented. The text and plate were republished to- coverplates forming alternating double biseries; interam- gether in 1872, with the two species cited as Hemicystites bulacrals squamose, imbricate. (s.g. Cystaster) granulatus and Agelacrinus (Hemisys- tites) stellatus. These are relatively common species and both conform to the genus Cystaster. On the other hand, Description Hall's (1852) illustration of Hemicystites parasiticus does The domal theca of Hemicystites is small and averages not accurately po-rtray the plating of the oral area and less than 10 mm in diameter. represents ambulacral coverplates as a single biseries The oral region includes four primary orals, two pairs rather than the actual double hiseries. Specimens of H. of shared coverplates, one hydropore oral, and at least one parasiticus are rare.