Copyright © 2006, The Paleonlological Society ORDOVICIAN POLYPLACOPHORA (MOLLUSCA) FROM NORTH AMERICA

RICHARD D. HOARE AND JOHN POJETA JR. Department of Geology, Bowling Green State University, Bowling Green, Ohio 43403 and U.S. Geological Survey and Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560

ABSTRACT—Abundant silicified polyplacophorans from numerous localities in the Ordovician in Kentucky and other localities in Virginia, Wisconsin, and Minnesota are described systematically. New species are: Spicuchelodes cressmani, Calceochiton floweri, Preacanthochiton baueri, Orthriochiton recavus, Helminthochiton blacki, H. marginatus, and Alastega martini; new genera and species are: Listrochiton weiri, Litochiton crebatus, and Amblytochiton incomptus; and new families are Litochitonidae and Alastegiidae. Hemithecella expansa Ulrich and Bridge in Butts, 1941 and Chelodes cf. C. mirabilis (Butts, 1926), from the Chepultepec Formation in Virginia are also described. Comparisons are made with Chelodes whitehousei Runnegar, Pojeta, Taylor, and Collins, 1979 from Australia and Calceochiton hachitae Flower, 1968 from New Mexico. Listings of the fauna associated with the chitons are given for the Kentucky occurrences; taphonomic discussions of these are included.

INTRODUCTION Kentucky. Thus, although widely distributed, polyplacophorans OF ALL Paleozoic mollusks, polyplacophorans are the least form a small part of the total moUuscan fauna. The oldest poly- known and understood; this is especially true of their ear- placophoran specimen found is a single plate from the Turinian liest history in Cambrian and Ordovician rocks. For this paper we (Blackriveran) Camp Nelson Limestone; the youngest specimen, have more specimens for study than had heretofore been available also a single plate, is from the Chatfieldian Devils Hollow Mem- worldwide for Ordovician chitons. Van Belle (1983) listed 10 ge- ber of the Lexington Limestone (Frey, 1995, p. 7) (Fig. 1). All neric names that had been applied to Ordovician polyplacophor- of the specimens are Turinian or Chatfieldian (Mohawkian, Mid- ans to that date. Subsequently, at least two additional generic dle Ordovician) in age (Leslie, 2000, p. 1,124). The Kentucky names have been used (Runnegar et al., 1979; Pojeta et al., 2003). specimens are classified in five new species placed in five genera, For the specimens described here, 11 generic names are used, two of which are new (Fig. 1). Taphonomic discussion and listing three of which are new and two others which had not been applied of associated faunas are given in Appendix B and Table 13. to Ordovician chitons. This 42% increase brings the number of Morphology.—In several instances, head and tail plates are known Ordovician chiton genera to 17. present along with the more numerous intermediate plates. Head Most of the specimens available for this study were collected and tail plates are often more difficult to differentiate in the Pa- by paleontologists and geologists of the U.S. Geological Survey leoloricata than in the Neoloricata where sutural laminae and/or and Kentucky Geological Survey as part of the Cooperative Geo- insertion plates are present. Head plates range from flat to trans- logic Mapping Program of the Commonwealth of Kentucky, versely arched, semioval, being wider than long, to subrectangular 1960-1978 (Cressman and Noger, 1981). The 17 tons (15,422 kg) in shape, longer than wide. The anterior and lateral slopes diverge of limestone yielded about 200,000 silicified Ordovician inverte- from a posterior apex varying in steepness, depending on the brates (Pojeta, 1979a). The vast majority of the specimens are magnitude of arching of the posterior margin. Ventrally, the pos- from Kentucky; however, a few are from Ohio and Indiana, and terior margin bears a short apical area or ridge. Tail plates are most of these are not silicified. The bulk of these fossils have usually longer than wide, or subquadrate, but may be triangularly been described in a series of monographs published as U.S. Geo- elongate in shape, and gently to strongly arched. A mucro is com- logical Survey Professional Papers (1066A-P) edited by Pojeta monly present either at or just anterior to the posterior margin. A (1979b-1995). jugum may be present, but is uncommon. An embayment or sinus In Kentucky, the Ordovician lithostratigraphy, facies analyses, in the anterior margin may be present and an apical area is not and environments of deposition of the rock units were dealt with present. by Cressman and Karklins (1970), Cressman (1973), Cressman Preservation.—In general, the silicification of Kentucky Or- and Noger (1976), and Weir et al. (1979, 1984). This information dovician mollusks (Pojeta and Runnegar, 1979; Wahlman, 1992; was summarized by Pojeta (1979c). Frey, 1995) is not as complete, or sturdy, as that of the brachio- Biostratigraphic correlation of the Ordovician rocks of Ken- pods (Neuman, 1967; Alberstadt, 1979; Howe, 1979; Pope, 1982). tucky, Indiana, and Ohio was conducted by the faculty and stu- As a working hypothesis, it is suggested that the differences in dents at Ohio State University (Sweet, 1979; Pojeta, 1979c, 1984). silicification reflect the original mineralogy of the shells—arago- Sweet (1984), Leslie (2000), and Richardson and Bergstrom nite in most mollusks and calcite in most articulate brachiopods (2003), among others, have considered the correlation of these (Carter, 1990, p. 68, 77, 97, 117, 143, 181, 265). Other areas rocks. having silicified faunas in limestones need to be examined. This paper is the fourth in a series of monographs dealing with Diversity.—Only two or three species are known from any of the Ordovician mollusks from Kentucky and nearby states: 1) the units indicating a low stratigraphic diversity during the Or- scaphopods (Pojeta and Runnegar, 1979); 2) monoplacophorans/ dovician in the United States. Upper Paleozoic occurrences of bellerophonts (Wahlman, 1992); and 3) nautiloid cephalopods polyplacophorans often show a greater diversity (e.g., Hoare and (Frey, 1995). Incidental to other studies, the rostroconchs were Smith, 1984; Debrock et al., 1984; Hoare, 2001). Cherns (2004, described by Pojeta and Runnegar (1976) as were some of the p. 454, fig. 6) discussed and diagrammed the known diversity of pelecypods (Pojeta, 1971, 1978, 1985, 1988, 1997; Pojeta and Paleozoic paleoloricate and neoloricate chiton species and indi- Palmer, 1976; Pojeta and Runnegar, 1985). Wagner (1990, p. 109- cated a bias caused by a few detailed studies. Two major peaks 111) described a species of lophospirid gastropod. of paleoloricates. Lower Ordovician and Middle Silurian, are Fifty-five thousand silicified mollusks were obtained using the present. The present study raises the Middle Ordovician count by method of Pojeta (1979c). Of these, 1,038 (1.9%) disarticulated over 150%. silicified plates of Ordovician Polyplacophora were found from Stratigraphic summary.—The disarticulated plates from central 18 localities (Appendix A) in the Inner Blue Grass Region of Kentucky occur in Mohawkian rocks (Middle Ordovician), in 1 HOARE AND POJETA

Kentucky from the Hitt Canyon Formation of the El Paso Group in New Clays Ferry Formation Mexico and Oneota Dolomite in Wisconsin; Runnegar et al. (1979) from the Gasconade Dolomite in Missouri; Stinchcomb Tanglewood and Darrough (1995) from the Gasconade Dolomite in Missouri;

Millersburg ) Hoare (2000b) from the Oneota Dolomite in Minnesota and _*^'*^Limestone ^ Odenville Formation in Alabama; Pojeta et al. (2003) from the

Hollow ? Forreston Member, Grand Detour Formation in Wisconsin, and Member ) Vendrasco and Runnegar (2004) from the upper Gasconade Do-

Member r'SulpherWell lomite in Missouri. Member SYSTEMATIC PALEONTOLOGY Brannon Member

Perryvllle The specimens included herein are reposited in the following Limestone Member places: 1) United States National Museum of Natural History Grier Virginia, Wisconsin (USNM); 2) New Mexico Museum of Natural History Limestone and Minnesota Member (NMMNH); 3) Department of Geology and Geophysics, Univer- sity of Minnesota (UMPC); and 4) Queensland Museum, Austra- Logana Member lia (QM). Eighteen localities (Appendix A) are in the Cambrian-Ordo- Curdsville Limestone Member vician register of the U.S. Geological Survey (USGS) in Reston, - ^ c o - Virginia, followed by a four-digit number and the letters CO, e.g., Tyrone Limestone u £ c USGS 6034-CO; if the four-digit number is preceded by the letter o c CO S fc CD 'D,' the locality is in the Cambrian-Ordovician register in the Den- o oj ^ Oregon Formation uj 3: a. ver catalog, e.g., USGS D-1138-CO. Additional locahty details, XXX including exact coordinates on the pertinent USGS geologic quad- Camp Nelson Limestone rangle maps, are given in USGS Professional Papers 1066A-P.

Class PoLYPLACOPHORA de Blainville, 1816 Diagnosis.—Mollusks with a head, elongated body, and dorsal shell ordinarily consisting of eight articulated plates; shell sur- rounded by a muscular mantle border that is covered by a cuticle in which spicules are embedded. Occurrence.—Upper Cambrian-Holocene. "O :£ .5 D ; ill 1 o o ^ Subclass PALEOLORICATA Bergenhayn, 1955 XXX Diagnosis.—Polyplacophorans with thick plates with large api- cal areas; shell of two calcareous layers, the outer tegmentum and FIGURE 1—Stratigraphic column for the Ordovician rocks of the Inner Blue Grass Region of central Kentucky in and around the city of Lex- the inner hypostracum; articulamentum lacking, sutural lamellae ington and stratigraphic distribution of the Ordovician species of po- and insertion plates absent. lyplacophorans described herein. X marks the rock units that yielded Occurrence.—Upper Cambrian-Lower Devonian. silicified chiton plates used in this study. (Adapted from Cressman and Karklins, 1970.) The approximate Ma dates taken from Webby et al. Order CHELODIDA Bergenhayn, 1943 (2004). Diagnosis.—Paleoloricates with elongate intermediate body plates not differentiated into lateral and central areas. Occurrence.—Upper Cambrian-Lower Devonian. both the Turinian and Chatfieldian stages. The Wisconsin speci- mens near Beloit are Turinian in age. The specimens from Vir- Family MATTHEVIIDAE Walcott, 1886 ginia, New Mexico, Minnesota, and other parts of Wisconsin are from Ordovician rocks in the Ibexian Series (Early Ordovician) Included genera.—Chelodes Davidson and King, 1874, Matth- (Fig. 1). The material from Australia, used for comparisons with evia Walcott, 1886, Hemithecella Ulrich and Bridge in Butts, the American specimens, is Datsonian in age (Late Cambrian). 1941, Eochelodes Marek, 1962, Calceochiton Flower, 1968, Spi- cuchelodes Chems, 1998a, and Eukteanochiton Vendrasco and PREVIOUS STUDIES Runnegar, 2004. Reports of North American Ordovician polyplacophorans were Diagnosis.—Chelodids with intermediate body plates signifi- made by Billings (1865) from the Black River Limestone, Ontar- cantly longer than wide, triangular in dorsal profile; apical area io, Canada; Butts (1926) from the Odenville and Chickamauga large; plates with significant overlap. limestones in Alabama; Powell (1935) from the Oneota Dolomite Occurrence.—Upper Cambrian-Lower Devonian. in Minnesota; Ulrich and Bridge in Butts (1941) from the Che- pultepec Dolomite in Virginia and Gasconade Dolomite in Mis- Genus CHELODES Davidson and King, 1874 souri; Cloud and Barnes (1946) from the Tanyard Formation and Type species.—Chelodes bergmani Davidson and King, 1874. El Paso Group in Texas; Wilson (1951) from the Black River Diagnosis.—Following Cherns (1998a): intermediate plates Limestone in Ontario, Canada; Bergenhayn (1960) from the Gas- wedge-shaped, arched, broad anteriorly, slowly tapering to a pos- conade Dolomite in Missouri; Sanders (1965) from the Maquo- terior point, which can be rounded; ventral apical area large, flat- keta Formation in Iowa and Illinois; Smith in Smith and Toomey tened to gently depressed, anterior edge roundly concave, not V- (1964) from the Kindblade Formation in Oklahoma; Spelman shaped, sinus shallow. (1966) from the Nittany Dolomite in Pennsylvania; Flower (1968) Occurrence.—Upper Cambrian-Lower Devonian. ORDOVICIAN POLYPLACOPHORA FROM NORTH AMERICA

FIGURE 2—Chelodes cf. C. mirabilis (Butts, 1926). Chepultepec Formation, Virginia. 1-11, Intermediate plates; 1-4, dorsal, ventral, left lateral, and anterior views, USNM 523869; 5-7, dorsal, right lateral, and ventral views, USNM 523870; 8-11, dorsal, ventral, anterior, and left lateral views, USNM 523871; 12-19, tail plates, 12, ventral view showing pit near posterior end, USNM 523872; 13-15, dorsal, ventral, and right lateral views, USNM 523873; 16-19, left lateral, anterior, ventral, and dorsal views, USNM 523874. All figures X2.

CHELODES cf. C. MIRABILIS (Butts, 1926) broad, anterior sinus; anterolateral corners narrowly rounded; pos- Figure 2 terolateral margins nearly straight or convex posteriorly; ventral surface more deeply concave in anterior one-third of length than Priscochitonl mirabilis BtJTTS, 1926, pi. 18, figs. 30, 31. posteriorly; apical area large, covering approximately one-third of Chelodes mirabilis (BUTTS). RUNNEGAR, POJETA, TAYLOR, AND COL- LINS, 1979, pi. 2, figs. 60, 61. length, extending laterally to near midlength. Head plate unknown. Description.—Large, thick, subtriangular plates; tail plate elon- Measurements.—See Table 1. gate with convex anterior margin, broadly convex posterolateral Material examined.—Three tail plates and three intermediate margins; lateral slopes steep posteriorly, more gentle anteriorly; plates, USNM 523869-523874. posterior apex overhanging margin above convex posterior slope; Occurrence.—Chepultepec Dolomite (Ibexian), at the south ventral surface concave with indication of small pocket posteri- portal of the Natural Tunnel, Scott Co., Virginia. Butts's holotype orly leading towards apex. specimen is from the Odenville Limestone (Whiterockian) near Intermediate plates broadly convex transversely, with shallow. Leeds, Alabama. Discussion.—The coarse siliceous replacement of the speci- mens has obliterated details of the ornamentation and some of the TABLE 1—Measurements (in mm) of Chelodes cf. C mirabilis (Butts). structure. The dorsal surface was probably smooth. Chelodes cf. C mirabilis differs from C bergmani, C. gotlandicus Lindstrom, USNM Length Width Height Plate 1884, and C actinis Cherns, 1998a by having a shallower anterior 523869 I5.5t 11.3 3.8 I sinus and, in the case of the last species, a larger apical area in 523870 13.8 12.8 6.5 I the intermediate plates. Tail plates cannot be compared because 523871 13.8 13.7 6.0 I they are known only in C cf. C mirabilis. The head plate of C 523874 18.3 10.4 5.7 T mirabilis is unknown while that of C. actinis is flat and elongate t Estimated. in shape. HOARE AND POJETA

Chelodes whitehousei Runnegar, Pojeta, Taylor, and Collins, Discussion.—Spicuchelodes cressmani differs from the type 1979 has narrower and more sharply triangular intermediate plates species S. pilatis by the lack of a spiculose dorsal ornamentation than C. mirabilis (Fig. 4.5-4.7). The tail plates are similar in and any indication of radial folds or central and lateral areas. Tail general, that of C. whitehousei being narrower, more strongly and head plates of the type species are unknown. arched transversely, and lacking the pit posteriorly on the ventral It has been possible to compare numerous specimens of Chel- surface (Fig. 4.8-4.11). The head plate of C. whitehousei is odes whitehousei, from the Datsonian (Upper Cambrian) Nin- strongly arched and slightly longer than wide (Fig. 4.1-4.4). maroo Formation of Queensland, Australia (Fig. 4), with several fragmental specimens of Calceochiton hachitae Flower, 1968 Genus SPICUCHELODES Cherns, 1998a from the Ibexian (Lower Ordovician) Hitt Canyon Formation of Type species.—Spicuchelodes pilatis Cherns, 1998a. New Mexico (Fig. 5.22-5.25) which have somewhat similar Diagnosis.—Cordate to elongate, triangular plates; intermediate shapes to S. cressmani. Also, numerous specimens of Calceochi- plates with shallow anterior concavity and large apical area with ton floweri n. sp. (Fig. 5.1-5.21) from the Lower Ordovician (Ib- V-shaped anterior margin; with or without surface ornament and exian) Oneota Dolomite near Sauk City, Wisconsin, are available dorsal radial folds. for study [Flower (1968) called these specimens Calceochiton cf. Occurrence.—Middle Ordovician (Turinian)-Middle Silurian C gibberosum (Sardeson, 1896)]. Unfortunately, the types of Cal- (Wenlockian). ceochiton hachitae were not available for examination. Our frag- Discussion.—Spicuchelodes differs from Chelodes in the sharp- mentary specimens of C hachitae (Fig. 5.22-5.25), as well as the ly triangular intermediate plates which have a more pointed pos- three specimens illustrated by Flower (1968), are difficult to com- terior apex and the pronounced V-shaped anterior margin of the pare with other taxa. However, the specimens from New Mexico ventral apical area. are quite different from the Wisconsin specimens which had pre- viously been placed in C. hachitae by Smith and Hoare (1987, p. SPICUCHELODES CRESSMANI new species 30). Figure 3 In comparison with Spicuchelodes cressmani, the plates of Cal- Diagnosis.—Tail plate elongately triangular with a narrow bor- ceochiton hachitae and C floweri are much thicker with a larger der on posterior ventral surface; intermediate plates narrowly tri- pocket beneath the apical area of the intermediate plates, a curved angular, strongly arched transversely, with large V-shaped apical instead of V-shaped anterior margin of the apical area, and the area enclosing a small pocket; head plate elongate oval. plates are consistently narrower (compare Figs. 3, 5, and Flower, Description.—Tail plate elongate, triangular, strongly arched 1968, pi. 1, figs. 1-9). transversely, gently arched longitudinally; anterior margin with Chelodes whitehousi also has much thicker plates than Spicu- shallow sinus; lateral slopes flat, extending from median angular- chelodes cressmani and has the anterior margin of the apical area ity; ventral surface with distinct, flat, narrow border posteriorly curved instead of V-shaped. The tail plate is narrower, more becoming narrower extending to near midlength; narrow, rounded sharply arched transversely, and often with a prominent overhang ridge, separated from flat border by narrow concave space which above the posterior margin. One of the tail plates of C. white- extends posteriorly towards apex forming a small pocket anterior housei shows evidence of breakage or predation (Fig. 4.8-4.11). to flat border; smooth except for faint comarginal growth lines. The posterior end has been removed and the individual was able Intermediate plates elongate, triangular, strongly arched trans- to secrete a new plate beneath the original. Evidently the damage versely; anterior margin with shallow sinus, posterolateral mar- to the shell-secreting mantle was not significant, or, the mantle gins straight to slightly convex; lateral slopes gently convex ex- was regenerated to be able to secrete new shell material. The head tending from median angularity; ventral surface with large, plate is subrectangular in shape rather than oval (Fig.4.1-4.4). triangular, concave apical area extending laterally past midlength; Eukteanochiton milleri Vendrasco and Runnegar, 2004 (fig. 12.1- apical area fits against ventral surface laterally, anterior portion 12.13), from the Upper Cambrian Red Tops Member, Notch Peak elevated medially forming a thin pocket; comarginal growth lines Formation of Utah, has a general shape similar to species of Spi- faint, rarely preserved. cuchelodes and Calceochiton but is described as having two tun- Head plate elongate oval, strongly arched; anterior margin con- nels which are not obvious in their illustrations. vex rounding into posterolateral margins; ventral surface with small apical area restricted to posterior end of concave ventral Genus CALCEOCHITON Flower, 1968 surface. Type species.—Calceochiton hachitae Flower, 1968. Etymology.—^For Earle R. Cressman, in acknowledgment of his Diagnosis.—Intermediate plates similar in shape to Spicuchel- outstanding work in studying, interpreting, and mapping the Mid- odes cressmani n. sp.; anterolateral areas projecting forward leav- dle Ordovician rocks of the Inner Blue Grass Region of Kentucky, ing a concave area between them; apical area half the length of and his extensive help in collecting the fossiliferous silicified the plate. blocks of rock used in this study. Occurrence.—Ordovician (Ibexian). Figured types.—WoXoiy^e, USNM 523886 (Fig. 3.29-3.31), USGS D-1138-CO; figured paratypes, USNM 523875-523882, CALCEOCHITON FLOWERI new species USGS 6034-CO; USNM 523883, 523885, 523887, USGS D- Figure 5.1-5.21 1138-CO. Calceochiton cf. gibberosum (SARDESON). FLOWER, 1968, p. 10, pi. 1, Unfigured paratypes.—USNM 523888, USGS 5078-CO, one figs. 10-24. plate; USNM 523888A, USGS 5081-CO, one plate; USNM [non] Ascoceras gibberosum SARDESON, 1896, p. 102, pi. 6, figs. 8-10. 523888B, USGS 6034-CO, 71 plates; USNM 523888C, USGS 6035-CO, 56 plates; USNM 523888D, USGS D-1138-CO, 144 Diagnosis.—^Long, triangular intermediate plates, broadly plates. arched transversely, strongly thickened slightly posterior of an- Specimens include two tail plates, one head plate, and 282 in- terior margin. termediate plates. Description.—^Intermediate plates elongate, triangular, broadly Measurements.—See Table 2. arched transversely, straight to convex longitudinally; anterior Occurrence.—Tyrone and Camp Nelson limestones (Turinian) margin concave between anterolateral corners; posterolateral mar- in Kentucky. gins straight or slightly concave; ventral surface concave with ORDOVICIAN POLYPLACOPHORA FROM NORTH AMERICA

FIGURE 3—Spicuchelodes cressmani n. sp. Tyrone Limestone, Kentucky. 1-27, Intermediate plates; 1-3, dorsal, ventral, and right lateral views, 6034- CO, USNM 523875; 4, 5, dorsal and ventral views, 6034-CO, USNM 523876; 6-8, dorsal, ventral, and right lateral views, 6034-CO, USNM 523877; 9-11, anterior, dorsal, and ventral views, 6034-CO, USNM 523878; 12, 13, dorsal and ventral views, 6034-CO, USNM 523879; 14-16, dorsal, anterior, and ventral views, 6034-CO, USNM 523880; 17-19, right lateral, dorsal, and ventral views, 6034-CO, USNM 523881; 20-22, dorsal, ventral, and anterior views, 6034-CO, USNM 523882; 25-25, left lateral, dorsal, and ventral views, D-1138-CO, USNM 523883; 26, 27, ventral and right lateral views, D-1138-CO, USNM 523884; 28-31, tail plates; 28, ventral view, D-1138-CO, USNM 523885, X3; 29-31, holotype, dorsal ventral, and left lateral views, D-1138-CO, USNM 523886, X3; 32-35, head plate, anterior, dorsal, ventral, and left lateral views, D-1138- CO, USNM 523887, X3. All figures X2 except where noted. HOARE AND POJETA

TABLE 2—Measurement (in mm) of Spicuchelodes ciessmani n. sp.

USNM Length Width Height Plate 523875 25.51 12.0 6.6 523877 27.0t 12.5 7.0 523879 21.5t 13.0 5.1 523882 17.5t 9.0 6.0 523884 20.5t 10.5 4.7 523878 22.5t 13.5t 7.0 523881 18.0 9.7 5.7 523880 13.0 8.5 4.6 523883 13.5 8.0 5.0 523887 8.8 5.3 3.0 H 523886* 12.7t 5.0t 3.5t T * Holotype. t Estimated.

apical area extending one-half or more of length of plate forming a large pocket; shell thickest slightly posterior to anterior margin giving the anterior portion of the plate a scooplike shape (Fig. 5.3); dorsal surface smooth except for comarginal growth lines anteriorly. Head and tail plates unknown. Etymology.—^For the late Rousseau H. Flower, who first studied these specimens and for his extensive paleontological and strati- graphic studies. Figured types.—^Holotype, NMMNH P-41263 (Fig. 5.19- 5.23); paratypes, NMMNH P-41255-P-41262, P-41264. Unfigured paratypes.—Over 100 specimens, P-41264. Measurements.—See Table 3. Occurrence.—Oneota Dolomite (Ibexian) in the vicinity of Sauk City, Sauk Co., Wisconsin. Discussion.—The specimens here assigned to the new species Calceochiton floweri were placed in the species C. cf. C. gibber- FIGURE 4—Chelodes whitehousei Runnegar, Pojeta, Taylor, and Collins, osum by Flower. In Sardeson's 1896 paper, cited by Flower, the 1979. Ninmaroo Formation, Queensland, Australia. 1-4, Head plate, only taxon to which Sardeson (p. 102) applied the name "gib- dorsal, ventral, anterior, and left lateral views, QMF 44551; 5-7, in- berosum" was what he considered to be a fragment of a cepha- termediate plate, dorsal, ventral, and right lateral views, QMF 44553; lopod Ascoceras gibberosum which he named as a new species. 8-11, tail plate, dorsal, posterior, right lateral, and ventral views of Apparently, Flower did not agree with Sardeson's placement of damaged plate (arrows indicate damaged area), QMF 44559. All figures A. gibberosum in the Cephalopoda. The one specimen of A. gib- X2. berosum figured by Sardeson is illustrated by cartoonlike line drawings that show what he called septa. This specimen, and an unstated number of others in Sardeson's possession in 1896, were Occurrence.—Ordovician (Ibexian). discarded in 1911 (R. E. Sloan, oral commun., 2003). Examina- tion of the specimens in the collection from Wisconsin described HEMITHECELLA EXPANSA Ulrich and Bridge in Butts, 1941 by Flower leaves considerable doubt that they are similar to the Figure 6 Sardeson's specimen of Ascoceras gibberosum and they are here Hemithecella expansa ULRICH AND BRIDGE IN BUTTS, 1941, p. 19, pi. described as the new species Calceochiton floweri. Because of the 68, fig. 6; RUNNEGAR, POJETA, TAYLOR, AND COLLINS, 1979, p. 1389, lost specimens, and poor illustration, the name Ascoceras gibber- pi. 1, figs. 31, 32; SMITH AND HOARE, 1987, p. 28; STINCHCOMB AND osum Sardeson, 1896 should be restricted to the lost material and DARROUGH, 1995, p. 58, figs. 6.7-6.15, 8.13, 8.14; VENDRASCO AND treated as a nomen dubium. RUNNEGAR, 2004, fig. 13.1-13.5. Calceochiton floweri differs from C. hachitae by being wider, more broadly rounded transversely, and developing a thicker shell Description.—^Probable tail plate thick, subtriangular, flatly just posterior to the anterior margin. The head and tail plates of arched medially with steep convex lateral and posterior slopes; C. hachitae are also unknown. Three fragmental specimens of C. anterior margin shallowly concave, posterior margin gently con- hachitae are illustrated in Figure 5.22-5.25. vex; ventral surface broadly concave. Spelman (1966, p. 100-102, pi. 20, figs. 10-25) found some Intermediate plates triangular; anterior margin concave, lateral poorly preserved chiton plates in the Stonehenge Limestone and margins convex anteriorly becoming straighter posteriorly leading Larke Dolomite in central Pennsylvania. The specimens from the to pointed apex; dorsal surface convex; ventral surface concave Larke Dolomite (figs. 19-25) have the characteristics of Calceo- leading posteriorly to long, narrow pocket under large apical area. chiton, similar to C. floweri. Head plate subquadrangular, strongly arched; anterior margin with shallow concavity arched dorsally; lateral margins convex, Genus HEMITHECELLA Ulrich and Bridge in Butts, 1941 posterior margins shallowly concave, not pointed; ventral surface Type species.—Hemithecella expansa Ulrich and Bridge in deeply concave with strong transverse ridge near midlength sep- Butts, 1941. arating shallower anterior area from deeper posterior area; comar- Diagnosis.—Intermediate plates anteriorly broad transversely ginal growth lines present laterally and anteriorly. as in Chelodes; long narrow pocket beneath large apical area. Measurements.—See Table 4. ORDOVICIAN POLYPLACOPHORA FROM NORTH AMERICA

FIGURE 5—Calceochiton floweri n. sp. Oneota Dolomite near Sauk City, Wisconsin. 1-21, Intermediate plates; 1, 2, dorsal and left lateral views, NMMNH P-41255; 3-5, anterior, dorsal, and ventral views, NMMNH P-41256; 6-8, dorsal, anterior, and ventral views, NMMNH P-41257; 9, 10, dorsal and ventral views, NMMNH P-41258; 11, 12, dorsal and ventral views, NMMNH P-41259; 13, 14, dorsal and ventral views, NMMNH P- 41260; 15, 16, dorsal and ventral views, NMMNH P-41261; 17, 18, dorsal and ventral views, NMMNH P-41262; 19-21, holotype, dorsal, ventral, and right lateral views, NMMNH 41263. 22-25, Calceochiton hachitae Flower, 1968. Hitt Canyon Formation, New Mexico. 22, 23, Intermediate plate fragment, ventral and anterior views, loc. 5500, NMMNH P-41251; 24, intermediate plate fragment, ventral view, loc. 5500, NMMNH P- 41252; 25, intermediate plate fragment, ventral view, loc. 5500, NMMNH P-41253. All figures X3.

TABLE 3—Measurements (in mm) of Calceochiton floweri n. sp. Material examined.—One probable tail plate, two head plates, and 25 intermediate plates, USNM 523889-523899. NMMNH Length Width Height Plate Occurrence.—Chepultepec Formation (Ibexian) at the south P-41255 10.7t 5.8 4.3 portal of the Natural Tunnel, Scott Co., Virginia. Also reported P-41256 17.0t 7.2 5.0 from the Gasconade Dolomite (Ibexian) in Missouri (Stinchcomb P-41257 12.7t 5.7 3.4 P-41258 15.3t 5.8 3.3 and Darrough, 1995). P-41259 11.ot 5.0t 3.5 Discussion.—All of the plates are incomplete to a greater or P-41260 15.3t 4.3 3.0 lesser extent and the coarse silicification distorts the surface and P-41261 15.0t 5.4 3.1 P-41262 17.2t 7.3 4.5 various characters. However, the general characteristics are un- P-41263* 19.7t 7.3 4.7 mistakable. * Holotype. The holotype of H. expansa is an internal mold of an inter- t Estimated. mediate plate from the Gasconade Dolomite in Missouri (USNM HOARE AND POJETA

FIGURE 6—Hemithecella expansa Ulrich and Bridge in Butts, 1941. Chepultepec Formation, Virginia. 1-4, Head plate, dorsal, right lateral, posterior, and ventral views, USNM 523889; 5-24, intermediate plates; 5-7, ventral, right lateral, and anterior views, USNM 523890; 8, ventral view, USNM 523891; 9, ventral view, USNM 523892; 10-12, ventral, dorsal, and left lateral views, USNM 523893; 13-15, ventral, right lateral, and dorsal views, USNM 523894; 16-18, dorsal, ventral, and anterior views, USNM 523895; 19-22, dorsal, ventral, right lateral, and posterior views, USNM 523896; 23, 24, dorsal and left lateral views, USNM 523897; 25-29, tail plate, dorsal, ventral, left lateral, posterior, and anterior views, USNM 523898. All figures X2. ORDOVICIAN POLYPLACOPHORA FROM NORTH AMERICA

TABLE 4—Measurements (in mm) of Hemithecella expansa Ulrich and Head plate strongly arched posteriorly; anterior margin convex Bridge. rounding into convex lateral margins; posterior margin not ob- served; ventral surface deeply concave posteriorly; dorsal surface USNM Lengtli Width Height Plate not observed. 523889 17.3 16.7 17.2 H Etymology.—^For Carl Bauer, operator of Bauer's quarry, near 523890 23.5 19.5 11.5 I Beloit, Wisconsin, who graciously allowed permission for col- 523891 22.5t — 9.8 I 523893 13.0 11.8 8.3 I lecting purposes. Access to the quarry is highly controlled re- 523895 13.3 11.9 12.0 I quiring Mr. Bauer's permission. 523898 13.2 13.0 6.0 T Figured types.—^Holotype, USNM 523969 (Fig. 7.27); para- t Estimated. types, USNM 523958-523963, 523965, 523967, 523969-523072. Unfigured paratypes.—^Thirty-three specimens, USNM 523974. 96211). It was illustrated for the first time by Runnegar et al. Specimens include one head plate, two tail plates, and 43 in- (1979, pi. 1, figs. 31, 32). Ulrich and Bridge in Butts (1941) termediate plates. illustrated a poorly preserved specimen from the Chepultepec For- Measurements.—See Table 5. mation in Virginia (USNM 97289), and indicated that the species Occurrence.—Forreston Member, Grand Detour Formation, is numerous at the South Portal of the Natural Tunnel in Virginia; Platteville Group (Turinian), Bauer's Quarry west of Beloit, Rock the specimens from this locality described here provide the op- County, Wisconsin. portunity to give a more complete description of H. expansa. The Discussion.—Preacanthochiton baueri mainly differs from P. intermediate plate illustrated in Figure 6.5 shows an almost exact cooperi in lacking pustulose ornament. Molds of P. cooperi il- duplicate of the ventral surface of the holotype internal mold. In lustrated by Runnegar et al. (1979, pi. 2, figs. 62, 64) show a many of the intermediate plates, the coarse siliceous preservation similar shape to some plates of P. baueri, although they are con- has blocked off the posterior pocket on the ventral surface. siderably smaller as in the tail plate illustrated by them (pi. 2, fig. 63). The specimens assigned by Bergenhayn (1960) to Preacan- Order SEPTEMCHITONIDA Bergenhayn, 1955 thochiton productus are placed in the new genus Listrochiton. Diagnosis.—Paleoloricates with intermediate plates differenti- Preacanthochiton was included under doubtful Paleozoic gen- ated into central and lateral areas. era by Van Belle (1975, p. 129) and was rejected as a chiton by Occurrence.—Ordovician-Devonian. him in 1983 (p. 154). Sirenko and Starobogatov (1977) believed that Preacanthochiton had not been demonstrated to be a chiton. Family PREACANTHOCHITONIDAE Bergenhayn, 1960 Vendrasco and Runnegar (2004, p. 984) recognized the Preacan- Diagnosis.—Chelodids with intermediate plates more or less thochitonidae as valid polyplacophorans. The specimens herein equidimensional in length and width, not elongate; shape variably placed in Preacanthochiton are clearly polyplacophorans, having quadrate, triangular, or slightly rectangular; very weak jugum head, intermediate, and tail plates, and apical areas. All specimens present, vague differentiation of lateral and central areas of inter- were collected by J. DuFoe, Rockton, Illinois, from the same bed mediate plates; apical area reduced. as Echinochiton dufoei Pojeta, Eernisse, Hoare, and Henderson, Occurrence.—Lower SkuUrockian (Upper Cambrian)-Chatfiel- 2003, p. 651, in Bauer's quarry. dian (Middle Ordovician). Discussion.—^Preacanthchitonids differ from Mattheviids in Genus LISTROCHITON new genus that the intermediate plates are not elongated, the apical area is Type species.—Listrochiton weiri n. sp. reduced, and a weak jugum is present. Included species.—Listrochiton weiri n. sp., Preacanthochiton productus Bergenhayn, 1960, Chelodesl sp. indet. Bergenhayn, Genus PREACANTHOCHITON Bergenhayn, 1960 1960. Type species.—Preacanthchiton cooperi Bergenhayn, 1960. Diagnosis.—Plates thick, smooth; tail plate elongate, subrect- Diagnosis.—Intermediate plates quadrate to triangular; orna- angular, with weak jugum ending in a mucro just anterior to pos- ment pustulose or not. terior margin, posterior margin arched dorsally; intermediate Occurrence.—Lower SkuUrockian (Upper Cambrian)-Turinian plates subtriangular with moderate to deep anterior sinus; head (Middle Ordovician). plate subcircular, coming to a point posteriorly. Description.—^Head plate semicircular, pointed posteriorly; in- PREACANTHOCHITON BAUERI new species termediate plates subtriangular, moderately arched, anterior mar- Figure 7 gin concave; tail plate elongate, subrectangular, strongly arched, Diagnosis.—Intermediate plates thin, flatly arched, subquad- mucro anterior to posterior margin, concave ventral surface com- rangular with triangular jugal area; ornament of growth lines and monly having pit beneath mucro. faint grooves radiating from apex. Etymology.—Greek, listron, spade or shovel, chiton, tunic re- Description.—Tail plate flatly arched, longer than wide with ferring to the shape of the intermediate plates. subparallel, gently convex, lateral margins; posterior margin con- Occurrence.—Eminence Dolomite (Upper Cambrian) of Mis- vex, anterior margin with shallow medial sinus; greatest width at souri; Lexington Limestone (Middle Ordovician) of Kentucky; point where lateral margins curve into posterior margins; low mu- and Gasconade Dolomite (Lower Ordovician) of Missouri. cro located anterior to posterior margin; surface smooth except Discussion.—^Bergenhayn (1960) included elongated tail plates for comarginal growth lines. in his definition of Preacanthochiton. However, tail plates of P. Intermediate plates thin, subquadrangular, flatly arched; lateral cooperi, the type species of the genus, are broader, flatter, and margins gently convex; posterior margins convex to bluntly mu- semioval in shape, as shown by Runnegar et al. (1979, p. 1391, cronate; anterior margin with broad, shallow sinus; lateral slopes pi. 2, figs. 62-66), where they figured tail and intermediate plates concave outlining a faint jugal area; faint grooves radiating from of P. cooperi; whereas, the tail plate of Listrochiton is elongate apex on lateral areas; ventral surface broadly concave with a low, and subrectangular (Fig. 8.34-8.49). The Cambrian Orthriochiton narrow, apical area bordering posterior margins; comarginal Vendrasco and Runnegar, 2004 differs from Listrochiton by hav- growth lines prominent anteriorly and laterally. ing straight-sided anterolateral margins on the intermediate plates. 10 HOARE AND POJETA

FIGURE 7—Preacanthochiton baueri n. sp. Forreston Member, Grand Detour Formation, Wisconsin. 1, 2, Head plate, ventral mold, dorsal and right lateral views, USNM 523970; 3-25, intermediate plates; 3-6, dorsal mold, dorsal cast, left lateral cast, and anterior cast, USNM 523958; 7, dorsal mold, USNM 523965; 8, ventral mold, USNM 523962; 9, 10, dorsal and ventral molds, USNM 523971; 11-14, dorsal mold, dorsal cast, left lateral cast, and anterior cast, USNM 523959; 15, 18, dorsal and ventral molds, USNM 523963; 16, dorsal mold, USNM 523960; 17, dorsal mold, USNM 523966; 19, dorsal mold, USNM 523972; 20, dorsal mold, USNM 523961; 21, dorsal mold, USNM 523964; 22-25, dorsal mold, dorsal cast, left lateral cast, and anterior cast, USNM 523967; 26, 27, tail plates; 26, ventral mold, USNM 523973; 27, holotype, ventral mold, USNM 523969. All figures X2. ORDOVICIAN POLYPLACOPHORA FROM NORTH AMERICA 11

TABLE 5—Measurements (in mm) of Preacanthochiton baueii n. sp. Discussion.—Listrochiton weiri differs from L. productus (Ber- genhayn, 1960) in that the tail plate has a more strongly elevated USNM Length Width Height Plate mucro at the end of a narrower jugal area. 523958 17.5 21.0 6.5t The specimens shown in Figure 8.17-8.20 are difficult to in- 523959 16.0 17.0 7.0t terpret. First impressions suggest that each represents two artic- 523960 10.5 11.5 — 523961 4.5 4.7 — ulated plates; however, it was not possible to discern two apical 523962 16.5t 18.0 — areas on either specimen. Thus, they are interpreted as single 523963 7.0 7.2 — plates showing unusual anterior growth. Similar patterns of plate 523964 11.0 9.0 — growth in the Silurian Chelodes and Thairoplax Cherns, 1988b, 523965 18.5 21.0t — 523966 15.5 16.0 — from Gotland, Sweden, are interpreted as indicating seasonal 523967 14.7 14.9 5.6 growth (Cherns, 1999, p. 174). 523968 9.0 8.6 — 523969* 13.0 10.7 — T Genus ORTHRIOCHITON Vendrasco and Runnegar, 2004 523970 10.2t 13.7 5.0t H Type species.—Orthriochiton utahensis Vendrasco and Run- * Holotype. negar, 2004. t Estimated. Emended diagnosis.—^Small; intermediate plates with straight side slopes; tail plate with posterior mucro, vertical to strongly sloping posterior margin, and pit underneath mucro; head plate flat, subcircular to more elongate, and transversely convex. vertical instead of sloping posterior end on tail plates with a ter- Occurrence.—Upper Cambrian (Millardian)-Lower Ordovi- minal mucro, and a smaller circular head plate. cian (Ibexian).

LiSTROCHiTON WEIRI new species ORTHRIOCHITON RECAVUS new species Figure 8 Figure 9 Diagnosis.—As for the genus. Diagnosis.—^Strongly arched plates; tail plate with a small pit Description.—Tail plate subrectangular, strongly arched trans- on ventral surface below mucro; head plate subquadrangular, versely, having subparallel, slightly convex, lateral margins; pos- transversely convex. terior margin flatly convex, arched dorsally; anterior margin with Description.—Tail plate subrectangular, strongly arched trans- shallow concavity; jugal area triangular, faintly set off from lateral versely, slightly convex longitudinally; lateral slopes steep, con- areas, ending just anterior to posterior margin and simulating a vex, posterior slope steep, extending from mucro located one- mucro; narrow marginal ridge or plate thickening sometimes pres- fourth to one-fifth the length from posterior margin; anterior ent ventrally on posterior margin; comarginal growth lines, when margin narrowly convex; ventral surface deeply concave with preserved, most prominent anterolaterally. small pit under position of mucro; surface smooth except for co- Intermediate plates subtriangular, flatly arched transversely; an- marginal growth lines. terior margin with shallow to deep sinus and strong convex an- Intermediate plates subtriangular, strongly arched transversely, terolateral margins; posterolateral margins convex; ventrally, thick; anterior margin strongly concave, posterolateral margins plates more deeply concave anteriorly, with large triangular apical convex; greatest thickness posterior to midlength changing con- area extending laterally to near midlength; comarginal growth cavity of ventral surface, posterior portion less deep; surface lines most evident anteriorly. smooth except for comarginal growth lines. Head plate small, subsemicircular, broadly arched transversely; Head plate subquadrangular with steep lateral slopes, anterior anterior margin flatly convex, arched slightly, curving uniformly slope less steep; lateral margins convex, anterior margin narrowly into linear posterior margins leading to apex; ventral surface with convex, posterior margin nearly straight; ventral surface more large triangular apical area extending to near midlength; faint deeply concave posteriorly than anteriorly; comarginal growth comarginal growth lines anteriorly. lines faint. Etymology.—^For Gordon W. Weir, U.S. Geological Survey, in Etymology.—^Latin, recavus, arched inward, concave. acknowledgment of his extensive work in studying, interpreting, Figured types.—^Holotype, NMMNH P-41274 (Fig. 9.25-9.27); and mapping the Upper Ordovician rocks of the Blue Grass Re- paratypes, NMMNH P-41265-P-41273, P-41275. gion of Kentucky, and his help in collecting the fossiliferous si- Unfigured paratypes.—Thirty-seven intermediate and tail licified blocks of the rock that made this study possible. plates, NMMNH P-41276. Figured types.—\io\oty^&, USNM 523919 (Fig. 8.35-8.37), Specimens include one head plate, four tail plates, and 43 in- USGS 6915-CO; paratypes, USNM 523900, 523902-523905, termediate plates. 523910, 523911, 523918, 523920, USGS 6915-CO; USNM Measurements.—See Table 7. 523901, 523906-523909, 523915-523917, 523921, USGS 5916- Occurrence.—Oneota Dolomite (Ibexian) in the vicinity of CO; USNM 523912-523914, 523922-523924, USGS 5015-CO. Sauk City, Wisconsin. Unfigured paratypes.—\JSHM 523925, USGS 6915-CO, 253 Discussion.—Orthriochiton recavus differs from O. utahensis plates; USNM 523925A, USGS 6916-CO, 190 plates; USNM in having less sharply arched intermediate plates, a broad U- 523925B, USGS 6138-CO, 15 plates; USNM 523925C, USGS shaped anterior sinus instead of being deeply V-shaped, and are 4928-CO, one plate; USNM 523925D, USGS 5036-CO, one more triangular in shape. The tail plate posterior to the mucro is plate. steeply convex rather than vertical. Specimens include six head plates, 12 tail plates, and 466 in- The silicified specimens of O. recavus studied are not well termediate plates. preserved. Some of the intermediate plates (Fig. 9.17, 9.18, 9.20- Measurements.—See Table 6. 0.22) appear to be elongate rather than equidimensional in length Occurrence.—Salvisa Bed, Perryville Limestone Member, Cor- and width. Other intermediate plates appear to be equidimensional nishville Bed, Perryville Limestone Member, Grier Limestone (Fig. 9.8, 9.13). The anterior end of the head plate is probably Member, and Devils Hollow Member, Lexington Limestone incomplete (Fig. 9.1, 9.2). The apparent lack of an apical area on (Chatfieldian) in Kentucky. the intermediate plates is probably preservational. 12 HOARE AND POJETA

FIGURE 8—Listrochiton weiri n. gen. and sp. Salvisa Bed, Perryville Limestone Member, Lexington Limestone, Kentucky. 1-5, Head plates; 1-3, dorsal, ventral, and posterior views, 6915-CO, USNM 523900; 4, 5, dorsal and right lateral views, 6916-CO, USNM 523901; 6-33, intermediate plates; 6, 7, dorsal and ventral views, 6915-CO, USNM 523902; 8, 9, dorsal and right lateral views, 6915-CO, USNM 523903; 10, dorsal view, 6915-CO, USNM 523904; 11, 12, dorsal and ventral views, 6915-CO, USNM 523905; 13, 14, dorsal and posterior views, 6916-CO, USNM 523906; 15, 16, dorsal and ventral views, 6916-CO, USNM 523907; 17, 18, dorsal and ventral views, 6916-CO, USNM 523908; 19, dorsal view, 6916-CO, USNM 523909; 20, dorsal view, 6915-CO, USNM 523910; 21, 22, dorsal and anterior views, 6915-CO, USNM 523911; 23, 24, right lateral and dorsal views, 5015-CO, USNM 523912; 25, 26, dorsal and ventral views, 5015-CO, USNM 523913; 27, dorsal view, 5015-CO, USNM ORDOVICIAN POLYPLACOPHORA FROM NORTH AMERICA 13

TABLE 6- -Measurements (in mm) of Listrochiton weiri n. gen. and sp. intermediate plates, but the plates are strongly pointed posteriorly with larger apical areas. USNM Length Width Height Plate 523900 5.7 7.3 2.8 H LITOCHITON CREBATUS new species 523901 5.0 6.0 4.3 H Figure 10 523902 7.0 5.9 2.9 523903 6.8 6.8 3.3 523904 8.1 6.7 2.7 non Ascoceras gibberosum SARDESON, 1896, p. 102, pi. 6, figs. 8-10; 523905 7.1 6.9 3.0 POWELL, 1935, p. 69, pi. 7, figs. 13-17. 523906 7.8 7.0 3.2 Priscochitonl gibberosum (SARDESON). STAUFFER AND THEIL, 1941, p. 523907 6.0 6.2 2.0 246. 523908 11.1 8.5 3.2 Chelodes gibberosus (SARDESON). SMITH IN SMITH AND TOOMEY, 1964, 523911 7.5 7.1 3.3 p. 14; SMITH AND HOARE, 1987, p. 29. 523912 7.1 6.8 2.9 523915 5.8 6.5 2.3 523917 6.1 8.0 3.3 Diagnosis.—As for the genus. 523919* 8.8 6.2 4.0 T Description.—Tail plate arched, subrectangular, side slopes flat; 523922 10.0 6.6 4.2 T anterior margin with deep U-shaped sinus; lateral margins nearly 523923 9.5 5.5 3.3 T 529924 10.5 5.6 3.4 T straight, parallel; posterior margin bluntly convex, arched dorsal- ly; ventral surface smooth, not thickened; border narrow, ridgelike ' Holotype. on posterolateral parts of plate; dorsal surface smooth with nu- merous fine and coarse comarginal growth lines. Intermediate plates longer than wide, strongly arched, side Family LITOCHITONIDAE new family slopes convex; anterior margin with deep, broad sinus; lateral Type genus.—Litochiton new genus. margins nearly straight, subparallel; posterior margin convex Diagnosis.—Chelodids with strongly arched, thick plates, lon- forming bluntly triangular termination; ventral surface with strong ger than wide with subparallel lateral margins; anterior margin break in concavity, one-quarter the length from posterior margin; concave; ventral surface with marked change in concavity; apical apical area narrow, ridgelike along posterior and lateral margins, area a narrow ridge on posterior and posterolateral margins. rarely extending anteriorly across posteroventral surface; some- Occurrence.—Oneota Dolomite (Ibexian; Lower Ordovician), times, narrow, deeper area borders anterior sinus ventrally; dorsal Minnesota. surface smooth with numerous comarginal growth lines. Discussion.—The Litochitonidae is distinguished by the later- Head plate unknown. ally subparallel elongate plates. The change in concavity on the Etymology.—^Latin, crebatus, thick. ventral surface and narrow ridgelike apical area on the interme- Figured types.—^Holotype, UMPC 8212 (Fig. 10.1-10.4); para- diate plates are much different from other families assigned to the types, UMPC 8214, 8214A-C, 8215A, B, E. Chelodida. Unfigured paratypes.—^Nine plates, UMPC 8214. Specimens include one tail plate and 18 intermediate plates. Genus LITOCHITON new genus Measurements.—See Table 8. Type species.—Litochiton crebatus n. sp. Occurrence.—Oneota Dolomite (Ibexian) near Rushford, Wi- Diagnosis.—Smooth, thick, strongly arched intermediate nona Co., Minnesota. plates; posterior margin bluntly convex to pointed; anterior mar- Discussion.—The taxonomic status of the collection of speci- gin with prominent sinus; apical areas narrow, ridgelike on pos- mens, here called Litochiton crebatus, has been misconstrued sev- terior and lateral margins; prominent transverse change in con- eral times in the literature. Flower (1968) misunderstood Asco- cavity of ventral surface. ceras gibberosum Sardeson, 1896 (see discussion under Description.—Intermediate plates smooth, subrectangular, Calceochiton floweri n. sp. above). Smith {in Smith and Toomey, thick, strongly arched, boxlike; anterior margin with deep sinus; 1964, p. 14), when examining what he thought to be the type posterior margins bluntly convex to pointed; apical area narrow, specimen of A. gibberosum, reckoned that it belonged to the Chel- ridgelike on posterior and lateral margins; tail plate smooth, sub- odidae; however, he was uncertain of the assignment to Chelodes. rectangular, sharply arched; posterior margin convex, arched dor- When Smith examined the collection of 19 specimens, he as- sally; narrow ridge bordering posterior and lateral margins ven- signed them to Chelodes gibberosus (Sardeson) (Smith and trally; dorsal surface of plates with distinct comarginal growth Hoare, 1987, p. 29). Herein, examination of the 19 specimens, lines. plus three additional specimens located at the Science Museum Etymology.—Greek, litos, plain, simple; chiton, tunic. of Minnesota, shows that they differ significantly from Chelodes, Occurrence.—Oneota Dolomite (Ibexian; Lower Ordovician), and from Sardeson's illustrations of Ascoceras gibberosum; and Minnesota. it was learned that they are not Sardeson's type specimens which Discussion.—Monotypic Litochiton differs from Chelodes in were apparently discarded in 1911 (see Calceochiton floweri lacking the large, triangular, apical area, the plates are more above). Labels with the 19 specimens may have been made by strongly and narrowly arched, and the shape of the plates is sub- the collector, C. R. Stauffer, or someone else at a later date; these rectangular rather than subtriangular. Listrochiton has triangular labels use Smith's species designation, but note incorrectly that intermediate plates. Thairoplax has subparallel margins on the the specimens are gastropods.

523914; 28, 29, dorsal and right lateral views, 6916-CO, USNM 523915; 30, 31, dorsal and anterior views, 6916-CO, USNM 523916; 32, 33, dorsal and ventral views, 6916-CO, USNM 523917; 34-49, tail plates; 34, dorsal view, 6915-CO, USNM 523918; 35-37, holotype, dorsal, posterior, and right lateral views, 6915-CO, USNM 523919; 38, 39, dorsal and ventral views, 6915-CO, USNM 523920; 40, 41, dorsal and posterior views, 6916-CO, USNM 523921; 42^4, dorsal, ventral, and posterior views, 5015-CO, USNM 523922; 45^7, dorsal, anterior, and left lateral views, 5015-CO, USNM 523923; 48, 49, dorsal and ventral views, 5015-CO, USNM 523924. All figures X3. 14 HOARE AND POJETA

FIGURE 9—Orthriochiton recavus n. sp. Oneota Dolomite near Sauk City, Wisconsin. 1-4, Head plate, dorsal, ventral, right lateral, and posterior views, NMMNH P-41265; 5-22, intermediate plates; 5-7, dorsal, ventral, and right lateral views, NMMNH P-41266; 8, 9, dorsal and anterior views, NMMNH P-41267; 10, 11, dorsal and posterior views, NMMNH P-41268; 12, 13, ventral and dorsal views, NMMNH P-41269; 14-16, dorsal, left lateral, and anterior views, NMMNH P-41270; 17-19, dorsal, ventral, and anterior views, NMMNH P-41271; 20-22, dorsal, left lateral, and ventral views, NMMNH P-41272; 25-29, tail plates; 23, 24, dorsal and ventral views, NMMNH P-41273; 25-27, holotype, dorsal, right lateral, and posterior views, NMMNH P-41274; 28, 29, dorsal and ventral views, NMMNH P-41275. All figures X4.

Family HELMINTHOCHITONIDAE Van Belle, 1975 Intermediate plates thin, smooth, shape variable, subquadran- Diagnosis.—^Septemchitonids with intermediate plates possess- gular to rectangular, or pointed posteriorly making them hexag- ing an anterior sinus of variable depth; shape not triangular. onal; flatly arched transversely; anterior margin with deep sinus; Occurrence.—Ordovician-Devonian. lateral margins essentially straight and subparallel; posterior mar- gins straight to slightly concave, subparallel to anterior margin; Genus HELMINTHOCHITON Salter, 1846 central jugal area low, fairly distinct from lateral areas; ventral Type species.—Helminthochiton grijfithi Salter, 1846. Diagnosis.—Helminthochitonids with quadrangular to rectan- gular intermediate plates. TABLE 7—Measurements (in mm) of Oithiiochiton recavus n. sp. Occurrence.—Ordovician-Devonian. Discussion.—The misapplication of Helminthochiton for upper NMMNH Length Width Height Plate Paleozoic taxa with sutural plates was detailed in Hoare (2002, P-41265 3.8 3.0 1.5 H p. 95). P-41266 4.3 3.5 2.9 P-41267 4.5t 3.8 2.8 HELMINTHOCHITON BLACKI new species P-41268 4.8t 3.8 2.5 P-41269 5.4 4.3 3.4 Figure 11.1-11.28 P-41270 5.2 4.5 3.2 Diagnosis.—Thin, flatly arched intermediate plates with sub- P-41271 8.4 5.5 3.8 P-41272 6.0t 4.0 2.8 parallel, straight lateral margins; jugal area present, not strongly P-41273 4.8t 3.0 2.1 T pronounced; narrow apical area bordering posterior margins. P-41274* 8.3 4.8 4.3 T Description.—Tail plate, strongly arched with flat lateral P-41275 7.0 4.5 4.0 T slopes; lateral margins convex converging on a convex posterior * Holotype. margin; low mucro anterior to posterior margin. t Estimated. ORDOVICIAN POLYPLACOPHORA FROM NORTH AMERICA 15

TABLE 8—Measurements (in mm) of Litochiton ciebratus n. gen. and sp.

UMPC Length Width Height Plate 8212* 15.5 8.6 9.0 I 82I4A 10.8 9.3 5.8 I 82I4B 12.2 10.0 6.8 I 82I4C 12.3t 8.8 5.2 T 82I5A 13.4 8.4 6.9 I 82I5B 13.1 10.4t 7.1 I 82I5E 12.7 9.8 6.0 I * Holotype. t Estimated.

5101-CO, one plate; USNM 523936E, USGS 4959-CO, one plate; USNM 523936F USGS 6134-CO, 15 plates. Specimens include one tail plate and 53 intermediate plates. Measurements.—See Table 9. Occurrence.—Curdsville and Grier Limestone members, Lex- ington Limestone (Chatfieldian) in Kentucky. Discussion.—Helminthochiton blacki differs from the Europe- an H. grijfithi, H. grayanus de Koninck, 1860, H. thraivensis Reed, 1911, and H. aequivoca Robson, 1913 in having much more flatly arched plates. In general, the intermediate plates of H. grayanus compare closely, in terms of the subquadrangular shape, to those of H. blacki. All species previously assigned to this genus from upper Pa- leozoic rocks have sutural laminae and are now placed in Gry- phochiton Gray, 1847. The Helminthochitonidae Van Belle, 1975 is based on Helminthochiton, having the type H grijfithi, which lacks sutural laminae. As known at present, helminthochitonids are limited to a pre-Carboniferous age; Sirenko (2003) gives their range as Ordovician-Devonian.

HELMINTHOCHITON MARGINATUS new species Figure 12 Diagnosis.—Tail plate oval with mucro located anterior to pos- terior margin; intermediate plates longer than wide, arched, with distinct jugum. Description.—Tail plate arched, oval, elongate, widest and highest posteriorly; jugal area narrow, mucro one-third of length anterior of posterior margin; posterior margin convex; lateral mar- gins convex converging towards narrowly convex anterior mar- FIGURE 10—Litochiton crebatus n. gen. and sp. Oneota Dolomite, Min- gin; ventral surface not observed; dorsal surface with prominent nesota. 1-17, Intermediate plates; 1-4, holotype, dorsal, left lateral, comarginal growth lines. posterior, and ventral views, UMPC 8212; 5-8, dorsal, ventral, left Intermediate plates longer than wide, subrectangular, moderate- lateral, and posterior views, UMPC 8215A; 9-12, dorsal, right lateral, ly arched; anterior margin with prominent sinus, anterolateral posterior, and ventral views, UMPC 8215E; 13, 14, dorsal and ventral margins sharply convex; lateral margins nearly parallel; posterior views, UMPC 8215B; 15, ventral view, UMPC 8214A; 16, 17, anterior and dorsal views, UMPC 8214B; 18-21, tail plate, dorsal, left lateral, margins convex, not pointed; dorsal surface with distinct jugum; posterior, and ventral views, UMPC 8214C. All figures X2. lateral areas concave marked by faint radial lines extending from apex, with prominent comarginal growth lines; ventral surface deeply concave beneath jugal area; apical area narrow, extending surface with narrow apical area extending to juncture of posterior to junction of posterior and lateral margins. and lateral margins; faint comarginal growth lines. Head plate arched posteriorly; anterior margin convex rounding Head plate unknown. smoothly into flatly convex lateral margins, posterior margin near- Etymology.—^For D. F. B. Black, U.S. Geological Survey, for ly straight; side slopes on ventral surface concave, venter deeply his extensive geologic mapping of the Ordovician rocks of Ken- concave medianly. tucky, and his help in collecting blocks of limestone containing Etymology.—^Latin, marginatus, furnished with a border. silicified fossils. Figured fypes.—Holotype, USNM 523981 (Fig. 12.18-12.21); Figured fypej.—Holotype, USNM 523927 (Fig. 11.3-11.5), paratypes, USNM 523975-523980, 523982, 524902-524904. USGS 6131-CO; paratypes, USNM 523926, 523928, 523930, Unfigured paratypes.—^Eleven specimens, USNM 524904A. 523933, 523934, USGS 6131-CO; USNM 523935, USGS 6134- Specimens include one head plate, one tail plate, and 20 inter- CO; USNM 523932, USGS 5101-CO; USNM 523929, USGS mediate plates. 4959-CO; USNM 523931, USGS 5096-CO. Measurements.—See Table 10. Unfigured paratypes.—USNM 523936A, USGS 6131-CO, 24 Occurrence.—Forreston Member, Grand Detour Formation, plates; USNM 523936B, USGS 5094-CO, one plate; USNM Platteville Group (Turinian), Bauer's Quarry west of Beloit, Rock 523936C, USGS 5096-CO, two plates; USNM 523936D, USGS County, Wisconsin. From the same bed as Echinochiton dufoei. 16 HOARE AND POJETA

FIGURE 11—Helminthochiton blacki n. sp. Curdsville and Grier Limestone members, Lexington Limestone, Kentucky. 1-25, Intermediate plates; 1, 2, dorsal and anterior views, 6131-CO, USNM 523926; 3-5, holotype, dorsal, ventral, and left lateral views, 4959-CO, USNM 523927; 6-8, dorsal, ventral, and left lateral views, 6131-CO, USNM 523928; 9, 10, dorsal and ventral views, 4959-CO, USNM 523929; 11-13, dorsal, ventral, and posterior views, 6131-CO, USNM 523930; 14-16, right lateral, dorsal, and ventral views, 5096-CO, USNM 523931; 17-19, dorsal, ventral, and anterior views, 5101-CO, USNM 523932; 20-22, left lateral, dorsal, and ventral views, 6131-CO, USNM 523933; 23-25, dorsal, ventral, and anterior views, 6131-CO, USNM 523934; 26-28, tail plate, posterior, dorsal, and ventral views, 6134-CO, USNM 523935. All figures X3.

Discussion.—Helminthochiton marginatus occurs with Prea- subrectangular plates with a distinct, narrower, jugal area and be- canthochiton baueri n. sp. and is readily distinguished in later comes sharply arched. growth stages by the difference in growth patterns. Both species In shape, H. marginatus is similar to Silurian species of Thai- have subquadrangular intermediate plates with less distinct jugal roplax, such as T. pelta Cherns, 1998b, T. birhombivalis Bergen- areas in early growth stages (compare Figs. 7, 12). Whereas P. hayn, 1955, and T. merriami Hoare, 2000a; however, these species baueri continues to develop subquadrangular plates with a weak of Thairoplax have prominent pointed shapes and large apical jugal area in latter growth, Helminthochiton marginatus developes areas. Species of Paleochiton Smith in Smith and Toomey, 1964 ORDOVICIAN POLYPLACOPHORA FROM NORTH AMERICA 17

TABLE 9- -Measurements (in mm) of Helminthochiton blacki n. sp. TABLE 10—Measurements (in mm) of Helminthochiton marginatus n. sp.

USNM Length Width Height Plate USNM Length Width Height Plate 523926 7.8 9.7 37 523975 11.5 8.8 3.0t 523928 9.0 9.6 3.0 523976 12.5 10.8 523930 12.8 11.4 5.3 523977 13.0 9.5 2.5t 523933 10.9 9.0 5.2 523978 6.9 6.9 — 523934 9.8 12.0 4.1 523979 11.0 7.0t — 523932 7.3 10.2 4.2 523980 8.0 87 — H 523931 7.3 6.9 4.7 523981* 10.5 9.2 2.3t T 523927* 11.7 11.7 5.7 523929 9.0 10.0 4.5 * Holotype. 523935 77 77 4.3 T t Estimated. ' Holotype. Occurrence.—Ordovician (Turinian) of North America and Si- lurian (Wenlockian) of Sweden. have more strongly arched intermediate plates with distinct apical Discussion.—Taxa of the Alastegiidae differ from other fami- areas and the tail plate is narrowly elongate, as in the Silurian P. lies of the Septemchitonida by the relatively short, broadly tri- siskiyouensis Hoare, 2000a. Kluessendorf (1987) described sev- angular, thin intermediate plates and posteriorly arched tail plates. eral Silurian chiton morphotypes from Wisconsin, Illinois, and Iowa, based upon internal molds. None of these approach H. mar- Genus ALASTEGA Cherns, 1998b ginatus in shape. Diagnosis.—Alastegiids with large apical areas on intermediate Family ALASTEGHDAE new family plates. Type genus.—Alastega Cherns, 1998b. Occurrence.—As for the family. Included genera.—The type genus and Amblytochiton n. gen. Diagnosis.—^Small septemchitonids with strongly to broadly ALASTEGA MARTINI new species arched plates; head plate subrectangular; intermediate plates with Figure 13 anterior sinus, triangular, not quadrangular or rectangular in Diagnosis.—Tail plate smooth, elongate, narrowly subtriangu- shape; tail plate arched posteriorly. lar, roundly arched transversely, posterior margin arched dorsally;

FIGURE 12—Helminthochiton marginatus n. sp. Forreston Member, Grand Detour Fomation, Wisconsin. 1, Head plate, ventral mold, USNM 523980; 2-17, intermediate plates; 2-5, dorsal mold, dorsal cast, left lateral cast, and anterior cast, USNM 523975; 6, ventral mold, USNM 523976; 7, dorsal mold, USNM 523979; 8, dorsal mold, USNM 523982; 9, 10, dorsal mold and dorsal cast, USNM 524902; 11, dorsal mold, USNM 524903; 12, 13, dorsal mold and dorsal cast, USNM 523977; 14-16, dorsal mold, dorsal cast, and ventral mold, USNM 524904; 17, ventral mold, USNM 523978; 18-21, tail plate, holotype, right lateral cast, posterior cast, dorsal cast, and dorsal mold, USNM 523981. All figures X2. 18 HOARE AND POJETA

FIGURE 13—Alastega martini n. sp. Salvisa Bed, Perryville Limestone Member, Lexington Limestone, Kentucky. 1-4, Head plate, dorsal, ventral, left lateral, and posterior views, 6915-CO, USNM 523937; 5-19, intermediate plates; J, 6, dorsal and ventral views, 6915-CO, USNM 523938; 7- 9, dorsal, ventral, and right lateral views, 6915-CO, USNM 523939; 10-12, dorsal, posterior, and ventral views, 6915-CO, USNM 523940; 13, 14, dorsal and ventral views, 6916-CO, USNM 523941; 15-17, dorsal, anterior, and ventral views, 6916-CO, USNM 523942; 18, 19, dorsal and anterior views, 6915-CO, USNM 523943; 20-25, tail plates; 20-22, right lateral, dorsal, and ventral views, 6915-CO, USNM 523944; 23-25, holotype, dorsal, anterior, and ventral views, 6915-CO, USNM 523945. All figures X3.

intermediate plates roundly arched, broad triangularly, pointed sharply projecting, leading to straight or slightly convex postero- with deep anterior sinus; head plate strongly arched, pointed. lateral margins, ending in a posterior apex; ventral surface with Description.—Tail plate roundly arched transversely, narrow, distinct, large, apical area becoming narrower laterally, extending subtriangular, anterior margin with moderately deep sinus, lateral to or past midlength; comarginal growth lines present. margins broadly convex, curving more strongly posteriorly to Head plate subquadrangular, strongly arched transversely; an- apex; posterior ventral margin arched dorsally with narrow thick- terior margin with shallow sinus; lateral and posterior margins ened margin, no distinct jugal area, lateral slopes convex; ventral flatly convex; ventral surface with large, triangular apical area surface smooth; comarginal growth lines present. extending laterally to junction of lateral and posterior margins; Intermediate plates thin, roundly arched, broadly triangular, prominent comarginal growth lines. pointed; anterior margin with deep sinus; anterolateral margins Etymology.—^For Martin Pojeta, brother of John Pojeta Jr. ORDOVICIAN POLYPLACOPHORA FROM NORTH AMERICA 19

TABLE 11—Measurements (in mm) of Alastega martini n. sp.

USNM Lengtli Width Height Plate 523943 9.3 10.3 4.0 I 523938 11.3 10.5 4.2 I 523940 7.5 8.7 4.0 I 523939 lO.O 8.8 4.3 I 523937 8.7 7.3 3.9 H 523942 11.4 9.5 3.5 I 523943 11.3t u.ot — I 923945* 14.2 7.3 4.0 T ^^^^r^ "l^^^^ ^V * Holotype. t Estimated.

Figured rypes.—Holotype, USNM 523945 (Fig. 13.23-13.25), USGS 6915-CO; paratypes, USNM 523937-523940, 523943, 523944, USGS 6925-CO; USNM 523941, 523942, USGS 6916- CO. Unfigured paratypes.—\JSiiM 523946, USGS 6915-CO, 85 plates; USNM 523946A, USGS 6916-CO, 112 plates; USNM 523946B, USGS 6136-CO, one plate. Specimens include two tail plates, one head plate, and 205 in- termediate plates. Measurements.—See Table 11. Occurrence.—Salvisa Bed, Perryville Limestone Member, Lex- ington Limestone (Chatfieldian) in Kentucky. ^^^Hi'.,/.;,/. "'^1 Discussion.—Alastega martini differs from A. lira Cherns, 1998b in having a subquadrangular head plate rather than an oval head plate, more flatly arched intermediate plates having a nar- rower and shallower anterior sinus and larger apical areas, and a more elongate tail plate. Genus AMBLYTOCHITON new genus ^^^F ^^H ^^^^T^^sH Type species.—Amblytochiton incomptus n. sp. Diagnosis.—^Small, flatly arched plates; tail plate subquadran- gular with terminal mucro; intermediate plates subtriangular, ^^j^^^fif^H ^h^^l^l pointed, with narrow apical area. ^^^^^^^^^^^^^^^^^-^ ^H Description.—Tail plate arched, subquadrangular with arched ^HB^I ^^^^^^^^^^^^^^^^H^^^l posterior margin and narrow ridge ventrally along posterior mar- ^i,:i':-.-;^ia v-^ gin; intermediate plates flatly arched, subtriangular, pointed, with VPHI ^^^^^^^T^^^^^^H distinct anterior sinus, and narrow apical area exending laterally ^^^^^^^^h^M^^^Rxr^l past midlength; head plate subrectangular, flatly arched. Etymology.—Greek, amblytos, bluntness; chiton, tunic. ^^^^^^Pt .1 Occurrence.—Tyrone Limestone (Turinian) in Kentucky. 1 J Discussion.—^Monotypic Amblytochiton differs from other ^^^^^^r ^^^^^^^^ i^ known lower Paleozoic genera in the combination of the subquad- rangular shape of the head and tail plates, thinness of the plates, narrow apical area, and subtriangular intermediate plates. Kind- HI bladochiton Van Belle, 1975 (=Eochiton Smith in Smith and FIGURE 14—Amblytochiton incomptus n. gen. and sp. Tyrone Limestone, Toomey, 1964) has subquadrangular and sharply arched inter- Kentucky. 1-4, Head plate, dorsal, ventral, anterior, and right lateral mediate plates, which are also true for Paleochiton. The inter- views, 6034-CO, USNM 523947; 5-16, intermediate plates; 5, 6, dorsal mediate plates of h'ochiton Smith in Smith and Toomey, 1964 are and anterior views, 6034-CO, USNM 523948; 7, dorsal view, 6034- wider than long. Alastega has an elongate tail plate which is less CO, USNM 523949; 8, dorsal view, 6034-CO, USNM 523950; 9, 10, sharply ridged than that of Amblytochiton and has much larger dorsal and ventral views, 6034-CO, USNM 523951; 11, 12, dorsal and apical areas on the intermediate plates. ventral views, 6034-CO, USNM 523952; 13, dorsal view, 6034-CO, USNM 523953; 14, 15, dorsal and right lateral views, 6034-CO, AMBLYTOCHITON INCOMPTUS new species USNM 523954; 16, dorsal view, 6034-CO, USNM 523955; 17-20, tail Figure 14 plate, holotype, dorsal, left lateral, posterior, and ventral views, 6034- CO, USNM 523956. All figures X3. Diagnosis.—As for the genus. Description.—Tail plate subquadrangular, strongly arched; lat- eral margins slightly convex; posterior margin nearly straight, Intermediate plates subtriangular, flatly arched transversely; an- arched dorsally; anterior margin unknown; jugal area faintly set terior margin with shallow to moderately deep sinus; lateral mar- off from lateral areas, mucro terminal; ventral surface with low, gins convex, converging posteriorly; posterior margins nearly narrow ridge bordering posterior margin extending onto lateral straight, pointed; ventral surface with low, narrow apical area ta- margins, ridge turns sharply dorsally to form posterior plate mar- pering laterally to junction of posterior and lateral margins; co- gin. marginal growth lines present. 20 HOARE AND POJETA

TABLE 12—Measurements (in mm) of Amblytochiton incomptus n. gen. BERGENHAYN, J. R. M. 1955. Die fossilen Schwedischen Loricaten nebst and sp. einer vorlayligen Revision des Systems der ganzen Klasse Loricata. Lunds Universitete Arsskrift, Nya Forhandlinger, Avdelningen, 2, USNM Length Width Height Plate 51(8): 1-46. 523947 7.3t 6.0 3.1 H BERGENHAYN, J. R. M. 1960. Cambrian and Ordovician loricates from 523948 8.5 7.0 3.2 I North America. Journal of Paleontology, 34:168-178. 523952 6.2t 6.8 3.1 I BILLINGS, E. 1854. On some new genera and species of Cystidae from 523956* 9.0t 7.2 4.5 T the Trenton Limestone. Canadian Journal, 2:270-271. BILLINGS, E. 1860. New species of fossils from the Lower Silurian rocks * Holotype. t Estimated. of Canada. Canadian Naturalist and Geologist, 5:161-177. BILLINGS, E. 1865. Paleozoic fossils, volume 1, containing descriptions and figures of new or little known species of organic remains from the Silurian rocks 1861-1865. Geological Survey of Canada, 426 p. Head plate subquadrangular, flatly arched; anterior and lateral BRANSTRATOR, J. W. 1979. Asteroidea (Echinodermata). U.S. Geological margins flatly convex, posterior margin unknown; anterior margin Survey Professional Paper, 1066-F, 7 p. slightly arched dorsally; ventral surface with indication of an api- BUTTS, C. 1926. Explanatory text to accompany the geologic map of the cal area extending laterally to midlength. state—the Paleozoic rocks. Geologic Survey of Alabama Special Re- Etymology.—^Latin, in, without; comptus, adorned. port, 14, 230 p. Figured fypes.—Holotype, USNM 523956 (Fig. 14.17-14.20), BUTTS, C. 1941. Geology of the Appalachian Valley in Virginia. Pt. IL USGS 6034-CO; paratypes, USNM 523947-523955. Fossil plates and explanations. Virginia Geological Survey Bulletin, 52, Unfigured paratype.—^USNM 523957. 271 p. Specimens include one head plate, one tail plate, and nine in- CARTER, J. G. (ED.). 1990. Skeletal Biomineralization: Patterns, Process- es, and Evaluating Trends. Vol. 1. Van Nostrand-Reinhold, New York, termediate plates. 832 p. Measurements.—See Table 12. CHERNS, L. 1998a. Chelodes and closely related Polyplacophora (Mol- Occurrence.—Tyrone Limestone (Turinian) in Kentucky. lusca) from the Silurian of Gotland, Sweden. Palaeontology, 41:545- Discussion.—None of the plates of A. incomptus is complete; 573. however, the characters, when pieced together, provide the basis CHERNS, L. 1998b. Silurian polyplacohoran molluscs from Gotland, Swe- for distinguishing the species. den. Palaeontology, 41:939-974. CHERNS, L. 1999. Silurian chitons as indicators of rocky shores and low- ACKNOWLEDGMENTS stand on Gotland, Sweden. Palaios, 14:172-179. We appreciate the assistance of A. B. Heckert, New Mexico CHERNS, L. 2004. Early Paleozoic diversification of chitons (Polyplaco- phora, MoUusca) based on new data from the Silurian of Gotland, Museum of Natural History, J. Hoff and K. C. Rogers, Science Sweden. Lethaia, 37:445-456. Museum of Minnesota, and D. L. Fox, Department of Geology CLOUD, P. E., AND V. E. BARNES. 1946. The EUenberger Group of central and Geophysics, University of Minnesota, for facilitating the loan Texas. University of Texas Publication, 4621, 473 p. of specimens. Likewise, P. Jell and K. Spring, Queensland Mu- CONRAD, T A. 1843. Observations on the lead-bearing limestone of Wis- seum, Brisbane, Australia, graciously gave us an extended loan consin, and descriptions of a new genus of trilobites and of fifteen new of specimens. B. S. Kues, University of New Mexico, was helpful Silurian fossils. Proceedings of the Academy of Natural Sciences of with our study of Flower's locality. R. E. Sloan, Department of Philadelphia, 1:329-334. Geology and Geophysics, University of Minnesota, provided CRESSMAN, E. R. 1968. Geologic map of the Salvisa Quadrangle, central helpful information concerning some of the Minnesota specimens. Kentucky. U.S. Geological Survey Map, GQ-760. CRESSMAN, E. R. 1972. Geologic map of the Danville Quadrangle, Mer- J. DuFoe generously gave us the specimens he collected from cer and Boyle counties, Kentucky. U.S. Geological Survey Map, GQ- near Beloit, Wisconsin; J. and M. L. Pojeta spent two days in the 985. field with him. We thank C. Bauer for allowing DuFoe and the CRESSMAN, E. R. 1973. Lithostratigraphy and depositional environments Pojetas to collect in his quarry. M. Balanc, USGS, picked through of the Lexington Limestone (Ordovician) of central Kentucky. U.S. the silicified residues from Kentucky separating the various major Geological Survey Professional Paper, 768, 61 p. taxa. S. M. Kidwell, Department of Geophysical Sciences, Uni- CRESSMAN, E. R. 1974. Geologic map of the Perry ville Quadrangle, Mer- versity of Chicago, read a draft of the taphonomic sections. We cer and Boyle counties, Kentucky. U.S. Geological Survey Map, GQ- are grateful for the identification of the associated invertebrate 1185. faunas by E. L. Yochelson, R. B. Neuman, J. M. Berdan, and W. CRESSMAN, E. R., AND O. L. KARKLINS. 1970. Lithostratigraphy and fauna of the Lexington Limestone (Ordovician) of central Kentucky. A. Oliver Jr., all of the U.S. Geological Survey. M. Parrish, De- Field trip No. 2 in Guidebook for Field Trips, 18* Annual Meeting partment of Paleobiology, Smithsonian Institution, drafted Figure Southern Section Geological Society of America. Kentucky Geological 1. The paper benefited from reviews by T. J. Dutro Jr. and J. E. Survey, Lexington, p. 17-28. Repetski, U.S. Geological Survey, L. Cherns, Department of CRESSMAN, E. R., AND M. C. NOGER. 1976. Tidal-flat carbonate envi- Earth Sciences, Cardiff University, P. Jell, Queensland Museum, ronments in the High Bridge Group (Middle Ordovician) of central and an anonymous reviewer. Kentucky. 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Pennsylvania Geological Survey sity Press, New York, 484 p. Bulletin, G47, 187 p. WEIR, G. W, W L. PETERSON, AND W C. SWADLEY. 1979. Lithofacies STAUFFER, C. R., AND G. A. THEIL. 1941. Paleozoic and related rocks and stratigraphic nomenclature of part of the Upper Ordovician section of southeastern Minnesota. Minnesota Geological Survey Bulletin, 29, of Kentucky. U.S. Geological Survey Map, 1-1155. 261 p. WEIR, G. W, W. L. PETERSON, AND W. C. SWADLEY. 1984. Lithostratig- raphy of Upper Ordovician strata exposed in Kentucky. U.S. Geolog- STINCHCOMB, B. L., AND G. DARROUGH. 1995. Some moUuscan Prob- lematica from the Upper Cambrian-Lower Ordovician of the Ozark ical Survey Professional Paper, 1151-E, 121 p. Uplift. Journal of Paleontology, 69:52-65. WETHERBY, A. G. 1881. Descriptions of new fossils from the Lower Silurian and Subcarboniferous rocks of Ohio and Kentucky. Journal of SWEET, W. C. 1979. 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U.S. Geological Survey Map, GQ-792. ULRICH, E. O. 1890b. New Lamellibranchiata, Number 1, containing de- WoLCOTT, D. E., AND E. R. CRESSMAN. 1971. Geologic map of the scriptions of new species of Modiolopsis. American Geologist, 5:270- Bryantsville Quadrangle, central Kentucky. U.S. Geological Survey 284. Map, GQ-945. ULRICH, E. O. 1890c. New Lamellibranchiata, Number 3, descriptions of new species, with remarks on others. American Geologist, 6:382-389. ACCEPTED 12 OCTOBER 2005 ORDOVICIAN POLYPLACOPHORA FROM NORTH AMERICA 23

APPENDIX A 6916-CO with the letters 'B,' 'C,' and 'D.' Cressman (1973, p. 6 and 24) named, numbered, and described the sections from which the collection COLLECTION LOCALITIES IN KENTUCKY came as Perryville Section A (=Perryville North), Section 30A (USGS USGS 5078-CO. Camp Nelson Limestone exposed along road up from 6915-CO and 6916-CO) and Perryville Section B (=Perryville South), Kentucky River lock number 7 to High Bridge, Kentucky, and junction Section 30B (USGS 5015-CO). with Kentucky Route 29, Jessamine Co., Wilmore Quadrangle. Sample USGS 6915-CO. Salvisa Bed, Perryville Limestone Member, Lexing- from 8.54 m above base of section. (Same locality as USGS 7875-CO.) ton Limestone, exposed in Boyle County quarry on the west side of U.S. USGS 5081-CO. Tyrone Limestone exposed in road and railroad cuts Route 68, 2.1 km northeast of Perryville, Boyle Co., Perryville Quadran- along road towards Kentucky utilities plant on east side of Blackburn gle. Sample from basal 0.61 m of bed on northwest wall of quarry. Memorial Bridge Crossing Kentucky River, Woodford Co., Tyrone Quad- USGS 6916-CO. Salvisa Bed, Perryville Limestone Member, Lexing- rangle. Sample from float 10.68 m below top of limestone. ton Limestone. Same locality as USGS 6915-CO. Sample from east wall USGS 6034-CO. Tyrone Limestone exposed on New Watts Mill Road, of quarry. 0.16 km southwest of intersection with Kentucky Route 39, Jessamine USGS 6138-CO. Comishville Bed, Perryville Limestone Member, Lex- Co. Sample from 34.2 m above base of section. Section G of Cressman ington Limestone. Same locality as 6136-CO. Sample from 4.9 m above and Noger (1976), very near the top of the exposure (marked by the letter Perryville-Tanglewood Members contact. "f"), immediately below the Pencil Cave Bentonite of Drillers [=Deicke USGS 5036-CO. Devils Hollow Member, Lexington Limestone, ex- K Bentonite; Kolata et al. (1996, p. 26); Leslie (2000) and Saltzman et posed in stream on Squires Road 2.9 km southwest of intersection with al. (2003)]. Also, locality 6034-CO is marked by the letters "AAA" on U.S. Route 421 (upstream 0.16 km), Fayette Co., Coletown Quadrangle. the geologic map of the Little Hickman Quadrangle (Wolcott, 1969). Sample from 18.3 m above base of Brannon Member. USGS 6035-CO. Tyrone Limestone. Same locality as USGS 6034-CO. Sample from 27.1 to 28.7 m above base of section. APPENDIX B USGS D-1138-CO. Tyrone Limestone exposed in creek to west and parallel with Marble Creek northwest of the YMCA Camp, Jessamine TAPHONOMY OF SILICIFIED KENTUCKY ORDOVICIAN CHITON-BEARING Co. Sample from 8.8 m above base of unit. USGS D-1138-CO is marked SHELL BEDS by the letter "R" on the geologic map of the Valley View Quadrangle (Greene, 1966). Using probable environments of deposition, silicified Kentucky Or- USGS 5101-CO. Lower part of the Curdsville Limestone Member, dovician mollusk-rich chiton-bearing shell beds can be grouped into those Lexington Limestone, exposed on Kentucky Route 169 just west of Hick- occurring in very shallow nearshore subtidal, lagoonal, and open marine man Creek crossing, Fayette Co. Sample from lower portion of limestone. deposits (Table 13). USGS 5101-CO is not marked on the geologic map of the Nicholasville Nearshore subtidal deposits.—The oldest abundant fauna is found in Quadrangle (MacQuown, 1968). the Tyrone Limestone (USGS 6034-CO and D-1138-CO). "The Tyrone USGS 6134-CO. Lower part of the Curdsville Limestone Member, Limestone accumulated in quiet shallow water and was periodically ex- Lexington Limestone, exposed in road 0.32 km west of Dix River cross- posed to the air" (Cressman, 1973, p. 13). Cressman and Noger (1976) ing of Kentucky Route 52, Garrard Co. Sample from lower 0.92 m of concluded that the Camp Nelson and Tyrone limestones (High Bridge member. USGS 6134-CO is marked on the geologic map of the Bryants- Group) were deposited in tidal flat and immediate subtidal carbonate en- ville Quadrangle by the letter 'H' (Wolcott and Cressman, 1971). vironments analogous to those seen today in the Bahamas and Florida USGS 6131 -CO. Upper part of the Curdsville Limestone Member, Lex- Bay. ington Limestone, exposed on Kentucky Route 33 just north of bridge MoUusks dominate these biopelsparite shell beds, being represented by crossing of Mocks Branch, 4.02 km north of Danville, Franklin Co. Sam- 5,332 specimens placed in 36 species. The moUuscan fauna is dominated ple from 7 m above Tyrone-Lexington contact. USGS 6131-CO is marked by pteriomorph pelecypods and gastropods. Of the 5,320 pelecypods, with a red 'X' on the graphic stratigraphic column on the geologic map 2,218 are pteriomorphs, of which 2,000 belong to the single species Cyr- of the Danville Quadrangle (Cressman, 1972). todonta subovata Ulrich, 1894a. The gastropods total c. 2,593 specimens, USGS 4928-CO. Grier Limestone Member, Lexington Limestone ex- but have not been studied in detail. The pelecypods are disarticulated as posed 0.81 km east and 2.58 km south of northwest corner of Salvisa are the polyplacophorans. Most of the cephalopods are pieces of phrag- Quadrangle, Anderson Co. Sample from 6.7 km below base of Brannon mocone or siphuncle; one nearly complete Oncoceras Hall, 1847 was Member found (Frey, 1995, pi. 19, figs. 11-14). Not all moUusk specimens could USGS 4959-CO. Grier Limestone Member, Lexington Limestone, ex- be identified to species, because some are small fragments probably re- posed in road on west side of Kentucky River at bridge crossing of Cen- sulting from incomplete silicification. tral Kentucky Parkway, on north side of parkway, Anderson Co. Sample The nonmoUuscan fauna is sparse both in number of species and di- from 45.4 to 46.4 m above Tyrone Limestone. USGS 4959-CO is from versity. Specimens were not counted, they are placed in nine species. just below the top of the Grier Limestone Member from Cressman's The overlying bentonite is assumed to account for the silicification of (1973, pi. 1) Salvisa B section (=Section 176) and is marked by the letter the fossils in this bed. The beds immediately below USGS 6034-CO are 'B' on the geologic map of the Salvisa Quadrangle (Cressman, 1968). micrites and pelmicrites having mud cracks and some brecciated layers, USGS 5094-CO. Grier Limestone Member, Lexington Limestone, ex- and generally lack fossils. USGS 6034-CO is the most mollusk-rich shell posed in road cuts along Devils Hollow Road 1.1 km south of Buttimer bed of any of the 1,100 fossil collections made during the Kentucky Hill, Franklin Co. Frankfort West Quadrangle. Sample from 13.7 m above mapping project. A total of 12,500 fossils were obtained; 10,000 of these Macedonia Bed. are mollusks that are not weathered or worn. USGS 5096-CO. Grier Limestone Member, Lexington Limestone, ex- USGS D-1138-CO is also from high in the Tyrone Limestone below posed in abandoned railroad bed near top of north bluff of Kentucky bentonite bands and the fossils are silicified. This collection is essentially River 0.64 km southeast of YMCA Camp, near the notation "YMCA in the same stratigraphic position, and has much the same lithology as Camp" on the geologic map of the Valley View Quadrangle (Greene, USGS 6034-C. The two collections are on adjacent east-west quadran- 1966), just east of the Kentucky River Fault, Jessamine Co. Sample from gles. The shell bed at USGS D-1138-CO has a much greater abundance near top of bluff. of the tabulate coral Tetradium cf. T. cellulosum (Hall, 1847) (identified USGS 6136-CO. Faulconer Bed, Perryville Limestone Member, Lex- by W. A. Oliver, USGS) and lacks the numerous pelecypods and ceph- ington Limestone, exposed in roadcut on Kentucky Route 52, 2.33 km alopods found in the shell bed at locality 6034-CO. east of junction with U.S. Route 150, 0.24 km east of crossing of Ken- In part, these differences in the two faunas recovered are probably the tucky Route 52 and Balls Branch Run, Boyle Co., Bryantsville Quadran- result of the differences in the sample sizes and the types of outcrops gle. Sample from basal 0.92 to 1.2 m of member. from which the samples were collected. The sample from USGS 6034- USGS 5015-CO. Salvisa Bed, Perryville Limestone Member, Lexing- CO was seven times the size taken at USGS D-1138-CO (Table 13) and ton Limestone, exposed in quarry 0.64 km south of Perryville on east was from a more complete exposure of the Tyrone Limestone. side of Mitchellsburg Road, east side of Chaplin River, Boyle Co. Sample Lagoonal deposits.—^The Salvisa Bed, Perryville Limestone Member, from 1.53 m above base of bed. On the geologic map of the Perryville Lexington Limestone, USGS 5015-CO, 6915-CO, and 6916-CO, is youn- Quadrangle, Cressman (1974) labeled USGS 5015-CO, 6915-CO, and ger than the Tyrone Limestone. "The light-gray calcilutite [of the Salvisa 24 HOARE AND POJETA

TABLE 13—Summary of number of species, specimens, and weight of rock TABLE 13—Continued. digested in the taphonomic analysis of Kentucky localities. ? = specimens not counted or identified. Number of Fauna species Number of specimens Nu:mber of Fauna sipecies Number of specimens Grier Limestone Member; 4959-CO [136.1 kg (300 lbs)] and 5096-CO [136.1 kg (300 lbs)] NEARSHORE SUBTIDAL DEPOSITS chitons 1 5 Tyrone Limestone; 6034-CO [665.9 kg ; (1,468 lbs)] pteriomorph pelecypods 3 39 and D-1138-CO [90.9 kg (200 lbs)] palaeotaxodont pelecypods 3 139 chitons 2 238 other pelecypods 2 3 and frags. pteriomorph pelecypods 4 2,218 nautiloids 1 2 palaeotaxodont pelecypods 3 55 gastropods 5 8H- nautiloids 18 180 monoplacophorans/bellerophonts 7 37 gastropods 7 c. 2,593 scaphopods 1 8 bellerophonts 2 48 Total mollusks 23 314-H Total mollusks 36 5,332 inarticulate brachiopods 1 4 strophomenid brachiopods 1 2 orthid brachiopods 2 55 pentamerid brachiopods 1 few strophomenid brachiopods 1 62 corals 2 7 rhynchonellid brachiopods 1 250 ostracodes 5 7 spiriferid brachiopods 1 450 Total other fauna 9 Total brachiopods 6 821 LAGOONAL DEPOSITS Salvisa Bed; 5015-CO [645.5 kg (1,423 lbs)], 6915-CO [241.3 kg (532 lbs)], and 6916-CO [107 kg (236 lbs)] chitons 2 674 Bed] resembles much of the limestone in the Tyrone Limestone" (Cress- pteriomorph pelecypods 5 369 man, 1973, p. 25). "Microscopically, the light-colored calcilutite ranges palaeotaxodont pelecypods 3 708 from featureless micrite to pelmicrite and pelsparite in which [occur] other pelecypods 4 48 micrite pellets" (Cressman, 1973, p. 28). Cressman (1973, p. 28-30) nautiloids 9 few frags. rostroconchs 1 25 noted that the Salvisa Bed was deposited in shallow quiet water, no more gastropods 5 92 (5015-CO only) than 1.83 m (6 ft) deep, protected by calcarenite bars of the contempo- monoplacophorans/bellerophonts 7 113 (5015-CO only) raneous Tanglewood Limestone Member, Lexington Limestone. Probably Total mollusks 27 2,029 these bars restricted circulation, causing higher salinites during Salvisa rhynchonellid brachiopods 1 1,444 deposition. Thus, it is likely that the silicified shell beds in the Salvisa spiriferid brachiopods 1 244 Bed were deposited in a lagoonlike environment. orthid brachiopods 2 31 The rocks are petroliferous beds of calcilutite 5-15 cm (2-6 in.) thick, strophomenid brachiopods 1 3 and differ markedly from the underlying and overlying units which are Total brachiopods 5 1,722 calcisiltite or have nodular bedding. The color of Salvisa rocks ranges corals 2 frags. from light to dark gray. Fossils are common. The lightest-colored beds trilobites 5 9 yielded few fossils. The darkest-colored beds are the most petroliferous 9 ostracodes 7 and the fossils are broken and fragmented and the fauna is dominated by Total other fauna 14 bryozoans and contains ostracodes. The intermediate-colored beds yield- OPEN-MARINE DEPOSITS ed the most whole fossils; in these beds, the whole shells were at various Lower part of the Curdsville Limestone Member; 5101-CO angles to bedding and the pelecypods were both convex side up or down. [362.4 kg (799 lbs)] and 6134-CO [286.7 kg (632 lbs)] The polyplacophorans are disarticulated; this is also largely the case with chitons 1 18 the pelecypods, and the shells were probably moved; although robust pteriomorph pelecypods 2 532 shells, such as the rhynchonellids, could remain articulated. The shells palaeotaxodont pelecypods 3 39 heterodont pelecypods 1 32 are not worn or abraded. A few of the cyrtodontid pelecypods were ar- other pelecypods 2 2 ticulated, but the valves separated as acid-etching progressed. In the ligh- nautiloids ? few frags. ter-colored beds, fossils tend to be whole and the fauna is dominated by gastropods 6 7 cyrtodontid and palaeotaxodont pelecypods, disarticulated chiton plates, monoplacophorans/bellerophonts 5 7 and Tetradium corals. Total mollusks 20 Mollusks (2,029 specimens) and brachiopods (1,722 specimens) dom- orthid brachiopods 5 13 (5101-COonly) inate the fauna. Mollusks are placed in 27 species. Pelecypods are rep- rhynchonellid brachiopods 1 25 (5101-COonly) resented by 1,125 valves, of which 369 are pteriomorphs and 708 are strophomenid brachiopods 2 4 (5101-COonly) palaeotaxodonts. The pteriomorph fauna is dominated by the species Cyr- spiriferid brachiopods 1 10 (5101-COonly) todonta subovata (252 specimens) and the palaeotaxodont fauna is dom- pentamerid brachiopods 1 7 Total brachiopods 10 inated by the species Deceptrix aff. D. hartsvillensis (Safford, 1869) (546 specimens). corals 2 frags. echinoderms 2 3 The brachiopod fauna is dominated by the rhynchonellid Orthorhyn- receptaculitid 1 2 chula linneyi (James, 1881) (1,444 specimens) and the spiriferid Zygos- Total other fauna 5 pira sp. (244 specimens). There are also 31 specimens of two species of orthids and three specimens of a strophomenoid. Upper part of the Curdsville Limestone Member: 6131-CO [320.7 kg (707 lbs)] The remaining fauna includes two species of corals, but is dominated by trilobites and ostracodes. chitons 1 25 pteriomorph pelecypods 2 1,254 In comparing the Tyrone Limstone faunas in which Spicuchelodes palaeotaxodont pelecypods 3 58 cressmani n. sp. occurs with those in the Salvisa Bed in which the nautiloids few frags. younger species Listrochiton weiri n. gen. and sp. occurs, the major gastropods 3 7 similarities are: 1) they both occur in similar rock types; 2) both contain monoplacophorans/bellerophonts 2 7 large numbers of pteriomorph and palaeotaxodont pelecypods; and 3) Total mollusks 11 both contain Tetradium Dana, 1846. The major differences are: 1) the orthid brachiopods 4 7 almost complete exclusion of nonmollusks in the Tyrone Limestone strophomenid brachiopods 2 7 (USGS 6034-CO) and the greater diversity of nonmollusks in the Sal- rhynchonellid brachiopods 1 7 7 visa Bed, to the point where mollusks and brachiopods occur in almost spiriferid brachiopods 1 equal numbers, although there are 26 species of mollusks compared to Total brachiopods 8 ORDOVICIAN POLYPLACOPHORA FROM NORTH AMERICA 25

five species of brachiopods, with two species dominating the brachio- Grier probably accumulated in depths of less than 15 m of water" (Cress- pod fauna; 2) the exclusion of identifiable cephalopods in the Salvisa man, 1973, p. 21). Bed; and 3) the significant arthropod fauna in the Salvisa Bed repre- USGS 4959-CO and 5096-CO are dominated numerically by gastro- sented by five species of trilobites and seven species of ostracodes, pods and brachiopods. Mollusks are placed in 23 species. Of the 181 although in the Tyrone Limestone (D-1138-CO), a significant ostracode valves of pelecypods, 125 belong to the palaeotaxodont species Deceptrix fauna occurs with Spicuchelodes cressmani. cf. D. hartsvillensis. The gastropod fauna is dominated by the species Open-marine deposits.—^The sequence of rock units from the Curds- Loxoplocus (Lophospira) burgenensis Ulrich and Scofield, 1897; speci- ville Limestone Member through the Grier Limestone Member, Lexington mens were not counted, but were estimated as some hundreds of individ- Limestone, represents a transgression and deeping water (Cressman, uals. 1973). "The basal Curdsville bioclastic calcarenites and calcirudites were Brachiopods are represented by six species. Of the 821 brachiopod deposited in agitated water of the inner infralittoral zone. The disconfor- specimens, 250 are Rhynchotrema increbescens (Hall, 1847) and 450 are mity [between the older Tyrone and the younger Curdsville] then resulted Zygospira sp. from a slight deepening of the water which permitted the formation of waves of sufficient energy to erode the uppermost part of the Tyrone OBSERVATIONS Limestone and to break, sort, and transport the debris of fossils that could thrive in the more aerated water" (Cressman, 1973, p. 13). 1. In all three environments of deposition, moUuscan diversity is greater "The bioclastic calcarenite and calcirudite, crossbedded in part, [of the than brachiopod diversity. lower Curdsville] indicate formation in a high-energy environment, prob- In the nearshore subtidal environment, mollusks and brachiopods ably in water above surf base; however, [the lower Curdsville] also con- total 38 species, of which mollusks represent 94.74%. Of the total tains beds of calcisiltite, unabraded fossils, and articulated pelecypods, number of species present, mollusks represent 83.72%; brachiopods all indicative of a low energy environment. The most likely explanation 4.65% of the species. of the frequent [changes in bed lithologies] is that the coarser fragments In comparing mollusk versus brachiopod species diversity in the accumulated in small bars while the finer material was deposited in to- other shell beds studied, the numbers are: Salvisa Bed, mollusks pographic lows. Migration of the bars would have resulted in interbedding 84.38%; lower Curdsville, mollusks 66.67%; upper Curdsville, mol- of coarser and finer grained sediments" (Cressman, 1973, p. 14). The lusks 57.89%; Grier Limestone, mollusks 79.31%. thin discontinuous bentonites in the Curdsville are thought to be the 2. Cephalopods are only significant in the nearshore subtidal deposits, source of the silica that replaced the calcium carbonate of the fossils. where they represent 50% of the mollusk species present, but only USGS 5101-CO and 6134-CO are from the lower Curdsville at the 3.38% of the identifiable specimens. start of the transgression and are shallow open-marine deposits. This part 3. In all three environments of deposition, pelecypod faunas are domi- of the Curdsville is: "crystalline, bioclastic limestones that consist of nated by palaeotaxodonts and pteriomorphs, to almost the complete calcirudites, crossbedded and ripple-marked calcarenites, and laminated exclusion of the other known subclasses. calcisiltites. The grains are abraded sorted fragments of crinoids, bryo- 4. In all three environments of deposition, pelecypod faunas are domi- zoans, and brachiopods. Whole and broken brachiopod and mollusk shells nated by a single species. are common, and many silicified" (Cressman, 1973). MoUusks are dom- 5. Gastropods are coequal to, or exceed, the pelecypods in number of inant, in both numbers and diversity. Brachiopod diversity is high but the specimens in the shallow subtidal and deeper water open-marine en- number of specimens is small compared to the moUusks. vironments of deposition. Mollusks are placed in 20 species. The pelecypods are represented by 6. In the lagoonal and open-marine environments of deposition, the bra- 605 valves, of which 466 belong to the pteriomorph species Vanuxemia chiopod fauna is dominated by one or two species. gibbosa Ulrich, 1894a. The univalves were not counted. 7. In all three environments of deposition, chitons show low diver- Brachiopods are represented by 10 species, but only the eight species sity. in USGS 5101-CO were counted. 8. In none of the collections of chiton plates was there a ratio of 1:6:1 The remaining identified fauna is two species of corals and two species of head, intermediate, and tail plates. of echinoderms. The upper Curdsville "consists of irregularly bedded fossiliferous lime- FAUNAL LISTS AND SPECIES COUNTS stone interbedded with bioclastic calcarenite" (Cressman, 1973, p. 13, 14). "The upper Curdsville was probably deposited in deeper water be- USGS 6034-CO cause none of the shell beds are composed of broken and abraded shells, MOLLUSCA as occurs in some beds of the lower Curdsville. This vertical sequence Polyplacophora:—Spicuchelodes cressmani n. sp., 79 intermediate of rock types in the Curdsville, high-energy, shallow-water deposits in plates; Amblytochiton incomptus n. sp., nine intermediate plates, one head the lower part grading to deeper water deposits at the top, record a marine plate; one tail plate. transgression" (Cressman, 1973, p. 14). Pelecypoda:—A total of 2,256 disarticulated valves of palaeotaxodonts USGS 6131-CO is from the upper Curdsville Limestone Member, Lex- and pteriomorphs were found. The most abundant species is the pteriom- ington Limestone. Only the chiton and pelecypod specimens were count- orph Cyrtodonta subovata Ulrich, 1894a, 2,000 valves. Other pteriom- ed. A total of approximately 2,000 specimens were obtained from this orphs are: Vanuxemia gibbosa Ulrich, 1894a, 180 valves; Vanuxemia sp. collection; of these, 1,312 were pelecypods. The pteriomorph Vanuxemia indet., 12 fragments; Cleionychia sp., 25 valves. gibbosa was represented by 1,247 valves. Mollusks are placed in 11 spe- The palaeotaxodonts are: Ctenodonta nasuta (Hall, 1847), 33 valves; cies. Brachiopods are represented by eight species. C. logani Salter, 1859, one valve; Tancrediopsis sp., 17 valves. The Grier Limestone Member of the Lexington Limestone is a deeper Bellerophontina:—Salpingostoma kentuckyense Ulrich and Scofield, water open- marine deposit compared to the Curdsville Limestone Mem- 1897, 45 specimens; Pterotheca expansa (Emmons, 1842), three speci- ber Of the environment of deposition of the Grier Limestone Member, mens. Cressman (1973, p. 19-20) stated: "The abundance, kind, and state of "Nautiloida":—The 180 specimens of nautiloids were studied by Frey preservation of the fossils and the poor sorting of the limestone indicate (1995). He listed 18 species-three ellesmerocerids, six othocerids, one that most of the member was deposited in shallow, aerated, only mod- endocerid, three actinocerids, one tarphycerid, and four oncocerids. erately agitated water Much of the sea floor was populated by a mixed Gastropoda:—The approximate number of identifiable gastropods is bryozoan-crinoid fauna. The lenticular and nodular beds very closely re- 2,500 specimens; however, they have not been studied systematically. semble structures in recent sediments that are attributed to churning by Wagner (1990) examined the lophospirids, but he did not publish the burrowing organisms. Some of the pelecypods were infaunal, but most results. of the churning must have been by soft-bodied organisms that left no OTHER FAUNA fossil record." "Currents were sufficient to supply oxygen and food to the large fauna The nonmoUuscan fauna from USGS Collection 6034-CO is sparse and of suspension feeders, distribute crinoid columnals, and winnow some of was not counted. Included in the fauna is the brachiopod Camerella sp. the carbonate mud, but they were too weak to thoroughly comminute and (identified by R. B. Neuman), the corals Lambeophyllum? sp. (Elias, sort the skeletal debris or to remove all of the lime mud. Much of the 1983) and Tetradium sp., and indeterminate ostracodes. 26 HOARE AND POJETA

USGS D-1138-CO USGS 6134-CO MOLLUSCA MOLLUSCA Polyplacophora:—Spicuchelodes cressmani n. sp., 145 intermediate Polyplacophora:—Helminthochiton blacki n. sp., 15 intermediate plates, one head plate, two tail plates. plates, one tail plate. Pelecypoda:—Tancrediopsis sp., four specimens; Cyrtodonta sp., one Pelecypoda:—The faunule is dominated by one pteriomorph species; specimen. Vanuxemia gibbosa, 415 valves; Cyrtodonta subovata, 59 valves; Cten- Gastropoda (identified by E. L. Yochelson):—Ninety-three specimens odonta aff. C. nasuta, four valves; C aff. C. longa, one valve; Tancre- assigned to the genera Loxoplocus {Lophospird) sp, lEotomaria sp., Hel- diopsis sp., 34 valves. icotoma sp., Trochomena {Trochomend) sp., T. (Trochomenella) sp., Hol- Gastropoda:—(identified by E. L. Yochelson, not counted); Loxoplocus opea sp., and Murchisonia (Hormotoma) sp. {Lophospira) sp. indet.; cf. Omospira sp.; IRaphistoma sp.; ILiospira sp.; Helicotoma sp. indet.; Murchisonia (Hormotoma) sp. indet. OTHER FAUNA Monoplacophora/Bellerophontina (identified by E. L. Yochelson, not Brachiopoda (identified by R. B. Neuman):—Sowerbyella sp., two counted):—Cyrtolites sp. indet; Sinuites sp. indet.; Carinaropsis sp, in- specimens. det.; cf. Tropidodiscus sp.; cf. Bucania sp. Ostracoda (identified by J. M. Berdan and Berdan (1984), not counted): OTHER FAUNA —Eoleperditia fabulites (Conrad, 1843), Cerartoleperditia kentuckyensis (Ulrich, 1891), Leperditella spp., Aptochilina sp., and Krausella sp. Brachiopoda (identified by R. B. Neuman, not counted):—Camerella? Corals (identified by W. A. Oliver):—Tetradium cf. T. cellulosum and sp.; Dalmanella sp.; Pionodemal sp.; Platystrophia amoena longicardi- a streptelasmid. nalis McEwan, 1919; Rafinesquina sp.; Rhynchotrema cf. R. increbescens (Hall, 1847); Zygospira sp. USGS 5015-CO, 6915-CO, AND 6916-CO Echinodermata (Parsley, 1981):—Amygdalocystites fiorealis Billings, MOLLUSCA 1854, one specimen. Receptaculids:—Two specimens. Polyplacophora:—Listrochiton weiri n. sp., 449 intermediate plates, six head plates, 12 tail plates; Alastega martini n. sp., 204 intermediate plates, USGS 5101-CO one head plate, two tail plates. MOLLUSCA Pelecypoda:—A total of 1,125 disarticulated valves, dominated by pteriomorphs and palaeotaxodonts, were counted. The pteriomorphs are: Polyplacophora:—Helminthochiton blacki n. sp., two intermediate Cyrtodonta subovata, three valves; C. grandis (Ulrich, 1890c), 252 valves. valves; Vanuxemia aff. V. sardesoni (Ulrich, 1892a), 97 valves; Ambon- Pelecypoda:—Vanuxemia gibbosa, 51 valves; Cyrtodonta subovata, ychia cf. A. ulrichi (Pojeta, 1962), 16 valves; Palaeopteria aff. P. parvula seven valves; Lyrodesma cf. L. acuminatum Ulrich, 1894a, one valve. Whiteaves, 1897, one valve. Gastropoda (identified by E. L. Yochelson):—Liospira sp. indet., one The palaeotaxodonts are: Ctenodonta nasuta, 119 valves; C. aff. C. specimen; Loxoplocus {Lophospira) sp. indet., two specimens. longa (Ulrich, 1892b), 43 valves; Deceptrix aff. D. hartsvillensis Safford, OTHER FAUNA 1869, 546 valves. The remaining 48 specimens are assigned to: Colpomya sp., eight Brachiopoda (identified by R. B. Neuman):—Dinorthispectinella (Em- valves; Lyrodesma sp., one valve; Whiteavesia sp., four valves; and a mons, 1842), two specimens; Hesperorthis sp., six specimens; Platystro- number of modiomorphid fragments. phia sp., two specimens; Rafinesquina sp., one specimen; Rhynchotrema Rostroconchia:—Bransonia cressmani Pojeta and Runnegar, 1976, 25 sp., 25 specimens; Sowerbyella curdsvillensis (Foerste, 1912), six speci- specimens. mens; Zygospira sp., 10 specimens; dalmanellid indet., three specimens. Gastropoda (identified by E. L. Yochelson, for collection 5015-CO Corals (identified by W A. Oliver, not counted):—Streptelasmid; ?A'yc- only):—Clathrospira cf. C. subconica (Hall, 1847), three specimens; Lox- topora sp. oplocus (Lophospira) humilus Ulrich and Scofield, 1897, eight speci- Echinodermata (Branstrator, 1979):—Stenaster cf. S. obtusus (Forbes, mens; L. (L.) medialis Ulrich and Scofield, 1897, four specimens; L. (L.) 1848), three brachial fragments. obliqua Ulrich and Scofield, 1897, 75 specimens; IStrophostylus sp. in- det., two specimens. USGS 6131-CO Monoplacophora/Bellerophontina (identified by E. L. Yochelson for MOLLUSCA collection 5015-CO only) (monographed by Wahlman, 1992):—IPilina Polyplacophora:—Helminthochiton blacki n. sp., 30 intermediate sp. indet., five specimens; Cyrtolites retrorsus Ulrich and Scofield, 1897, plates. four specimens; ITropidodiscus cf. T. subacutus (Ulrich and Scofield, Pelecypoda:—Vanuxemia gibbosa, 1,247 valves; Cyrtodonta subovata, 1897), 10 specimens; Bucania subalata Ulrich and Scofield, 1897, 15 seven specimens; Similodonta aff. S. hermitagensis Bassler, 1932, 52 specimens; Bucanopsis carinifera Ulrich and Scofield, 1897, 14 speci- specimens; Tancrediopsis cuneata (Hall, 1856), five specimens; Cteno- mens; Sphenosphaera clausus (Ulrich and Scofield, 1897), 50 specimens; donta cf. C. nasuta (Hall, 1847), one specimen. Carinaropsis cymbula (Hall, 1861), 15 specimens. Gastropoda (identified by E. L. Yochelson, not counted):—Loxoplocus OTHER FAUNA {Lophospira) cf. L. (L.) medialis; Liospira sp. indet.; Murchisonia {Hor- motoma) sp. indet. Brachiopoda (identified by R.B. Neuman for 6915-Co and 6916-CO) Monoplacophora/Bellerophontina (identified by E. L. Yochelson, not (monographed by Alberstadt, 1979; Howe, 1979; and Walker, 1982):— counted):—IBucania sp. indet; Sphenospira sp. indet. Hebertella frankfortensis Foerste, 1909, 24 specimens; Orthorhynchula linneyi, 1,444 specimens; Zygospira sp., 244 specimens; Platystrophia OTHER FAUNA sp., seven specimens; Rafinesquina sp., three specimens. Brachiopoda (identified by R. B. Neuman, not counted):—Dalmamella Corals (identified by W. A. Oliver Jr, not counted):—Tetradium cf. T. fertilis (Ulrich in Bassler, 1909); Dinorthis pectinella; Hesperorthis sp.; fibratum Safford, 1856; T. cf. T. ulrichi Bassler, 1932. Platystrophia amoena McEwan, 1919; Rafinesquina sp; Rhynchotrema Trilobites (Ross, 1967, 1979), not counted):—Isotelus gigas Dekay, cf. R. increbescens; Sowerbyella curdsvillensis; Zygospira sp. 1824; Gravicalymene hageni Ross, 1967; Decoroproetus sp.; Primaspis sp.; Acidaspis? sp. FAUNA OF COLLECTION USGS 4959-CO Ostracoda (Warshauer and Berdan, 1982; Berdan, 1984):—Bivia tum- MOLLUSCA idula (Ulrich, 1891) (not counted); B. linneyi (Ulrich, 1891), 11 speci- mens; Teichochilina jonesi (Wetherby, 1881) (not counted); Ceratopsis Polyplacophora:—Helminthochiton blacki n. sp., two intermediate asymmetrica Warshauer and Berdan, 1982, one specimen and many frag- plates. ments; C. intermedia Ulrich, 1894b, seven specimens and many frag- Pelecypoda:—Cyrtodonta subovata, 12 valves and many fragments; ments; Bolopisthia sculptilis (Ulrich, 1890b), two specimens; Pheloby- Vanuxemia gibbosa, seven valves and many fragments;. Ambonychia sp. thocypris cylindrica (Hall, 1871), 10 specimens. indet., five valves; Ctenodonta aff. C. logani, nine valves. ORDOVICIAN POLYPLACOPHORA FROM NORTH AMERICA 27

Scaphopoda:—Rhytiodentalium kentuckyensis Pojeta and Runngear, Pelecypoda:—Deceptrix cf. D. hartsvillensis, 125 specimens; Cteno- 1979, eight specimens. donta socialis Ulrich, 1894a, two specimens; Ambonychia radiata Hall, Gastropoda (identified by E. L. Yoclielson):—Loxoplocus (Lophospira) 1847, 10 specimens; Cycloconcha aff. C. ovata Ulrich, 1893, one spec- burgenensis Ulrich and Scofield, 1897, 30 specimens; Murchisonia (Hor- imen; Modiolodon oviformis (Ulrich, 1890a), two specimens and 30 frag- motoma) salteri nitida Ulrich and Scofield, 1897, 50 specimens. ments. Monoplacophora/Bellerophontina (identified by E. L. Yochelson):— Nautiloids (Frey, 1995):—Isorthoceras albersi (Miller and Faber, Bucania sp. indet. (not counted); Bucanopsis carinifera, four specimens; 1894), two specimens. Sphenosphaera clausus, seven specimens; Carinaropsis cymbula, two Gastropoda (identified by E. L. Yochelson):—Liospira progne (Bill- specimens. ings, 1860) (not counted); Clathrospira subconica, one specimen; Lox- oplocus {Lophospira) burgenensis, hundreds of specimens; Holopea sp., OTHER FAUNA one specimen. Brachiopoda (identified by R. B. Neuman):—Hebertella frankfortensis, Monoplacophora/Bellerophontina (identified by E. L. Yochelson):— 10 specimens; Lingulellal sp., four specimens; Rafinesquina sp., 50 spec- Sphenosphaera troosti burgenensis (Ulrich and Scofield, 1897), nine imens; Rhynchotrema increbescens, 250 specimens; Zygospira sp., 250 specimens; S. clausus, 10 specimens; Cyrtolites retrorsus, two specimens; specimens. Bucania cf. B. subalata, two specimens; Bucanopsis carinifera, three specimens. FAUNA OF COLLECTION USGS 5096-CO OTHER FAUNA MOLLUSCA Brachiopoda (identified by R. B. Neuman):—Hebertella frankfortensis, Polyplacophora:—Helminthochiton blacki n. sp., three intermediate 35 specimens; Pionodema sp., 10 specimens; Rafinesquina sp., 12 spec- plates. imens; Zygospira sp., 200 specimens.