Middle and Upper Ordovician Nautiloid Cephalopods of the 

Cincinnati Arch Region of Kentucky, Indiana, and Ohio

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P

Prepared in cooperation with the Commonwealth of Kentucky, 

University of Kentucky, and Kentucky Geological Survey
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Middle and Upper Ordovician Nautiloid Cephalopods of the 

Cincinnati Arch Region of Kentucky, Indiana, and Ohio

By ROBERT C. FREY

CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY 

AND NEARBY STATES

Edited by JOHN POJETA,JR.

U. S. GEOLOGICAL SURVEY PROFESSIONAL PA PER 1066-P

Prepared in cooperation with the Commonwealth of Kentucky, 

University of Kentucky, and Kentucky Geological Survey

Stratigraphic distribution, pakoecology, biogeography, and 

systematic paleontology of 50 species of Ordovician nautiloids 

from the midcontinent

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1995
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

GORDON P. EATON, Director

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government.

Library of Congress Cataloging in Publication Data

Frey, Robert C.

Middle and Upper Ordovician nautiloid cephalopods of the Cincinnati arch region of

Kentucky, Indiana, and Ohio / by Robert C. Frey. 

p. cm. — (U.S. Geological Survey professional paper; 1066-P) (Contributions to the

Ordovician paleontology of Kentucky and nearby states) 

Includes bibliographical references and index. 

Supt. of Docs, no.: 119.16:1066-P 

1. Nautiloidea, Fossil—Kentucky. 2. Nautiloidea, Fossil—Indiana. 3. Nautiloidea,

Fossil—Ohio. 4. Paleontology—Ordovician. 5. Animals, Fossil—Kentucky.

6. Animals, Fossil—Indiana. 7. Animals, Fossil—Ohio. I. Title. II. Series.

III. Series: Contributions to the Ordovician paleontology of Kentucky and nearby states. 

QE807.N4F74 1995

564'.52'0977—dc20 94-27353

CIP

For sale by U.S. Geological Survey, Information Services 

Box 25286, Federal Center, Denver, CO 80225
CONTENTS

Abstract.............................................................................................

Introduction......................................................................................

Acknowledgments ...........................................................................

Regional Ordovician Paleogeographic Setting.............................

Ordovician Lithostratigraphy in the Cincinnati Arch Region....

Middle Ordovician Champlainian Provincial Series

Lithostratigraphy in Kentucky ........................................

High Bridge Group.................................................................

Lexington Limestone..........................................'...................

Upper Ordovician Cincinnatian Provincial Series

Lithostratigraphy .............................................................

Edenian Stage.........................................................................

Maysvillian Stage...................................................................

Richmondian Stage................................................................

Distribution and Fauna! Affinities of Ordovician Nautiloids in

the Cincinnati Arch Region.........................

Nautiloid Fauna of the Tyrone Limestone......

Rocklandian Nautiloid Extinction....................

Nautiloid Fauna of the Lexington Limestone.,

Page 

PI

2

3

3

4

6

6

6

9

9

10

10

12

15

Distribution and Fauna! Affinities of Ordovician Nautiloids in

the Cincinnati Arch Region—Continued 

Nautiloid Fauna of the Cincinnatian Provincial Series .........

Edenian Nautiloid Fauna.................................................

Maysvillian and Early Richmondian Nautiloid Fauna. 

Nautiloid Fauna of the Leipers Limestone....................

Middle and Late Richmondian Nautiloid Faunas.........

Late Ordovician Extinction Event............................................

Nautiloid Taphonomy...........................................................................

Nautiloid Biostratinomy............................................................

Silicified Nautiloids....................................................................

Nonsilicified Nautiloids.............................................................

Nautiloid Classification.......................................................................

Systematic Descriptions......................................................................

Systematic Paleontology.....................................................................

References Cited...................................................................................

Appendix: Locality Register................................................................

Index......................................................................................................

Page

P16

16

17

19

19

20

21

21

22

22

23

24

27

113

120

125

ILLUSTRATIONS

	[Plates follow index)

PLATE 1. Cartersoceras and Murrayoceras

2. Pojetoceras and Pleurorthoceras

3. Ordogeisonoceras and Geisonoceras

4. Proteoceras and Treptoceras

5-8. Treptoceras

9. Monomuchites

10. Isorthoceras

11. Polygrammocerast

12. Polygrammoceras, Anaspyroceras, and Gorbyoceras

13. Richmondoceras

14. Cameroceras

15. Vaginoceras

16. Triendocerast and Actinoceras

17. Actinoceras

18. Ormoceras, Deiroceras, and Orthonybyoceras

19. Plectoceras, Trocholites, and Oncoceras

20. Oncoceras, Bdoitoceras, Maelonoceras, Laphamoceras, Allumettoceras, Augustoceras, and Manitoulinoceras

21. Diestoceras and Beloitoceras

22. Diestoceras and Beloitoceras

III
IV CONTENTS

Page

FIGURE 1. Map showing Middle Ordovician paleogeography in Eastern North America............................................................................................ P4

2,3. Charts showing:

2. Ordovician lithostratigraphy in the Cincinnati arch region............................................................................................................. 5

3. Lexington Limestone lithostratigraphy............................................................................................................................................... 7

4,5. Diagrams showing:

4. External features of nautiloids............................................................................................................................................................ 25

5. Internal features of nautiloids.............................................................................................................................................................. 26

6. Drawing showing internal features of Cartersoceras shideleri........................................................... ......................................................... 29

7. Bivariate plot of measurements made on specimens of Pojetoceras floweri and Orthoceras regularis .......................................... 34

8. Drawing showing internal features of Pojetoceras fioweri .............................................................................................................. 36

9-12. Bivariate plot of measurements made on specimens of:

9. Pleurorthoceras clarksvillense and P. seUcirkense....... ........................................................................................................ 38

10. "Orthoceras" amplicameratum .......................................................................................................................................... 41

11. Middle Ordovician species of Proteoceras...... ..................................................................................................................... 44

12. Cincinnatian species of Treptoceras....... ............................................................................................................................. 48

13. Drawings comparing adapical siphuncle segment shape for specimens of Treptoceras duseri and T.fosteri ................................. 49

14-16. Bivariate plots of measurements made on specimens of Treptoceras duseri, T.fosteri, and T. cincinnatiensis ............................ 50

17. Drawings comparing external ornament in species of Monomuchites from the USGS 6034-CO collection in the Tyrone

Limestone............................................................................................................................................................................^ 57

18-19. Bivariate plots of measurements made on specimens of:

18. Isorthoceras... ..................................................................................................................................................................... 61

19. Richmondoceras brevicameratum and Treptocerasfosteri.. .............................................................................................. 72

20. Drawings comparing cross-sectional features of specimens of Cameroceras rowenaense, C. trentonense, and C. inaequabile..... 75

21. Bivariate plot of measurements made on specimens of Cameroceras rowenaense and C. trentonense .......................................... 76

22. Diagram of siphuncular structure in Triendocerasf davisi ............................................................................................................. 80

23. Diagrams showing important morphological features used to distinguish species ofActinoceras .................................................. 83

24. Bivariate plots of measurements made on specimens of Ormoceras ferecentricum, O. aUumettense, and O. cannonense............ 87

25. Drawing reconstructing the complete shell of Plectoceras cf. P. carletonense from the USGS 6034-CO collection in the Tyrone

Limestone................................................................................................................................................................................................... 93

26. Drawings of the apertures of species of Diestoceras.. ..................................................................................................................... 107

TABLES

Page

TABLE 1. Distribution of species of nautiloids in the Tyrone Limestone, the Lexington Limestone, and the Clays Ferry Formation

in the Blue Grass region of Kentucky....................................................................................................................................................... Pll

2. Comparison of the 6034-CO nautiloid fauna from the Tyrone Limestone with nautiloid taxa from coeval strata exposed in

Eastern and Central North America.......................................................................................................................................................... 12

3. List of Middle Ordovician (Blackriveran and Rocklandian) nautiloid genera from Eastern North America.......................................... 14

4. Nautiloid species from the Strodes Creek Member of the Lexington Limestone, north-central Kentucky............................................. 17

5. Distribution of species of nautiloids from the Cincinnatian Provincial Series in the Cincinnati arch region......................................... 18

6-11. Comparisons of the morphological features of:

6. Baltoceratids Cartersoceras and Murrayoceras......... ...................................................................................................................... 30

7. Cincinnatian species of Treptoceras. ................................................................................................................................... 48

8. Species of Monomuchites from the Middle Ordovician Rocklandian Stage of Eastern North America................................... 56

9. Species of Cameroceras from the Middle Ordovician of New York and the Upper Ordovician of the Cincinnati arch

region of Kentucky, Indiana, and Ohio......................................................................................................................................... 76

10. Middle Ordovician (Blackriveran and Rocklandian) species ofActinoceras from Eastern North America............................. 84

11. Cincinnatian species of Diestoceras................................................................................................................................................... 106
CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS 

OF THE CINCINNATI ARCH REGION OF KENTUCKY, INDIANA,

AND OHIO

By ROBERT C. FREY

ABSTRACT

This paper describes the taxonomy, phylogenetic relations, biostratigraphy, biogeography, and paleoecology of 50 species and 30 genera 

of Middle and Upper Ordovician (Rocklandian to Richmondian) nautiloid cephalopods from the Cincinnati arch region of Kentucky, Indiana, 

and Ohio. The study centers on collections of silicified material made by 

the U.S. Geological Survey and the Kentucky Geological Survey during 

the geologic mapping program of the State of Kentucky. This material, 

primarily of Middle Ordovician age, is augmented by additional nonsilicified specimens from the Upper Ordovician Cincinnatian Provincial 

Series in Kentucky, Indiana, and Ohio.

Silicifed collections from the Ordovician of Kentucky yielded a 

number of more or less complete, uncrushed, nautiloid specimens that 

commonly preserve the details of the shell's external ornament. Key 

internal features, such as connecting rings and septal necks, are often 

lacking, complicating systematic placement of some orthocerid taxa. 

Critical camera! and endosiphuncular deposits are, however, well preserved in some actinocerid and endocerid taxa Well-preserved nautiloids from the Cincinnatian Provincial Series consist primarily of 

calcite-replaced internal molds from clay shale units in Indiana and 

Ohio, and from the Leipers Limestone in south-central Kentucky. Additional well-preserved, but fragmentary nautiloids also occur in the Hitz 

Limestone Member of the Saluda Formation (Richmondian) in southeastern Indiana and in equivalent rocks in adjacent portions of northern 

Kentucky.

Nautiloids from the Tyrone Limestone (Middle Ordovician, Rocklandian) in central Kentucky consist of 18 species belonging to 14 genera, representing 6 nautiloid orders. This fauna is characterized by an 

abundance of small longicones, namely, the baltoceratids Cartersoceras 

and Murrayoceras and the orthocerids Pojetoceras and Proteoceras, 

plus the large actinocerid Actinoceras, the large endocerid Vaginoceras, 

the annulated orthocerid Monomuchites, and a number of oncocerids: 

species of Oncoceras, Beloitoceras, Maelonoceras, and Laphamoceras. 

The coiled tarphycerid Plectoceras is also present, but typically is represented by fragmentary specimens.

Nautiloid faunas in the overlying Lexington Limestone (Middle 

Ordovician, Kirkfieldian and Shermanian) in central Kentucky are less 

diverse, being most abundant in collections from low-energy, deeperwater fades in the Logana Member and Grier Limestone Member.

Manuscript approved for publication May 31,1994.

Faunas consist of abundant small longicones, primarily the orthocerid 

Isorthoceras, and lesser numbers of the orthocerids Gorbyoceras and 

Polygrammoceras, the endocerid Cameroceras, and the oncocerids 

Oncoceras and Attumettoceras. Nautiloid faunas increase in diversity 

toward the top of the Middle Ordovician section in northern Kentucky. 

Isorthoceras occurs in association with the orthocerids Ordogeisonoceras and Treptoceras and with the small coiled tarphycerid Trocholites 

in the Point Pleasant Tongue of the Clays Ferry Formation.

A low-diversity nautiloid fauna consisting of the small orthocerid 

Treptoceras and the endocerid Triendoceras'? occurs in the basal portions of the succeeding Cincinnatian Provincial Series in the KentuckyIndiana-Ohio area (Kope Formation, Edenian, and Maysvillian). Abundant well-preserved specimens of several species of the orthocerid Treptoceras and the large endocerid Cameroceras occur in younger 

Maysvillian to early Richmondian blocky claystone fades within the 

Fairview, Grant Lake, and Bull Fork Formations. A diverse nautiloid 

fauna characterized by the abundance of the large discosorid Faberoceras and the slender oncocerid Augustoceras, as well as the ubiquitous 

Treptoceras and Cameroceras occurs in the Leipers Limestone (Maysvillian) in the valley of the Cumberland River in south-central Kentucky.

Younger Richmondian nautiloid faunas in the upper part of the 

Cincinnatian Provincial Series in the region consist of a diverse set of 

immigrant taxa, more characteristic of older or equivalent carbonate 

fades exposed in the Western United States, Canada, and northern 

Greenland. These faunas are species of the orthocerids Gorbyoceras and 

Pleurorthoceras, the ascocerid Schuchertoceras, the actinocerids 

Armenoceras and Lambeoceras, the coiled tarphycerid Charactoceras, 

and numerous oncocerids. The latter include Beloitoceras, Neumatoceras, Manitoidinoceras, Oonoceras, and Diestoceras. These taxa are 

common to fades within the Saluda, Whitewater, upper part of the Bull 

Fork, and Drakes Formations in Indiana, southwestern Ohio, and northcentral Kentucky.

Several families within the order Orthocerida are redefined, and 

the diagnostic morphologic features of the endocerids Cameroceras and 

Vaginoceras are clarified. Three new genera, all members of the order 

Orthocerida, are described. These are Pojetoceras, type species P.Jloweri, new species, from the Tyrone Limestone in Kentucky; Ordogeisonoceras, type species O. amplicameratum (Hall), from the Point Pleasant 

Tongue of the Clays Ferry Formation in northern Kentucky, and Richmondoceras, type species R. brevicameratum n. sp., from the Saluda 

Formation in Indiana and the upper part of the Bull Fork Formation in 

Ohio. Additional new species described here are Cartersoceras popei,

PI
P2 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

Monomuchites obliguum, M. annularis, and Oncoceras major, all from 

the Tyrone Formation in central Kentucky; Cameroceras rowenaense 

from the Leipers Limestone in south-central Kentucky; and Triendoceras1? davisi from the Kope Formation in northern Kentucky.

Nautiloids from Middle and Upper Ordovician strata in the Cincinnati arch region can be divided into four major time-bounded faunas, 

separated by regional environmental and (or) biological events. A major 

extinction of nautiloid taxa coinciding with a widespread sea-level 

regression and a catastrophic volcanic event separates the diverse, tropical "Black River" fauna (Chazyan to Rocklandian) from the 

species-poor "Trenton" fauna characteristic of the Lexington Limestone 

(Kirkfieldian and Shermanian). A regional transgressive event coupled 

with an increase in clastic sedimentation in the area led to the development of the "Cincinnatian" fauna characteristic of Edenian to early Richmondian strata across the area This fauna is superseded by the 

"Richmondian" fauna in the middle and late Richmondian, following 

another regional transgressive event and a shift to more carbonate-rich 

lithofacies. This fauna is an immigrant fauna that was derived from older 

Edenian and Maysvillian faunas characteristic of carbonate platform 

fades in western and arctic portions of North America This "Richmondian" fauna was terminated by the Late Ordovician mass extinction 

event, which is associated with the withdrawal of epeiric seas from the 

Cincinnati arch region.

INTRODUCTION

This study is one of a series of papers documenting 

the Ordovician fossils of the Cincinnati arch region of 

Kentucky, Indiana, and Ohio. Previous chapters in this 

series are the introductory chapter, Chapter A, by Pojeta 

(1979); papers on the articulate brachiopods, Neuman 

(1967), Chapter B (Alberstadt, 1979), Chapter C (Howe, 

1979), Chapter L (Pope, 1982), and Chapter M (Walker, 

1982); trepostome and cystoporate bryozoans, Chapter I 

(Karklins, 1984); corals, Chapter N (Elias, 1983); symmetrical univalved mollusks, Chapter O (Wahlman, 1992); trilobites, Ross (1967), Chapter D (Ross, 1979); ostracodes, 

Chapter H (Warshauer and Berdan, 1982); and Chapter J 

(Berdan, 1984); echinoderms, Chapter K (Parsley, 1981); 

edrioasteroids, Chapter E (Bell, 1979); asteroids, Chapter 

F (Branstrator, 1979); and a discussion of conodont faunas and their biostratigraphy in the region, Chapter G 

(Sweet, 1979).

This chapter describes the nautiloid cephalopod faunas of the Middle Ordovician (Rocklandian) Tyrone Limestone and the overlying Middle Ordovician (Kirkfieldian 

and Shermanian) Lexington Limestone from the Blue 

Grass region of central and north-central Kentucky. Additional nautiloids from the Upper Ordovician Cincinnatian 

Provincial Series in northern Kentucky, the Cumberland 

region of south-central Kentucky, and portions of Indiana 

and southwestern Ohio are also described. An index map 

of the area of this report is presented by Pojeta (1979, 

fig. 3).

With a few notable exceptions, nautiloid cephalopods from the Ordovician section exposed in the study 

area, especially faunas from the Middle Ordovician

Tyrone Limestone and Lexington Limestone, have not 

been previously extensively studied in a comprehensive 

manner. S.A. Miller (1875) described and illustrated a 

number of species of "Orthoceras" and "Cyrtoceras" primarily from the Cincinnatian Provincial Series exposed in 

the Cincinnati, Ohio, area. Hall and Whitfield (1875) 

described the additional species, Orthoceras carleyi, O. 

duseri, O. turbidum, and Gomphoceras eos., from Upper 

Ordovician strata exposed in southwestern Ohio. James 

(1886) published a compendium of the described Ordovician cephalopod taxa from the Cincinnati area, consisting 

of brief descriptions and notations on the occurrence of 

these taxa within these rocks. Miller and Faber (1894) 

described Orthoceras ludlowense and O. aWersi from the 

Middle Ordovician rocks of north-central Kentucky and 

Gomphoceras indianense from Cincinnatian strata in 

Indiana. Cumings (1908) presented descriptions and illustrations of a number of the more common species of nautiloids that had been described from Upper Ordovician 

strata in Indiana over the previous half century. Foerste 

(1910) identified the endocerid Suecoceras inaequabile 

(Miller) from the Waynesville Formation in Ohio, 

described Orthoceras hammelli from the Hitz Limestone 

Member of the Saluda Formation in Indiana, and Orthoceras bilineatum-frankfortense and Orthoceras (Loxoceras} milleri from what he called the Trenton Limestone 

of the Blue Grass region of Kentucky. In a second paper, 

Foerste (1912) described Orthoceras tyronensis from the 

Tyrone Limestone in central Kentucky. Bassler (1915) 

included Ordovician nautiloids from the region in his 

index of Ordovician and Silurian fossils, borrowing 

heavily from a list of taxa and their occurrences provided 

by Nickles (1902). Foerste (1914a) described Orthoceras 

rogersensis from the "Cynthiana Formation" exposed at 

Rogers Gap in north-central Kentucky. Foerste published 

a number of papers through the 1920's and early 1930's, 

illustrating and redescribing a number of nautiloids from 

the Ordovician strata exposed in the area. The same 

author (Foerste, 1928b) erected the new genus Troedssonoceras and figured and described under this name a 

specimen from the Leipers Formation of south-central 

Kentucky. Foerste (1929b) figured the apical end of an 

endocerid from Richmondian rocks in Indiana and 

described and illustrated Trocholites faberi from the 

"Cynthiana Limestone" of north-central Kentucky.

The first modern systematic study of nautiloids from 

the region was the study by Foerste and Teichert (1930) 

describing actinocerid cephalopods from Kentucky and 

adjacent portions of Tennessee and Missouri. This paper 

provided detailed descriptions and photographic plates of 

six species of Actinoceras and one species of Ormoceras 

from the Tyrone Limestone in central Kentucky, one species each of Actinoceras and Deiroceras from the Curdsville Limestone Member of the Lexington Limestone in
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P3

the same area, and Ormoceras? covingtonense from the 

"Maysville Group" (Upper Ordovician) of northern Kentucky. Flower (1942) described an unusual nautiloid fauna 

from a lens within the Middle Ordovician "Cynthiana 

Limestone" exposed at the Poindexter Quarry in 

north-central Kentucky. This paper was followed by his 

classic monograph on nautiloid cephalopods from the 

Cincinnati area (Flower, 1946). This volume reviewed 

nautiloid systematics, the history of nautiloid study in the 

region, the distribution of nautiloids throughout the 

Ordovician strata exposed in the Kentucky-Indiana-Ohio 

area, and provided descriptions and photographic plates 

of numerous new and previously described nautiloid taxa. 

Flower's study concentrated on species from younger 

Cincinnatian rocks in the Cincinnati area, but omitted discussions of the abundant orthocerid and endocerid nautiloids present in these strata, deferring description and 

study of these forms to a later time.

Since the publication of Flower's monograph, very little has been published concerning the paleontology of 

nautiloids from the Ordovician of the KentuckyIndiana-Ohio area Flower (1955c) described trace fossils 

he ascribed to nautiloid activity from the "McMillan Formation" at Cincinnati, Ohio, and later (Flower, 1957b) 

described the paleoecology of several nautiloid assemblages from the Cincinnatian Provincial Series in southwestern Ohio. Aronoff (1979) documented the 

morphological distinctiveness of the actinoceroid Orthonybyoceras Shimizu and Obata, type species O. covingtonense from the Upper Ordovician of northern Kentucky, 

and the orthocerid Treptoceras Flower, type species T. 

duseri, from equivalent strata in southwest Ohio. Frey 

(1981) noted the presence of the aberrant orthocerid nautiloid Narthecoceras in Upper Ordovician rocks in southwestern Ohio and discussed its paleobiogeographic 

significance. Frey (1988, 1989) described the paleoecology of a well-preserved nautiloid fauna from the Treptoceras duseri shale unit in southwestern Ohio, illustrating 

a number of the taxa present.

ACKNOWLEDGMENTS

I thank John Pojeta of the U.S. Geological Survey 

(USGS) for his encouragement, support, and editorial 

assistance during the course of this study. Also, I express 

my appreciation to W.A. Ausich, S.M. Bergstrom, and the 

staff of the Department of Geological Sciences at Ohio 

State University for use of library and laboratory facilities. Special thanks go to C. Teichert for his comments 

concerning nautiloid systematics. J.A. Catalani, R.E. 

Crick, and W.C. Swadley critically read an earlier draft of 

this paper and offered many helpful suggestions that substantially improved its quality. M. Balanc developed and 

printed many of the photographs used here. Thanks also

go to W. Berry, University of California at Berkeley 

(UCal); J. Thompson at the U.S. National Museum 

(USNM); F. Escrivan of the Museum of Comparative Zoology (MCZ) at Harvard; N. Landman and M. Hinkley of the 

American Museum of Natural History (AMNH); J. Marak 

of the Limper Museum of Geology at Miami University 

(MU); and D. Meyer of the University of Cincinnati (UC) 

for the loan of specimens critical to the completion of this 

study. I also wish to acknowledge my debt of gratitude to 

members of USGS and Kentucky Geological Survey field 

parties, who collected much of the Kentucky silicified 

material in the 1960's, and to the late R.H. Flower and R.A. 

Davis of the College of Mt. St. Joseph, who initially assembled and organized the bulk of the collection of nautiloids 

described here.

REGIONAL ORDOVICIAN PALEOGEOGRAPHIC 

SETTING

The Ordovician strata exposed in the Cincinnati arch 

region of Kentucky, Indiana, and Ohio were deposited on 

the southeastern portion of a cratonic platform that made 

up much of the Laurentian continent in the early Paleozoic. Modern paleogeographic reconstructions for the 

Ordovician (Scotese and McKerrow, 1990) place the Kentucky-Indiana-Ohio area in tropical or subtropical latitudes, 20°-30°S of the Ordovician equator and within the 

"carbonate belt" (Witzke, 1990). For much of the Ordovician, this region was inundated by a shallow epicontinental seaway, its lithofacies, fossils, and sedimentary 

structures all indicating intertidal to subtidal marine conditions and maximum water depths of 82-98 ft (25-30 m).

The central Kentucky Blue Grass region was the site 

of nearly continuous, very shallow water, carbonate platform deposition throughout much of Ordovician time 

(Cressman, 1973; Cressman and Noger, 1976). Adjacent 

portions of the northern Kentucky-Indiana-Ohio area 

formed the shallow, northward-ramping margin of what 

has been termed the Lexington Platform by Mitchell and 

Bergstrom (1991) and gently sloped toward deeper water 

basins to the north and west (Cressman, 1973) (fig. 1). 

Throughout the Ordovician, a series of volcanic islandarcs collided with the eastern margin of the Laurentian 

continent, culminating in the Middle Ordovician Taconic 

orogeny. This resulted in the formation of a rising landmass that produced a clastic source area along the eastern margin of the continent (Bird and Dewey, 1970; 

Ettensohn, 1991). Vast quantities of detrital sediments 

were eroded from this Taconic landmass and were deposited as the Queenston delta, which spread clastic sediments north and west into adjacent epeiric sea-shelf areas 

(Denison, 1976). These clastic sediments, mostly fine silt 

and clay, began to appear in the Kentucky-Indiana-Ohio 

area in the late Middle Ordovician (Kirkfieldian) and
P4 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

- - - - -Z-L^^----------/1 .1.1.1.1

FIGURE 1.—Late Middle Ordovician (Kirkfieldian and Shermanian) 

paleogeography in Eastern North America (Laurentia). Volcanic island 

arcs occur in the Taconic foreland basin. Star symbol indicates 

probable source area for Deicke Bentonite bed (modified from 

Mitchell and Bergstrom, 1991).

increased throughout the succeeding Late Ordovician. 

This sediment influx resulted in the deposition of increasingly clastic lithofacies in the region, from the pure carbonates of the Middle Ordovician High Bridge Group to 

the dominantly mudstone facies at the top of the Upper 

Ordovician Cincinnatian Provincial Series.

In addition to the effects of tectonism in the east, 

sedimentation in the Cincinnati arch area in the Ordovician was affected by sea-level fluctuations that resulted in 

the development of at least three post-Tyrone Limestone 

transgressive-regressive cycles, at least one cycle during 

the deposition of the Middle Ordovician Lexington Limestone (Cressman, 1973) and two or three during the 

deposition of the Upper Ordovician Cincinnatian

Provincial Series (Hay, 1981; Tobin, 1982; Shrake and others, 1988).

ORDOVICIAN LITHOSTRATIGRAPHY 

IN THE CINCINNATI ARCH REGION

Ordovician rocks in the East-Central United States 

are exposed at the surface along a series of north-southtrending structural highs that extend across portions of 

central Tennessee, central Kentucky, western Ohio, and 

eastern Indiana. This north-south trend roughly parallels 

the trend of the Appalachian basin to the east. Wahlman 

(1992) used the term "Cincinnati arch" for this entire
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P5

Point Pleasant Tongue of Clays Ferry Formation

Bigby and Cannon 

Limestones 

undivided

FIGURE 2.—Ldthostratigraphic relations of Middle and Upper Ordovician stratigraphic units in the Cincinnati arch region of 

Kentucky, Indiana, Ohio, and Tennessee (modified from Wahlman, 1992; after Sweet, 1979).

structural trend. He noted that the arch consisted of five 

primary structural elements. These are, from north to 

south, the Kankakee arch of Indiana and the Flndlay arch 

of Ohio, which merge near Cincinnati; the Jessamine 

dome in central Kentucky; the Cumberland sag of the 

Kentucky-Tennessee border; and the Nashville dome of 

central Tennessee. The nautiloid faunas described here 

come from the Ordovician strata exposed in the Cumberland sag in south-central Kentucky, in the vicinity of the 

Jessamine dome in central Kentucky, and northward from 

the tristate region of northern Kentucky, southeastern 

Indiana, and southwestern Ohio.

Specifically, nautiloid faunas described here were 

collected from the Tyrone Limestone of the Middle Ordovician High Bridge Group and the overlying Middle-Upper 

Ordovician Lexington Limestone, both exposed in the 

Inner Blue Grass region of central Kentucky. Additional 

nautiloid specimens are described from the Upper Ordovician Cincinnatian Provincial Series exposed in northern 

Kentucky and adjacent portions of Indiana and Ohio.

These consist of nautiloids from the Clays Ferry and Kope 

Formations in northern Kentucky; the Leipers Limestone 

in south-central Kentucky; the Fairview, Grant Lake, and 

Bull Fork Formations in southwestern Ohio; and the Dillsboro Formation, the Saluda Formation, and the Hitz Limestone Member of the Saluda Formation in southeastern 

Indiana (fig. 2). Brief descriptions of most of these lithostratigraphic units are found in the work by Pojeta (1979). 

More detailed descriptions of the Tyrone Limestone are 

found in Cressman and Noger (1976), descriptions of the 

various members of the Lexington Limestone in Cressman (1973), and descriptions of a majority of the Upper 

Ordovician lithostratigraphic units are in Weir and others 

(1984). Wahlman (1992) also gave an extensive account of 

the regional Ordovician lithostratigraphy and nomenclatural history of these stratigraphic units. The present 

work has only a broad overview of Ordovician lithostratigraphy and depositional environments across the 

northern Cincinnati arch region during the time of deposition of the Tyrone Limestone, the Lexington Limestone,
P6 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

and the Cincinnatian Provincial Series. An expanded 

description of the Tyrone Limestone is provided, as this 

formation was not extensively discussed by either Pojeta 

(1979) or Wahlman (1992), and it is the source of a large 

collection of nautiloids that is described here for the first 

time.

MIDDLE ORDOVICIAN CHAMPLAINIAN

PROVINCIAL SERIES LITHOSTRATIGRAPHY

IN KENTUCKY

HIGH BRIDGE GROUP

The High Bridge Group consists of 590-750 feet (ft) 

(180-229 meters (m)) of high-calcite limestone and dolostone and is exposed in the Inner Blue Grass region of 

Kentucky, primarily in the gorge of the Kentucky River 

and tributaries southwest of Lexington. The High Bridge 

Group, Middle Ordovician (Blackriveran and Rocklandian) in age, consists of the oldest strata exposed in Kentucky, hi ascending order, it consists of the 

shallow-marine, burrow-mottled Camp Nelson Limestone 

(Blackriveran); the intertidal dolostone and cryptalgal 

limestones of the Oregon Formation (Blackriveran); and 

the complex intertidal and shallow subtidal marine facies 

of the Tyrone Limestone (Blackriveran-Rocklandian). hi 

this study, only Tyrone Limestone taxa were examined.

Tyrone Limestone.—hi central Kentucky, the Tyrone 

Limestone is 55-155 ft (17-47 m) thick, thickening at the 

expense of the underlying dolostone and dense limestone 

of the Oregon Formation. Cressman and Noger (1976) and 

Kuhnhenn and others (1981) describe the formation as 

consisting of basal argillaceous dolomitic micrite (5-50 ft 

thick), followed by up to 50 ft of interbedded micrite, biopelmicrite, and biopelsparite, and an upper 40-ft interval 

consisting of interbedded argillaceous dolomitic micrite, 

cherty burrowed micrite, and biopelmicrite. The formation thins to the north and east within the central Kentucky area The Tyrone Limestone is conformable with 

the underlying Oregon Formation but has a disconformable contact with the overlying Lexington Limestone.

Two distinct altered volcanic ash beds occur in the 

upper half of the formation and can be correlated with 

similar K-bentonite beds in the upper Mississippi valley, 

central Tennessee, and the southern Appalachians (Huff 

and Kolata, 1990; Bergstrom and others, 1991). The Pencil 

Cave bentonite of drillers occurs about 21 ft (7 m) below 

the top of the formation and can be traced throughout the 

outcrop area (Cressman and Noger, 1976). The Mud Cave 

bentonite of driller, when present, marks a disconformity 

between the Tyrone and the overlying Lexington Limestone. The Mud Cave bentonite is locally eroded away at 

the contact with the Lexington Limestone, particularly in

the area north of the Kentucky River in central Kentucky 

(Cressman, 1973, fig. 7).

Cressman and Noger (1976) described the various 

lithofacies within the Tyrone Limestone as being representative of alternating supratidal islands (mud-cracked 

argillaceous dolostone), intertidal mudflats (burrowed 

micrite with ostracodes), and shallow, subtidal marine 

conditions (fossiliferous micrite and biopelsparite). The 

latter facies contains a fauna that consists of the coral 

Tetradium, bryzoans, gastropods, polyplacophorans, nautiloids, and pelecypods. Subtidal marine facies thicken to 

the south from the type locality at Tyrone, in Woodford 

County, Ky.

Ross and others (1982) assigned a Middle Ordovician 

(Blackriveran and Rocklandian) age to the Tyrone Limestone in the Lexington region of central Kentucky. These 

authors correlate the Tyrone Limestone with the lower 

half of the Carters Limestone in central Tennessee; the 

Ottosee Shale, Mocassin Limestone, and Eggleston Formation in eastern Tennessee; the upper half of the Platteville Formation and the basal portion of the Decorah Formation in Iowa, Missouri, Wisconsin, and Minnesota and 

the Platteville Group, Decorah "Subgroup" in Illinois; and 

the Watertown, Selby, and Napanee Limestones in New 

York.

All of the Tyrone nautiloids described here are from 

USGS collection 6034-CO. This silicified collection is from 

a hard, white to gray, crystalline fossiliferous limestone 

unit, 3 ft thick, exposed 25 ft (8 m) below the Pencil Cave 

bentonite. This unit is well exposed in roadcuts along 

Watts MiU Road, 0.8 mi (1.3 km) south of Sulfur Well, Jessamine County, Ky. (Little Hickman 7.5 min. quadrangle, 

Little Hickman A section). Petrographically, this limestone would be classified as a biopelsparrudite (classification of Folk, 1962) or a fossiliferous grainstone 

(classification of Dunham, 1962). The unit contains poorly 

sorted whole and fragmentary silicified shells of nautiloids, gastropods, solitary corals, trepostome bryozoans, 

and pelecypods, plus intraclasts consisting of subrounded 

fragments of micrite, all in a matrix of sand-sized peloidal 

and skeletal grains.

LEXINGTON LIMESTONE

The Lexington Limestone, Middle Ordovician and 

Late Ordovician (Kirkfieldian to Edenian) in age, is well 

exposed in the Inner Blue Grass region of central Kentucky (Sweet, 1979; Wahlman, 1992). The formation consists of approximately 300 ft (98 m) of thin-bedded 

fossiliferous limestone, calcarenite, and calcilutite, and 

lesser amounts of clay shale and siltstone. The formation 

(Pojeta, 1979, p. A10) has been divided into 12 named 

members and several named beds (fig. 3). Limestone 

facies have more siliciclastic sediments than those of the
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P7

SOUTH CENTRAL KENTUCKY NORTH

Clays Ferry Formation

Sulphur Well Member —— —? —<r"—— —— —— ~?' —— —— —— ~

Brannon Member

Tanglewood

Limestone

Member

Perrywille Limestone 

Member

Tanglewood Limestone Member

Grier Limestone Member

Logana Member

Curdsville Limestone Member

FIGURE 3.—Facies relations among the lithostratigraphic units 

of the Lexington Limestone and Clays Ferry Formation in 

central Kentucky. Taken from Wahlman (1992) who 

modified the figure from Cressman (1973) and an 

unpublished Cressman figure. Cressman (written

commun., January 1994) added the modifications shown 

herein: (1) the position of the Strodes Creek Member (SCM) 

of the Lexington Limestone and (2) the approximate Middle 

Ordovician-Upper Ordovician boundary shown by the dashed 

line bearing question marks.

underlying Tyrone Limestone, reflecting an increase in the 

influx of sediments from the rising tectonic belts to the 

east. Many of these carbonates also differ texturally from 

Tyrone lithologies in being coarser grained shelly packstone and grainstone in contrast to the fine-grained, dense 

micritic limestone, dolostone, and cryptalgal limestone of 

the Tyrone Limestone. Beginning with deposition of the 

Lexington Limestone, the abundance and diversity of 

shelly benthic filter-feeding faunas increases, especially 

brachiopods, bryozoans, pelecypods, and crinoids. This is 

in contrast to the typically lower diversity Tetradiumostracode-mollusk biota characteristic of marine facies 

within the Tyrone Limestone. Lithofacies and faunas collectively indicate a change from a restricted, low-energy 

carbonate platform that consisted of a mosaic of subtidal 

marine coralline thickets, shallow-marine lagoons, and 

intertidal mudflats (Cressman and Noger, 1976; Kuhnhenn 

and others, 1981) to a more open-shelf, higher energy, 

subtidal marine carbonate ramp complex that dipped to 

the north (Cressman, 1973).

Coeval with the carbonate ramp environments of the 

Lexington Limestone in Kentucky were similar carbonate 

shelf environments to the south in central Tennessee 

(Nashville Group; Wilson, 1949) and to the northeast into 

New York (Trenton Group; Titus and Cameron, 1976; 

Titus, 1982). Immediately to the northwest of Kentucky 

was the Sebree trough, a deeper water linear trough that

extended from central Ohio southwestward through 

southern Indiana, western Kentucky, and western Tennessee (fig. 1). This trough was the site of graptolitic shale 

deposition (Cressman, 1973; Bergstrom and Mitchell, 

1990). A shallow-water carbonate shelf flanked this 

trough to the northwest and was continuous from Iowa in 

the west (Galena Formation), northeastward into Ontario 

and Quebec (Simcoe and Ottawa Groups).

In Kentucky the basal member of the Lexington 

Limestone, the Curdsville Limestone Member (Kirkfieldian), records the initial marine transgression over the 

eroded surface of the Tyrone Limestone. The Curdsville 

Limestone Member consists of 20-40 ft of cross-bedded 

basal grainstone beds that grade up into lower-energy fossiliferous packstone and grainstone beds having a diverse 

fauna of brachiopods, bryozoans, pelecypods, trilobites, 

and crinoids. The Curdsville Limestone Member is overlain conformably by the interbedded, thin, planar, argillaceous limestone and shale of the Logana Member 

(Kirkfieldian), up to 50 ft thick, thickening north across 

central Kentucky, or the nodular Grier Limestone Member 

(fig. 3). Cressman (1973) indicated that the Logana Member represented the height of the initial marine transgression, deposited under quiet-water conditions at water 

depths below wave base and containing a more sparse 

fauna of dalmanellid brachiopods, bryozoans, pelecypods, univalved mollusks, and nautiloids. The Logana
P8 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

Member interfingers with and is overlain by the Grier 

Limestone Member (Kirkfieldian and Shermanian), consisting of 100-180 ft of thin, irregularly bedded, often nodular, very fossiliferous limestone. These limestones 

contain a diverse marine fauna of brachiopods, bryozoans, and crinoids in coarser grained lithologies and ostracodes, univalved mollusks, and pelecypods in finer 

grained, more argillaceous lithologies. Cressman (1973) 

inferred that the Grier Limestone Member was deposited 

under shallow-water (less than 50 ft deep), well-aerated, 

but normally low energy subtidal marine conditions.

In latest Middle Ordovician and earliest Late Ordovician times (Shermanian-Edenian), there was subsidence 

in the southern half of the Lexington platform and the formation of a west-northwest-trending bank (Tanglewood 

bank of Hrabar and others, 1971) across the north-central 

portion of the platform (Cressman, 1973, pis. 9c-d). Interbedded, thin argillaceous limestone and shale of the Brannon Member were deposited in the subsiding basin to the 

south. High-energy grainstone facies were deposited in 

the vicinity of the bank (Tanglewood Limestone Member). 

Nodular, very fossiliferous limestones of the Millersburg 

Member were deposited to the east (Cressman, 1973, pis. 

9c-d). These extensively bioturbated limestones were 

deposited in shallow marine subtidal environments in 

water depths of less than 45 ft. Between the Tanglewood 

Limestone Member and Millersburg Member in the 

east-central Blue Grass region there occurs the Strodes 

Creek Member of the Lexington Limestone. This unit consists of up to 30 ft of "bouldery" gray, micrograined limestone and characteristically abundant, large 

stromatoporoids. Black and Cuppels (1973) inferred 

low-energy, quiet-water, mud-bottom marine conditions 

for the Strodes Creek Member and development of local 

stromatoporoid biostromes. These biostromes provided a 

habitat for a diverse fauna of orthid and rhynchonellid 

brachiopods, bryozoans, the coral Favistina, pelecypods, 

univalved mollusks, nautiloids, trilobites, and ostracodes. 

Other named members and named beds of the Lexington 

Limestone are discussed by Cressman (1973) and Pojeta 

(1979).

Above the Lexington Limestone, thin-bedded, planar 

packstones and clay shales of the Clays Ferry Formation 

were deposited at the northward-sloping northern edge of 

the platform in deeper water, low-energy, mud-bottom 

environments. Water depths in these environments were 

estimated by Cressman (1973) to have exceeded 80 ft (24 

m), below fair-weather wave base, but within the zone of 

storm-current reworking. These facies extend north into 

Ohio as the Point Pleasant Tongue of the Clays Ferry Formation (Swadley and others, 1975). The Point Pleasant 

Tongue consists of 100 ft of interbedded fossiliferous 

limestone and shale that underlies the Kope Formation in 

the Cincinnati, Ohio, area.

UPPER ORDOVICIAN CINCINNATIAN 

PROVINCIAL SERIES LITHOSTRATIGRAPHY

The Upper Ordovician (Edenian to Richmondian) 

Cincinnatian Provincial Series continues the trend initiated in the underlying Lexington Limestone, namely lithofacies indicating the increasing influx of fine-grained 

clastic sediments into the northern Cincinnati arch region 

from the Taconic landmass to the east. These lithofacies, 

collectively as much as 985 ft (323 m) thick, consist primarily of interbedded clay shale, fossiliferous wackestone and packstone, having less amounts of siltstone, 

dolomitic mudstone, and dolomitic limestone. Marine faunas are diverse and abundant in most of these facies, 

dominated by brachiopods, trepostome bryozoans, and 

crinoids in skeletal facies and by mollusks and trilobites 

in mudstone facies (Frey, 1987b).

The tristate area surrounding Cincinnati, Ohio (Kentucky-Indiana-Ohio), exposes the type section for the 

Upper Ordovician Cincinnatian Provincial Series of North 

America. The Cincinnatian Provincial Series is divided 

into three stages. These are, in ascending order, the Edenian, the Maysvillian, and the Richmondian Stages. The 

following overview of Upper Ordovician lithostratigraphy 

in the region is organized by stage and presented in 

ascending order. The complex facies relations of these 

formations across the Cincinnati arch region are illustrated in figure 2.

EDENIAN STAGE

During Edenian time, transgressive conditions were 

prevalent across much of the northern Cincinnati arch 

region, inundating much of the Lexington platform under 

shallow seas having water depths of at least 80 ft (24 m). 

These low-energy, muddy-bottom environments were the 

site of the deposition of the widespread clay shale and 

thin limestone of the Clays Ferry Formation, which reach 

a maximum thickness of 250 ft in the southwestern Outer 

Blue Grass region (Weir and others, 1984, pi. 9). To the 

north, the Clays Ferry Formation interdigitates with the 

more clastic-rich facies of the Kope Formation, thinning 

northward due to the thickening wedge of mudstone and 

shale of the Kope (up to 280 ft thick in southwestern 

Ohio). Biotas in both formations are most common in the 

thin wackestone or packstone beds and consist of small 

dalmanellid and plectambonitid brachiopods, bryozoans, 

small pelecypods, gastropods, monoplacophorans, nautiloids, trilobites, ostracodes, and crinoids. These 

low-energy, mud-bottom environments were periodically 

reworked by storm events, commonly resulting in sets of 

storm-formed "tempestite" beds consisting of fining-up 

packets of packstone/grainstone-siltstone-shale (Hay and 

others, 1981; Meyer and others, 1981; Tobin, 1982;
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P9

Kepferle and others, 1987; Shrake and others, 1988). In 

the northern Kentucky-southwestern Ohio area there is 

an increase in limestone beds upsection, indicating a shallowing of conditions upward toward the partially equivalent and overlying more calcareous, shallow-water 

Fairview Formation.

MAYSVILUAN STAGE

Shallower water marine conditions returned to the 

Lexington platform area in central Kentucky in Maysvillian time, resulting in the deposition of the thin-bedded, 

locally nodular, fossiliferous limestone of the Galloway 

Creek Limestone across much of the central Kentucky 

region. The even-bedded fossiliferous limestone and shale 

of the Fairview Formation were deposited at the same 

time in somewhat deeper water environments at the 

northern edge of the platform in the northern Kentuckysouthwestern Ohio area. These latter strata, 40-130 ft 

thick, represent transitional environments between the 

deep-water, transgressive conditions associated with the 

underlying Kope Formation and the very shallow water, 

locally shoaling conditions, inferred for basal portions of 

the overlying Grant Lake Limestone. Preserved biotas in 

these carbonate facies are dominated by diverse brachiopods and trepostome bryozoans, evidence of the development of dense bryozoan thickets that supported large 

populations of "nestling" brachiopod species. Associated 

with these thicket facies are lesser numbers of mollusks, 

trilobites, ostracodes, and crinoids.

By late Maysvillian time, restricted, very shallow 

water, low-energy environments were prevalent across 

the south-central portion of the Lexington platform, 

resulting in the deposition of the sparsely fossiliferous 

calcitic and dolomitic mudstone and micrograined limestone of the Ashlock Formation (Weir and others, 1984). 

More fossiliferous, open-marine facies of the Grant Lake 

Limestone were deposited to the north in the Maysville 

and Covington, Ky, areas. This formation, consisting of 

up to 160 ft of irregularly bedded, poorly sorted fossiliferous limestone, extends northward into southwestern 

Ohio, where it contains more shale as a result of the 

somewhat deeper water, lower energy, bottom conditions 

inferred for this area at this time (Schumacher and others, 

1991).

Coeval with the above-stated lithostratigraphic units 

are the irregularly bedded, nodular, fossiliferous limestone and thin shale of the Leipers Limestone, exposed in 

the Cumberland sag region along the Kentucky-Tennessee 

State line. This formation, up to 180 ft thick in this area, 

overlies the even-bedded limestone of the Catheys Formation and, in south-central Kentucky, is overlain by the 

dolostone and mudstone of the Cumberland Formation 

(Weir and others, 1984). Flower (1946) described the

occurrence of two distinct coralline biostromes in the 

lower half of the Leipers Limestone. The inferred environment of deposition was a shallow-marine, mixed carbonate and clastic bottom that becomes lower energy with 

time, the lithofacies becoming more fine-grained upsection. This normal marine environment had a diverse fauna 

of brachiopods, bryozoans, the coral Tetradium, gastropods, nautiloids, pelecypods, ostracodes, and trilobites.

RICHMONDIAN STAGE

Shallow epeiric seas again transgressed across the 

northern portion of the Cincinnati arch region in early 

Richmondian time, leading to the deposition of the interbedded clay shale and thin fossiliferous limestone of the 

Bull Fork Formation (10-240 ft thick) across northern 

Kentucky and southwestern Ohio. The lithologically and 

faunally similar upper Dillsboro Formation was deposited 

at the same time in adjacent portions of southeastern 

Indiana (Sweet, 1979). These interbedded shales and limestones were deposited in deeper water, lower-energy environments, compared with the underlying, primarily 

carbonate facies of the Grant Lake Limestone. Water 

depths were below fair-weather wave base but within the 

zone of storm-current reworking, similar to those inferred 

for the Clays Ferry and Kope Formations (Weir and others, 1984). Preserved faunas contains diverse, abundant 

brachiopods, bryozoans, corals, stromatoporoids, gastropods, nautiloids, pelecypods, ostracodes, trilobites, and 

crinoids.

Very shallow water, restricted marine and intertidal 

mudflat conditions continued to occur across central 

Kentucky, resulting in the deposition of the dolomitic 

mudstone and micrograined limestone of the Ashlock 

Formation and the overlying Rowland Member of the 

Drakes Formation. Limestone beds in these units commonly contain mud cracks (Weir and others, 1984) and 

are only sparsely fossiliferous having local occurrences of 

brachiopods, bryozoans, gastropods, and ostracodes.

In later Richmondian time, regressive conditions 

spread throughout the northern Cincinnati arch region, 

the central Kentucky area being the site of complex facies 

consisting of alternating thin, shallow-marine and intertidal mudflat lithofacies. These are the coralliferous, thinbedded limestone and shale of the Bardstown Member of 

the Drakes Formation, 20-65 ft thick, exposed along the 

western edge of the Outer Blue Grass region, and the 

maroon and green dolomitic mudstones of the Preachersville Member of the Drakes, 100 ft thick in the southeastern Blue Grass region and thinning to the northwest (Weir 

and others, 1984, pi. 7). The latter member is inferred to 

represent restricted shallow-marine and intertidal mudflat environments that prograded into the northern
P10 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

Cincinnati arch region from the southeast, indicative of 

the distal edge of the Queenston delta.

The Saluda Formation, consisting of a broad lens of 

sparsely fossiliferous dolomitic limestone and calcitic 

dolostone, was deposited at the same time along a 

north-south trend through southeastern Indiana and 

northern Kentucky. The formation (recognized as the 

Saluda Dolomite Member of the Drakes Formation in 

Kentucky), averages 52 ft in thickness between Madison, 

Ind. and Jefferson County, Ky. Thickness decreases north 

of Madison, where the formation wedges out due to the 

irregularly bedded, very fossiliferous limestones of the 

Whitewater Formation, which thickens to 90 ft northward 

at Richmond, Ind. The Saluda Dolomite Member thins 

southward to a thickness of 20 ft in Marion County, Ky. In 

the Madison, Ind^Jefferson County, Ky, area, the Saluda 

Formation or Saluda Dolomite Member is separated from 

overlying Silurian limestones by the Hitz Limestone Member of the Saluda, or the Hitz Limestone Bed of the Saluda 

Dolomite Member for Indiana or Kentucky, respectively, 

consisting of up to 15 ft of interbedded, thin, fossiliferous 

limestone, shale, and dolomitic limestone (Kepferle, 

1976).

Hatfield (1968) described the Saluda Formation as 

being deposited under very shallow-water, possibly hypersaline, lagoonal conditions that developed behind an initially northward-advancing and then southward-retreating 

coral-sponge bank. The Whitewater Formation and the 

Hitz Limestone represent the return of more normal 

marine shallow water conditions to the area prior to the 

development of the regional erosional surface that separates these Ordovician strata from the overlying Silurian 

carbonates. Along the east flank of the Cincinnati arch in 

southwestern Ohio and adjacent portions of north-central 

Kentucky, this erosional surface truncates the upper portions of the Bull Fork Formation or the Preachersville 

Member of the Drakes Formation.

DISTRIBUTION AND FAUNAL AFFINITIES

OF ORDOVICIAN NAUTILOIDS 

IN THE CINCINNATI ARCH REGION

Study of the Middle and Upper Ordovician nautiloids 

of the Cincinnati arch region of Kentucky, Indiana, and 

Ohio has led to the recognition of four major 

time-bounded Ordovician nautiloid faunas in this region. 

These are characteristic of four time intervals: Blackriveran to Rocklandian, Kirkfieldian to early Edenian, middle 

Edenian to early Richmondian, and middle Richmondian 

to late Richmondian. The Edenian to Richmondian nautiloid fauna, in turn, can be further subdivided into three 

distinctive subfaunas characteristic of specific time intervals and (or) paleogeographic regions within the 

Cincinnatian Provincial Series in the tristate area of

northern Kentucky, southeastern Indiana, and southwestern Ohio.

The four major nautiloid faunas—"Black River" 

(found in the Tyrone Limestone and equivalent units), 

"Trenton" (found in the Lexington Limestone and equivalent units), "Cincinnatian" (found in the Kope Formation 

through part of the Bull Fork Formation and equivalent 

units), and "Richmondian" (found in part of the Bull Fork 

Formation through the Saluda Formation and equivalent 

units)—are separated by three regional sedimentologicalpaleontological events. A regional unconformity and a 

major extinction of nautiloid taxa separate the nautiloid 

faunas of the Tyrone and Lexington Limestone. A marine 

transgression coupled with an influx of clastic sediments 

from the rising tectonic areas in eastern Laurentia led to 

the more gradual turnover in nautiloid faunas from the 

Lexington Limestone to the Edenian Clays Ferry and 

Kope Formations. Within the Cincinnatian Provincial 

Series, the early Richmondian transgression coincides 

with the migration into the Kentucky-Indiana-Ohio area of 

the "Richmondian" nautiloid fauna derived from taxa 

more characteristic of coeval or slightly older Edenian 

and Maysvillian faunas in the Western United States, Canada, the Arctic archipelago, and Greenland (Flower, 1946, 

1976; Frey, 1981). Flower (1942, 1946) also indicated an 

earlier incursion of these "Arctic" nautiloid taxa into the 

area, associated with the latest Shermanian to Edenian 

transgressive episode (Clays Ferry and Kope Formations). These Upper Ordovician nautiloid faunas were terminated by the Late Ordovician mass extinction event 

(Sheehan, 1988; Brenchley, 1989) associated with the 

withdrawal of epeiric seas from the Cincinnati arch 

region.

NAUTILOID FAUNA OF THE TYRONE LIMESTONE

The nautiloid fauna from the 6034-CO collection in 

the Tyrone Limestone consists of at least 18 species, 

belonging to 14 genera, representing 6 nautiloid orders. A 

complete listing of the nautiloid species identified from 

this collection is provided in table 1. The collection is 

dominated numerically by the small longiconic baltoceratids Cartersoceras shideleri Flower (pi. 1, figs. 1-6), C. 

popei new species (n. sp.) (pi. 1, figs. 7-10), and Murrayoceras cf. M. murrayi (Billings) (pi. 1, figs. 12-17), and 

the small longiconic orthocerids Pojetocerasfloweri n. sp. 

(pi. 2, figs. 1-9) and Proteoceras tyronensis (Foerste) (pi. 

4, figs. 1-7). Small, typically fragmentary specimens of 

oncocerid nautiloids are second in abundance to the 

small longiconic taxa. Many of these specimens, however, 

are too incomplete to identify to the genus. Identified 

oncocerids from the 6034-CO collection are Oncoceras 

major n. sp. (pi. 19, figs. 11-15), Beloitoceras cf. B. 

huronense (Billings) (pi. 20, figs. 3P6), Laphamoceras cf.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION Pll

TABLE 1.—Distribution of species of nautiloid cephalopods in the Tyrone Limestone of the High Bridge Group, 

Members of the Lexington Limestone, and the Clays Ferry Formation, all Middle Ordovician from the Blue 

Grass region of central Kentucky

[Data include only those nautiloid species described in this paper, based on U.S. Geological Survey silicified collections and on 

museum collections. Middle Ordovician stratigraphic units from which no nautiloid species were recovered are omitted. 

TY, Tyrone Limestone; CF, Clays Ferry Formation; Members of the Lexington Limestone are designated: CL, Curdsville 

Limestone; LO, Logana; GL, Grier Limestone; ML, Millersburg; SC, Strodes Creek. X indicates presence of species]

Species TY CL LO GL ML SC CF Location

Ellesmerocerida

Cartersoceras popei X 

Cartersoceras shideleri X 

Murrayoceras cf. M. murrayi X

Orthocerida

Pojetoceras floweri X 

Anaspyroceras cylindricum X 

Ordogeisonoceras amplicameratum 

Proteoceras tyronensis X 

Isorthoceras albersi X 

Isorthoceras rogersensis

Gorbyoceras cf. G. tetreauense X 

Monomuchites annularis X 

Monomuchites obliquum X 

Monomuchites cf. M. costalis X 

Polygrammoceras sp A. 

Polygrammoceras? sp. B X 

Polygrammoceras? cf sp. P. A

Endocerida

Cameroceras cf. C. trentonense 

Vaginoceras sp. A X 

Vaginoceras sp. B X

Actinocerida

Actinoceras altopontense X 

Actinoceras kentuckiense X 

Actinoceras curdsvillense X 

Ormoceras ferecentricum X 

Deiroceras curdsvillense X

Tarphycerida

Plectoceras cf. P. carletonense X 

Trocholites faberi

Oncocerida

Oncoceras major X 

Oncoceras sp. X 

Beloitoceras cf. B. huronense X 

Maelonoceras cf. M. praematurum X 

Laphamoceras cf. L. scofieldi X 

AUumettoceras cf. A. tenerum X

6034-CO 

6034-CO 

6034-CO

6034-CO 

Curdsville, Ky. 

X Ludlow, Ky.

6034-CO

XX X 5067-CO, 5073-CO, 5092-CO 

X Rogers Gap, Ky.

5073-CO, 5092-CO, 7791-CO 

6034-CO 

6034-CO 

6034-CO

X 5067-CO

6034-CO

X 7310-CO

X 4073-CO 

6034-CO 

5072-CO

6034-CO, High Bridge, Ky. 

6034-CO; High Bridge, Ky. 

Curdsville, Ky. 

6034-CO; High Bridge, Ky. 

5100-CO; Curdsville, N.Y.

6034-CO 

X Sadieville, Ky.

6034-CO

4879-CO, 4883-CO 

6034-CO 

6034-CO 

6034-CO 

4865-CO, 6419-CO
P12 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

TABLE 2.—Comparison of the nautiloid fauna from the 6034-CO 

collection in the Tyrone Limestone in Jessamine County, Ky. 

with those described from equivalent strata exposed in 

Eastern and Central North America

[Data from (1) Catalan! (1987), (2) Steele and Sinclair (1971), (3) Wilson 

(1961), (4) Foerste (1932, 1933), (5) Flower (1984) plus manuscript 

notes and plates, and (6) Hall (1847)]

Tyrone Taxa

Kentucky

Black ,, T r» ,, ,„ Black River m ^ -,i «• i! Leray-Rockland „ Platteville River" „,, * T . , Group

,„. . 0 . T , Ottawa Lowland „, , _. Minnesota St. Joseph „ . . Black River 

„,. .14 T , Ontario- Wisconsin 1 '^ Lsl. Quebec „ , o Q 1^

Ontario4

valley 

New York6

Ellesmerocerida

Cartersoceras XXX X

Murray oceras XXX X 

Orthocerida

Pojetoceras X X

Polygrammoceras1?

Monomuchites XXX X

Proteoceras X XX 

Endocerida

Vaginoceras X XX 

Actinocerida

Actinoceras XXX X

Ormoceras XX X 

Tarphycerida

Plectoceras X XX 

Oncocerida

Oncoceras XXX X

Beloitoceras XX X

Laphamoceras X X

Maelonoceras 

Species in common 11/14 8/14 12/14 8/14

L. scofieldi Foerste (pi. 20, figs. 13-18), and Maelonoceras 

cf. M. praematurum (Billings) (pi. 20, figs. 7-12). Lesser 

numbers of the large cumulated orthocerid Monomuchites 

annularis n. sp. (pi. 9, figs. 1-3, 11-15), the actinocerids 

Actinoceras altopontense Foerste and Teichert (pi. 17, 

figs. 6-10), A. kentuckiense Foerste and Teichert (pi. 17, 

figs. 1-5), and Ormoceras ferecentricum Foerste and 

Teichert (pi. 18, figs. 1-7), and the large endocerid Vaginoceras sp. A (pi. 15, figs. 1^4, 8-12), are also present in 

the 6034-CO collection. The tarphycerid Plectoceras cf. P. 

carletonense Foerste occurs in this collection but is 

known only from fragmentary specimens (pi. 19, figs. 1- 

3).

Sloan (1987) placed the Blackriveran-Rocklandian 

boundary at the Deicke Bentonite bed (Willman and 

Kolata, 1978). This bed is regarded as being equivalent to 

the Pencil Cave bentonite of drillers in central Kentucky 

(Huff and Kolata, 1990). This would make the nautiloid

fauna from the 6034-CO collection Blackriveran in age, as 

it occurs 25 ft (8 m) below the Pencil Cave bentonite of 

drillers at the Little Hickman section. Sweet (1984), however, placed the Blackriveran-Rocklandian boundary at 

the base of the Platteville Formation in Minnesota, well 

below the Deicke Bentonite bed, indicating a probable 

Rocklandian age, for the 6034-CO fauna. Until these differences in opinion are resolved, the specific age of the 

diverse Tyrone nautiloid fauna in the Tyrone is uncertain, 

but it can be placed with confidence in the latest Blackriveran-Rocklandian interval.

The nautiloid fauna from the Tyrone Limestone is 

similar to nautiloid faunas described from coeval strata at 

other localities in Eastern North America. This "Black 

River" nautiloid fauna is characterized by the association 

of species of the actinocerids Actinoceras, Gonioceras, 

and Ormoceras] the endocerid Vaginoceras; the baltoceratids Cartersoceras and Murrayoceras; the orthocerids 

Proteoceras and Monomuchites; the oncocerids Oncoceras, Beloitoceras, Laphamoceras, and Zittelloceras; and 

the tarphycerids Avilionella, Barrandeoceras, and Plectoceras. This diverse fauna is characteristic of shallowwater carbonate facies deposited in cratonic shelf seas in 

eastern Laurentia in the post-Whiterockian Middle Ordovician. Elements of this fauna made their initial appearance in Chazyan strata in the Lake Champlain region of 

New York and Canada (Ruedemann, 1906; Foerste, 1938; 

Flower, 1955b). The fauna became more diverse and more 

widespread in succeeding Blackriveran and Rocklandian 

times. Seventy-six species of nautiloids, belonging to 39 

genera and 8 orders, have been reported from the Blackriveran to early Rocklandian rocks in Wisconsin, Minnesota, and Illinois (Catalani, 1987). Wilson (1961) listed 75 

species, belonging to 29 genera and 6 orders, from the 

coeval "Leray-Rockland beds" exposed in the Ottawa 

Lowland region of Ontario and Quebec. The Tyrone Limestone nautiloid fauna described here is compared with 

these faunas plus those from the "Black River Formation" 

exposed on St. Joseph Island in Lake Huron (Foerste, 

1932 and 1933) and the Black River Group in New York 

(Hall, 1847) in table 2.

ROCKLANDIAN NAUTILOID EXTINCTION

This diverse and widespread "Black River" nautiloid 

fauna thrived in carbonate shelf environments in eastern 

Laurentia, including Kentucky, for approximately 4 million years (m.y). This nautiloid fauna was rather abruptly 

terminated (in the geologic sense) in the late Blackriveran 

or Rocklandian by an extinction event that may have 

taken place over a time span of less than a million years 

(455^54 Ma; Sloan, 1987). The 6034-CO collection in the 

Tyrone Limestone comes from a limestone bed 25 ft 

below the Pencil Cave bentonite of drillers and 46 ft
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P13

below the Tyrone Limestone-Lexington Limestone contact. There are no data on nautiloid faunas from this intervening 46 ft interval in the Tyrone Limestone. With the 

possible exception of Vaginoceras sp., none of the 18 species identified from this Tyrone Limestone collection 

occur in the overlying basal Curdsville Limestone Member of the Lexington Limestone (Kirkfieldian). Five out of 

14 of the genera present in the Tyrone Limestone (36 percent) became extinct prior to the deposition of the Curdsville Limestone Member, hi contrast to the Tyrone 

Limestone fauna, the identified nautiloid fauna from the 

Curdsville Limestone Member consists of only four species, belonging to four genera and three orders.

Catalani (1987) listed 76 species of nautiloids, 

belonging to 39 genera and 8 orders from the various formations of the Platteville Group in Illinois or the Platteville Formation in Wisconsin. He listed only 13 species, 

belonging to 10 genera and 4 orders, from the overlying 

Decorah Shale (Rocklandian and Kirkfieldian) in the 

same area Only four Platteville species occur in the overlying Decorah Shale, indicating extinction of 95 percent of 

the Platteville species in the latest Blackriveran to early 

Rocklandian. Eight out of the 39 listed Platteville genera 

(21 percent) were extinct prior to the deposition of the 

Decorah Shale.

Wilson (1961) listed 75 species belonging to 29 genera and 6 orders from the "Leray-Rockland beds" exposed 

in the Ottawa region of Ontario and Quebec. Only nine 

species, belonging to eight genera and four orders, are 

listed for the overlying Hull beds (Kirkfieldian). Wilson 

listed seven species that crossed over from the "LerayRockland beds" into the Hull beds, indicating that 91 percent of the Leray-Rockland species became extinct prior 

to the deposition of the Hull. Seven out of the 29 genera 

(24 percent) listed for the "Leray-Rockland beds" do not 

occur in the overlying Hull beds.

Hall (1847), Young (1943), Flower (1952, 1957a), and 

Cameron and Mangion (1977) have collectively listed 18 

species of nautiloids, belonging to 14 genera and 6 orders 

from the Watertown Limestone (Blackriveran) in New 

York. Titus and Cameron (1976) listed only three species 

of nautiloids, representing two genera and two orders, 

from the overlying Napanee Limestone (Rocklandian). 

The same authors listed three nautiloid species from the 

overlying Kings Falls Limestone (Kirkfieldian). None of 

the Watertown Limestone nautiloid species occur in the 

overlying Napanee or Kings Falls Limestones. Five out of 

14 genera (36 percent) were extinct regionally by the time 

of the initial deposition of the Napanee Limestone.

All of these examples documented from the literature 

indicate a major turnover in nautiloid taxa in latest Blackriveran to early Rocklandian time. The interval of time 

during which this regional extinction event occurred 

appears to have been geologically short. This extinction is

significant not only for the large number of species that 

became extinct, but also for the large number of genera 

that became extinct. A search of the literature has indicated that the "Black River" nautiloid fauna consisted of 

at least 54 genera belonging to 8 orders. Twenty-six genera (48 percent) were extinct prior to the deposition of 

Kirkfieldian strata in eastern Laurentia (table 3). Succeeding Kirkfieldian nautiloid faunas throughout eastern Laurentia were depauperate in terms of taxonomic diversity, 

especially in comparison with the older Black River 

fauna

Some Blackriveran genera apparently found refugia 

in similar tropical carbonate platform environments in 

central Tennessee and in western and northern portions 

of Laurentia (Foerste and Teichert, 1930; Flower, 1957a). 

Some of these taxa became significant components of 

younger Shermanian to Richmondian nautiloid faunas in 

these regions. These were actinocerids like Actinoceras 

and Ormoceras, true Endoceras, and the oncocerid 

Beloitoceras. Other genera that were evidently terminated 

throughout their geographic range are the baltoceratids 

Cartersoceras and Murrayoceras, the orthocerids Monomuchites and Proteoceras, the tarphycerids Avilionella, 

Barrandeoceras, and Plectoceras, and the oncocerid 

Maelonoceras. The endocerid Vaginoceras occurred in 

the Kirkfieldian Curdsville Limestone Member in Kentucky and then became extinct. Similarly, the actinocerid 

Gonioceras survived into the lower members of the Decorah Shale in the upper Mississippi valley region and then 

went extinct. Taxa like Anaspyroceras, Gorbyoceras, Deiroceras, Oncoceras, and Zittelloceras continue into the 

Kirkfieldian and Shermanian in eastern Laurentia, apparently unaffected by this extinction.

Determining the specific cause(s) of this turnover in 

nautiloid taxa is difficult. There is a widespread regional 

unconformity at the base of the Kirkfieldian across much 

of Eastern North America. This unconformity has been 

recognized in Kentucky (Cressman, 1973), central Tennessee (Wilson, 1949; Wahlman, 1992), the upper Mississippi 

valley region (Sloan, 1987; Kolata, 1987), the Upper Peninsula of Michigan (Votaw, 1980), and the Adirondack uplift 

region of New York (Cameron and Mangion, 1977). This 

unconformity is apparently absent in the Ottawa Lowlands region of Ontario and Quebec, and no significant 

break in sedimentation is noted within the "Ottawa 

Megagroup" (Wilson, 1961; Cameron and Mangion, 1977). 

Although no distinct unconformity was recognized at this 

interval in southern Ontario, Liberty (1969) has indicated 

shoaling facies corresponding to this time interval within 

the Bobcaygeon Formation.

The widespread nature of this unconformity indicates a major marine regression from these cratonic shelf 

areas at this time. This regression may have been the 

result of collisional events along the eastern margin of
P14 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

TABLE 3. — Middle Ordovician (Blackriveran and Rocklandian)

nautiloid genera from Eastern North America (Laurentia)

[Data from Foerste (1932, 1933), Flower (1952), Flower and Teichert

(1957), Wilson (1961), Catalan! (1987), and Stait (1988). IL, Illinois;

KY, Kentucky; LAB, Labrador; MN, Minnesota; MO, Missouri; NFL,

Newfoundland; NY, New York; ONT, Ontario; PA, Pennsylvania; QUE,

Quebec; TN, Tennessee; WI, Wisconsin. *, genera that went extinct at

the end of the Rocklandian]

Genus Distribution

Order Ellesmerocerida

1. Cyrtocerina WI, MN, ONT

2. Cartersoceras* KY, TN, ONT

3. Munuyoceras* KY, NY, ONT

Order Orthocerida

4. Anaspyroceras NY, ONT, QUE

5. Metaspyroceras WI, MN

6. Pojetoceras KY, ONT

7. Proteoceras* KY, ONT, NFL

8. Monomuchites* KY, WI, MN, NY, ONT

9. Gorbyoceras QUE, NFL

10. Whitfieldoceras WI, ONT

Endocerida

11. Endoceras NY, ONT, NFL

12. Vaginoceras KY, NY, ONT, QUE, NFL

. onocerida

13. Actinoceras KY, TN, MO, WI, MN, PA, NY, ONT,

QUE, NFL

14. Gonioceras* TN, WI, MN, IL, NY, QUE, NFL

15. Deiroceras MN, NY, ONT, QUE

16. Ormoceras KY, TN, NY, ONT, QUE

Ascocerida

17. Hebertoceras(?~)* IL

18. Redpathoceras* QUE

Tarphycerida

19. Avilionella* TN, WI

20. Bairandeoceras* TN, ONT

21. Bodeiceras* WI

22. Centrocyrtoceras TN, ONT, QUE

23. Chidleyenoceras* LAB, NFL

24. Paquettoceras* QUE

25. Plectoceras* KY, TN, WI, IL, NY, ONT, QUE

26. Rhynchorthoceras* NFL

Oncocerida

27. Beloitoceras KY, WI, MN, IL, ONT

28. Oncoceras KY, ONT, QUE

29. Richardsonoceras WI, ONT, QUE

30. Laphamoceras KY, MN

31. Zittelloceras WI, ONT, QUE, NFL

TABLE 3. — Middle Ordovician (Blackriveran and Rocklandian)

nautiloid genera from Eastern North America (Laurentia) —

Continued

Genus Distribution

Oncocerida — Continued

32. Maelonoceras* KY, ONT

33. Cyrtorizoceras WI, MN

34 DutilBithocBTd's* IL

35. Ehlersoceras* ONT

36. Kentlandoceras* IND, WI, ONT

37. Loganoceras* ONT, QUE

38. Rizosceras ONT

39. Romingeroceras* ONT

40. Scofieldoceras* MN

41. Allumettoceras MN, ONT, QUE

42. Tripteroceras WI, MN, NY, ONT, QUE

43. Fayettoceras(?) WI

44. Manitoulinoceras(?~)ONT

45. Staufferoceras MN

46. Valcouroceras(?~)* WI

47. Actinomotjtha* WI, MN

48. Danoceras ONT

49. Diestoceras ONT

Discosorida

50. Reedsoceras WI

51. Ruedemannoceras* TN

52. Simardoceras* QUE

53. Sinclairoceras* QUE

54. Teichertoceras QUE

There were 26/54 genera (48 percent) extinct by the end of the 

Rocklandian.

Laurentia (Kay, 1951; Neuman, 1955; Bird and Dewey,

1970; Ettensohn, 1991), due to sea-level fluctuations associated with continental glaciation in North Africa being

initiated at this time (McKerrow, 1979) or due to a combination of these events.

There is also evidence of a change in lithofacies from

nearly pure carbonate platform facies in the Blackriveran

and Rocklandian to mixed carbonate and clastic facies in

the Kirkfieldian and Shermanian. This appears to be true 

for much of Eastern North America (Wilson, 1949; Liberty,

1969; Cressman, 1973; Titus and Cameron, 1976; Cameron

and Mangion, 1977; Sloan, 1987). As indicated above, this

increase in clastic sedimentation is the result of successive collisional events between volcanic arc belts and the

eastern margin of Laurentia, leading to the development

of a siliciclastic source area (Taconic landmass) to the
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P15

east (Bird and Dewey, 1970; Ettensohn, 1991) and uplift 

along the Transcontinental arch in the west (Witze, 1980; 

Sloan, 1987). Sediments eroding off of these rising landmasses spread into acUacent cratonic shelf areas.

Due to this sediment influx, Kirkfieldian and younger 

marine environments were more mud-rich, necessitating 

the development of new marine faunas adapted to these 

mud-bottom conditions. These fauna! changes were evident to many of the paleontologists who have studied 

these faunas over the past 150 years, leading to the traditional differentiation of Middle Ordovician Mohawkian 

fossil biotas into either "Black River" or "Trenton" faunas 

(Hall, 1847; Winchell and Schuchert, 1895; Raymond, 

1903; Kay, 1937; Young, 1943; Cooper, 1956). This change 

in benthic faunas would have, in turn, impacted the nautiloid faunas feeding on these organisms, possibly leading 

to the turnover in nautiloid faunas that occurred at this 

time.

Huff and Kolata (1990) traced the Deicke Bentonite 

Bed from southern Minnesota through eastern Missouri, 

across Kentucky and Tennessee, and into the valley and 

ridge of the southern Appalachians. Equivalent bentonite 

beds in Kentucky and Tennessee have also been termed 

the Pencil Cave bentonite of drillers or T-3 bentonite. As 

indicated above, the Pencil Cave occurs in the upper 50 ft 

of the Tyrone Limestone in central Kentucky, 25 ft above 

the biosparrudite that is the source of the 6034-CO collection of Tyrone nautiloids. Huff and Kolata (1990) describe 

the Deicke bed as ranging from 5 cm to 1.5 m thick and 

believe it represents the accumulation of air-fall volcanic 

ash on a shallow-marine platform during Rocklandian 

time. These authors noted that this bentonite bed thickens toward the southeast, indicating a volcanic source 

area that was probably east of the Tennessee-Georgia 

State line (fig. 1). They suggested that Southern Hemisphere trade winds carried the ash northwest across the 

craton. The Deicke was considered to be a single-graded 

bed and the result of a solitary eruptive event. Taking into 

account postdepositional compaction, Huff and Kolata 

estimated that the original volume of ash deposited was 

1,122 cubic kilometers (km3). They indicated that the 

Deicke Bentonite Bed and the overlying Millbrig Bentonite Bed (Willman and Kolata, 1978) are among the largest 

air-fall pyroclastic deposits reported from the geologic 

record. By way of comparison, the 1815 eruption of 

Tambora in Indonesia, one of the most violent eruptions 

recorded during historical times, had a volume of 175 km3 

(Self and others, 1984).

Sloan (1987) describes the Deicke volcanic eruption 

as the cause of a major provincial extinction event in the 

upper Mississippi valley region. At the species level, he 

lists conodont extinction at 10 percent, brachiopod 

extinction at 39 percent, gastropod extinction at 80 percent, trilobite extinction at 90 percent, and echinoderm

extinction at 100 percent. As indicated above, nautiloid 

extinction at or near this horizon in this region was 95 

percent based on the data presented by Catalani (1987). 

Sloan (oral commun., 1992) described these extinctions 

as varying variable from class to class but averaging 65 

percent at the species level. He indicated that this extinction event marked the "Black River"-"Trenton" fauna! 

boundary. Sloan also pointed out that the level of generic 

extinction was, however, much lower. Based on Catalani's 

(1987) list of taxa, 21 percent of the nautiloid genera in 

the Platteville Formation (or Group) became extinct at 

this time. Citing Kunk and Sutter (1984), Kolata and others (1986), and Samson (1986), Sloan gave the Deicke volcanic event an age of 454.2 Ma.

Several models proposed recently to explain the terminal Cretaceous extinction event (Sharpton and Ward, 

1990) have postulated that large volumes of dust in the 

atmosphere generated by a bolide impact or by a large 

volcanic event would have had a catastrophic effect on 

both terrestrial and marine ecosystems. Deleterious conditions associated with these events are abrupt climatic 

cooling, the emission of large volumes of toxic gases, 

acidic rainfalls, and disruption of food chains. Huff and 

Kolata (1990) have suggested that the Middle Ordovician 

Deicke and Millbrig volcanic events deposited ash rapidly 

over broad areas and ejected large amounts of volcanic 

ash to high levels in the atmosphere. Consequently, these 

occurrences would both be expected to result in conspicuous extinction events.

Flower (1946, 1976) considered "Black River" nautiloid faunas (Blackriveran and Rocklandian) in Eastern 

North America to be tropical faunas compared with middle "Trenton" nautiloid faunas (Kirkfieldian and Shermanian), which he termed cooler water, temperate faunas. If 

Flower is correct, then this would give some support to 

the idea that climatic cooling resulting from either the 

Deicke or the Millbrig volcanic events contributed to the 

Rocklandian turnover in nautiloid faunas in Laurentia. 

Huff and others (1992), in discussing the biological effects 

of the widespread Millbrig ash fall, citing the work of 

Sharpf (1990) in Kentucky, indicated that this volcanic 

event had a minimal impact on benthic faunas. Sharpf 

suggested that the turnover from "Black River" to "Trenton" faunas was more likely the result of environmental 

change associated with the transgression early during the 

deposition of the Trenton Group. More detailed study of 

faunas on either side of the Deicke and Millbrig Bentonite 

Beds in Kentucky and elsewhere is needed to better 

understand the causes of this extinction event.

NAUTILOID FAUNA OF THE LEXINGTON LIMESTONE

As indicated above, the later Middle Ordovician 

"Trenton" nautiloid fauna in Kentucky and elsewhere in
P16 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

Eastern North America is depauperate in terms of diversity in comparison with pre-Kirkfieldian Middle Ordovician "Black River" fauna (table 1). Kirkfieldian nautiloids, 

including Lexington Limestone taxa, are associated with 

mixed carbonate-clastic, shallow-marine shelf facies 

across Eastern North America. Faunas similar to the Lexington Limestone nautiloid fauna occur in the Galena Formation in Wisconsin or Galena Group in Minnesota and 

Illinois (Catalani, 1987), the Trenton Group in New York 

(Hall, 1847; Titus and Cameron, 1976); the Verulam and 

Lindsay Formations in southern Ontario (Liberty, 1969); 

and the Hull and Sherman Fall Formations in the Ottawa 

region of Ontario and Quebec (Wilson, 1961).

The nautiloid fauna collected from basal portions of 

the Curdsville Limestone Member of the Lexington Limestone in the central Blue Grass region is distinct from that 

in overlying Lexington Limestone strata in Kentucky in its 

relict "Black River" appearance. Blackriveran holdovers 

are Actinoceras curdsviUense Foerste and Teichert (pi. 

17, fig. 11), Deiroceras curdsviUense Foerste and Teichert 

(pi. 18, figs. 8, 9), Vaginoceras sp. B (pi. 15, figs. 5-7), and 

Anaspyroceras cf. A. cylindricum (Foerste) (pi. 12, fig. 

5). None of these taxa are present in collections from 

overlying members of the Lexington Limestone in Kentucky (table 1). Foerste (1910) also described "Orthoceras" bilineatum-frankfortense from "the cherty 

limestone beneath the Logana Bed." It is not known 

whether this limestone bed is part of the Curdsville Limestone Member or forms the base of the overlying Logana 

Member. This species appears to be assignable to the 

genus Gorbyoceras Shimizu and Obata.

Nautiloids in the Logana Member are abundant but of 

low diversity, the silicified collections from central Kentucky containing only three recognizable species. Faunas 

are dominated numerically by the small longiconic pseudorthocerid Isorthoceras albersi (Miller and Faber) (pi. 

10, figs. 1-9), and contain lesser numbers of the annulated 

longiconic orthocerid Gorbyoceras cf. G. tetreauense Wilson (pi. 12, fig. 3) and the depressed orthoconic oncocerid 

Allumettoceras cf. A. tenerum (Billings) (pi. 20, figs. 19- 

22). This nautiloid fauna, especially the abundance of 

Isorthoceras albersi, is characteristic of the remainder of 

the Lexington Limestone.

Nautiloid diversity increases in the overlying Grier 

Limestone Member (Shermanian), where there are 

numerous specimens of Isorthoceras albersi (pi. 10, figs. 

1-9) associated with the longiconic orthocerid Polygrammoceras sp. A (pi. 12, figs. 1, 2), the endocerid Cameroceras cf. C. trentonense Conrad (pi. 14, figs. 3, 4), and the 

oncocerid Oncoceras sp. (pi. 20, figs. 1, 2). The Grier 

Limestone Member nautiloid fauna is most similar to the 

nautiloid fauna described by Hall (1847) and Titus and 

Cameron (1976) from the Trenton Group in New York.

Nautiloids from collections in the upper Middlelower Upper Ordovician Millersburg Member in central 

Kentucky consist only of the orthocerid Isorthoceras 

albersi. Nautiloids in the Strodes Creek Member in the 

vicinity of Winchester, Ky, consist of well-preserved 

calcite-replaced internal molds of the large longiconic 

orthocone Polygrammocerast cf. sp. A (pi. 11, figs. 1-3) 

and fragmentary specimens of a small, slender cyrtocone 

similar to the discosorid Faberoceras sonnenbergi 

Flower.

Flower (1942) described a diverse nautiloid assemblage from a fossiliferous lens exposed at the Poindexter 

Quarry at Cynthiana, Ky. This fauna contains six species 

of the slender cyrtoconic oncocerid Oonoceras and lesser 

numbers of the oncocerids Oncoceras and Rizosceras, 

and rare specimens of the longiconic orthocerid 

Isorthoceras and the actinocerids Deiroceras and Orthonybyoceras. Flower also described the actinocerids 

Armenoceras vaupeli and Troedssonoceras obscuroliratum, the oncocerid Danoceras cynthianense, and the discosorids Faberoceras ooceriforme, F. saffordi, F 

sonnenbergi, and Reedsoceras mcfarlani, all from the 

"Cynthiana Limestone" at Cynthiana, Ky. Comparison of 

nautiloid material from Winchester and Cynthiana indicates similar preservation and lithologies. Black and Cuppels (1973) indicate that the Strodes Creek Member 

extends northward from Winchester to Cynthiana. This 

evidence suggests that all of these nautiloid taxa may 

come from the Strodes Creek Member. If so, the Strodes 

Creek Member contains the most diverse nautiloid fauna 

in the Lexington Limestone exposed in the Blue Grass 

region of Kentucky (table 4). This nautiloid fauna consists 

of largely endemic taxa whose closest affinities are with 

nautiloids from the Catheys Formation in central Tennessee (Bassler, 1932) and nautiloid faunas from the Leipers 

Limestone (Late Ordovician, Edenian and Maysvillian) in 

the Cumberland valley in south-central Kentucky (Flower, 

1946).

NAUTILOID FAUNA OF THE CINCINNATIAN 

PROVINCIAL SERIES

EDENIAN NAUTILOID FAUNA

As indicated above, the central Kentucky region and 

adjacent portions of northern Kentucky, southeastern 

Indiana, and southwestern Ohio were inundated by a 

marine transgression in the latest Shermanian and Edenian. The deeper water marine environments generated 

by this transgression were the sites of the deposition of 

the clay shale, siltstone, and thin fossiliferous limestone 

of the Clays Ferry and Kope Formations throughout this 

area. Cressman (1973) and Weir and others (1984) indicate that both of these stratigraphic units were deposited
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P17

TABLE 4.—Nautiloid species from the Strodes Creek Member of 

the Lexington Limestone, north-central Kentucky

[Data for species from the Cynthiana, Ky., area from Flower (1946); data 

for species from the Winchester, Ky., area from collections made by 

USGS field parties and the writer's field work in the area. PO, Poindexter Quarry; CY, Cynthiana, Ky, area; WIN, Winchester, Ky., area; 

7310-CO, USGS collection locality number]

Species Occurrence

Order Orthocerida

1. Isorthoceras praenuntium

2. Polygrammoceras*? sp. 

Order Endocerida

3. Cameroceras sp. 

Order Actinocerida

4. Armenoceras vaupeli

5. Deiroceras perisiphonatum

6. Troedssonoceras obscuroliratum

7. Orthonybyoceras? perseptatus 

Order Oncocerida

8. Oncoceras carlsoni

9. O.fossatum

10. O. sp.

11. Oonoceras acutum

12. O. gracilicurvatum

13. O. multicameratum

14. O. planiseptum

15. O. suborthoforme

16. O. triangulatum

17. O.? brevidomum

18. Rizosceras graciliforme

19. R. conicum

20. Danoceras cynthianaense

21. Diestoceras sp. 

Order Discosorida

22. Faberoceras ooceriforme

23. F. saffordi 

, 24. F. sonnenbergi

PO

WIN (7310-CO)

CY

PO 

PO 

CY 

PO

PO

CY

CY

PO

PO

PO, WIN (7328-CO)

PO

PO

PO

PO

PO

PO

CY

PO

CY

CY, WIN (7331-CO)

CY, WIN (7310-CO)

at water depths at or below 80 ft (24 m), below fairweather wave base, but still within the zone of stormcurrent reworking.

Nautiloids are locally common in the interbedded 

clay shale and thin limestone of the Clays Ferry Formation in north-central Kentucky and the Point Pleasant 

Tongue of the Clays Ferry Formation in the greater Cincinnati region of northern Kentucky and southwestern 

Ohio. Characteristic species are the small longiconic 

orthocerids Isorthoceras albersi (pi. 10, figs. 1-9) and /.

rogersensis (Foerste) (pi. 10, figs. 10-12); Treptoceras cf. 

T. duseri (Hall and Whitfield); the large longiconic orthocerid Ordogeisonoceras amplicameratum (Hall) (pi. 3, 

figs. 1-3); an unidentified species of the endocerid Cameroceras, the coiled tarphycerid Trocholites faberi, Foerste, and the oncocerid Oncoceras covingtonense Flower.

Nautiloid faunas in the more clay-rich Kope Formation are dominated by common, but typically incomplete 

specimens of the longiconic orthocerid Treptoceras 

transversum (Miller) (pi. 8, figs. 4-9) and the large 

endocerid Triendoceras? davisi n. sp. (table 5). The latter 

species is typically represented in these strata by only the 

matrix-filled molds of the siphuncle tube (pi. 16, figs. 1-5). 

Less common in the Kope Formation are specimens of 

Ordogeisonocems amplicamevutum (pi. 3, figs. 4, 5, 8) 

and Trocholites faberi (pi. 19, figs. 6-10). Flower (1946) 

also lists rare specimens of the oncocerids Augustoceras? 

sp. and Diestoceras? edense Flower and the discosorids 

Faberoceras magister (Miller), Westonoceras ventricosum Flower, and W.? ortoni (Meek) from the Kope Formation at Cincinnati.

Clays Ferry and Kope nautiloid faunas are most similar to the coeval Utica Shale fauna in New York (Hall, 

1847; Ruedemann, 1926) and the fauna of the Whitby Formation in southern Ontario (Liberty, 1969). Associated 

with the regional transgressive event represented by the 

deposition of these formations in the Cincinnati arch 

region is a brief incursion of the so-called "Arctic" fauna 

into the northern Kentucky-southwestern Ohio region 

(Flower, 1946, 1976). This "Arctic" nautiloid fauna has 

been described from late Middle Ordovician (Shermanian) to Late Ordovician (Richmondian) tropical platform 

facies in New Mexico (Flower, 1970), Wyoming (Foerste, 

1935; Miller and Carrier, 1942), Manitoba (Foerste, 1929b), 

the Hudson Bay region (Nelson, 1963), the Canadian Arctic Archipelago (Miller and others, 1954), and northern 

Greenland (Troedsson, 1926). Edenian elements of this 

fauna in the Cincinnati area are species of the oncocerid 

Diestoceras and the discosorid Westonoceras. This incursion of these "Arctic" nautiloid taxa into the Cincinnati 

arch region coincides with the fuller development of this 

fauna to the north in the Cobourg Limestone in Ontario, 

Quebec, and adjacent portions of New York (Flower, 

1952; Wilson, 1961; Liberty, 1969).

MAYSVILLIAN AND EARLY RICHMONDIAN 

NAUTILOID FAUNA

Nautiloids are abundant and typically well preserved 

in a number of blocky claystone beds in the Fairview Formation, Grant Lake Limestone, and Bull Fork Formation 

(Maysvillian-early Richmondian) in northern Kentucky, 

southeastern Indiana, and southwestern Ohio. Nautiloid
P18 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

TABLE 5.—Distribution of species of nautiloid cephalopods in the Upper Ordovician Cincinnatian Provincial Series in the Cincinnati

arch region to Kentucky, Indiana, and Ohio

[Data include only those nautiloid species described in this paper, primarily nonsilicified material from museum collections. Upper Ordovician stratigraphic units from which no nautiloid species are described are omitted. CF, Clays Ferry Formation; KO, Kope Formation; LL, Leipers Limestone; 

FA, Fairview Formation; GL, Grant Lake Limestone; BF, Bull Fork Formation; DR, Drakes Formation; SA, Saluda Formation; WW, Whitewater 

Formation; HL, Hitz Limestone Member. X indicates presence of species. For locality information, see appendix]

Species CF KO LL FA GL BF DR SA WW HL Location

Orthocerida

Pleurorthoceras darks villense

Ordogeisonoceras amplicameratum

Tfeptoceras bymesi

Treptoceras cincinnatiensis

Treptoceras duseri

7} -ep toceras fosteri

Treptoceras transversum

Gorbyoceras gorbyi

Gorbyoceras hammelli

Richmondoceras brevicameratum 

Endocerida

Cameroceras rowenaense

Cameroceras? sp.

Tti,endoceras? davisi 

Actinocerida

Orthonybyoceras dyeri

X IND-1, OH-7, OH-15

X Cincinnati, Ohio

X OH-4

X XX KY-3, OH-6 to 9,6127-CO

X XXX KY-3, OH-2,3,5-9

X IND-1, 2; OH-6 to 9

X X KY-1,2

X IND-4 

X X IND-4 to 6

X X Osgood, Ind.; OH-10

X KY-4

X KY-5

X KY-1,2

XXX Covington, Ky., Cincinnati,

	Ohio

Tarphycerida

Trocholi tes faber i

Oncocerida

Beloitoceras amoenum

Beloitoceras bucheri

Augustoceras shideleri

Manitoulinoceras gyroforme

Dies toceras indianense

Diestoceras shideleri

Dies toceras eos

X KY-1

X X IND-7, OH-13

X IND-4

X KY-4

X OH-12

X IND-4

X IND-4

X OH-10

faunas in these claystone beds are usually of low diversity, dominated by an abundance of several species of the 

longiconic orthocerid Treptoceras Flower. These species 

are T. duseri (Hall and Whitfield) (pi. 4, figs. 8-12; pi. 5, 

figs. 1-6), T. fosteri (Miller) (pi. 5, figs. 7-9; pi. 6, figs. 1-3, 

5, 7, 8), and T. cincinnatiensis (Miller) (pi. 7, figs. 1-8; pi. 

8, figs. 1-3). Species of Treptoceras typically make up 75 

percent of the nautiloids present in these strata, usually 

associated with lesser numbers of the endocerid Cameroceras inaequabile (Miller), the actinocerid Orthonybyoceras dyeri (Miller) (pi. 18, figs. 10-17), and rare 

specimens of the oncocerids Oncoceras and Manitoulinoceras (Frey, 1988, 1989). This is the typical "Cincinnatian" fauna that is characteristic of shallow-marine strata 

of this age across the northern Cincinnati arch region.

Nautiloids are less common in brachiopod-bryozoan 

packstone facies of the Galloway Creek Limestone, the 

Fairview Formation, and the Grant Lake Limestone in the 

Kentucky-Indiana-Ohio region. Specimens are often fragmentary and consist of poorly preserved internal molds. 

Faunas in these limestones are also dominated by species 

of Treptoceras and Cameroceras, appearing with less 

common specimens of the actinocerids Orthonybyoceras 

dyeri and Tr'oedssonoceras turbidum (Hall and
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P19

Whitfield) and rare specimens of the oncocerids Beloitoceras and Oncoceras (Flower, 1946).

Nautiloid taxa in Maysvillian and early Richmondian 

strata in the Cincinnati region are also characteristic of 

the "Lorraine" fauna of Foerste (1914b). This fauna is well 

developed in coeval clastic marine facies of the Pulaski 

Formation in New York (Hall, 1847; Ruedemann, 1926) 

and in the Georgian Bay Formation in southern Ontario 

(Parks and Fritz, 1922; Foerste, 1924a; Liberty, 1969).

NAUTILOID FAUNA OF THE LEIPERS LIMESTONE

The Leipers Limestone (Edenian and Maysvillian) 

exposed in the Cumberland River valley in south-central 

Kentucky has a distinctive, diverse nautiloid fauna of 17 

species belonging to 9 genera. These nautiloid taxa consist of four species of the large discosorid Faberoceras 

and three species of the slender cyrtoconic oncocerid 

Augustoceras, associated with the oncocerids Danoceras 

and Oncoceras, as well as the ubiquitous orthocerid Treptoceras and the endocerid Cameroceras (Flower, 1946). 

The latter genus is represented by C. rowenaense n. sp. 

(pi. 14, figs. 1, 2). The most abundant nautiloid in collections available to the writer is the oncocerid Augustoceras shideleri Flower (pi. 20, figs. 23-27).

Flower (1946) indicated that nautiloids were most 

abundant in two Tetradium biostromal beds in the lower 

half of the formation. The Leipers Limestone nautiloid 

fauna is endemic to the outcrop belt in south-central Kentucky, and some of the characteristic genera also occur in 

the Catheys Formation and the Leipers Limestone in a4jacent portions of central Tennessee (Bassler, 1932). Many 

of the Leipers Limestone nautiloid taxa also occur in similar facies in the older Strodes Creek Member of the Lexington Limestone (Shermanian and Edenian) in eastcentral Kentucky.

MIDDLE AND LATE RICHMONDIAN NAUTILOID FAUNAS

Younger Richmondian strata in the northern Cincinnati arch region of Kentucky, Indiana, and Ohio indicate 

the influx of many new nautiloid taxa into the region 

(Flower, 1946,1976; Frey, 1981). As indicated above, these 

immigrant taxa have their origin in the distinctive "Arctic" 

nautiloid fauna characteristic of late Middle Ordovician to 

Late Ordovician tropical carbonate platform facies in 

western and northern portions of North America (Foerste, 1929a). The incursion of these taxa into the KentuckyIndiana-Ohio area coincides with an early Richmondian 

transgression across the area and the subsequent 

shallowing-up cycle in which there is a shift from primarily clastic to carbonate sedimentation (fig. 2 and table 5).

The "Richmondian" fauna from the northern Cincinnati arch region consists of smaller, local versions of the 

giant forms characteristic of this "Arctic" nautiloid fauna. 

These Ohio valley species also differ from the typical 

"Arctic" fauna characteristic of Wyoming, Manitoba, and 

the Hudson Bay region in the absence of many important 

taxa. These are the actinocerids Actinoceras, Kochoceras, 

and Huronia; the orthocerid Ephippiorthoceras', the tarphycerids Aspidoceras, Digenoceras, and Wilsonoceras; 

and the discosorids Cyrtogomphoceras, Westonoceras, 

and Winnipegoceras. The "Richmondian" fauna in the 

Cincinnati arch region is more similar to nautiloid faunas 

described from the more carbonate-rich facies of the 

Maquoketa Shale (Late Ordovician, Maysvillian and Richmondian) in northeast Iowa and Minnesota (Foerste, 

1936a). The Ohio valley "Richmondian" fauna is also similar to coeval nautiloid faunas described from the Vaureal 

Formation on Anticosti Island, Quebec (Foerste, 1928a) 

and the Whitehead Formation at Perce, Quebec (Foerste, 

1936b).

The first incursions of this "Arctic" fauna into the 

Kentucky-Indiana-Ohio area during Richmondian times 

occur within the "Waynesville" biofacies (in the sense of 

Wahlman, 1992, p. 19) in the Bull Fork Formation (early 

Richmondian) in southwestern Ohio. Early immigrants 

are the ascocerid Schuchertoceras obscurum Flower and 

the annulated orthocerid Gorbyoceras curvatum Flower, 

both in the Treptoceras duseri shale unit (Frey, 1988, 

1989). The longiconic orthocerid Pleurorthoceras clarkesviUense (Foerste) (pi. 2, figs. 10-15), the aberrant "flatfish" actinocerid Lambeoceras richmondense (Foerste), 

and the large oncocerid Diestoceras waynesvillense 

Flower occur slightly higher up (30-40 ft) within the formation in southwestern Ohio (Flower, 1946).

The "Arctic" nature of the "Richmondian" fauna in 

the tristate area reaches its fullest development, however, 

in the Bardstown Member of the Drakes Formation in 

northwest Kentucky, in the overlying Saluda Dolomite 

Member in northwest Kentucky and adjacent portions of 

southeastern Indiana, and in the Whitewater Formation in 

southeastern Indiana, A compilation of data from field 

work done for this report in Indiana and Ohio and a list of 

taxa presented by Flower (1946) indicate the presence of 

65 described nautiloid species in these strata, belonging 

to 24 genera and 7 orders. Only about 20 of these species, 

however, are abundant enough to be commonly encountered in these strata. A number of late Richmondian nautiloid taxa from the Saluda Formation, its Hitz Limestone 

Member, and the overlying Whitewater Formation in 

southeastern Indiana are described and illustrated here. 

These taxa are the large longiconic orthocerid Richmondoceras brevicameratum n. sp. (pi. 13, figs. 1-4), the 

annulated orthocerids Gorbyoceras gorbyi (Miller) (pi. 

12, figs. 12, 13) and G. hammelli (Foerste) (pi. 12, figs. 4,
P20 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

6, 7, 10, 11), and the oncocerids Beloitoceras amoenum 

(Miller) (pi. 22, fig. 2), B. bucheri Flower (pi. 22, figs. 4, 5), 

Diestoceras shideleri (Foerste) (pi. 21, figs. 1, 2, 5; pi. 22, 

figs. 1, 3) and D. indianense (pi. 22, figs. 6-9).

The top of the Upper Ordovician rocks in southwestern Ohio consists primarily of blue clay shale and thin fossiliferous limestone west of the Dayton, Ohio, area and 

maroon and pale green mudstone interspersed with minor 

thin siltstone and limestone southeast of Dayton. In 

southwestern Ohio the blue shale and limestone facies is 

referred to as either the Bull Fork or Whitewater Formation (Weir and others, 1984, p. 81-90; Shrake and others, 

1988), and the maroon and green mudstone facies is 

placed within the Preachersville Member of the Drakes 

Formation. The contact between these units is gradational and diachronous across southwestern Ohio, with 

the Preachersville Member thickening to the southeast 

(Sweet, 1979).

These formations in southwestern Ohio contain a 

sparse nautiloid fauna consisting of the ubiquitous Treptoceras and Cameroceras plus the large longiconic orthocendRichmondoceras brevicameratum (pi. 13, figs. 5-8), 

rare specimens of the actinocerid Lambeoceras richmondense (Foerste), and the oncocerids Beloitoceras amoenum Miller (pi. 21, fig. 3), Manitoulinoceras gyroforme 

Flower (pi. 20, figs. 28, 29), and Diestoceras eos (Hall and 

Whitfield) (pi. 21, fig. 4). All of these taxa were collected 

from the blue shale and thin limestone lithology ^uppermost Bull Fork Formation).

The writer has collected a small, incomplete oncocerid (cf. Beloitoceras} from the maroon mudstone facies 

in Adams County, Ohio. Flower (1957b) also listed Treptoceras associated with trilobites and eurypterids from this 

lithology exposed at Manchester, Adams County, Ohio. 

Nautiloids have not been described from the same facies 

in adjacent portions of northern Kentucky.

LATE ORDOVICIAN EXTINCTION EVENT

One of the largest extinction events in the Phanerozoic fossil record occurred at the Ordovician-Silurian 

boundary. Sepkoski (1982) has estimated that 22 percent 

of all marine invertebrate families became extinct during 

this event, second in magnitude only to the extinction at 

the Permian-Triassic boundary. Brenchley (1989) summarized the effects of this extinction on the major invertebrate groups, noting that the Late Ordovician extinction 

sharply reduced the number of genera and species among 

trilobites, nautiloids, corals, brachiopods, crinoids, graptolites, conodonts, and acritarchs. Both sessile filter feeders and vagile benthos were affected. His figures indicate 

that graptolite genera were reduced nearly 100 percent, 

corals and trilobites suffered 75 percent extinction at the

genus level, crinoid genera suffered 70 percent extinction, 

and brachiopod genera were reduced by 25 percent.

House (1988) indicated approximately 100 nautiloid 

genera in the Upper Ordovician and a loss of nearly 55 

percent of these genera by the end of the period. The 

writer's tabulations of Upper Ordovician nautiloid taxa 

from the published literature indicate that Richmondian 

nautiloid faunas in Laurentia consisted of 48 genera 

belonging to 8 orders. Succeeding Gamachian faunas, 

known primarily from Anticosti Island, Quebec (Foerste, 

1928a), are represented by 15 genera belonging to 6 

orders. The nautiloid order Ellesmerocerida went extinct 

at this time, and the order Endocerida was reduced to 

several poorly known species of Cameroceras and 

Endoceras and the problematic genus Humeoceras. Only 

13 genera survived from the Ordovician into the Silurian, 

indicating an extinction of 73 percent of Richmondian 

nautiloid genera by the end of the Gamachian. These Silurian survivors are elements of the Ordovician "Arctic" 

fauna that persisted into the Silurian in carbonate basin 

areas in the Hudson Bay region of Canada (Foerste and 

Savage, 1927; Flower, 1968b) and in the Anticosti Island 

region of Quebec (Foerste, 1928a).

In the northern Cincinnati arch region, nautiloids 

declined from a high of 65 species, belonging to 24 genera, 

in the late Richmondian Saluda and Whitewater Formations to 7 species, belonging to 6 genera in the youngest 

Ordovician rocks immediately below the Brassfield Limestone (Silurian-Llandoverian) in southeastern Indiana, In 

southwestern Ohio, nautiloid diversity drops from a high 

of eight species belonging to seven genera in the upper 

part of the Bull Fork Formation to a low of two species 

belonging to two genera in the Preachersville Member of 

the Drakes Formation, within 10 ft of the OrdovicianSilurian contact. While Brassfield Limestone nautiloids 

are poorly known and in need of study, the possible 

exception being the orthocerid Treptoceras, none of the 

Richmondian genera occur in the overlying Silurian. The 

Brassfield Limestone nautiloid fauna in the KentuckyIndiana-Ohio region (Foerste, 1893) is a mix of Ordovician survivors and direct descendants (orthocerids Treptoceras Flower and Euorthoceras Foerste, actinocerid 

Ormoceras Saeman, and the discosorid Glyptodendron 

Claypole) plus a number of newly evolved, distinctly Silurian taxa (actinocerid Elrodoceras Foerste and the discosorid Discosorus Hall).

The mass extinction event of the Late Ordovician is 

coincident with a worldwide regressive episode that has 

been associated with continental glaciation centered in 

African and South American portions of Gondwanaland 

(Berry and Boucot, 1973; Denison, 1976; Brenchley and 

Newall, 1980; Brenchley, 1984). This extinction has been 

attributed to climatic cooling (Stanley, 1984a, 1984b), a 

loss of shallow-marine shelf area (Sheehan, 1988), and a
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P21

combination of these factors (cooling, regression, 

changes in ocean chemistry, and paleogeography), all 

associated with the growth and decay of the Gondwanan 

ice sheets (Brenchley, 1989). A lack of supporting 

geochemical evidence across the Ordovician-Silurian 

boundary makes an extraterrestrial impact unlikely as the 

cause of this extinction (Orth and others, 1986).

Sedimentological and paleontological evidence suggests that the late Richmondian (=Ashgillian) extinction 

in Laurentia was primarily the result of the regression of 

shallow epicontinental seas off extensive cratonic shelf 

areas, eliminating marine habitats and the "perched faunas" that were dependent on these environments (Sheehan, 1988), the so-called "species-area effect" (MacArthur 

and Wilson, 1963). Evidence of this Late Ordovician 

regression is well documented in the northern Cincinnati 

arch area.

In the Kentucky-Indiana-Ohio region, this Late 

Ordovician regression is represented by the Richmondian 

shallowing-up cycle, consisting of the basal deeper water 

marine shelf shale and fossiliferous limestone of the Bull 

Fork Formation grading up into shallow water carbonates 

(Saluda and Whitewater Formations) in western portions 

of the Cincinnati arch region and intertidal mudstone and 

mud-cracked siltstone (Preachersville Member of the 

Drakes Formation) along the east flank of the arch (fig. 

2). Uppermost Ordovician strata (Gamachian) are not 

exposed anywhere in the Cincinnati arch region. Contrary 

to the observations of Gray and Boucot (1972), at most 

localities studied for this report in southeastern Indiana 

and southwestern Ohio, a disconformity marks the 

Ordovician-Silurian boundary. This distinctive erosional 

surface is diachronous across the region, being older to 

the southeast and younger in the western portions of the 

Cincinnati arch region (Sweet, 1979) (fig. 2).

Uppermost Ordovician nautiloid faunas in the Cincinnati arch region are dominated by elements of the "Arctic" 

fauna, characterized by Flower (1946, 1976) as being a 

tropical fauna. Nautiloids from the Ordovician rocks, 

immediately underlying the Brassfield Limestone (Llandoverian, C1-C2) in Decatur County, Ind. (Fluegeman and 

Pope, 1983) have "Arctic" affinities. These taxa consist of 

the endocerid Endoceras, the oncocerids Beloitoceras 

and Oonoceras, and large tarphycerids tentatively 

assigned to Charactoceras Foerste andDeckeroceras Foerste. Ordovician nautiloid taxa surviving into the Early Silurian in Laurentia are also largely members of this 

"Arctic" fauna (Foerste and Savage, 1927; Foerste, 1928a; 

Flower, 1968b). These taxa are associated with carbonate 

platform facies in the Hudson Bay region and mixed carbonates and shale at Anticosti Island, Quebec. Succeeding 

Llandoverian nautiloid faunas across Laurentia are also 

primarily tropical taxa associated with carbonate platform facies. This "Discosorus-Huronia fauna" consists of

a mix of Ordovician "Arctic" relict forms and new actinocerid and discosorid taxa, the latter two orders being typically most abundant in tropical carbonate facies (Flower 

and Teichert, 1957; Flower, 1957b, 1968b). None of these 

occurrences seem to support the idea that climatic cooling associated with the Late Ordovician glaciation was a 

major factor affecting the extinction of these nautiloid 

taxa in Laurentia in the late Richmondian, as a majority of 

the surviving taxa were stenothermic tropical forms.

NAUTILOID TAPHONOMY

NAUTILOID BIOSTRAHNOMY

Nautiloid remains occur in a number of the lithofacies that make up the Ordovician strata exposed in Kentucky and adjacent States. Nautiloid preservation in these 

rocks is a function of several factors: original depositional 

environment; nautiloid shell strength, morphology, and 

size; and effects of a variety of postdepositional processes. The latter are biological processes like bioturbation, mechanical processes like storm reworking of 

bottom sediments, and chemical processes such as dissolution and replacement of the original aragonitic shell.

Nautiloids are typically restricted to subtidal marine 

facies representative of the environments occupied by the 

living cephalopod. Reports of extensive postmortem 

transport of Nautilus shells in the Indo-Pacific region 

(Stenzel, 1964; Toriyama and others, 1965; Teichert, 1970), 

coupled with descriptions of a number of currentaffected, shallow-water, or strand-line nautiloid assemblages (Miller and Furnish, 1937; Reyment, 1958, 1968; 

Zinsmeister, 1987), have led to the general assumption 

that many or all fossil nautiloid accumulations were 

deposited after some unknown period or distance of 

transport from the habitat of the living nautiloid animal. 

Many Paleozoic nautiloids possessed phragmocones that 

were counterweighted against positive buoyancy and 

probably would have rapidly filled with water and sank 

after death (Crick, 1988,1990; Frey, 1989). Studies of Nautilus (Chamberlain and others, 1981) have indicated that 

extensive postmortem drift of Nautilus is a relatively rare 

event. Ordinarily, upon the death of the animal, the shells 

sink to the sea floor in the area in which the animals lived. 

Studies of the ontogeny of living Nautilus (Saunders and 

Spinosa, 1979; Landman and others, 1983) indicate that 

these cephalopods lack a planktonic larval stage capable 

of being dispersed by oceanic currents. Additionally, the 

distribution of adult Nautilus is constrained by stretches 

of deep water in excess of 800 m (2,625 ft) as well as areas 

of open ocean (Ward, 1987). These studies of living Nautilus coupled with investigations of the biogeography of 

fossil nautiloids (Flower, 1957b, 1976; Crick, 1980, 1990; 

Frey, 1989) indicate that nautiloids were not part of the
P22 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

nekton, but were nektobenthic, that is, part of the 

shallow-shelf benthos and capable of dispersal only along 

continuous shelf areas or over shallow stretches of open 

ocean. The facies distribution of the nautiloid taxa 

described here also supports this point of view

SILICIFIED NAUTILOIDS

Many of the nautiloids described here, especially 

specimens from the Tyrone Limestone and the Lexington 

Limestone, are silicified. These specimens were obtained 

from bulk rock collections (36,000 pounds (Ibs) of limestone) made by USGS field parties in the 1960's and 

1970's. Details of this acid-etching program can be found 

in the works by Pojeta (1979) and Pope (1982). Silicified 

nautiloid material presents both problems and opportunities in terms of nautiloid study. As indicated by Flower 

(1965), nautiloids are often common in massive-bedded 

limestone facies, but they are difficult to study because of 

the complexity of extracting large nautiloid shells from 

these dense limestones. Usually, only fragments of such 

specimens can be obtained. Lower Paleozoic nautiloid 

species are often based on single fragments or a number 

of fragments representing different parts of one or more 

specimens.

Silicified material from the Ordovician of Kentucky 

yielded a number of more or less complete, uncrushed 

specimens, commonly with details of the shell's exterior 

ornament preserved. Unfortunately, key internal features, 

especially septal necks and connecting rings, typically are 

not preserved, making family- and genus-level identifications difficult. These features are especially critical in the 

systematic treatment of morphologically conservative 

longiconic groups, namely, the baltoceratids, orthocerids, 

and actinocerids. These taxa make up the bulk of the nautiloids from Ordovician strata in Kentucky. Surprisingly, 

camera! and endosiphuncular deposits are commonly preserved in these specimens (pis. 1, 4, 17) and can, if sufficiently developed, give some indication of siphuncle 

segment shape and septal neck type. Coarse silicification 

typically destroys key internal features of the siphuncle 

used to differentiate endocerid taxa. Fortunately, in the 

case of the Tyrone Limestone material, silicification was 

such that these important features were preserved 

(pi. 15).

Silicified nautiloid material from the 6034-CO collection in the Tyrone Limestone consisted of many unidentifiable fragments and fewer sections of phragmocone up 

to 35 cm in length. Baltoceratids and orthocerids in this 

collection consist primarily of adapical portions of phragmocones (less than 15 cm in length) that lack preserved 

body chambers (pis. 1, 2, 4, 9). Endocerids and actinocerids consist of larger portions of the phragmocone (15-35 

cm in length) that preserve the large siphuncle and

attached camerae (pis. 15, 17). Oncocerids are preserved 

as adapical portions of the phragmocone, rarely having 

shells that have body chambers intact (pi. 19, figs. 11-15; 

pi. 20, figs. 7-12). Tarphycerids are preserved as the inner 

whorls of the coiled phragmocone (pi. 19, figs. 1-3) and 

fragments of the body chamber. The fragmental nature of 

this assemblage as well as the enclosing biopelsparite 

lithology attest to deposition in a shallow-water, wave- or 

current-affected environment. However, the poor sorting 

of this nautiloid material suggests only periodic current 

reworking of these shells, reworking by episodic storms 

rather than the constant milling action of "normal" wave 

and current activity in a shoaling environment.

The basal Curdsville Limestone Member of the Lexington Limestone yielded less well preserved, coarsely 

silicified, fragmentary phragmocones and external molds 

(pi. 17, fig. 11; pi. 18, figs. 8, 9). In contrast, nautiloids 

from the overlying Logana Member and Grier Limestone 

Member of the Lexington Limestone and from the Clays 

Ferry Formation consist of finely silicified fragmentary 

and complete phragmocones that have the external ornament well preserved (pi. 10, figs. 4-7; pi. 12, figs. 1, 2; pi. 

20, figs. 1, 2, 19-22). The more complete nature of this 

material is probably a function of the lower energy, 

quiet-bottom environments indicated for these stratigraphic units.

NONSILICIFIED NAUTILOIDS

Nautiloid specimens from more clastic-rich lithofacies of the Lexington Limestone and the overlying Cincinnatian Provincial Series in the Kentucky-Indiana-Ohio 

area usually are poorly preserved, matrix-filled internal 

molds or better preserved, calcite-replaced internal 

molds. Shell exteriors are rarely encountered, usually as 

external or composite molds or, less commonly, as the 

calcite-replaced outer shell. Nautiloids in shalier, mudrich facies are commonly complete and consist of the 

phragmocone and the body chamber but are usually 

crushed and flattened by compaction of the enclosing 

sediment. These molds typically fail to preserve the critical internal structures of the siphuncle. Nautiloid material 

from the various limestone lithologies in Cincinnatian 

strata often consists of fragmentary material that is generally less deformed than specimens from shalier facies. 

Preservation of internal features is dependent on whether 

or not the septa and siphuncle are replaced by calcite. 

Silicification is uncommon in Cincinnatian rocks and, if 

present, is commonly coarse and incomplete. Replacement of nautiloid shells by sparry calcite is far more common and results in the best preserved nautiloids collected 

from these Upper Ordovician rocks. However, in some 

specimens, especially endocerids, the coarse sparry
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P23

calcite has obliterated the critical internal structure of the 

siphuncle.

Claystone facies and, less commonly, thin packstone 

beds in the Kope, Clays Ferry, Fairview, Grant Lake, and 

Bull Fork Formations locally yield abundant wellpreserved nautiloids. This material typically consists of 

complete, calcite-replaced phragmocones with body 

chambers more or less intact (pi. 3, figs. 1-5; pi. 4, figs. 8- 

12; pi. 5; pi. 6; pi. 7). Some of these also preserve the outer 

shell, occasionally with the original color pattern of the 

shell (pi. 6, fig. 3). Similar calcite-replaced material is also 

common in the dense, dark-gray fossiliferous wackestone 

of the Leipers Limestone in south-central Kentucky (pi. 

14, figs. 1, 2; pi. 20, figs. 23-27). Less well preserved, but 

commonly complete, matrix-filled internal molds are 

locally common in the muddy wackestone facies of the 

Mount Auburn Member of the Grant Lake Formation 

(Schumacher and others, 1991) in the Cincinnati area; in 

local facies within the Bull Fork Formation in southwestern Ohio (pi. 2, figs. 10-15; pi. 6, figs. 4, 8; pi. 13, figs. &-8); 

and in dense, micritic limestone beds within the Saluda 

Formation in southeastern Indiana (pi. 12, figs. 12, 13; pi. 

13, figs. 1, 3, 4; pi. 21, figs. 1, 2). Spar-replaced, well-preserved fragmentary nautiloid material is abundant in the 

thin, platy, silty limestone of the Hitz Limestone Member 

at the top of the Saluda Formation in southeastern Indiana and northern Kentucky (pi. 12, figs. 4, 6, 7,10,11).

NAUTILOID CLASSIFICATION

The classification used here for the higher level 

nautiloid taxa is that of Teichert (1988). Teichert's classification divides the nautiloid cephalopods into four subclasses: the Orthoceratoidea, consisting of the orders 

Ellesmerocerida, Orthocerida, and Ascocerida, plus a 

number of short-lived Cambrian orders (Chen and 

Teichert, 1983); the Endoceratoidea, consisting of the 

order Endocerida and the problematic Interjectocerida; 

the Actinoceratoidea, consisting of the order Actinocerida; and the Nautiloidea, consisting of the orders Tarphycerida, Oncocerida, Discosorida, and Nautilida. As 

emphasized by Crick (1988) and by Wade (1988), this classification stresses the importance of buoyancy regulation 

as the central problem that fueled the evolution of the 

group. Morphological differentiation of these taxa centers 

on the development of various buoyancy-regulating 

devices. Crick (1988) noted that the Paleozoic evolutionary history of the cephalopods is "a series of experiments 

in an attempt to find the most energy-efficient compromise between buoyancy regulation, stability, orientation, 

locomotor design, and environment." Crick also listed five 

major solutions to the buoyancy control problem that 

were devised by these nautiloids. These are (1) short 

orthoconic and cyrtoconic longicones with water ballast

(Ellesmerocerida and the various Cambrian orders); (2) 

large orthoconic and cyrtoconic longicones with calcareous ballast (Ellesmerocerida, Orthocerida, Endocerida, 

Actinocerida); (3) orthoconic and cyrtoconic brevicones 

with water ballast (Oncocerida and Discosorida); (4) 

planispiral coiling (Tarphycerida, Nautilida); and (5) shell 

truncation (Ascocerida and rare Orthocerida).

Family- and genus-level systematics largely follow 

Teichert and others (1964) with the exception of the 

Orthocerida and the Tarphycerida The familial descriptions for the orthocerid Orthoceratidae, Michelinoceratidae, and Geisonoceratidae are emended to better 

define these groups. Descriptions of a number of genera 

within these families were also revised to better define 

these taxa The classification of the Tarphycerida used 

here is that of Flower (1984); however, the Barrandeocerida is abandoned and its families placed in the Tarphycerida New genera described are the longiconic orthocerids 

Pojetoceras, Ordogeisonoceras, and Richmondoceras. 

Familial and generic differentiation of taxa stresses the 

morphology of the siphuncle and the septa, especially 

siphuncle segment position, segment shape, segment 

diameter, endosiphuncular deposits, and nature of the 

septal necks.

The species problem in nautiloid systematics.— 

Species-level nautiloid taxa tend to be, on the whole, 

poorly defined. Most described Paleozoic species are 

based on fragmentary, often poorly preserved material. 

Studies of the few well-preserved, complete fossil nautiloids known to the writer have indicated that pronounced 

ontogenetic changes in the details of the shell morphology are typical of these nautiloid taxa. Species based on 

fragmentary specimens often have been found to represent separate ontogenetic stages of the same animal. This 

is certainly the case for the various species that have been 

assigned to the orthocerid genus Treptoceras Flower, 

which is the dominant nautiloid taxon in the Upper 

Ordovician rocks exposed in the Kentucky-Indiana-Ohio 

region.

Other studies of existing nautiloid species indicate 

that taxa were defined on the basis of criteria that took 

into account the nature of preserved epizoan organisms 

encrusting the nautiloid shell, stratigraphic occurrence, 

and type of preservation. Some species have been defined 

entirely on the basis of external shell features (shell 

shape, rate of shell expansion, size, external ornament), 

while others are known only from internal molds or isolated siphuncles. This often results in the naming of at 

least two taxa, representing the external and internal features of a single species. Additionally, as has been noted 

by Aronoff (1979) and Dzik (1984), there have been very 

few studies that have evaluated intraspecific variation in 

fossil nautiloids. This is due to the lack of the large numbers of specimens needed to characterize this variation
P24 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

and the description of most nautiloid species on the basis 

of one or a few specimens that are typically incomplete. 

All of this indicates that Paleozoic nautiloid species are 

probably oversplit and that consistent criteria for defining 

nautiloid species are largely lacking.

Morphological features traditionally used to differentiate longiconic nautiloid taxa (orthocerids, endocerids, 

actinocerids) consist primarily of the external characteristics of the conch. These are features like shell size, 

external shell ornament, shell cross sectional shape, rate 

of shell expansion (apical angle), camera! length, and 

suture type (fig. 4). The studies of Hyatt (1900), Teichert 

(1933), Flower (1939, 1946), and Flower and Kummel 

(1950) recognized the importance of the morphology of 

the siphuncle as a tool to distinguish various longiconic 

taxa. This morphology takes into account such attributes 

as siphuncle segment position within the shell, segment 

shape, segment diameter relative to total shell diameter, 

septal neck type, connecting ring structure, and the presence and structure of endosiphuncular deposits. A 

descriptive terminology developed to further define these 

features. These descriptive terms, unfortunately, were 

often ambiguous and came to mean different things to different people.

An attempt to correct this problem was made by 

Aronoff (1979), who proposed to standardize measurements of various features of longiconic nautiloid shells, 

especially siphuncle segment position and segment 

shape, and use these quantitatively to define longiconic 

taxa. His terminology is used here. Siphuncle position is 

measured using the segment position ratio (SPR). This 

indicates the position of the mid-axis of the siphuncle segment (fig. 55), measured from the venter, relative to the 

total diameter of the shell at the same point. SPR values 

range from dorsal (SPR greater than (>) 0.75), to middorsal (SPR=0.75), supracentral (SPR values between 0.50 

and 0.75), to central (SPR=0.50), subcentral (SPR values 

between 0.25 and 0.50), midventral (SPR=0.25), and ventral (SPR less than (<) 0.25) (fig. 5A). The shape of the 

siphuncle segment is expressed as the segment compression ratio (SCR), the ratio of segment height to segment 

length (fig. 5-B). SCR values range from depressed elongate (SCR less than 1.0, height is < length), to equiaxial 

(SCR=1.0; height is equal to length), to compressed (SCR 

> 1.0; height is greater than length) (fig. 5(7). These measurements are taken along the dorsal-ventral plane of the 

nautiloid shell and are used in conjunction with the traditional morphological features listed above (figs. 4 and 5) 

to define the longiconic nautiloid taxa described here. In 

this paper, nautiloids are subdivided into the following 

groups on the basis of size: small (less than 30 cm in 

length), medium (30-100 cm in length), and large (in 

excess of 100 cm). With respect to the rate of shell expansion, the following descriptive terms will be used: gradually expanding (apical angle less than 6 degrees); 

moderately expanding (apical angle 7-9 degrees); and 

rapidly expanding (apical angle greater than 9 degrees).

Differentiating members of the cyrtoconic/breviconic 

Oncocerida is likewise beset with a number of difficulties. 

This is particularly true of the Oncoceratidae, the most 

abundant oncocerids in these Ordovician strata. Genera 

and species have been differentiated primarily on the 

basis of shell outline, which takes into account the 

amount of shell curvature, shell cross section shape, and 

features of the body chamber and the aperture. As 

pointed out by Flower (1946), these features can be dramatically altered by deformation affecting the shell during 

the course of fossilization. This is not a problem with the 

well-preserved, generally uncrushed silicified material 

from the Tyrone and Lexington Limestones (pis. 19 and 

20), but is a significant factor complicating generic and 

specific identifications of matrix-filled internal molds in 

the more argillaceous Cincinnatian Provincial Series 

strata (pis. 20, 21, and 22). More of a problem in the case 

of the silicified material is the incomplete nature of most 

specimens, the collections consisting largely of smalldiameter (less than 10 millimeters (mm) in diameter) 

adapical portions of the phragmocone. Most published 

Ordovician oncocerid taxa have been described from 

more adoral portions of the phragmocone plus the associated body chamber. Adapical portions of many of these 

described species are unknown. Consequently, trying to 

determine the affinities of these adapical oncocerid shell 

fragments is difficult, if not impossible. Other features 

used to distinguish oncocerid taxa are siphuncle segment 

diameter and shape, septal necks, connecting ring structure, camera! length, and suture pattern.

Tarphycerid taxa are distinguished by their general 

shell shape (evolute coiled, serpenticone, or gyrocone), 

whorl cross section, siphuncle position, thickness of the 

connecting rings, and septa! neck type. Other features of 

taxonomic importance are the length of the body chamber, aperture configuration, cameral length, suture pattern, and external shell ornament. Unfortunately, most of 

the Ordovician tarphycerids described here are fragmentary, and species identifications are very tentative, if any 

assignment can be made at all.

SYSTEMATIC DESCRIPTIONS

Descriptions of the nautiloid species described here 

are organized in the following manner. First, there is a 

diagnosis summarizing the distinctive features of the 

taxon. This is followed by the taxonomic description, the 

first paragraph of which describes the morphological features of the shell that can be observed in hand specimen 

(fig. 4). These features are arranged in a hierarchy from
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION

A B

P25

FIGURE 4.—External morphological features used to differentiate nautiloid taxa 

described and illustrated here. A, Rate of shell expansion (apical angle): 

1, gradually expanding orthoconic longicone (apical angle less than 6 

degrees); 2, moderately expanding (apical angle 6.5-8.5 degrees); 3, rapidly 

expanding (apical angle more than 9 degrees). B, Shell cross-sectional 

shape: 1, depressed (Trocholitesy 2, circular (Richmondocerasy 

3, compressed (Maelonoceras). C, Camera! length: 1, short camera! lengths, 

the camera! length/diameter (CL/D) less than one-fifth (Cartersocerasy

2. moderate camera! lengths, CL/D one-fifth to one-fourth (Treptoceras~);

3. long camera! lengths, CL/D greater than one-third (Pleurorthoceras). 

D, Shell ornament: 1, raised longitudinal lirae (Isorthocerasy 2, incised 

longitudinal striae (Polygrammocerasy 3, transverse annulations 

(Monomuchitesy
P26 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

CLMIDDORSAL_ __ _

SPR

.75

CENTRAL

FIGURE 5.—Internal morphological features used to differentiate nautiloid taxa 

described and illustrated here. A, Siphuncle segment position ratio (SPR). 

B, Siphuncle segment measurements: CL, camera! length; AA, segment axis; 

BB, segment height; CC, segment length; R, radius. C, Siphuncle segment 

compression ratio (SCR): 1, SCR less than 1.0, height less than length, depressed 

(Ordogeisonoceras); 2, SCR=1.0, height equal to length, equiaxial (Treptocerasy, 

3, SCR greater than 1.0, height greater than length, compressed (Actinoceras). 

D, Camera! deposits: 1, planar mural deposits (Pleurorthoceras); 

2, mural-episeptal deposits (Treptoceras); 3, hyposeptal and episeptal deposits 

(Ordogeisonoceras). E, Types of endosiphuncular deposits: 1, endosiphuncular 

rod (Murrayoceras); 2, endocones (Cameroceras); 3, parietal deposits 

(Treptoceras); 4, annulosiphonate deposits (Actinoceras') (A, B modified from 

Aronoff, 1979).
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P27

the more general to the more specific: (1) general shell 

morphological type (orthoconic longicone, cyrtoconic 

longicone, cyrtoconic brevicone, etc.), (2) maximum 

observed shell diameter and estimated maximum length, 

(3) apical angle (angle of shell expansion), (4) crosssectional shape of shell, (5) suture pattern, (6) camera! 

length, (7) nature of the body chamber including 

periphract type, and (8) external shell ornament. The second paragraph describes the internal features of the shell, 

primarily the attributes of the siphuncle (fig. 5), which are 

(1) position of the siphuncle within the shell (SPR), (2) 

siphuncle segment diameter relative to shell diameter, (3) 

siphuncle shape (SCR), (4) nature of septal necks, (5) 

connecting ring structure, (6) endosiphuncular deposits if 

present, and (7) camera! deposits if present.

These descriptive paragraphs are followed by sections on the known stratigraphic and geographic occurrences of the species, a list of the specimens studied, and 

remarks. The latter section compares the species with 

other members of the same genus, describes observed 

variation within the specimens studied, and makes observations on the relative abundance of the species within 

the stratigraphic unit(s) in which it is found.

SYSTEMATIC PALEONTOLOGY

PHYLUM MOLLUSCA LINNAEUS

CLASS CEPHALOPODA CUVIER

SUBCLASS ORTHOCERATOIDEA KUHN

Generally small, predominantly orthoconic, less commonly cyrtoconic nautiloids that employed a variety of 

solutions to solve the problem of buoyancy regulation, 

including retention of cameral fluid within the camerae, 

crowding of septa to reduce cameral chamber volume, 

and various types of calcareous ballast, secreted within 

cameral chambers and (or) within the siphuncle tube. 

Connecting rings thick, complex in primitive forms, 

becoming thin and homogeneous in later stocks. Septal 

necks achoanitic, loxochoanitic, orthochoanitic, suborthochoanitic, or cyrtochoanitic. Periphract dorsomyarian; 

body chambers tubular, comparatively long. Central stock 

from which all other cephalopod groups evolved.

Stratigraphic range.—Upper Cambrian to Triassic.

ORDER ELLESMEROCERIDA FLOWER

Predominantly small, generally smooth, compressed 

cyrtoconic or orthoconic nautiloids with comparatively 

short phragmocones equipped with closely spaced septa 

and ventral tubular siphuncles with short elliptochoanitic 

septal necks and primitively thick, structurally complex 

connecting rings. Methods of buoyancy control typically 

employed were an abbreviated phragmocone, the crowding of septa, a moderate- to large-diameter, probably

tissue-filled siphuncle, and the possible retention of cameral fluid within cameral chambers with the siphuncle 

tube sealed off by diaphragms in some taxa.

Stratigraphic range.—Upper Cambrian to Upper 

Ordovician.

Remarks.—This order contains the most primitive 

nautiloids; typically small, compressed, endogastric cyrtocones and orthocones with closely spaced septa and 

large-diameter, tubular ventral siphuncles. Siphuncles are 

characterized by thick, complex, layered connecting rings 

and short orthochoanitic septal necks. However, as indicated by Furnish and Glenister (1964), a multitude of morphological forms are included in the order such that a 

central defining morphological theme is hard to pinpoint. 

In all probability, the order is an artificial grouping of 

early evolutionary experiments in nautiloid morphology. 

Chen and Teichert (1983) have split off several of the 

Cambrian groups into separate orders, among them the 

Plectronocerida and the Protactinocerida. Other distinctive groups within the Ellesmerocerida that may constitute separate order-rank taxa are the longiconic 

Baltoceratidae and Protocyloceratidae, the strongly compressed Bassleroceratidae, and the Bathmoceratidae and 

Cyrtocerinidae, both characterized by greatly thickened, 

complex connecting rings.

Ellesmerocerids are most abundant in Upper Cambrian and Lower Ordovician strata The order declined 

significantly at the end of the Early Ordovician (Arenigian), represented in the Middle Ordovician by the longiconic baltoceratids, the bizarre bathmoceratids, and the 

breviconic cyrtocerinids. Upper Ordovician relict taxa are 

the long-ranging genus Cyrtocerina Billings and the problematic slender cyrtocone Shideleroceras Flower, both 

from the Cincinnatian Provincial Series in the KentuckyIndiana-Ohio region (Flower, 1946).

FAMILY BALTOCERATIDAE KOBAYASHI

Slender, smooth orthoconic longicones, subcircular 

to depressed in cross section, with moderately large, ventral siphuncles that come to assume a more central position in some advanced forms. Siphuncles lacking 

diaphragms, having connecting rings thinner, less complex in structure than those of other members of the 

order. Septal necks orthochoanitic or suborthochoanitic. 

Calcareous deposits, both endosiphuncular and cameral, 

well-developed. Endosiphuncular deposits consisting of 

tubular calcareous rods that are typically depressed circular in section, lie against the ventral wall of the siphuncle, 

are blunt or acute adorally, thickening adapically, and 

eventually completely fill the adapical portions of the 

siphuncle tube. Cameral deposits typically mural-
P28 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

episeptal, restricted to the adapical half of the phragmocone.

Stratigraphic range.—Lower Ordovician (Ibexian 

Provincial Series) to Middle Ordovician (Rocklandian 

Stage).

Remarks.—Good descriptions and illustrations of the 

structures that are characteristic of this family are found 

in the works by Flower (1964a, 1964b), Hook and Flower 

(1977), and Dzik (1984). The evolution of nautiloids with 

orthoconic longicone shells resulted in a variety of 

devices to control buoyancy and rotational instability 

inherent to shells with this morphology. As noted by Hook 

and Flower (1977), the late Ibexian was a time of intense 

morphological experimentation among small orthoconic 

longicones in which many of these devices were utilized. 

The most successful solution found in these longicones 

was the development of calcareous deposits concentrated 

adapically and ventrally, counterbalancing the buoyant 

effect of the gas-filled camerae and allowing these longicones to maintain horizontal equilibrium. This calcareous 

ballast approach would be utilized by longiconic nautiloids throughout the Paleozoic and into the succeeding 

Triassic (Crick, 1988).

The Baltoceratidae constitute the earliest development of this calcareous ballast approach, in which deposits were secreted both within the camerae and the 

siphuncle tube. This family forms the transitional group 

linking the ancestral Ellesmerocerida with the succeeding 

Orthocerida. Members of the Orthocerida differ from the 

Baltoceratidae primarily in the more central position of 

the siphuncle, compared with the more ventral position of 

these structures in the latter group, and in the presence of 

thin, homogeneous connecting rings, compared with the 

layered rings in these baltoceratids. Both orders have 

small- to moderate-size (less than 100 cm in length) orthoconic longicone shells with comparatively long body 

chambers, nearly tubular siphuncle segments with orthochoanitic septal necks, endosiphuncular deposits, and 

cameral deposits.

As noted by Hook and Flower (1977), endosiphuncular deposits may occur as the only device to regulate 

buoyancy and provide rotational stability, or they may 

occur in combination with cameral deposits. In the 

Baltoceratidae, the Protocycloceratidae, and the Troedssonellidae and Narthecoceratidae in the Orthocerida, 

endosiphuncular deposits are volumetrically more significant and played a greater role in regulating buoyancy than 

in the Orthoceratidae, the Geisonoceratidae, and other 

members of the Orthocerida Endosiphuncular deposits 

in the Orthoceratidae and other orthocerids usually are 

less extensively developed, consisting of septal annuli 

and (or) parietal linings of connecting ring walls.

GENUS CAKTERSOCERAS FLOWER

Type species.—Cartersoceras shideleri Flower, 

1964a, p. 121; by original designation; Carters Limestone, 

Rocklandian Stage, Middle Ordovician, Tennessee.

Description.—Small, moderate to rapidly expanding 

baltoceratids, depressed ovate in cross section, having 

venter flattening during ontogeny. Camerae short; sutures 

sloping from the dorsum to the venter adapically, leading 

to the development of a broad lobe ventrally. Body chamber unknown. Shell surface smooth.

Siphuncle initially subcentral, moving to a more ventral position during ontogeny. Segments expanded, equiaxial to slightly compressed, having suborthochoanitic 

septal necks. Connecting rings thickening adorally with 

lamellar microstructure. Siphuncle with an endosiphuncular rod that tapers adorally to an acute point. 

Mural-episeptal cameral deposits.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Rocklandian Stage), Eastern North America 

(Laurentia).

Remarks.—Flower (1964a) erected this genus for a 

species formerly assigned to Murrayoceras Foerste that 

possessed siphuncle segments that are convex in outline 

compared with the subtubular, depressed segments characteristic of true Murrayoceras. In his paper, Flower indicated that there is some gradation from Murrayoceras to 

Cartersoceras in terms of segment shape and suggested 

that this characteristic is indicative of the close phylogenetic relation between these taxa. Restudy of the internal 

structures of the type species of Murrayoceras, M. murrayi (Billings) and other members of the genus is necessary to ascertain whether the differences between these 

taxa are significant enough to define two separate genera. 

For the purposes of this study, specimens with convex 

siphuncle segments are placed in Cartersoceras Flower; 

those with more tubular, depressed segments are retained 

in Murrayoceras Foerste.

CARTERSOCERAS SHIDELERI YLOWER, 1964A 

Plate 1, figures 1-6, 11

Cartersoceras shideleri Flower, 1964a, p. 122, pi. 26, figs. 

3, 4, 8-11.

Diagnosis.—Small, moderately expanding species of 

Cartersoceras with cameral lengths one-fourth to 

one-eighth the diameter of the shell and an endosiphuncular rod that is circular in cross section.

Description.—Small (less than 25 cm in length and 

up to 3.0 cm in diameter), moderately expanding (apical 

angle 8-9 degrees) orthoconic longicones that are 

depressed ovate in section, the venter becoming distinctly 

flattened with ontogeny. Sutures sloping adapically from 

the dorsum to the venter to form a broad ventral lobe. 

Camerae short with cameral lengths decreasing with
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P29

ontogeny from one-fourth the diameter of the shell at a 

diameter of 10 mm to nearly one-eighth the diameter of 

the shell at diameters of 25 mm or greater. Body chamber 

incompletely known. Shell exterior smooth.

Siphuncle subcentral adapically (SPR=0.40 at a diameter of 10 mm), becoming midventral with ontogeny 

(SPR=0.25 at a diameter of 25 mm). Siphuncle segments 

slightly expanded, compressed, somewhat heart-shaped, 

the SCR values increasing with ontogeny from 1.2 at a 

shell diameter of 10 mm to 1.66 at a shell diameter of 20 

mm. Connecting rings thickening adorally, having a lamellar microstructure. Endosiphuncular rod filling the 

siphuncle tube adapically and tapering to an acute point 

adorally. Rod circular in cross section. Adoralmost camera! deposits mural-episeptal, well-developed ventrolaterally.

Stratigraphic range and geographic occurrence.— 

Middle Ordovician, the Rocklandian part of the Tyrone 

Limestone in the Blue Grass region of central Kentucky 

and the equivalent Carters Limestone in the Nashville 

dome region of central Tennessee.

Studied material.—Holotype (USNM 302549) and 

paratype (USNM 302550) from the Carters Limestone, 

Beech Grove, Tenn.; USNM 158627 (pi. 1, fig. 3), 158631 

(pi. 1, figs. 1, 2, 4-5), 158633 (pi. 1, fig. 6), 158635, 468656 

(pi. 1, fig. 11), 468657-468661, plus 14 additional silicified 

specimens (USNM 468662), all from the 6034-CO collection, upper half of the Tyrone Limestone, Little Hickman 

section A, Jessamine County, Ky.

Remarks.—The bulk of the silicified specimens of 

Cartersoceras from the USGS 6034-CO collection appear 

to be assignable to the type species of the genus C. shideleri Flower. The holotype and paratype are sectioned 

specimens from the Carters Limestone in Tennessee. The 

Kentucky material is similar to the type material in the 

angle of expansion, depth of camerae at similar diameters, siphuncle diameter at similar diameters, and outline 

of the siphuncle segments. Siphuncle segment position is 

indeterminable in the type material, as both specimens 

are thin sections ground into the enclosing limestone 

matrix. Septal necks and connecting rings are not preserved in the etched silicified Kentucky material, 

although camera! deposits and the endosiphuncular rod 

are well preserved in these specimens (pi. 1, figs. 3, 6). 

Septal necks and connecting rings are, however, present 

in a sectioned specimen (USNM 468656) from the 

6034-CO collection (pi. 1, fig. 11; fig. 6) and further validate assignment of these Kentucky specimens to the C. 

shideleri.

Cartersoceras shideleri differs from the associated 

C. popei n. sp. in being a less rapidly expanding form, in 

possessing somewhat longer camerae at comparable shell 

diameters, in possessing less compressed siphuncle segments at comparable diameters, and in the circular cross

FIGURE 6.—Camera lucida drawing of a dorsal-ventral section 

through a specimen of Cartersoceras shideleri from the 

6034-CO collection in the Tyrone Limestone (USNM 468656). 

Note thin cameral deposits and endosiphuncular rod. 

Compare with plate 1, figure 11.

section of the endosiphuncular rod (pi. 1, figs. 3-6) compared with the plano-convex section of this feature in C. 

popei (pi. 1, figs. 9, 10). Cartersoceras shideleri differs 

from the baltoceratid Murrayoceras cf. M. murrayi 

(Billings) from the same strata in being a more rapidly 

expanding shell with distinctly expanded siphuncle
P30 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

TABLE 6.—Comparisons of the morphological features of the 

three species of baltoceratid nautiloids common to the USGS 

6034-CO collection from the upper half of the Tyrone 

Limestone, Jessamine County, Ky.

[Data from silicified specimens listed in text CUD, ratio of cameral 

length to shell diameter; SPR, segment position ration; SD/D, ratio of 

siphuncle diameter to shell diameter; mm, millimeter]

_ , Cartersoceras Carteroceras *? Feature . ., . . . cfm. shidelen popei * murrayi

Apical angle, degrees

Diameter 25 mm

CL/D

SPR

SD/D

Diameter 20 mm

CL/D

SPR

SD/D

Diameter 15 mm

CL/D

SPR

SD/D

Diameter 15 mm

3L/D

SPR

SD/D

9

0.12

.15

.30

.25

.175

.32

.235

.20

.33

.266

10

0.12

.20

.20

.15

.25

.25

.12

.29

.26

.133

.33

.30

6

0.16

.16

.16

.175

.205

.175

.20

.23

.23

segments in contrast to the nearly tubular siphuncle segments in M. cf. M. murrayi (pi. 1, figs. 14, 16). Table 6 

compares the morphological features of these three baltoceratid taxa from the Tyrone Limestone.

Another species assigned to Cartersoceras by Flower 

(1964a) are specimens identified by Wilson (1961) as Sactoceras? ottawaense (Billings) from the "Leray-Rockland 

beds" (Middle Ordovician, Rocklandian) exposed in the 

Ottawa region of Ontario and Quebec. This species has a 

similar rate of shell expansion (apical angle 9 degrees) as 

well as similar cameral lengths and siphuncule diameters 

compared with the Kentucky material. Study of more 

extensive, better preserved material from the Ottawa 

River section may indicate that these Canadian specimens 

and the Kentucky material represent the same species. If 

this proves to be the case, the Canadian species would 

have priority.

Within the 6034-CO collection from the Tyrone Limestone, C. shideleri is the most abundant nautiloid species 

encountered, represented by 25 etched specimens consisting of portions of the phragmocone 4 cm or more in 

length, numerous smaller, fragmentary specimens, and 15

specimens still in matrix. Recognizable specimens typically consist of adapical portions of the phragmocone 40- 

87 mm in length. Complete body chambers are not known 

from specimens from this silicified collection. C. 

shideleri occurs associated with a diverse nautiloid fauna 

consisting of less abundant representatives of the baltoceratids C. popei n. sp. andMurrayoceras cf. M. murrayi 

(Billings), the orthocerids Pojetoceras floweri n. sp., Proteoceras tyronensis (Foerste), and Monomuchites annularis n. sp., uncommon specimens of Vaginoceras, 

Actinoceras, and Ormoceras, plus small oncocerids and 

fragmentary specimens of the tarphycerid Plectoceras.

As indicated above, species of Cartersoceras appear 

to be restricted to Middle Ordovician (Rocklandian) shallow marine carbonate facies across eastern and southern 

portions of Laurentia. No specimens referable to the 

genus were identified from collections from the overlying 

Lexington Limestone in the central Kentucky area.

CARTERSOCERAS POPEI NEW SPECIES

Plate 1, figures 7-10

Diagnosis.—Rapidly expanding species of Cartersoceras with cameral lengths from one-fifth to one-eighth 

the diameter of the shell, highly compressed siphuncle 

segments (SCR values up to 2.25), and an endosiphuncular rod that is plano-convex in cross section, bisected by a 

dorsal groove.

Description.—Small (up to 20 cm in length and shell 

diameters up to 3.0 cm), rapidly expanding (apical angle 

10 degrees), orthoconic longicones, depressed ovate in 

cross section, the venter becoming flatter with ontogeny. 

Sutures sloping from the dorsum to the venter adapically, 

forming a broad ventral lobe. Camerae short, with cameral length decreasing with ontogeny, ranging from 

one-fifth the diameter of the shell at a diameter of 10 mm 

to one-eighth the diameter of the shell at a diameter of 20 

mm or more. Body chamber unknown. Shell exterior 

smooth.

Siphuncle subcentral in position (SPR=0.45) at a 

diameter of 10 mm, becoming ventral with ontogeny 

(SPR=0.20 at diameters of 25 mm or more). Siphuncle 

segments expanded, heart-shaped, compressed, the SCR 

values increasing with ontogeny from 1.75 at a diameter 

of 10 mm to 2.25 at shell diameters of 15 mm or more. 

Endosiphuncular rod completely filling the siphuncle 

tube adapically and tapering adorally to an acute end. Rod 

flattened dorsally throughout its length and adapical sections marked by a longitudinal medial groove, giving the 

rod a notched, heart-shaped cross section adapically and 

a plano-convex section adorally. Adoralmost cameral 

deposits mural-episeptal, well-developed ventrolateraUy.

Stratigraphic range and geographic occurrence.— 

Upper half of the Tyrone Limestone (Rocklandian Age 

portion) exposed at the Little Hickman section A,
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P31

Jessamine County, Ky. (collection 6034-CO), which is the 

type locality. (See locality register (appendix) for USGS 

collection localities.)

Studied materials.—Holotype (USNM 158625) (pi. 1, 

figs. 7, 9) and paratypes USNM 158624 (pi. 1, fig. 10), 

158632, 468663, and 468664 (pi. 1, fig. 8), and five other 

specimens (USNM 468665), all from the USGS 6034-CO 

collection.

Remarks.—Comparisons with the type species, C. 

shideleri, are given above. The consistent nature of the 

variation between these specimens in the 6034-CO collection indicates that these differences are real and not the 

result of silicification or other taphonomic processes. 

Morphological comparisons of these species are presented in table 6. Within the USGS 6034-CO collection, C. 

popei is less abundant than C. shideleri, making up 

slightly less than one-third of the identified specimens of 

Cartersoceras in this collection. It shares with the latter 

species the same fauna! associates.

No other species of Cartersoceras known to the 

writer possesses the dorsally flattened endosiphuncular 

rod characteristic of C. popei, although the cross sectional shape of this feature is known with certainty only 

for the type species. Cartersoceras popei is distinguished 

at once from the associated baltoceratid Murrayoceras 

cf. M. murrayi in its more rapidly expanding shell and in 

the expanded, compressed nature of the siphuncle segments, in contrast to the nearly tubular segments in M. cf. 

M. murrayi.

Etymology.—This species is named in honor of John 

K. Pope, a scholar of the Ordovician paleontology of the 

Cincinnati, Ohio, region.

GENUS MURRAYOCERAS POERSTE

Type species.—Orthoceras murrayi Billings, 1857, p. 

332; designated by Foerste, 1926, p. 312; Black River Formation, Blackriveran Stage, Middle Ordovician, Ontario.

Description.—Small to medium-sized, gradual to 

moderately expanding orthoconic longicones, depressed 

ovate in cross section, more flattened on venter, having 

dorsum evenly rounded. Sutures sloping adapically from 

the dorsum to the venter, forming a broad, shallow ventral 

lobe. Camerae short. Body chamber poorly known, apparently lengthy, at least one-fourth the total length of the 

shell. Shell exterior smooth or marked with fine, raised 

transverse growth lines.

Siphuncle subcentral initially, becoming ventral with 

ontogeny. Siphuncle moderately large in diameter, segments subtubular. Septal necks short, aneuchoanitic to 

orthochoanitic. Connecting rings thick, laminated, typically concave or sinuate. Siphuncle with a tubular endosiphuncular rod that tapers adorally to an acute end. 

Adoralmost camera! deposits episeptal, well-developed 

ventrolaterally.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Whiterockian? to Rocklandian Stages) in 

Eastern North America (Laurentia).

Remarks.—Flower (1964a) distinguished Murrayoceras from Cartersoceras on the basis of the shape of 

the siphuncle segments, which are tubular or subdued 

sinuate in Murrayoceras, but are distinctly expanded, 

convex in Cartersoceras. Flower (1964a) noted that some 

species of Murrayoceras exhibited ontogenetic changes 

in the nature of the connecting rings, from distinctly concave adapically to sinuate adorally. Study of a suite of 50 

silicified specimens from the 6034-CO locality and comparisons with other figured species of both genera indicate that species assigned to Cartersoceras consist of 

smaller, more rapidly expanding shells compared with 

established species of Murrayoceras. Additionally, during 

ontogeny, specimens of Cartersoceras become more 

strongly depressed than Murrayoceras and have a flatter 

venter.

Typical Murrayoceras appears earlier than Cartersoceras and is most abundant in older Middle Ordovician 

(Blackriveran) carbonates in New York and adjacent portions of Ontario and Quebec. Cartersoceras is apparently 

restricted to younger Rocklandian carbonates, especially 

in Kentucky, Tennessee, the upper Mississippi valley, and 

the Ottawa Lowland in Canada.

MURRAYOCERAS CF. M. MURRAYI (BILLINGS), 1857 

Plate 1, figures 12-17

Orthoceras murrayi Billings, 1857, p. 332.

Jovellania murrayi (Billings). Foord, 1891, p. 338, figs.

50a-c.

Murrayoceras murrayi (Billings). Foerste, 1926, p. 312. 

Murrayoceras murrayi (Billings). Foerste, 1928a, p. 314,

pi. 75, fig. 5. 

Murrayoceras murrayi (Billings). Foerste, 1932, p. 121,

pi. 21, fig. 2. 

Murrayoceras murrayi (Billings). Wilson, 1961, p. 40,

pi. 9, figs. 6, 7, pi. 11, figs. 3, 4.

Diagnosis.—Small, slender species of Murrayoceras, depressed ovate in cross section, having cameral 

lengths one-fourth to one-eighth the diameter of the shell. 

Description.—Small (at least 30 cm in length and up 

to 2.8 cm in diameter), slender (apical angle 6-6.5 

degrees), orthoconic longicones, depressed ovate in cross 

section, having venter becoming flatter during ontogeny. 

Sutures straight, transverse dorsally and laterally, turning 

adapically at the ventral margins, forming a broad, shallow ventral lobe. Camerae short, decreasing in length 

with ontogeny, the cameral lengths ranging from 

one-fourth the diameter of the shell at a diameter of 10 

mm to one-eighth the diameter of the shell at diameters in 

excess of 25 mm. Body chamber unknown. Exterior 

marked by fine transverse growth lines.
P32 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

Siphuncle subcentral (SPR=0.30) at shell diameters 

less than 15 mm, becoming ventral (SPR=0.175) at diameters greater than 20 mm. Siphuncle segments subtubular, 

the segment diameter ranging from one-fourth the diameter of the shell at a diameter of 10 mm to one-sixth the 

diameter of the shell at diameters greater than 15 mm. 

Septal necks and connecting rings poorly known. Endosiphuncular rod filling adapical portions of the siphuncle 

and tapering adorally to an acute end. Rod extending 

adorally to shell diameters up to 20 mm in diameter. 

Adoralmost cameral deposits consisting of ventral and 

lateral planar episeptal deposits.

Stratigraphic and geographic occurrence.—Upper 

half of the Tyrone Limestone (Rocklandian Age part) 

exposed at the Little Hickman A section, Jessamine 

County, Ky.

Studied materials.—Specimens studied were a suite 

of silicified specimens from the USGS 6034-CO collection: 

USNM 158637, 468672 (pi. 1, fig. 16), 468673 (pi. 1, fig. 17), 

468674 (pi. 1, figs. 12,13), and 468675 (pi. 1, figs. 14,15).

Remarks.-Silicified specimens of Murrayoceras 

from the Tyrone Limestone in Kentucky appear to be 

most similar to the type species of the genus, M. murrayi 

(Billings) from the Middle Ordovician "Black River Formation" exposed on St. Joseph Island, Lake Huron, 

Ontario. Both the Tyrone Limestone specimens and a syntype of M. murrayi (Geological Survey of Canada specimen number 1723) have slender, depressed, longiconic 

shells, the cameral lengths ranging from one-fifth the 

diameter of the shell at diameters less than 20 mm to oneeighth the diameter of the shell at diameters greater than 

25 mm and subtubular siphuncle segments with diameters 

one-fifth to one-seventh the diameter of the shell. 

Detailed comparisons between the Kentucky material and 

the Canadian types are difficult, as the silicified specimens from the Tyrone Limestone represent phragmocones 20 mm or less in diameter, whereas the Canadian 

material is represented by more adoral portions of the 

phragmocone greater than 17 mm in diameter. Conclusive 

assignment of the Kentucky material to M. murrayi 

awaits comparisons of larger suites of more complete, 

comparable specimens from both localities.

The Kentucky specimens of Murrayoceras are less 

similar to M. carletonense Foerste, a slender species from 

the Lowville Formation (Middle Ordovician, Blackriveran) exposed in southern Ontario. Murrayoceras carletonense possesses more closely spaced septa in 

comparison with to the Tyrone Limestone specimens, 

which have sutures that slope in a more pronounced manner from the dorsum to the venter. This Canadian species, 

however, is also based on the more adoral portions of the 

phragmocone, broader in diameter than is known for the 

Kentucky specimens, making conclusive comparisons difficult

Murrayoceras cf. M. murrayi is apparently an 

uncommon species in the USGS 6034-CO collection, represented by fewer than two dozen fragmentary silicified 

specimens. This species is much less common than associated species of the genus Cartersoceras. Species of 

Cartersoceras can be distinguished from M. cf. M. murrayi in their more rapidly expanding shell form and in the 

distinctly expanded nature of the siphuncle segments in 

these specimens.

ORDER ORTHOCERIDA KUHN

Small to large (rarely in excess of 2 m in length), 

orthoconic or cyrtoconic longicones with smooth to elaborately ornamented shells. Siphuncles central or subcentral in position, comparatively narrow in diameter relative 

to the diameter of the shell. Thin homogeneous connecting rings and orthochoanitic, suborthochoanitic, or cyrtochoanitic septal necks. Dominant method of buoyancy 

regulation is the secretion of calcareous ballast in adapical portions of the phragmocone, typically consisting of 

both cameral and endosiphuncular deposits. Cameral 

deposits are volumetrically more significant and served as 

the primary buoyancy control structures in most members of the order, consisting of complex mural, episeptal, 

and hyposeptal deposits. Endosiphuncular deposits typically consisting of septal annuli, parietal deposits, or 

siphuncle linings. Body chambers lengthy, commonly 

making up to one-fourth the total length of the shell. 

Periphract dorsomyarian. Protoconchs typically globular.

Stratigraphic range.—Lower Ordovician to Upper 

Triassic.

Remarks.—The higher level systematic classification 

of this group is difficult due to the seemingly simple, conservative morphology of many members and the fragmentary nature of most described taxa (W.C. Sweet, oral 

commun., 1990). The current classification (Teichert and 

others, 1964) is often confusing and inconsistent. It is 

beyond the scope of this paper to attempt to tackle the 

reorganization of this order, but several taxa are redefined 

or emended in an attempt to develop a more consistent 

classification. Taxonomy is based on a combination of 

morphological features such as general shell shape and 

size; body chamber length relative to phragmocone 

length; length of cameral chambers; position, shape, and 

diameter of siphuncle segments; features of septal necks; 

and the morphology and development of cameral and 

endosiphuncular deposits. External ornament of the shell 

is thought to be less significant than previous classifications have indicated, significant at the genus level but no 

higher.

Sweet (1964) and Teichert (1988) divided the Orthocerida into two superfamilies: the orthochoanitic Orthoceratacea and the cyrtochoanitic Pseudorthoceratacea.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P33

Members of the Orthoceratacea are known from the 

Lower Ordovician (upper Ibexian) and are the dominant 

orthocerids in the Ordovician and succeeding Silurian. 

The development of cyrtochoanitic forms from existing 

orthochoanitic stocks occurred early in the history of the 

order, the oldest known pseudorthocerataceans dating 

from the early Middle Ordovician (late Whiterockian). 

Members of the Pseudorthoceratacea are locally common 

in the latter half of the Ordovician, and then become the 

dominant orthocerids in the Devonian and succeeding 

Carboniferous. Wade (1988) has regarded the differences 

between these two superfamilies to be sufficient to warrant placing the Pseudorthoceratacea in a separate order, 

the Pseudorthocerida. For the purposes of this paper, 

both the Orthoceratacea and the Pseudorthoceratacea are 

retained in the order Orthocerida.

FAMILY ORTHOCERATIDAE M'COY

Smooth to ornamented, small to medium-sized, gradually expanding, slender longicones, circular in cross section; straight transverse sutures and long camerae with 

widely spaced, strongly curved septa. Camera! length typically from one-third to greater than one-half the diameter 

of the shell. Body chambers tubular, one-fourth the total 

length of the shell. Aperture straight, transverse, lacking a 

hyponomic sinus.

Siphuncle central or subcentral with narrow, tubular 

or slightly expanded siphuncle segments that are longer 

than wide. Septal necks short, orthochoanitic or suborthochoanitic. Connecting rings thin, homogeneous. Endosiphuncular deposits restricted to adapical portions of the 

phragmocone, consisting of small annuli and (or) parietal 

deposits. Camera! deposits developed adapically, consisting of mural-episeptal and hyposeptal deposits that 

largely fill camera! chambers ventrally prior to their 

development dorsally. Protoconchs globular.

Stratigraphic range.—Lower Ordovician (Ibexian 

Provincial Series) to Upper Triassic.

Remarks.—Sweet (1964) subdivided this family into 

four subfamilies. These were the Orthoceratinae, which 

are distinguished by body chambers marked by deep 

longitudinal furrows; the Michelinoceratinae, which consisted of smooth Orthoceratidae with central or excentric 

siphuncles and well-developed camera! deposits; the 

Kionoceratinae, which is made up of taxa with welldeveloped longitudinal external ornament; and the Leurocycloceratinae, consisting of transversely ornamented 

forms. Body chambers are poorly known for many members of this family, such that the prevalence of the furrowed body chambers in these nautiloids is not known. 

The Kionoceratinae currently consists of genera with 

both expanded, cyrtochoanitic siphuncle segments 

(Kionoceras Hyatt, Ohioceras Shimizu and Obata, and

Polygrammoceras Foerste) as well as more typical Orthoceratidae with tubular siphuncles (Parakionoceras Foerste), and seem to be a totally artificial grouping of taxa. 

The Leurocycloceratinae consists of taxa with tubular 

siphuncle segments and distinctive transverse annuli. 

Leurocycloceras Foerste, however, has long camerae and 

long septal necks in contrast to the short camerae and 

short orthochoanitic septal necks characteristic of 

Anaspyroceras Shimizu and Obata. The internal features 

of Metaspyroceras are poorly known and require further 

documentation.

Michelinoceras Foerste and other genera with slender shells, narrow tubular siphuncle segments, very long 

camerae, and long septal necks (that is, Arkonoceras 

Flower, Leurocycloceras Foerste, and Plagiostomoceras 

Teichert and Glenister) are viewed as being sufficiently 

distinct from other orthoceratids to constitute a separate 

family, the Michelinoceratidae. In contrast to the primarily Ordovician distribution of the Orthoceratidae, members of the Michelinoceratidae are most numerous in the 

succeeding Silurian and Devonian. The wide septal foramina and broad, subtubular siphuncle segments typical of 

Kionoceras suggest placement of this genus in the family 

Geisonoceratidae. The familial affinities of Anaspyroceras, Metaspyroceras, Ohioceras, Parakionoceras, and 

Polygrammoceras remain unknown pending better documentation of the key internal features of these genera.

POJETOCERAS NEW GENUS

Type species.—Pojetoceras Jloweri, n. sp., Tyrone 

Limestone, Rocklandian Stage, Middle Ordovician, Kentucky.

Description.—Small, slender, gradually expanding 

orthoconic longicones, circular in cross section with 

straight, transverse sutures. Camerae long, with camera! 

lengths averaging one-third the diameter of the shell, 

becoming slightly shorter with ontogeny. Body chamber 

unknown. Shell exterior smooth.

Siphuncle supracentral to subcentral in position, segments tubular, typically twice as long as wide. Siphuncle 

segments narrow in diameter, with short, orthochoanitic 

septal necks and thin, homogeneous connecting rings. 

Endosiphuncular deposits developed adapically along the 

ventral siphuncle wall, consisting of thin parietal deposits 

that form adoral to septal necks. Camera! deposits welldeveloped, consisting of complex mural-episeptal and 

hyposeptal deposits that form ventrally prior to their 

development dorsally.

Stratigraphic and geographic occurrence.—Lower 

Ordovician (Ibexian Provincial) to Middle Ordovician 

(Shermanian Stage), North America (Laurentia).

Remarks.—This genus is erected for a group of 

small, smooth orthoceratids with narrow, supracentral to
P34 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

subcentral, tubular siphuncle segments that were originally described from the Early Ordovician of the Western 

United States. Flower (1962) and Hook and Flower (1977) 

referred these forms with some reservations to the genus 

Michelinoceras Foerste. Michelinoceras is based on 

Orthoceras michelini Barrande (=O. grande Meneghini) 

from the Upper Silurian (Ludlovian) of Czechoslovakia 

and Sardinia From descriptions and good illustrations of 

this species (Barrande, 1866-1870; Serpagli and Gnoli, 

1977), M. michelini differs significantly from these 

Ordovician orthoceratids in the possession of much 

longer septal necks, longer camerae at comparable diameters, and narrower, more tubular siphuncle segments. 

Additionally, endosiphuncular deposits, which are well 

developed in Pojetoceras, are currently not known for 

Michelinoceras based on M. michelini.

Pojetoceras is probably most similar to true Orthoceras Bruguiere, based on O. regularis Schlotheim from 

the early Middle Ordovician "Orthoceras Limestone" of 

the Baltic region. Both taxa are slender, gradually expanding longicones with narrow central or subcentral, tubular 

siphuncle segments equipped with short orthochoanitic 

septal necks. Cameral deposits, consisting of thin 

mural-episeptal deposits, are known for O. regularis 

(Flower, 1964b, pi. 4, figs. 6, 7), but are restricted to portions of the phragmocone less than 10 mm in diameter. 

Endosiphuncular deposits are not known for the type species of Orthoceras, but related species illustrated by Dzik 

(1984, fig. 34, pi. 22, fig. 8) indicate the presence of small 

annuli and thin parietal deposits in adapical portions of 

the phragmocone. The body chamber of Orthoceras is 

long and tubular and marked by three distinctive linear 

furrows. The body chamber is currently unknown for species of Pojetoceras. Pojetoceras differs from Orthoceras 

in the possession of shorter camerae and somewhat 

broader siphuncle segments at comparable diameters. 

There is, additionally, more extensive development of 

both camera! and endosiphuncular deposits in Pojetoceras compared with their weak development or absence 

at similar diameters in Orthoceras. Although the adoral 

portions of specimens of Pojetoceras are currently 

unknown, maximum observed diameters (up to 1.5 cm) in 

large collections from Kentucky indicate that Pojetoceras 

is a smaller form than typical Orthoceras (known lengths 

in excess of 50 cm and having shell diameters of up to 2.5 

cm). Figure 7 is a graphic plot comparing camera! length 

relative to shell diameter for Pojetoceras floweri and 

Orthoceras regularis.

Pojetoceras is also similar in gross shell morphology 

to the Late Ordovician orthoceratid Pleurorthoceras 

Flower. Both of these taxa have slender, gradually 

expanding shells with comparatively long camerae and 

central to subcentral, narrow, tubular siphuncle segments. Pojetoceras differs from Pleurorthoceras in pos6 8 10 12 14 

SHELL DIAMETER, IN MILLIMETERS

16 18 20

FIGURE 7.—Bivariate plot of camera! length and shell diameter 

for specimens of Pojetoceras floweri (circles) and 

Orthoceras regularis (triangles). Data for P. floweri from 

paratypes USNM 468677-468679 and suite of specimens 

USNM 468684. Data for O. regularis from Flower (1962). 

Note the longer camerae in O. regularis compared with 

camera! lengths at comparable diameters in specimens of 

P. floweri.

sessing broader siphuncle segments relative to shell 

diameter; in having short orthochoanitic septal necks, 

compared with the suborthochoanitic septal necks in the 

latter genus; in the development of complex episeptal and 

hyposeptal camera! deposits in Pojetoceras, compared 

with the simple mural-episeptal deposits in Pleurorthoceras] and in the presence of endosiphuncular deposits in 

Pojetoceras and their absence in species of Pleurorthoceras. Species of Pleurorthoceras also appear to grow to a 

larger size compared with species of Pojetoceras, reaching lengths in excess of 60 cm and shell diameters up to 

3.0 cm. Maximum lengths known for species of Pojetoceras are less than 30 cm and shell diameters up to 1.5 cm. 

As currently known, species assignable to Pojetoceras range from the Lower Ordovician (late Ibexian Provincial Series) to the Middle Ordovician Shermanian 

Stage. The genus appears to be restricted in its distribution to cratonic carbonate facies in Laurentia. Early 

Ordovician species assigned to Pojetoceras are Michelinoceras floridaense Hook and Flower, M. metteni Hook 

and Flower, and a number of other unnamed, fragmentary 

specimens of "Michelinoceras" described and illustrated 

by Hook and Flower (1977) from the late Ibexian Florida 

Mountains Formation in southwest New Mexico. Other 

Lower Ordovician representatives of the genus are a number of fragmentary specimens referred to as Michelinoceras spp. and collected from the Wan Wan Limestone in 

the Ibex area of Utah (Hook and Flower, 1977).
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P35

Younger Middle Ordovician examples of Pojetoceras 

are "Orthoceras" shumardi Billings from the Mingan 

Formation (Chazyan Stage) exposed in the Mingan 

Islands, Quebec (Foerste, 1938); the type species P. floweri n. sp. from the Tyrone Limestone (Rocklandian) in 

Kentucky; a species referred to as "Michelinoceras sp. 3" 

from the "Braeside Beds" (Blackriveran) exposed in the 

Ottawa region of Ontario (Steele and Sinclair, 1971); and 

Orthoceras beltrami Clarke from the "Prosser Member of 

the Trenton" at Wykoff, Mum. (Foerste, 1932). Undescribed species that are possibly assignable to Pojetoceras have been collected by the writer from the Stones 

River Group (Middle Ordovician, Blackriveran) in central 

Tennessee and the Mountain Lake Member of the Bromide Formation (Blackriveran) in the Criner Hills, in 

Oklahoma.

Etymology.—This genus is named for John Pojeta, 

Jr., in recognition of his work organizing and directing the 

Kentucky Ordovician paleontology program and for his 

encouragement and support of this writer's study of the 

nautiloid faunas collected as part of this program.

POJETOCERAS FLOWERTNEW SPECIES

Plate 2, figures 1-9

Diagnosis.—Small, slender, orthoconic longicone 

with cameral lengths from one-half to one-fifth the diameter of the shell and subcentral depressed siphuncle segments whose diameters are one-sixth to one-ninth the 

diameter of the shell and that contain, adapically, thin 

ventral parietal deposits.

Description.—Small (observed lengths of up to 25 

cm and having diameters of up to 1.5 cm), gradually 

expanding (apical angle 3-3.5 degrees) orthoconic longicones, circular in cross section with straight transverse 

sutures. Camerae lengths ranging from one-half the diameter of the shell at diameters less than 5 mm to nearly 

one-fourth the diameter of the shell at diameters greater 

than 13 mm. Body chamber unknown. Shell exterior 

smooth.

Siphuncle supracentral (SPR=0.60) at shell diameters 

less than 7 mm, becoming central (SPR=0.50) at diameters of 7-12 mm, and then subcentral (SPR less than 0.50) 

in adoral portions of the shell greater than 12 mm in diameter. Siphuncle segments tubular to subtubular, narrow in 

diameter, from one-sixth to one-ninth the diameter of the 

shell, the segment diameter decreasing relative to shell 

diameter with ontogeny. Septal necks short, orthochoanitic. Connecting rings thin, homogeneous. Endosiphuncular deposits consisting of thin parietal deposits lining 

ventral portions of adapical siphuncle segments that fuse 

to form a continuous ventral lining with ontogeny. Dorsal 

endosiphuncular deposits unknown. Cameral deposits 

complex, botryoidal episeptal and hyposeptal deposits 

that fill ventral and lateral portions of cameral chambers

with ontogeny. Thin, planar episeptal deposits dorsally 

that form later than ventral and lateral deposits. Variably 

developed ventral medial mural delta

Stratigraphic range and geographic occurrence.— 

Tyrone Limestone (Rocklandian Age part), exposed in 

Jessamine County, Ky.

Studied material.—Holotype (USNM 468676) (pi. 2, 

figs. 1, 9), eight paratypes: USNM 468677 (pi. 2, figs. 2, 3), 

468678 (pi. 2, figs. 4, 6), 468679 (pi. 2, fig. 5), 468680, 

468681 (pi. 2, fig. 7), 468682, 468683 (pi. 2, fig. 8), and 

468684, and a suite of fragmentary silicified specimens 

(USNM 468685), all from USGS collection 6034-CO from 

the upper half of the Tyrone Limestone exposed at the Little Hickman section A, Jessamine County, Ky., which is 

the type locality. The holotype (USNM 468676) is a 

dorsal-ventral thin section prepared by R.H. Flower (pi. 2, 

figs. 1, 9; figure 8) that illustrates the key internal features 

of P. floweri.

Several additional small silicified fragments 

(468685A) from USGS collection D1138-CO from a section 

29 ft (10 m) above the base of the Tyrone Limestone at 

West Marble Creek, Jessamine County, Ky, are also tentatively assigned to P. floweri.

Remarks.—Pojetoceras floweri is the second most 

abundant nautiloid species identified from the USGS 

6034-CO collection from the Tyrone Limestone. It is second in abundance only to the small, depressed baltoceratid Cartersoceras shideleri. This abundance is measured 

in terms of identifiable fragments present in collections 

studied by the writer. When added together, specimens of 

Cartersoceras and Pojetoceras constitute approximately 

70 percent of the identifiable nautiloid material in the 

6034-CO collection. Specimens of P. floweri studied consist of silicified portions of phragmocones 5-75 mm in 

length. Composite specimens reconstructed using this 

fragmentary material indicate that P. floweri was a very 

slender orthoconic longicone that reached lengths of up 

to 25 cm and shell diameters up to 1.5 cm (see pi. 2, figs. 

3-5).

Pojetoceras floweri is most similar to a species figured by Steele and Sinclair (1971, pi. 11, figs. 11, 12) and 

identified as Michelinoceras sp. 3. This species was represented by only three fragmentary silicified phragmocones 

that indicate a small, slender orthoconic longicone with 

comparatively long camerae. Cameral lengths were equal 

to one-half the diameter of the shell at shell diameters of 

5-6 mm. The siphuncle was described as small in diameter and centrally located, the septal necks and connecting 

rings are not preserved. Michelinoceras sp. 3 was collected from the Braeside Limestone in the Ottawa valley 

in eastern Ontario, the strata are roughly equivalent in age 

to the Tyrone Limestone in Kentucky. These Canadian 

specimens may, after further study, prove to be assignable 

to P. floweri.
P36 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

FIGURE 8.—Camera lucida drawing of sectioned holotype of 

Pojetoceras floweri (USNM 468676) from the 6034-CO 

collection in the Tyrone Limestone. Compare with plate 2, 

figures 1, 9. Venter to the right. Note complex development of 

ventral camera! deposits and thin adapical parietal deposits.

Pojetoceras floweri is also similar to Orthoceras shumardi Billings from the Middle Ordovician (Chazyan) 

Mingan Formation exposed in the Mingan Islands in the 

Gulf of St. Lawrence, Quebec (Foerste, 1938, pi. 17, fig. 3). 

This Chazyan species appears to be assignable to Pojetoceras on the basis of its very slender, gradually expanding 

longiconic shell, deep camerae, and narrow-diameter, 

supracentral to central tubular siphuncle segments. Pojetoceras shumardi appears to differ from P. floweri in having deeper camerae and a more dorsally located siphuncle 

at comparable shell diameters.

Also tentatively assigned to Pojetoceras are a number 

of species described by Hook and Flower (1977) from 

older Early Ordovician (Ibexian)carbonates in New Mexico. These species, uMichelinocerasn floridaense and "M." 

melleni, are both known from single specimens, both consisting of phragmocone fragments 50 mm in length and 

less than 8 mm in maximum diameter. Both specimens 

exhibit the diagnostic features of Pojetoceras. Detailed 

comparisons with the type species, P. floweri, cannot be 

made until more adoral portions of these New Mexico 

species are known. Numerous other specimens described 

by Hook and Flower (1977) as undescribed species of 

Michelinoceras are also too fragmentary to compare with 

P. floweri.

Etymology.—This species is named in honor of the 

late R.H. Flower, who did the initial study of the 6034-CO 

fauna and who did much to encourage this writer in his 

studies of Ordovician nautiloids.

GENUS PLEUROBIHOCERAS FLOWER

Type species.—Orthoceras clarksviUense Foerste, 

1924b, p. 220; designated by Flower, 1962, p. 35; Waynesville Formation, Richmondian Stage, Upper Ordovician, 

Ohio.

Description.—Medium-sized, slender, gradually 

expanding orthoconic longicones; circular in section with 

straight, transverse sutures. Cameral lengths from 

one-third to nearly one-half the diameter of the shell, with 

strongly curved, widely spaced septa. Body chamber long 

and tubular. Shell exterior smooth.

Siphuncle slightly ventral of center, narrow in diameter, the subtubular segments only slightly expanded 

within camerae, twice as long as wide. Septal necks short, 

suborthochoanitic. Endosiphuncular deposits unknown. 

Cameral deposits well developed, initially mural, becoming mural-episeptal with ontogeny and deposits thickening ventrally to form a midventral boss.

Stratigraphic range and geographic occurrence.— 

Upper Ordovician (Maysvillian to Richmondian Stages), 

Laurentia.

Remarks.—Flower (1962) erected this genus for Late 

Ordovician orthoceratids that differed from earlier forms, 

such as true Orthoceras, by the presence of suborthochoanitic rather than orthochoanitic septal necks and 

through the development of strictly mural camera! deposits compared with the episeptal deposits characteristic of 

earlier orthoceratids. Study of Flower's figured specimens 

(MU 268T, 269T) as well as his figures (1962, pi. 6, fig. 4), 

indicates that camera! deposits are initially mural but 

become episeptal with ontogeny, forming a distinctive 

transverse adapical groove ventrally that is visible in 

internal molds of the camerae (pi. 2, fig. 10).
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P37

Pleurorthoceras differs from all associated taxa in 

the Cincinnatian Provincial Series exposed in the Kentucky-Indiana-Ohio area, in the combination of a slender, 

gradually expanding shell, long camerae, and a narrow, 

subtubular subcentral siphuncle. The type species P. 

clarksviUense is an uncommon form, occurring as fragmentary specimens in argillaceous wackestone facies in 

the upper part of the Bull Fork Formation (Upper Ordovician, Richmondian) in southwestern Ohio and acjjacent 

portions of southeastern Indiana. The only other species 

currently placed in Pleurorthoceras is P. selkirkense 

(Whiteaves) from the Selkirk Member of the Red River 

Formation (Upper Ordovician, Maysvillian) and the overlying Stony Mountain Formation (Upper Ordovician, 

Richmondian) in the Winnipeg region of Manitoba.

PLEURORTHOCERAS CLARKSVILLENSE (FOERSTE), 1924B

Plate 2, figures 10-15

Orthoceras clarkesviUense Foerste, 1924b, p. 220, pi. 42,

figs. 1A-B. 

Michelinoceras clarkesviUense (Foerste). Foerste, 1932,

p. 72. 

Pleurorthoceras clarksviUense (Foerste). Flower, 1962, p.

36, pi. 6, figs. 1-4.

Diagnosis.—Species of Pleurorthoceras distinguished by camera! lengths that range from one-half the 

diameter of the shell at diameters of 15 mm or less to 

one-third the diameter of the shell at diameters of 30 mm; 

narrow, subtubular, central to subcentral siphuncle segments one-eighth the diameter of the shell.

Description.—Medium-sized (lengths in excess of 65 

cm and having shell diameters of up to 3.0 cm), slender, 

gradually expanding (apical angle of 4-5 degrees), orthoconic longicones; circular in cross section with straight, 

transverse sutures. Camera! lengths decreasing with 

ontogeny from one-half the diameter of the shell at shell 

diameters of 15 mm or less to one-third the diameter of 

the shell at a diameter of 30 mm. Body chamber tubular, 

one-fourth the total length of the shell, aperture unknown. 

External shell surface smooth.

Siphuncle central in position (SPR=0.50) at shell 

diameters of 15 mm or less, then becoming subcentral 

with ontogeny (SPR=0.45 at diameters of 20 mm and 0.30 

at a diameter of 30 mm). Segments only slightly 

expanded, subtubular, the SCR values ranging from 0.285 

(depressed) in adapical portions of the shell 15 mm or 

less in diameter to 0.33 (depressed) in portions of the 

shell 20-30 mm in diameter. Siphuncle segments narrow, 

from one-eighth to one-tenth the diameter of the shell. 

Septal necks short, suborthochoanitic. Connecting rings 

thin, homogeneous. Known portions of the siphuncle 

devoid of endosiphuncular deposits. Ventral mural deposits well-developed in adapical portions of large specimens 

at shell diameters less than 22 mm. Deposits becoming

episeptal adapically with ontogeny. Adoralmost dorsal 

camera! deposits thin, mural.

Stratigraphic range and geographic occurrence.— 

Upper half of the Bull Fork Formation ("Waynesville" and 

"Liberty" biofacies) (Upper Ordovician, Richmondian 

Stage) in Warren and Clinton Counties in southwestern 

Ohio and in Union, Franklin, and Dearborn Counties in 

southeastern Indiana.

Studied material.—Holotype, USNM 48255 (pi. 2, fig. 

12), internal mold of a phragmocone 130 mm in length, 

"Waynesville Formation," Blanchester, Clinton County, 

Ohio; hypotypes MU 268T (pi. 2, figs. 13-15) and MU 269T 

(pi. 2, fig. 10) figured by Flower (1962), "Liberty Formation," Addisons Creek, Preble County, Ohio; MU 444T (pi. 

2, fig. 11), "Liberty Formation," Oldenburg, Franklin 

County, Ind.; and measured suites of specimens: MU 

29853 (nine specimens), "Liberty Formation," Addisons 

Creek, Preble County, Ohio; MU 29854, "Liberty Formation," Liberty, Union County, Ind.; MU 29855 (five specimens), "Liberty Formation", Oldenburg, Franklin County, 

Ind., and MU 29856 (five specimens), "Liberty biofacies" 

within the upper part of the Bull Fork Formation, Caesars 

Creek dam site, Warren County, Ohio.

Remarks.—Pleurorthoceras clarksviUense is an 

uncommon species, there being only 23 specimens known 

to the writer, most from the Shideler Collection at Miami 

University, Oxford, Ohio. The species is apparently 

restricted to the upper 15 ft of the "Waynesville biofacies" 

and the succeeding 20 ft of the overlying "Liberty biofacies" within the upper half of the Bull Fork Formation 

exposed in Clinton, Warren, and Preble Counties in Ohio. 

Additional material has been collected from the same 

strata in Franklin, Union, and Dearborn Counties in Indiana, The species has not yet been identified from equivalent strata in northern or central Kentucky.

Specimens of P. clarksviUense are commonly holoperipherally encrusted by the bryozoan Spatiopora sp. 

along with the "worm tube" Comulites flexuosus (Hall). 

The exteriors of specimens from the Addison's Creek and 

Oldenburg localities, including body chambers, are 

entirely covered with these encrusting bryozoans. Evidence from these specimens and associated specimens of 

the proteoceratid Treptoceras indicates that these bryozoans were preferentially encrusting live nautiloid hosts 

(Baird and others, 1989).

Pleurorthoceras clarksviUense is distinct from the 

other described species of Pleurorthoceras, P. selkirkense 

(Whiteaves) from the Selkirk Member of the Red River 

Formation (Upper Ordovician) of southern Manitoba, in 

possessing shorter camerae and narrower siphuncle segments at comparable shell diameters. At shell diameters 

of 15 and 20 mm, camera! lengths in P. selkirkense are 

from five-sixths to two-thirds the diameter of the shell 

(Flower, 1962, pi. 5, figs. 1-17). Camerae at the same
P38 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

15 -

14

13

c/) 12 - 

cc

P 11-

LLJ

| 10

^ 9

_ A

10 15 20 25 30 

SHELL DIAMETER, IN MILLIMETERS

35 40

5 i-

< I- 3 S w C ^

u] n

^ 2

B

10 15 20 25 30 

SHELL DIAMETER, IN MILLIMETERS

35

_J 

40

FIGURE 9.—Bivariate plots comparing specimens of Pleurorthoceras clarksvittense (circles) with a specimen of P. 

selkirkense (Whiteaves) from the Red River Formation in 

Manitoba (triangles). A, Cameral length versus shell 

diameter. B, Siphuncle diameter versus shell diameter. 

Data for P. selkirkense from Flower (1962).

diameters in P. clarksvittense average from one-half to 

three-eights the diameter of the shell. Siphuncle segments 

average one-fifth the diameter of the shell in specimens of 

P. selkirkense figured by Flower, compared with segment 

diameters that average one-eighth the diameter of the 

shell at comparable shell diameters in P. clarksvittense. 

Differences between these two species are presented 

graphically in figure 9.

Pleurorthoceras clarksvittense is somewhat similar 

to Ordogeisonoceras amplicameratum (Hall) from older 

Shermanian and Edenian strata in the Cincinnati, OhioCovington, Ky., area in the gradual expansion of the shell 

and the development of lengthy camerae. It differs from 

this species in being a smaller shell with subcentral

siphuncle segments and short suborthochoanitic septal 

necks compared with the middorsal segments with moderately long orthochoanitic septal necks characteristic of 

O. amplicameratum. Siphuncle segments in adapical portions of O. amplicameratum develop small anmilosiphonate deposits that are absent in P. clarksvittense. Cameral 

deposits in the Richmondian species consist of 

mural-episeptal deposits compared with the massive ventral hyposeptal and episeptal deposits and thin dorsal 

episeptal deposits developed in O. amplicameratum.

Pleurorthoceras clarksvittense differs from the Middle Ordovician (Rocklandian) orthoceratid Pojetoceras 

Jloweri in being a larger shell with simpler mural-episeptal camera! deposits and no endosiphuncular deposits. 

The smaller Tyrone Limestone species has complex 

episeptal and hyposeptal camera! deposits and, adapically, ventral parietal deposits lining the siphuncle connecting the ring wall.

FAMILY GEISONOCERATIDAE ZHURAVLEVA

Medium to large (up to 2 m in length), straight to 

slightly curved, generally gradually expanding orthoconic 

longicones, circular to slightly depressed in cross section 

with typically straight, transverse sutures. Cameral length 

moderate to long, one-fourth to one-half the diameter of 

the shell. Body chamber comparatively short, typically 

less than one-fourth the total length of the shell, distinctly 

constricted just adapical of the straight, transverse aperture. Shells smooth to elaborately ornamented with longitudinal, oblique, and (or) transverse elements.

Siphuncle segments moderately wide, diameters 

one-sixth to one-fourth the diameter of the shell, typically 

middorsal to central in position. Segments only slightly 

expanded, depressed, subtubular, with septal foramina 

wide relative to the diameter of the siphuncle segment. 

Thin connecting rings with moderately long, orthochoanitic to suborthochoanitic septal necks. Endosiphuncular 

deposits limited in volume compared with camera! deposits, consisting of annuli and parietal deposits that are typically continuous with camera! deposits. Well-developed 

camera! deposits adapically, consisting of planar dorsal 

episeptal deposits and massive, botryoidal hyposeptal 

and episeptal deposits ventrally.

Stratigraphic range.—Middle Ordovician (Chazyan 

Stage) to Middle Devonian (Eifelian Stage).

Remarks.—This seems to be a natural grouping of 

related genera that form the dominant group of orthocerid nautiloids in the Silurian. The family originally was 

defined on the basis of the occurrence of an orthochoanitic or suborthochoanitic siphuncle coupled with endosiphuncular deposits consisting of small annuli and (or) 

parietal deposits that grow adorally against connecting 

ring walls (Flower, 1939; Sweet, 1964). Subsequent study
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P39

of other orthocerid taxa, in particular, the Orthoceratidae 

(Hook and Flower, 1977; Dzik, 1984), has indicated that 

these characteristics are not unique to the 

Geisonoceratidae.

The Geisonoceratidae, however, differ from Orthoceras and other orthoceratids in being larger, less slender 

forms that possess more expanded, broader, less tubular, 

dorsally located siphuncle segments with broad septal 

foramina, generally shorter camera! chambers, and more 

extensive development of camera! and endosiphuncular 

deposits at comparable stages of growth. This combination of features is used here to define members of this 

family.

A distinctive feature of this family is the supracentral 

to middorsal position of the siphuncle. Previous workers 

have inferred that siphuncles in members of this family 

were subcentral to midventral in position (Sweet, 1964). 

Specimens of Geisonoceras rivale (Barrande), Harrisoceras laurelense Flower, Jonesoceras jonesi (Barrande), 

Mesnaquaceras curviseptum Flower, Temperoceras temperans (Barrande), Virgoceras palemon (Barrande), and 

the species described below all demonstrate the more 

massive development of cameral deposits on the side of 

the shell opposite the siphuncle (pi. 3, figs. 4, 5,10). These 

deposits are assumed to be developed more massively 

ventrally in order to lower the center of gravity, further 

stabilizing these longiconic shells. If this assumption is 

correct, then the siphuncles in most members of this family are supracentral in position. Similar supracentral 

siphuncles are found in Proteoceras Flower and in early 

growth stages of some species of Treptoceras Flower, 

both members of the Proteoceratidae.

The oldest members of this group are Stereoplasmoceras longicameratum from the Middle Ordovician 

(Llandeilan) "Cephalopod Shale" in Norway (Sweet, 1958) 

and Mesnaquaceras curviseptum from the lower 

Chazyan Day Point Limestone in New York (Flower, 

1955b). Other Ordovician Geisonoceratidae are a new 

genus described below, currently known from uppermost 

Middle Ordovician (Shermanian) limestones and shales in 

New York, Kentucky, and the Canadian Arctic. The 

Silurian acme of this family consists of the genera Geisonoceras Hyatt, Columenoceras Barskov, Harrisoceras 

Flower, Jonesoceras Barskov, Kionoceras Hyatt, Protokionoceras Grabau and Shimer, Temperoceras Barskov, 

Vericeras Kolebaba, and Virgoceras Flower. These taxa 

are all known from Llandoverian to Pridolian carbonate 

facies in Eastern and Central North America (Foerste, 

1928c) and from portions of Europe (Barrande, 1874) and 

Sardinia (Serpagli and Gnoli, 1977). Well-preserved material is also known from Devonian carbonates exposed in 

the Atlas Mountains of Morocco. In North America, Devonian representatives are poorly known, the Geisonoceras 

teicherti Flower from the lower Middle Devonian Onondaga Limestone of New York being the only 

well-documented species (Flower, 1939).

ORDOGEISONOCERAS NEW GENUS

Type species.—Orthoceras amplicameratum Hall, 

1847, p. 205; Trenton Limestone, Shermanian Stage, Middle Ordovician, New York.

Description.—Large, gradually expanding orthoconic longicones, circular in cross section with straight, 

transverse sutures. Cameral lengths nearly one-half the 

diameter of the shell adapically, decreasing in length relative to shell diameter with ontogeny. Body chamber long 

and tubular, aperture unknown. Shell with a subdued 

ornament of fine longitudinal lirae.

Siphuncle situated close to the dorsal margin of the 

shell with elongate, depressed segments at diameters 

from one-fifth to one-seventh the diameter of the shell. 

Septal necks moderately long, orthochoanitic with broad 

septal foramina, nearly the diameter of the siphuncle segments. Connecting rings thin, segments only slightly 

expanded within camerae. Endosiphuncular deposits 

consisting of small annuli developed both dorsally and 

ventrally, restricted to adapical portions of the phragmocone. Well-developed cameral deposits adapically, the 

adoralmost deposits consisting of massive botryoidal 

hyposeptal and episeptal deposits ventrally and planar 

episeptal deposits dorsally. Dorsal deposits forming later 

than ventral deposits.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Shermanian Stage) to Upper Ordovician 

(Edenian Stage), North America (Laurentia).

Remarks.—This genus was erected for several large, 

gradually expanding orthoconic longicones that are 

known from latest Middle Ordovician (Shermanian) platform carbonates in northern Kentucky, New York, 

Ontario, and Baffin Island and range into equivalent or 

slightly younger mudstone facies of the Utica Shale in 

New York and Ontario and the Kope Formation in the Cin- - 

cinnati, Ohio, region. These longiconic nautiloids are distinguished by their comparatively long camerae and 

dorsal siphuncles with slightly expanded, elongate 

siphuncle segments.

Ordogeisonoceras is similar internally to later Silurian taxa such as Geisonoceras Hyatt, differing from this 

genus only in the more dorsal position of the siphuncle in 

Ordogeisonoceras (pi. 3, figs. 4, 5, 8, 10). Externally, 

Ordogeisonoceras has a subtle ornament of fine longitudinal lirae with alternating heavier and finer elements. Geisonoceras is a slightly endogastrically curved longiconic 

shell marked by broad, low, transverse bands. 

Ordogeisonoceras is also similar to Stereoplasmoceras 

longicameratum Sweet from the older Middle Ordovician 

(Llandeilan) "Cephalopod Shale" of Norway. It differs
P40 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

from this form in the apparent greater curvature of the 

ventral septal necks in S. longicameratum. Ordogeisonoceras apparently became extinct in the Late Ordovician 

(Edenian), leaving a gap of about 20 m.y. before the recurrence of members of the Geisonoceratidae in carbonate 

facies in Laurentia in the late Llandoverian.

Etymology.—The genus takes its name from its 

occurrence in Ordovician strata and its similarity to the 

younger Silurian genus Geisonoceras Hyatt.

OEDOGEISONOCERAS AMPLICAMERATUM (HALL), 1847 

Plate 3, figures 1-8

Orthoceras amplicameratum Hall, 1847, p. 205, pi. 51,

figs. la-g.

Orthoceras amplicameratum Hall. James, 1886, p. 237. 

Orthoceras ludlowense Miller and Faber, 1894b, p. 139-

140, pi. 7, figs. 1-2. 

Geisonoceras amplicameratum (Hall). Ruedemann,

1926, p. 90-91, pi. 11, fig. 1; pi. 12, figs. 2, 3. 

Michelinoceras ludlowense (Miller and Faber). Flower,

1946, p. 107,108. 

Michelinoceras ludlowense (Miller and Faber). Flower,

1957b, p. 833, fig. 3B.

Diagnosis.—Very large, gradually expanding orthoconic longicone distinguished by camera! lengths that 

decrease with ontogeny from one-half to one-sixth the 

diameter of the shell, middorsal subtubular siphuncle segments whose diameters average one-sixth the diameter of 

the shell, marked by a subdued external ornament of 

alternating fine and heavy longitudinal lirae.

Description.—Large (lengths in excess of 1.25 m and 

having shell diameters up to 10.5 cm), gradually expanding (apical angle 4-4.5 degrees), orthoconic longicones, 

circular in cross section with straight transverse sutures. 

Cameral length slightly less than one-half the diameter of 

the shell at diameters of 30 mm or less, decreasing with 

ontogeny to minimal camera! lengths one-sixth the diameter of the shell at a diameter of 90 mm. Body chamber at 

least one-fifth the total length of the shell; aperture 

unknown. Subdued external ornament of alternating 

heavy and fine longitudinal lirae, six fine lirae occurring 

for each heavy lira,

Siphuncle segments supracentral (SPR=0.68-0.72) at 

shell diameters less than 35 mm, becoming middorsal to 

dorsal in position (SPR greater than or equal to (>) 0.75) 

at shell diameters in excess of 35 mm, and middorsal 

(SPR=0.75) at the maximum known shell diameter (90 

mm). Segments subtubular, slightly expanded within camerae, longer than wide (SCR=0.40-0.50), diameters averaging one-sixth the diameter of the shell. Septal necks 

moderately long, orthochoanitic with broad septal foramina from two-thirds to three-fourths the maximum diameter of the segment. Connecting rings very thin, often not 

preserved. Small (less than 1 mm in diameter) annulosiphonate deposits occur dorsally and ventrally in adapical 

portions of phragmocones less than 35 mm in diameter. 

Cameral deposits well-developed in adapical portions of 

shells 40 mm or less in diameter, the adoralmost deposits 

consisting of botryoidal hyposeptal and episeptal deposits 

ventrally and planar dorsal episeptal deposits. Cameral 

deposits forming ventrally prior to their development 

dorsally.

Stratigraphic range and geographic occurrence.— 

Point Pleasant Tongue of the Clays Ferry Formation in 

northern Kentucky and the Kope Formation in the northern Kentucky-Cincinnati, Ohio, region (Shermanian and 

Edenian Stages). Elsewhere the species occurs in the 

Glendale and Poland Members of the Denley Limestone 

(Middle Ordovician, Shermanian Stage) in New York; 

Utica Shale (Upper Ordovician, Edenian-Maysvillian) in 

New York; and Whitby Formation (Upper Ordovician, 

Edenian) in southern Ontario.

Studied material.—Syntypes of Orthoceras amplicameratum Hall, AMNH 29686, AMNH 29687, AMNH 

29688 (pi. 3, figs. 6, 7), Trenton Limestone, Middleville, 

N.Y.; syntypes of O. ludlowense Miller and Faber, UC 6457 

(pi. 3, figs. 1-3) and UC 357 (two specimens), base of the 

"Hudson River Group" at Ludlow, Ky; UC 18224, label just 

reads "Cynthiana"; and UC 18229 (pi. 3, figs. 4, 5, 8), "50 

foot level" above the Ohio River, Cincinnati, Ohio.

Specimen AMNH 29688 is here designated the 

lectotype of Orthoceras amplicameratum Hall (1847); 

specimens AMNH 29686 and 29687 are designated paralectotypes of O. amplicameratum Hall.

Remarks.—While it is not possible to confirm the 

nature of the siphuncle segments in the types of O. amplicameratum, comparisons of the type specimens of Orthoceras amplicameratum Hall with those of O. ludlowense 

Miller and Faber indicate that these taxa are one and the 

same, based on similarities in shell size, apical angle, camera! length, and siphuncle position. These similarities are 

presented graphically in figure 10.

Ordogeisonoceras amplicameratum is a rare or 

uncommon species in uppermost Middle Ordovician 

(Shermanian) and lower Upper Ordovician (Edenian) 

strata exposed in the northern Kentucky-Cincinnati, 

Ohio, region. The species is most common in the planarbedded fossiliferous limestone and shale of the Point 

Pleasant Tongue of the Clays Ferry Formation exposed 

along the Ohio River valley in northern Kentucky. In these 

strata, O. amplicameratum is found as well preserved, 

but incomplete internal molds, the septa, endosiphuncular, and camera! deposits replaced with calcite. These 

fragmentary individuals occur in association with more 

common specimens of the small orthocerid Isorthoceras 

albersi (Miller and Faber) and the small tarphycerid Trocholites faberi Foerste.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P41

20 -

10

10 15 20 25 30 35 40 

SHELL DIAMETER, IN MILLIMETERS

45 50

1.00

050

0.60

0.40

0.20

B

10 15 20 25 30 35 40 

SHELL DIAMETER, IN MILLIMETERS

45 50

FIGURE 10.—Bivariate plots comparing specimens of 

"Orthoceras" amplicameratum Hall and "Orthoceras" 

ludlowense Miller and Faber. A, Cameral length versus 

shell diameter. B, Segment position ratio (SPR) versus 

shell diameter. Data for "0." amplicameratum (squares) 

from lectotype and paralectotype AMNH 29688 and 29687. 

Data for "0." ludlowense (circles) from syntypes UC 6457 

and 18229 (see pi. 3).

Ordogeisonoceras amplicameratum appears to be a 

more common species in interbedded dark limestone and 

shale facies within the Denley Limestone (Middle Ordovician, Shermanian) and the black shale facies of the Utica 

Shale (Upper Ordovician) in northern New York and adjacent portions of southern Ontario. In these shelf-edge 

facies, 0. amplicameratum occurs in association with 

abundant small longiconic nautiloids assignable to Isorthoceras Flower, the small coiled nautiloid Trocholites, 

plus the monoplacophoran Sinuites, the trilobites Flexicalymene and Isotelus, and a number of small strophomenid and orthid brachiopods. This is the same fauna 

associated with the species in the northern Kentucky 

area.

The only other species recognized by the writer as 

belonging to Ordogeisonoceras is a specimen described 

as "Orthoceras sp." by Foerste (1928d) and listed by him 

as coming from strata "corresponding to the Red River 

Formation" (Upper Ordovician, Edenian and Maysvillian) 

exposed in the Putnam Highlands in western Baffin Island 

in the Canadian Arctic. This specimen (University of 

Michigan, Museum of Paleontology no. 10261) differs 

from 0. amplicameratum in having a more gradually 

expanding shell (apical angle 3 degrees) and longer

camerae (cameral length greater than one-half the diameter of the shell at a shell diameter of 50 mm) at comparable shell diameters.

FAMILY PROTEOCERATIDAE FLOWER

Smooth or ornamented, small to medium-sized (less 

than 65 cm in length), moderately to rapidly expanding 

orthoconic or cyrtoconic longicones. Circular to slightly 

depressed in cross section, straight transverse sutures 

and short to moderately long camerae with septa exhibiting only weak curvature. Body chambers typically 

one-fourth the total length of the shell. Periphract dorsomyarian. Body chamber constricted just adapical to 

aperture.

Siphuncle segments typically supracentral in position 

initially, moving to a more ventral position with ontogeny. 

Segments expanded equiaxial or compressed in early and 

intermediary stages, decompressing with ontogeny, producing subtubular, depressed segments adorally. Septal 

necks of moderate length, recurved, sometimes recumbent, cyrtochoanitic most of the length of the phragmocone, often becoming suborthochoanitic in adoralmost 

septa. Connecting rings thin, homogeneous in structure. 

Endosiphuncular deposits typically well developed adapically, consisting of annuli that grow primarily forward to 

form parietal deposits that fuse to form ventral endosiphuncular linings adapically. Cameral deposits consisting 

of lobate mural-episeptal and hyposeptal deposits that 

develop ventrally prior to their dorsal development. 

Medial mural delta formed in most taxa.

Stratigraphic range.—Middle Ordovician (Chazyan 

Stage) to Upper Silurian (Ludlovian Series).

Remarks.—This family was formed for the reception 

of Ordovician orthocerids that developed compressed 

siphuncle segments and recurved cyrtochoanitic septal 

necks. The morphology of this group parallels that of the 

Pseudorthoceratidae, the predominant orthocerid family 

in younger Devonian and Carboniferous strata. Flower 

(1962) indicated that the Proteoceratidae differ from the 

Pseudorthoceratidae in (1) the form of the endosiphuncular deposits, which thicken where the segment curves 

adorally from the septal foramen versus more uniform 

development in the Pseudorthoceratidae, and (2) the 

ontogenetic decompression of the siphuncle segments in 

the Proteoceratidae compared with the lack or weak 

expression of such decompression in the Pseudorthoceratidae. Unfortunately, the complete or nearly complete 

specimens necessary to document ontogenetic differences in siphuncle segment shape are largely lacking for 

both of these families. Well-preserved, nearly complete 

material is known for Cyrtactinoceras Hyatt, Proteoceras 

Flower, and TYeptoceras Flower within the Proteoceratidae, and all three illustrate well the ontogenetic
P42 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

decompression of the siphuncle segments (pi. 5, figs. 1- 

4). The few members of the Pseudorthoceratidae in which 

a significant portion of the phragmocone is known (Adnatoceras Flower, Mooreoceras Miller, Dunbar, and Condra, 

Paramooreoceras Zhuravleva, and Pseudorthoceras 

Girty) do not exhibit this pronounced decompression of 

siphuncle segments and have endosiphuncular deposits 

that lack the adoral thickening typical of Proteoceras and 

Treptoceras. Thus, it is suggested that Flower's criteria for 

differentiating these families might be valid. More complete specimens representative of both families are 

needed to further validate their distinctiveness. Two genera, Isorthoceras Flower and Gorbyoceras Shimizu and 

Obata, originally placed in the Proteoceratidae by Flower, 

appear to lack siphuncle segment decompression 

(Aronoff, 1979; Flower, 1946) and are placed here in the 

Pseudorthoceratidae. The annulated orthocerid Monomuchites Wilson is retained in the Proteoceratidae, although 

questionably, since there is a lack of knowledge concerning the shape of its siphuncle segments, its endosiphuncular deposits, and how both change with ontogeny.

GENUS PROTEOCERAS FLOWER

Type species.—Oonoceras perkinsi Ruedemann, 

1906, p. 499; designated by Flower, 1955b, p. 821; upper 

part of the Chazy Limestone, Chazyan Stage, Middle 

Ordovician, New York.

Description.—Small, moderate to rapidly expanding 

orthoconic longicones that are slightly curved endogastrically in adapical portions of the shell. Circular in cross 

section with straight transverse sutures. Camerae short to 

moderate in length, typically decreasing with ontogeny 

relative to shell diameter. Body chamber one-fourth the 

total length of the shell, slightly constricted just adapical 

of aperture. Exterior smooth, marked dorsally by fine longitudinal color bands.

Assuming an endogastrically curved shell, the 

siphuncle is initially middorsal, moving to a more central 

position with ontogeny. Expanded globular siphuncle segments adapically, decompressing with ontogeny, the 

adoral segments nearly tubular, longer than wide. Septal 

necks cyrtochoanitic, recurved with free brims. Connecting rings thin, homogeneous. Endosiphuncular deposits 

consisting of annuli that thicken adorally adjacent to septal necks and that grow forward with ontogeny to form 

thin parietal deposits that fuse into an endosiphuncular 

lining. Well-developed cameral deposits adapically, consisting of planar mural-episeptal deposits dorsally and 

thick, botryoidal mural-episeptal deposits ventrally.

Stratigraphic range and geographic occurrence.— 

Middle Ordovician (Chazyan to Rocklandian Stages) in 

Eastern North America (Laurentia).

Remarks.—This genus was erected by Flower 

(1955b) for small cyrtochoanitic longicones from early 

Middle Ordovician strata in Eastern North America 

These nautiloids are remarkable for the pronounced 

changes in the shape and position of the siphuncle segments with ontogeny, coupled with the presence of endosiphuncular deposits that consist of annuli that are 

thickest just adoral of septal necks.

There is some uncertainty as to the orientation of 

shells assigned to this genus. Flower (1955b) believed 

these shells were endogastrically curved, the siphuncle 

located dorsally initially, moving to a more central position with ontogeny. As evidence of this orientation, 

Flower cited (1) the more massive development of cameral deposits adjacent to the concave side of the shell, 

opposite the siphuncle, and (2) the similar thickening of 

endosiphuncular deposits and their earlier development 

on the side of the siphuncle facing the concave portion of 

the shell. These ballast deposits are assumed to be thicker 

ventrally in order to lower the shell's center of gravity, further stabilizing these longiconic shells.

Dorsally situated siphuncles are not typical of most 

members of the Orthocerida. Most taxa assigned to this 

order have either central or subcentral siphuncles. One 

other member of the Proteoceratidae, Treptoceras 

Flower, exhibits supracentral siphuncle segments in early 

growth stages, the siphuncle moving to a subcentral position with ontogeny. Some species of the annulated orthocerid Monomuchites, also placed in the Proteoceratidae 

by Flower (1962), have siphuncle segments that are 

supracentral in position (pi. 9, figs. 3, 4, 17, 19). Members 

of the Geisonoceratidae, described above, also exhibit 

more massive development of cameral deposits on the 

side of the shell opposite the siphuncle, suggesting dorsal 

siphuncle segments.

Proteoceras is currently known from Chazyan carbonates in the Champlain basin in Upstate New York and 

adjacent portions of Vermont and Quebec. Flower (1955b) 

suggested that Middle Ordovician (Blackriveran) species 

described by Foerste (1932, 1933) as members of the 

genus Sactoceras Hyatt might also be assignable to Proteoceras. These species were described from the "Black 

River Formation" exposed on St. Joseph Island in Lake 

Huron, Ontario. Similarly, Sactoceras tyronensis (Foerste) from the Tyrone Limestone in central Kentucky is 

also placed here in Proteoceras, extending the stratigraphic range of the genus into the Rocklandian.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P43

PROTEOCERAS TYRONENSIS (FOERSTE), 1912

Plate 4, figures 1-7

Orthoceras tyronensis Foerste, 1912, p. 139, pi. 10, figs.

5a-b. 

Sactoceras tyronensis (Foerste). Foerste, 1933, p. 6, pi.

10, fig. 5. 

Sactoceras josephianum Foerste, 1933, p. 2-4, pi. 9, figs.

2a-b, 3a-b.

Sactoceras josephianum Foerste. Wilson, 1961, p. 64-65, 

pi. 25, fig. 9.

Diagnosis.—A slender, slightly endogastrically 

curved species of Proteoceras with camera! lengths from 

one-third to one-fifth the diameter of the shell and siphuncle segments that change position from supracentral to 

subcentral with ontogeny and that, adapically, are globular, equiaxial to slightly compressed in shape at diameters 

from one-fourth to one-fifth the diameter of the shell.

Description.—Small (phragmocone lengths of at 

least 20 cm and having diameters up to 2.4 cm), slender 

(apical angle 6-7 degrees), slightly endogastrically curved 

orthoconic longicones; circular in cross section with 

straight transverse sutures. Camera! lengths decreasing 

with ontogeny from one-third the diameter of the shell at 

diameters less than 10 mm to one-fifth the diameter of the 

shell adorally at shell diameters in excess of 20 mm. Body 

chamber lengthy, tubular; aperture unknown. Shell surface smooth.

Siphuncle segments central adapically (SPR=0.50 at 

diameters of 10 mm or less), then becoming supracentral 

(SPR=0.53-0.57) for much of the known length of the 

phragmocone, and then subcentral (SPR=0.47-0.48) in 

adoral portions greater than 15 mm in diameter. Segments 

globular, equiaxial at diameters of 10 mm or less, becoming compressed (SCR= 1.14-1.16) at shell diameters 

between 10 and 15 mm. Segment shape in more adoral 

portions of shell unknown. Segment diameters between 

one-fourth and one-fifth the diameter of the shell. Septal 

necks cyrtochoanitic with recurved, free brims. Endosiphuncular deposits developed adapically, consisting of 

ventral parietal deposits that fuse to form a continuous 

endosiphuncular lining. Camera! deposits developed 

adapically, the adoralmost deposits consisting of lobate, 

botryoidal episeptal deposits ventrally and a welldeveloped medial mural delta (pi. 4, fig. 5).

Stratigraphic range and geographic occurrence.— 

Rocklandian part of the Tyrone Limestone, Inner Blue 

Grass region of central Kentucky; "Black River Formation," Middle Ordovician (Blackriveran? Stage), St. 

Joseph Island, Lake Huron, Ontario; and "Leray-Rockland 

beds" (Middle Ordovician, Rocklandian Stage), Ottawa 

region, Ontario and Quebec.

Studied material.—Holotype, USNM 87109, Tyrone 

Limestone, 30 ft below the top of the formation, High

Bridge, Ky.; USNM 158629 (pi. 4, figs. 1-3), 468686, 

468687, 468688 (pi. 4, fig. 6), 468689 (pi. 4, figs. 5, 7), and 

468690 (suite of 10 specimens), all from USGS 6034-CO 

collection, Little Hickman section A, Jessamine County, 

Ky.

Remarks.—Foerste (1912) based his description of 

this species on several small (less than 4.0 cm in length), 

fragmentary specimens that were chiefly remarkable for 

the holoperipheral encrustation of the shells by the problematic sponge Dermatostroma tyronensis Foerste. The 

other salient features of this species, as described by Foerste, were an orthoconic shell, circular in section, its apical angles varying from 6 to 10 degrees. In the original 

description the siphuncle in this species was described as 

being "linear in form" and "about 2/3 of a millimeter in 

diameter" at a diameter of 7 mm. In a later paper, Foerste 

(1933) described the species as having subglobular 

siphuncle segments at shell diameters of 11 mm and a 

shell that was "very slightly curved lengthwise." The nautiloid specimens described here from the 6034-CO collection correspond well with Foerste's brief description of 

"Orthoceras" tyronensis. The general shell morphology, 

siphuncle segment position and shape, and the nature of 

endosiphuncular and cameral deposits in this species all 

indicate placement in the genus Proteoceras Flower.

Specimens of P. tyronensis are common within the 

silicified USGS 6034-CO collection from the Tyrone Limestone, 46 ft below the top of the formation at the Little 

Hickman section. Specimens are typically fragmentary, 

consisting of adapical portions of phragmocones less than 

1.5 cm in diameter. Proteoceras tyronensis is the fifth 

most common longiconic nautiloid present in the 6034-CO 

collection, behind the two species of Cartersoceras, Pojetoceras floweri, and Monomuchites annularis. It shares 

the same fauna! associates with these species.

Proteoceras tyronensis differs from the type species 

of Proteoceras, P. perkinsi (Ruedemann) plus the associated P. pulchrum Flower, both from the upper part of the 

Chazy Limestone (Middle Ordovician, Chazyan Stage) of 

New York, in having a more slender, less rapidly expanding shell and an apical angle of 6-7 degrees compared 

with values of 8-10 degrees for these Chazyan species. 

These differences are presented graphically in figure 11. 

Proteoceras tyronensis is most similar to "Sactoceras" 

josephianum Foerste, a slender, slightly curved species 

of Proteoceras from equivalent Blackriveran and Rocklandian strata exposed on St. Joseph Island in Lake Huron 

(Foerste, 1933). Both species have slightly curved, slender shells (apical angle 6-7 degrees) and siphuncles that 

are slightly dorsal of center with globular siphuncle segments. Curiously, the specimens of P. josephianum 

described and figured by Foerste (1933, pi. 9, figs. 2a, 3a) 

are also encrusted by a species of Dermatostroma.
P44 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

5

to 4 DC

LUI 3

=! 2

6 8 10 12 14 16 18 20 22 

SHELL DIAMETER, IN MILLIMETERS

24 26

FIGURE 11. — Bivariate plot of camera! length versus shell 

diameter for Middle Ordovician species of Proteoceras 

from Eastern North America. Species are P. tyronensis 

(Foerste) from the USGS 6034-CO collection in the Tyrone 

Limestone (circles), and P. perkinsi (Ruedemann) 

(squares) and P. pidchrum Flower (triangles) figured by 

Flower (1955b) from the Chazy Limestone in New York.

Foerste (1933) described "Sactoceras" josephianum as 

being similar to "Orthoceras" tyronensis, remarking that 

it differed from this species only in the larger size of the 

St. Joseph Island specimens. Specimens of P. tyronensis 

from the USGS 6034-CO collection are equal in size to 

Foerste's figured specimens of US" josephianum, and it is 

concluded that these species are synonyms; P. tyronensis 

has priority.

Orthoceras huronense Billings and Sactoceras pictolineatum Foerste, both from Blackriveran strata exposed 

on St. Joseph Island, also appear to be assignable to Proteoceras. Both of these species differ from P. tyronensis 

in having more rapidly expanding shells and apical angles 

of 8 and 8.5 degrees, respectively. The figured specimen of 

P. huronense (GSC 1724) preserves a dorsal color pattern 

of seven to eight moderately thick longitudinal brown 

bands, whereas the specimen of P. pictolineatum figured 

by Foerste (1932, pi. 9, figs. 5a-b) has a dorsal color 

pattern of numerous (27+) fine, longitudinal, dark lines. 

Color patterns are unknown for specimens of P. 

tyronensis.

GENUS TREPTOCERAS FLOWER

Type species. — Orthoceras duseri Hall and Whitfield, 

1875, p. 97; designated by Flower, 1942, p. 16; Waynesville 

Formation, Richmondian Stage, Upper Ordovician, Ohio.

Description. — Small to medium-sized, generally 

moderately expanding orthoconic longicones, circular in 

cross section with straight, transverse sutures. Camera! 

lengths ranging from one-fourth to one-seventh the diameter of the shell, typically decreasing with ontogeny relative to shell diameter. Body chamber one-fourth the total 

length of the shell; aperture straight, transverse, no ventral sinus. Periphract dorsomyarian. Shell basically 

smooth, marked by fine longitudinal lirae and transverse

growth lines. Dorsum marked by longitudinal color 

bands.

Siphuncle supracentral or central initially, some distance ventral of center in adoral portions of large specimens. Segments expanded, heart-shaped, equiaxial 

initially, becoming compressed, beadlike, and then 

decompressing in later growth stages, the segments 

depressed, longer than high. Segment diameter ranging 

from one-fourth to one-seventh the diameter of the shell, 

decreasing with ontogeny. Septal necks cyrtochoanitic; 

dorsal brims recumbent, ventral brims recurved but free. 

Connecting rings thin, homogeneous. Adapical portions 

of phragmocone with endosiphuncular deposits consisting of annuli that thicken adorally, ae^jacent to septal 

necks and grow forward to form parietal deposits ventrally and simple annuli dorsally. Parietal deposits fuse 

adapically to form a continuous ventral endosiphuncular 

lining with ontogeny. Camera! deposits completely filling 

chambers in adapical half of large phragmocones; adoralmost deposits mural-episeptal, initiated ventrally and laterally before developing dorsally.

Stratigraphic and geographic range.—Upper Ordovician (Edenian to Richmondian Stages), Eastern North 

America (Laurentia).

Remarks.—As was indicated by Flower (1946), Treptoceras is the most common nautiloid taxon encountered 

in the Upper Ordovician section exposed in the Cincinnati, Ohio, region, which takes into account acjjacent portions of Kentucky and Indiana. Many species have been 

described from these strata in this area (Miller, 1875; 

James, 1886). Most of these species, however, were 

described from fragmentary specimens, some representing different ontogenetic stages of the same nautiloid. The 

incomplete, often poorly preserved nature of most 

museum material, coupled with the pronounced ontogenetic changes characteristic of the genus, makes 

species-level systematic study of the genus difficult. To 

complicate matters further, Miller (1875) did not designate types, and the location of some of his figured specimens is unknown. Material that this writer believes to be 

the original figured specimens and that are listed as being 

type specimens on their museum labels are the holotype 

of Orthoceras duseri Hall and Whitfield (University of 

California at Berkeley, UCal 34325) and the holotype of 

Orthoceras cincinnatiensis Miller (Harvard Museum of 

Comparative Zoology, MCZ 3404). Specimens similar to 

those figured by Miller (1875, 1881) and listed as "cotypes" in the collections of the University of Cincinnati 

(UC) are the "co-types" of Orthoceras fosteri Miller (UC 

356) and O. transversa Miller (UC 1328). These specimens, in conjunction with the original species descriptions and illustrations plus well-preserved, nearly 

complete specimens collected by the writer, indicate the 

presence of at least four distinct species of Treptoceras in
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P45

Cincinnatian Provincial Series strata exposed in the 

Kentucky-Indiana-Ohio region.

In the past there has been some confusion as to the 

affinities of Treptoceras. Flower (1942, 1957a), citing the 

nature of the endosiphuncular deposits and the ontogenetic decompression of siphuncle segments, placed the 

genus in the Actinocerida, Teichert and Glenister (1953) 

decided that Treptoceras was a synonym of Orthonybyoceras Shimizu and Obata, the latter name having priority. 

Flower removed Orthonybyoceras (=Treptoceras) from 

the Actinocerida and placed this genus in a new family, 

the Proteoceratidae, within the Orthocerida, Aronoff 

(1979) clarified the taxonomic positions of both of these 

genera and demonstrated that Orthonybyoceras is an actinocerid distinct from Treptoceras, which he retained in 

the Proteoceratidae. Both taxa occur in the Upper Ordovician strata exposed in the Cincinnati region. Orthonybyoceras is an uncommon form in the Fairview Formation in 

northern Kentucky and in adjacent portions of Ohio and a 

rare element in the lower part of the Bull Fork Formation 

in Indiana and Ohio (pi. 18, figs. 10-17). Treptoceras, on 

the other hand, is ubiquitous to nearly every stratigraphic 

unit within the Upper Ordovician section exposed in the 

Kentucky-Indiana-Ohio area (pi. 4, figs. 8-12, pis. 5-8).

As indicated in Frey (1987a, 1989), species of Treptoceras are largely restricted to clastic or mixed clasticcarbonate shallow-marine facies of Late Ordovician Age 

in Eastern and Central North America (Laurentia). The 

genus has not been identified from coeval carbonate platform facies exposed in Western and Arctic North America. Species of Treptoceras from outside the northern 

Cincinnati arch region are T maquoketense (Foerste) 

from the "Elgin Shale" in Iowa (Upper Ordovician, 

Maysvillian); T manitoulinense (Foerste) from the Georgian Bay Formation (Upper Maysvillian and Richmondian) in southern Ontario; and species referred to as 

either "Actinoceras" crebriseptum (Hall) or "Orthoceras" 

lameUosum Hall, both from the Pulaski Formation 

(Maysvillian) of New York and the Georgian Bay Formation exposed at Toronto in Ontario. Additional species 

possibly assignable to Treptoceras are "Ormoceras" lindsleyi Foerste and Teichert from the Cannon Limestone 

(Middle Ordovician, Shermanian) of central Tennessee. 

This species, if indeed a species of Treptoceras, would 

mark the earliest known occurrence of the genus. More 

complete specimens of this Middle Ordovician species are 

needed to determine its affinities to Treptoceras.

Species of Treptoceras described by Flower (1942) 

from the "Cynthiana Limestone" (=Strodes Creek Member 

of the Lexington Limestone) at Cynthiana, Ky., are known 

only from solitary incomplete specimens sectioned horizontally, obscuring some of the diagnostic features of 

these species. Aronoff (1979) placed "Treptoceras" persiphonatum Flower (1942, pi. 4, fig. 2) with question in Deiroceras, based on its globular siphuncle segments, long 

septal necks, and comparatively deep camerae. He did not 

attempt to determine the systematic affinities of the other 

two species described by Flower from the same limestone 

lens at the same locality. The broad siphuncle segments in 

"T" perseptatum Flower (1942, pi. 1, fig. 1) are suggestive 

of Ormoceras or Orthonybyoceras. The apparently short, 

recumbent septal necks in this specimen indicate placement in Orthonybyoceras. The narrow diameter, slightly 

expanded, barrel-shaped siphuncle segments and gently 

recurved, free cyrtochoanitic septal necks in "T." praenuntium Flower (1942, pi. 1, fig. 2) indicate placement of 

this species in the Pseudorthoceratidae, possibly in Isorthoceras Flower.

Foerste (1893) described a number of small orthoconic longicones from the overlying Lower Silurian (Llandoverian, Aeronian) Brassfield Limestone in southwestern 

Ohio. He placed these species in a new genus, Euorthoceras, but did not formally describe the distinguishing features of this genus nor designate a type species. Restudy 

of the types of the two best known species referred to the 

genus, E. ignotum Foerste (USNM 88554) and E. erraticum Foerste (USNM 88549), reveals that these species 

belong to two different genera. Euorthoceras ignotum is 

a gradually expanding, slender longicone (apical angle 5 

degrees) with short camerae and an internal structure 

similar to that of Isorthoceras Flower, having subcentral, 

very slightly expanded, barrel-shaped siphuncle segments 

with short, cyrtochoanitic septal necks. Mural-episeptal 

deposits are known from shell fragments less than 18 mm 

in diameter. No endosiphuncular deposits are preserved 

in the suite of USNM specimens. Euorthoceras erraticum 

is a more rapidly expanding form (apical angle 7 degrees) 

with a smooth exterior and short camerae. The siphuncle 

is similar to that of Treptoceras in that it migrates from a 

middorsal to a midventral position with ontogeny and 

possesses globular, equiaxial segments adapically that 

decompress to form slightly expanded, subtubular segments with ontogeny. Septal necks are short, recurved, 

cyrtochoanitic. Episeptal camera! deposits are present in 

adapical portions of the phragmocone less than 16 mm in 

diameter. Endosiphuncular deposits consist of parietal 

deposits ventrally and thin annuli dorsally, observed in 

the phragmocone at diameters less than 14 mm.

Euorthoceras, based on E. ignotum, is a member of 

the Pseudorthoceratidae, closely related to Ordovician 

taxa like Isorthoceras Flower. Euorthoceras, based on E. 

erraticum, is a member of the Proteoceratidae, closely 

related to, if not in fact, a species of the genus Treptoceras 

Flower. As indicated above, Foerste did not designate a 

type species for Euorthoceras (Teichert, 1940). The first 

species Foerste unquestionably assigned to Euorthoceras 

was E. ignotum (Foerste, 1893, p. 539). As such, this species is here designated the type species of Euorthoceras,
P46 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

and the genus assumes the characters of this species, 

namely, a slender, gradually expanding longicone with 

barrel-shaped siphuncle segments and short, recurved 

septal necks with free brims. Euorthoceras erraticum is 

removed from Euorthoceras and is tentatively placed in 

the genus Treptoceras Flower, pending further study. 

Other species assignable to Euorthoceras, based on E. 

ignotum, are E. cf. E. virgulatum (Hall) from the Brassfield Limestone in Ohio and southeastern Indiana and 

Euorthoceras sp. from the Ekwan River Formation 

(Lower Silurian, Llandoverian) of the James Bay Lowland, 

Quebec (Flower, 1968b). Treptoceras'? erraticum, (Foerste), if determined to be a valid species of Treptoceras, 

would be the youngest known member of the genus.

TREPTOCERAS DUSERI (HALL AND WHTTFIELD), 1875

Plate 4, figures 8-12; plate 5, figures 1-6

Orthoceras duseri Hall and Whitfield, 1875, p. 97, pi. 3,

figs. 2-4.

Orthoceras duseri Hall and Whitfield. James, 1886, p. 241. 

Orthoceras duseri Hall and Whitfield. Cumings, 1908,

p. 1036, pi. 52, figs. 2-2b. 

Orthoceras duseri Hall and Whitfield. Bassler, 1915,

p. 904. 

Orthoceras duseri Hall and Whitfield. Parks and Fritz,

1922, p. 16-17, pi. 2, fig. 1; pi. 4, figs. 7, 8. 

Tieptoceras duseri (Miller). Flower, 1942, p. 16-17. 

Orthonybyoceras duseri (Hall and Whitfield). Teichert

and Glenister, 1953, p. 223. 

Orthonybyoceras duseri (Hall and Whitfield). Flower,

1957a, p. 56-57. 

Treptoceras duseri (Hall and Whitfield). Aronoff, 1979,

p. 113-116, figs. 2a-c, 3d-e.

Treptoceras duseri (Hall and Whitfield). Frey, 1988, p. SI84, pi. 1, figs. 1-6; pi. 2, figs. 1-6; pi. 3, figs. 2-4; figs. 3,

5, 6, 8.

Diagnosis.—Large, moderately expanding species of 

Treptoceras having siphuncle segments one-sixth to onefourth the diameter of the shell that change shape with 

ontogeny from equiaxial to compressed and position from 

central to subcentral; becoming equiaxial or depressed 

and midventral in the adoralmost segments of large 

specimens.

Description.—Medium-sized (up to 46 cm in length 

and 5.5 cm in diameter), moderately expanding (apical 

angle 7.5-8.5 degrees) orthoconic longicone, circular in 

cross section with straight transverse sutures. Camerae 

short, lengths initially one-fourth the diameter of the 

shell, decreasing with ontogeny to one-sixth or oneseventh the diameter of the shell in adoral portions 20-35 

mm in diameter. Body chamber at least one-fourth the 

total length of the shell; aperture straight, transverse, 

lacking sinus. Periphract dorsomyarian. Shell exterior

essentially smooth, marked by fine transverse growth 

lines and fine longitudinal lirae.

Siphuncle segments central in position (SPR=0.50) at 

a diameter of 15 mm, migrating with ontogeny to a subcentral position (SPR=0.29-0.33) at a diameter of 27 mm, 

and midventral in position (SPR=0.25) in adoral portions 

40 mm in diameter. Segments initially equiaxial at diameters less than 15 mm, becoming compressed (SCR=1.06- 

1.42) between diameters of 15 and 25 mm, equiaxial 

between diameters of 25 and 30 mm, then depressed for 

the remaining length of shell (SCR < 1.0). Segment diameter from one-fourth to one-sixth the diameter of the shell, 

decreasing with ontogeny. Septal necks cyrtochoanitic; 

dorsal brims recumbent, ventral brims recurved but free. 

Dorsal brims suborthochoanitic at shell diameters greater 

than 35 mm. Endosiphuncular deposits consisting of dorsal annuli and ventral parietal deposits, restricted to 

adapical half of large shells. With ontogeny, ventral parietal deposits fuse to form a continuous ventral endosiphuncular lining adapically. Adoralmost cameral deposits 

mural-episeptal, the deposits completely filling camerae 

in adapical half of large shells.

Stratigraphic and geographic occurrence.—Basal 

portions of the Fairview Formation, Hamilton and Brown 

Counties in southwest Ohio and Campbell and Kenton 

Counties in northern Kentucky; "Waynesville biofacies" 

(in the sense of Wahlman, 1992) in the Bull Fork Formation (Upper Ordovician, Richmondian) in Clinton and 

Warren Counties in southwest Ohio and Dearborn and 

Franklin Counties in southeastern Indiana. With question, 

from the upper part of the Clays Ferry Formation (Upper 

Ordovician, Edenian), Scott County, Ky.

Studied material—Holotype, UCal 34325 (pi. 4, figs. 

8-10), from "shales of the Hudson River Group near 

Waynesville, Ohio"; MU 417T (pi. 5, figs. 1-6) from the 

Treptoceras duseri shale unit exposed along Harpers 

Run, Warren County, Ohio; several suites of specimens 

from the T. duseri shale unit: MU 17170 (three specimens) 

from the Caesars Creek dam site, Warren County, Ohio; 

MU 17171 (two specimens) from Stony Hollow, north of 

Clarksville, Clinton County, Ohio; MU 17172 (four specimens) from the Route 42 roadcut northeast of Waynesville, Warren County, Ohio; MU 17173 (nine specimens) 

from Harpers Run, Warren County, Ohio; plus additional 

material from the Clays Ferry Formation, at Sadieville, 

Scott County, Ky. (USNM 468719); the basal Fairview Formation at Georgetown, Brown County, Ohio (MU 7871) 

and at Dent, Hamilton County, Ohio (MU 29766, pi. 4, fig. 

11), and USNM 468727 from the base of the Reidlin Road 

section, Forest Hills, Kenton County, Ky. (pi. 4, fig. 12).

Remarks.—Treptoceras duseri is the type species for 

the genus Treptoceras Flower. The species is known primarily from the T. duseri shale unit within the "Waynesville biofacies" of the Bull Fork Formation (Upper
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P47

Ordovician, lower Richmondian) in Warren and Clinton 

Counties in southwestern Ohio. In this claystone unit the 

species is represented by abundant, largely complete, 

well-preserved, calcite-replaced internal molds (pi. 4, figs. 

8-10; pi. 5, figs. 1-6). The distinctive preservation of nautiloids from the T. duseri shale unit indicates that this claystone is also the source of the holotype.

An internal mold with the general morphological features of T. duseri is present in USGS collection 7471-CO 

from the Edenian part of the Clays Ferry Formation at 

Sadieville, Scott County, Ky. (USNM 468719). The internal 

details of the siphuncle segments are not known for this 

specimen, and better preserved material is necessary to 

determine the affinities of this Clays Ferry species.

Additional well-preserved and comparatively complete material assignable to T. duseri is known from the 

interbedded claystone and thin packstone beds at the 

base of the Fairview Formation exposed in Brown and 

Hamilton Counties in the vicinity of Cincinnati, Ohio (pi. 

4, fig. 11). Fragmentary material referable to this species 

has been collected from the same strata exposed along I275E in Kenton County, Ky. (pi. 4, fig. 12). Less well preserved, large phragmocones (up to 50 cm in length) possibly assignable to T. duseri are common in the Mount 

Auburn Member of the Grant Lake Formation (Maysvillian) in parts of Butler and Warren Counties in Ohio.

Treptoceras duseri is most similar to the associated 

species, T. fosteri (Miller). It differs from T. fosteri in its 

more rapidly expanding shell (apical angle 7.5-8.5 

degrees compared with apical angle 5.5-6.0 degrees in T. 

fosteri), the more central position of the siphuncle segments in T. duseri at comparable diameters (table 7 and 

fig. 12), and the shape of the siphuncle segments, the 

compressed segments in T. duseri lacking a well-developed zone of adnation compared with a well-developed 

dorsal zone of adnation in T. fosteri (fig. 13). The ranges 

of these two species overlap stratigraphically and geographically. In the T. duseri shale unit, sampled suites of 

specimens indicate that these species occur in the same 

beds, T. fosteri being slightly more abundant (AT=83) than 

T. duseri (AT=73) (Frey, 1989). Elsewhere, however, one or 

the other species is predominant, the second species typically being absent. Treptoceras duseri or a closely related 

form is the most abundant nautiloid in the Mount Auburn 

Member of the Grant Lake Formation, while a species 

similar to T. fosteri is predominant in the underlying Corryville Member of the same formation, both in southwestern Ohio. Treptoceras duseri has not been identified from 

strata younger than the upper part of the "Waynesville 

biofacies" in the Bull Fork Formation in southwestern 

Ohio and southeastern Indiana. Treptoceras fosteri or a 

closely related species (pi. 6, figs. 4, 8) is the most abundant nautiloid species in the "Liberty biofacies" (in the

sense of Wahlman, 1992) in overlying portions of the Bull 

Fork Formation.

Treptoceras duseri is also similar to the associated T. 

cincinnatiensis (Miller). Both species are moderate to 

rapidly expanding, rather large species of Treptoceras, 

having central to subcentral siphuncle segments at comparable diameters, and well-developed adapical endosiphuncular deposits consisting of dorsal annuli and ventral 

parietal deposits. Treptoceras duseri is distinct from T. 

cincinnatiensis in the less central position of the siphuncle in the adoral portions of large specimens (table 7 and 

fig. 12); in the narrower diameters of the siphuncle segments at comparable shell diameters (segment heights 

averaging one-seventh the diameter of the shell at diameters in excess of 30 mm in T. duseri compared with segment heights one-fifth the diameter of the shell at the 

same diameters in T. cincinnatiensis)', and in the 

mural-episeptal nature of last-formed camera! deposits in 

T. duseri in contrast to the episeptal and hyposeptal 

deposits in T. cincinnatiensis (compare pi. 5, figs. 1-6 

with pi. 7, figs. 4-6). Treptoceras duseri and T. cincinnatiensis overlap throughout most of their respective 

ranges, notably in the basal Fairview Formation in northern Kentucky and in the "Waynesville biofacies" within 

the Bull Fork Formation in southwestern Ohio and southeastern Indiana As indicated above, T. duseri is absent 

from the overlying "Liberty biofacies" in the Bull Fork 

Formation in the same area, whereas T. cincinnatiensis 

or a similar form is uncommon in these strata. Comparisons of the critical morphological features used to distinguish these Cincinnatian species of Treptoceras are 

presented graphically in figures 14-16.

Ward (1987) has remarked that species of living Nautilus, upon sexual maturity, reach a maximum size at 

which growth slows or ceases. In Nautilus the attainment 

of sexual maturity is marked by thickening of the last 

formed septum and is preceded by approximation of the 

last two or three septa Not all specimens of Nautilus, 

however, exhibit septal approximation (Ward, 1987). 

Large specimens of T. duseri (MU 417T, pi. 5, fig. 1) and 

the associated species T. cincinnatiensis (MU 443T, pi. 8, 

fig. 3) show similar abrupt septa approximation adorally. 

At a diameter of 40 mm in T. duseri, camera! length 

decreases from 5.5 mm to lengths of 1.5 and 1.3 mm in the 

last formed camerae. At a diameter of 55 mm in T. cincinnatiensis, camera! length decreases from 9 mm to lengths 

of 5 mm and then 3 mm in adoralmost camerae. These 

examples suggest that these species of Treptoceras had a 

maximum size that could be attained, roughly shell 

lengths of approximately 46 cm at diameters of 5.5 cm in 

T. duseri and a length of 55 cm and a diameter of 7.5 cm 

for specimens of T. cincinnatiensis. Septal approximation was also observed in specimens of T. cf. T. fosteri 

from the "Liberty biofacies" in the Bull Fork Formation in
P48 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

TABLE 7. — Comparisons of the morphological features of species

of Treptoceras from the Bull Fork Formation in the

Kentucky-Indiana-Ohio area showing differences in shell

expansion, cameral length, siphuncle position, segment

shape, and siphuncle diameter relative to shell diameter

[Data from specimens listed in text CL/D, ratio of cameral length to

shell diameter; SPR, siphuncle segment position ratio; SCR, siphuncle segment compression ratio; SD/D, ratio of siphuncle diameter to

shell diameter; mm, millimeter]

F tur T. T. T.ct T.

duseri fosteri T. fasten cincinnatiensis

Apical angle, degrees 7.5-8.5 6 5-6 8.5-9

Diameter 35 mm

CL/D 0.17 0.12 0.185

SPR .285 .23 .34

SCR .83 1.00 1.40

SD/D .125 .12 .20

Diameter 30 mm

CL/D .166 0.133 .133 .166

SPR .30 .23 .23 .33

SCR 1.00 .875 1.10 1.20

SD/D .166 .166 .16 .20

Diameter 25 mm

CL/D .19 .14 .16 .16

SPR .36 .24 .28 .40

SCR 1.25 1.14 1.00 1.50

SD/D .20 .16 .20 .24

Diameter 20 mm

CL/D .18 .15 .20 .20

SPR .38 .30 .30 .50

SCR 1.25 1.16 1.00 1.375

SD/D .25 .175 .225 .275

Diameter 15 mm

CL/D .20 .166 .25 .27

SPR .50 .46 .31 .50

SCR 1.33 1.20 1.00 1.375

SD/D .26 .20 .25 .30

Diameter 10 mm

CL/D .20 .30

SPR .50 .55

SCR 1.25 1.20

SD/D .25 .35

.45

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ANGLE OF EXPANSION

FIGURE 12. — Bivariate plot of segment position ratio (SPR)

versus apical angle for species of Treptoceras from the

Bull Fork Formation in the Cincinnati arch region of

Kentucky, Indiana, and Ohio. Measurements of SPR in all

specimens taken at a shell diameter of 27 mm. Species are

T. duseri, N=17 (solid circles); T. fosteri, N=22 (open

circles); and T. cincinnatiensis, N=12 (triangles), where 

AT is number of specimens measured.

southwestern Ohio (MU 420T, pi. 6, fig. 4), indicating maximum lengths of 60 cm and diameters up to 5.5 cm for this

species.

JREPTOCERAS FOSTERI (MILLER), 1875

Plate 5, figures 7-9; plate 6, figures 1-5, 7, 8

Orthoceras fosteri Miller, 1875, p. 127.

Orthoceras fosteri Miller. Miller, 1881, p. 319, pi. 8,

figs. 7-7a,

Orthoceras duseri Hall and Whitfield. Parks and Fritz,

1922, pi. 4, fig. 7.

Treptoceras duseri (Hall and Whitfield). Frey, 1988, pi. 1,

figs. 4, 5.

Diagnosis. — Medium to large, slender, gradually

expanding species of Treptoceras with narrow siphuncle

segments one-seventh to one-sixth the diameter of the

shell that change shape with ontogeny from compressed

to depressed and position from central to ventral.

Description. — Medium-sized (up to 45 cm in length

and having shell diameters up to 4.0 cm), slender,
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P49

A

B

FIGURE 13.—Comparison of siphuncle segment morphology from adapical 

portions of specimens of Treptoceras duseri (A) and T. fosteri (B). Both 

sections represent portions of the phragmocone between 15 and 20 mm in 

diameter and 20 mm in length. Note the strong development of dorsal annuli 

in A and their weak development or absence in B. Also note the welldeveloped dorsal adnation of adoral portions of segments in T. fosteri (B) and 

the weak development of this feature in T. duseri (A). A, From MU 417T (pi. 

5, figs. 3, 5), locality OH-8. B, From MU 17175A, locality OH-7.

gradually expanding (apical angle 5.5-6.0 degrees) orthoconic longicone, circular in cross section with straight 

transverse sutures. Camera! lengths short, decreasing 

with ontogeny from lengths one-fourth the diameter of 

the shell initially to one-seventh the diameter of the shell 

in more adoral portions of phragmocones 20-35 mm in 

diameter. Body chamber one-fourth the total length of the 

shell; aperture straight, transverse. Periphract dorsomyarian. Shell exterior essentially smooth, marked by 

fine transverse growth lines and longitudinal lirae. Dorsal 

shell surface marked by an alternating sequence of fine 

and heavy longitudinal color bands (pi. 6, fig. 3).

Siphuncle segments central or subcentral in position 

(SPR=0.45-0.50) at diameters of 10 mm, becoming ventral

with ontogeny (SPR < 0.25 at diameters greater than 25 

mm). Segments compressed most of the length of the 

phragmocone (SCR= 1.15-1.25 at diameters from 10-25 

mm), becoming equiaxial at diameters of 25-30 mm and 

depressed (SPR < 1.0) at diameters in excess of 30 mm. 

Segments narrow in diameter, from one-sixth to one-seventh the diameter of the shell. Septal necks cyrtochoanitic most of the length of the siphuncle, dorsal brims 

strongly recumbent, ventral brims recurved but free. Segments compressed, heart-shaped, having the dorsal portion of the connecting ring adnate to the adoral septum. 

Endosiphuncular deposits restricted to the adapical half 

of large specimens, dorsal annuli absent or greatly 

retarded in their development; ventral parietal deposits
P50 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

6 -

A A

A

A

A

A A 

A o

e

10 20 30 40 

SHELL DIAMETER, IN MILLIMETERS

50

FIGURE 14.—Bivariate plot of camera! length versus shell 

diameter in species of Treptoceras from the Bull Fork 

Formation in the Cincinnati arch region. Species are T. 

duseri (solid circles), T. fosteri (open circles), and T. 

cincinnatiensis (triangles).

6 —

oc 4 —

A

A

A

A

s

O 

O

A

10 20 30 40 

SHELL DIAMETER, IN MILLIMETERS

50

FIGURE 15.—Bivariate plot of siphuncle diameter versus shell 

diameter in species of Treptoceras from the Bull Fork 

Formation in the Cincinnati arch region. Species are T. 

duseri (solid circles), T. fosteri (open circles), and T. 

cincinnatiensis (triangles).

r- A A

0.50

O

H

QC

2 0.40

K 

O

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LLJ

^ 0.30

0

LU 

CO

0.20

A

o A A

A •

§ A

o

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o

o

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1 1 1 1

A A

A

A A 

• A

• A A

• • A 

O • • • 

O O •

o o

o o

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1 1 1 1 1

fusing to form continuous ventral endosiphuncular lining 

adapically with ontogeny. Adoralmost camera! deposits 

mural-episeptal, the deposits completely filling camerae 

in adapical half of large shells.

Stratigraphic and geographic occurrence.— 

"Waynesville biofacies" within the Bull Fork Formation 

(Upper Ordovician, Richmondian Stage) in Warren and 

Clinton Counties, Ohio, Franklin and Dearborn Counties, 

Ind.

10 20 30 40 

SHELL DIAMETER, IN MILLIMETERS

50

FIGURE 16.—Bivariate plot of segment position ratio versus 

shell diameter for species of Treptoceras from the Bull 

Fork Formation in the Cincinnati arch region. Species are 

T. duseri (solid circles), T. fosteri (open circles), and T. 

cincinnatiensis (triangles).

Studied material.—Lectotype, UC 356 (pi. 5, fig. 8), 

"Richmond Formation, Waynesville beds, Clinton County, 

Ohio"; MU 418T (pi. 5, figs. 7, 9), Treptoceras duseri shale 

unit exposed along Harpers Run, Warren County, Ohio; 

hypotypes MU 419T (pi. 6, fig. 1) and MU 276T (pi. 6, fig. 

3), T. duseri shale unit, Route 42 roadcut, Warren County, 

Ohio; hypotype UC 28389 (pi. 6, fig. 2), Waynesville Formation, Oldenburg, Franklin County, Ind.; and studied 

suites of specimens from the T. duseri shale unit: MU 

17175 (five specimens) from the Caesars Creek dam site, 

Warren County, Ohio; MU 17176 (four specimens) from 

Stony Hollow, north of Clarksville, Clinton County, Ohio; 

MU 17178 (six specimens) from Harpers Run, Warren 

County, Ohio; and three specimens from the Dyche Collection (Miami University) De 856a-c, locality unknown.

Additional material possibly referable to this species 

consists of less well preserved internal molds from the 

"Liberty biofacies" in the Bull Fork Formation. Figured 

specimens are MU 420T (pi. 6, fig. 4) from Flat Fork 

Creek, Warren County, Ohio; and MU 422T (pi. 6, fig. 8) 

from a roadcut at the junction of Routes 380 and 22, Clinton County, Ohio. Additional measured specimens are MU 

29858 (five specimens) from Caesars Creek dam site, Warren County, Ohio; MU 29859 (three specimens) from the 

roadcut at junction of Routes 380 and 22, Clinton County, 

Ohio; and MU 29860 (five specimens) from the area of 

Oxford, Butler County, Ohio.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P51

Remarks.—"Orthoceras" fosteri was described by 

Miller (1875) from two fragmentary internal molds referable to this species figured in a later paper by the same 

author (Miller, 1881, pi. 8, figs. 7-7a). Miller distinguished 

the species on the basis of its large, gradually expanding 

shell, shallow camerae one-eighth the diameter of the 

shell, and an excentric siphuncle consisting of ovate segments "representing the appearance of a string of oval 

beads." He listed the species as occurring in "Clinton 

County, Ohio, in the upper part of the Cincinnati Group." 

The drawings of Miller's figured specimens show two 

fragments, one 65 mm in length has diameters of 33 and 

25 mm, and a second specimen 46 mm in length has diameters of 27 and 20 mm. Both specimens have an apical 

angle of 6.5 degrees.

A number of incomplete specimens, listed as "cotypes" of Orthoceras fosteri, "Richmond Formation, Clinton County, Ohio," were found in the collections of the 

University of Cincinnati (UC 356). The distinctive preservation of these specimens indicates they were collected 

from the T. duseri shale unit. Among these specimens are 

two continuous sections of a phragmocone, one 65 mm in 

length has diameters of 28 and 20 mm, the second 44 mm 

in length has diameters of 20 mm and 13 mm. Uncompressed portions of this specimen have an apical angle of 

6 degrees. This specimen may represent one or both of 

Miller's figured specimens, although there are minor differences in the respective shell diameters, assuming the 

illustrations in Miller (1881) are accurate representations 

of the specimens. This specimen is figured here (pi. 5, fig. 

8) and is designated the lectotype of T. fosteri (Miller). A 

second, more complete specimen from the T. duseri shale 

at Harpers Run, Warren County, Ohio (MU 418T, pi. 5, figs. 

7,9), illustrates the morphology of the adapical portion of 

the phragmocone.

Miller (1875) remarked that O. fosteri most nearly 

resembled O. byrnesi Miller but differed from that species in having a larger shell with shorter camerae and 

siphuncle segments proportionally smaller in diameter. 

Miller (1875) listed O. byrnesi as occurring in the "hills 

back of Cincinnati; range unknown." No material similar 

to the sectioned specimen of O. byrnesi figured by Miller 

was found in the suite of specimens listed as "co-types" of 

O. byrnesi in the University of Cincinnati collections. 

Miller did not designate a type specimen for this species.

Studies of nearly complete specimens of Cincinnatian Treptoceras indicate that the camera! length and the 

diameter and shape of siphuncle segments vary with 

ontogeny. Discriminating species of Treptoceras requires 

nearly complete sectioned phragmocones. Miller's 

descriptions and measurements of nearly complete specimens of T. fosteri from the T. duseri shale unit (pi. 5, fig. 

7) suggest that Miller's distinctions between "Orthoceras" 

fosteri and "O." byrnesi might be the result of these taxa

being described from different ontogenetic stages of the 

same species. The specimen of O. byrnesi figured by 

Miller (1875, fig. 13) represents a section of phragmocone 

less than 20 mm in diameter. The specimens of O. fosteri 

described by Miller in the same paper are adoral portions 

of larger specimens, in excess of 30 mm in diameter. The 

only significant difference observed in these taxa, based 

on Miller's figures, is the apical angle: 5 degrees in O. 

byrnesi and 6-6.5 degrees in O. fosteri. Specimens 

assigned to T. fosteri from the T. duseri shale exhibit apical angles from 5.5 to 6.0 degrees. A specimen from the 

Corryville Member of the Grant Lake Formation in Clermont County, Ohio (MU 11035), has an apical angle of 5 

degrees and closely resembles Miller's figured specimen 

of O. byrnesi (pi. 6, fig. 6). These two species may prove 

to be synonymous upon further study of larger suites of 

complete material. This writer has elected to retain these 

taxa as separate species, pending a more thorough search 

for Miller's figured specimen of Orthoceras byrnesi.

Comparisons of T. fosteri with the associated T. 

duseri are discussed above under the remarks for the latter species. Although Miller (1881) considered these species to be synonyms, careful study of well-preserved 

material from the T. duseri shale indicates to this writer's 

satisfaction that they are distinct species. Treptoceras fosteri is a more gradually expanding species with siphuncle 

segments that are more ventral in their position at comparable shell diameters (table 7 and fig. 12); the segments 

lack dorsal annuli in adapical portions of the phragmocone. At most localities exposing the claystones of the T. 

duseri shale in southwestern Ohio, T. fosteri is the most 

abundant species of Treptoceras present, followed by T. 

duseri and lesser numbers of T. cincinnatiensis. The latter species is distinct from T. fosteri in its more robust, 

rapidly expanding shell, broader diameter siphuncle segments, and more central location of these segments at 

comparable diameters.

Rather poorly preserved internal molds of a similar, 

large (up to 60 cm in length), gradually expanding species 

of Treptoceras with siphuncle segments identical to those 

in T. fosteri occur in the overlying "Liberty biofacies" of 

the Bull Fork Formation in southwestern Ohio and adjacent portions of southeastern Indiana (pi. 6, figs. 2, 4, 8). 

These specimens differ from specimens of T. fosteri from 

the T. duseri shale in having more gradually expanding 

shells and, for the majority of these upper Bull Fork specmiens, in having apical angles of 5-5.5 degrees compared 

with typical values of 5.5-6.0 degrees for the "Waynesville" forms. These "Liberty" specimens seem to be a more 

slender variant of T. fosteri and are very similar to Miller's 

species T. byrnesi. This variant is the most abundant nautiloid in the upper half of the Bull Fork Formation in 

southeastern Indiana and southwestern Ohio.
P52 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

IREPTOCERAS CINCINNATIENSIS (MILLER), 1875 

Plate 7, figures 1-8; plate 8, figures 1-3

Orthoceras cincinnatiensis Miller, 1875, p. 127. 

Orthoceras cincinnatiensis Miller. Miller, 1881, p. 319, pi.

8, figs. 5-5a.

Treptoceras duseri (Hall and Whitfield). Frey, 1988, pi. 3, 

fig. 1.

Diagnosis.—Large, rapidly expanding species of 

Treptoceras with broad siphuncle segments one-fourth to 

one-fifth the diameter of the shell that are compressed, 

heart-shaped most of the length of the siphuncle, and that 

change position with ontogeny from supracentral to subcentral.

Description,—Medium-sized (up to 55 cm in length, 

having shell diameters up to 7.5 cm), rapidly expanding 

(apical angle 8.5-9.5 degrees) orthoconic longicone; circular in cross section with straight, transverse sutures. 

Camera! lengths one-fourth the diameter of the shell at 

diameters less than 10 mm, decreasing with ontogeny to 

one-seventh the diameter of the shell at shell diameters in 

excess of 40 mm. Body chamber one-fourth the total 

length of the shell; aperture straight, transverse, lacking 

sinus. Periphract dorsomyarian. Shell exterior essentially 

smooth, marked with fine transverse growth lines.

Siphuncle supracentral (SPR > 0.50) in position at 

diameters less than 10 mm, becoming subcentral in position with ontogeny (SPR=0.30 at a diameter of 40 mm). 

Segments slightly compressed (SCR=1.25) at diameters 

less than 10mm, becoming more compressed with ontogeny (SCR= 1.33-1.50 at diameters of 10-35 mm), and 

slightly compressed, heart-shaped, in adoral portions of 

large specimens (SCR=1.20 at diameters in excess of 35 

mm). Segments broad for the genus, averaging between 

one-fourth and one-fifth the diameter of the shell. Endosiphuncular deposits extensively developed adapically, consisting of dorsal annuli and ventral parietal deposits that 

fuse into a continuous lining with ontogeny. Adoralmost 

cameral deposits consisting of distinct episeptal and 

hyposeptal elements, the deposits completely filling camerae in adapical half of large shells.

Stratigraphic and geographic occurrence.—Basal 

Maysvillian part of the Fairview Formation in northern 

Kentucky; "Waynesville" and "Liberty" biofacies within 

the Bull Fork Formation (Upper Ordovician, Richmondian Stage) in Warren, Clinton, Butler, and Preble Counties, Ohio, and Franklin County, Ind.; Rowland Member of 

the Drakes Formation (Upper Ordovician, Richmondian 

Stage) in Nelson County, Ky.

Studied material.—Holotype, Harvard University, 

Dyer Collection, MCZ 3404 (pi. 7, figs. 2, 3, 5), Upper 

Ordovician, Cincinnati, Ohio, area; MU 423T (pi. 7, fig. 1), 

T. duseri shale, Bull Fork Formation, Stony Hollow, Clinton County, Ohio; MU 424T, MU 425T (pi. 7, fig. 8), and MU

426T (pi. 7, figs. 4, 6, 7), T. duseri shale, Bull Fork Formation, Harpers Run, Warren County, Ohio; MU 427T (pi. 8, 

fig. 1), Bull Fork Formation, Brookville Lake dam site, 

Franklin County, Ind.; MU 443T (pi. 8, fig. 3) and MU 445T 

(pi. 8, fig. 2), Bull Fork Formation, Oxford, Butler County, 

Ohio; USNM 468691a and 468691b, Rowland Member of 

the Drakes Formation, Nelsonville, Ky; measured suites 

of specimens from the T. duseri shale unit: MU 17174 

(two specimens) from Stony Run, Warren County, Ohio; 

MU 17179 (two specimens) from Stony Hollow at Clarksville, Clinton County, Ohio; MU 17184 (four specimens) 

from Caesars Creek dam site, Warren County, Ohio; MU 

17185 (one specimen) from the U.S. Route 42 roadcut, 

Warren County, Ohio; and MU 17186 (four specimens) 

from Harpers Run, Warren County, Ohio. Additional measured specimens from the "Liberty biofacies" in the Bull 

Fork Formation are MU 29862 (one specimen) from the 

Dayton, Ohio, area; MU 29863 (one specimen) from the 

Caesars Creek dam site, Warren County, Ohio; and MU 

29864 (two specimens) from Oxford, Butler County, Ohio.

Remarks.—This species was described by Miller 

(1875) and figured by him in a later paper (Miller, 1881, pi. 

5-5a). He listed this species as occurring in strata 

"exposed in the hills back of Cincinnati; range unknown." 

Miller (1875, p. 128) referred to a specimen of this species 

in the C.B. Dyer collection that was 6 in. in length, and 

having a diameter at the small end of 3/10 in. and at the 

large end of 1.15 in., and having 42 camerae. This specimen (pi. 7, figs. 2, 3, 5) is preserved in the Dyer Collection 

at the Museum of Comparative Zoology at Harvard (MCZ 

3404), is labeled as the holotype of Orthoceras cincinnatiensis, and is so recognized here. There is no precise 

Stratigraphic information associated with the holotype. 

The distinctive preservation of this specimen indicates it 

is probably from the T. duseri shale unit in either Warren 

or Clinton Counties, Ohio. It should be noted, however, 

that similar, well-preserved calcite-replaced internal 

molds occur in the basal Fairview Formation in northern 

Kentucky and adjacent portions of the Cincinnati, Ohio, 

area. These strata also conceivably could be the source of 

the holotype.

The species is an uncommon form in the basal Fairview Formation in northern Kentucky; the incomplete 

specimens collected by the writer were from exposures 

along Interstate Route 275E in Kenton County, Ky. Treptoceras cincinnatiensis is most abundant in the T. duseri 

shale unit within the "Waynesville biofacies" in the lower 

part of the Bull Fork Formation in southwestern Ohio (pi. 

7). In this shale, it is the third most abundant nautiloid 

species present, behind the previously described species 

of Treptoceras. Morphological comparisons with the associated T. duseri (Hall and Whitfield) and T. fosteri 

(Miller) are provided in the remarks sections for these 

species. Treptoceras cincinnatiensis occurs sporadically
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P53

throughout the overlying portions of the Bull Fork Formation in Ohio and southeastern Indiana (pi. 8, figs. 1-3). 

Fragmentary silicified material assignable to the species 

occurs in the equivalent Rowland Member of the Drakes 

Formation in the vicinity of Bardstown, in north-central 

Kentucky.

Outside of the northern Cincinnati arch region, a similar species occurs in the Georgian Bay Formation (Upper 

Ordovician, Richmondian) in southern Ontario. Parks and 

Fritz identified this species as Actinoceras cf. clouei (Barrande) and illustrated a specimen from this strata at Toronto, Ontario (Parks and Fritz, 1922, pi. 4, fig. 5). Copper 

(1978, pi. 5, fig. 5) illustrated a similar form from equivalent strata exposed on Manitoulin Island that he identified 

as Ormoceras piso Billings. This species appears to be 

very similar in all aspects to the specimens of Treptoceras 

cincinnatiensis described here.

JREPTOCERAS TRANSVERSUM (MILLER), 1875 

Plate 8, figures 4-9

Orthoceras transversa Miller, 1875, p. 129, fig. 15.

Orthoceras hindei James, 1878, p. 6, pi. 1.

Orthoceras hindei James. James, 1886, p. 240-241, pi. 4,

figs. 4a-d.

Orthoceras cf. O. transversum Miller. Ruedemann, 1926, 

p. 87, pi. 12, fig. 5.

Diagnosis.—Small, slender species of Treptoceras 

distinguished by its external ornament of coarse, raised 

transverse lirae and its small-diameter, subcentral, 

slightly compressed to equiaxial siphuncle segments.

Description.—Small (up to 30 cm in length and up to 

2.5 cm in diameter), slender, rather gradually expanding 

(apical angle 6-6.5 degrees), orthoconic longicone; circular in section with straight, transverse sutures. Camera! 

lengths ranging from one-fourth to one-sixth the diameter 

of the shell, decreasing with ontogeny. Body chamber 

long, approximately one-fourth the total length of the 

shell. External ornament consisting of coarse, closely 

spaced, raised transverse lirae uniformly developed the 

length of the shell.

Siphuncle subcentral the known length of the shell, 

ranging from nearly central adapically (SPR=0.44 at a 

diameter of 8 mm) to nearly midventral positions adorally 

(SPR=0.275 at a diameter of 20 mm). Siphuncle segments 

slightly compressed adapically (SCR=1.16 at diameters 

less than 15 mm) and decompressing with ontogeny, 

becoming equiaxial (SCR=1.0) adorally at diameters 

greater than 20 mm. Segments narrow, ranging from 

one-fifth to one-sixth the diameter of the shell. Septal 

necks short, recurved, cyrtochoanitic. Endosiphuncular 

deposits consisting of ventral parietal deposits developed 

at diameters less than 15 mm. Dorsal deposits unknown. 

Adoralmost camera! deposits of the mural type.

Stratigraphic and geographic occurrence.—The 

Edenian portions of the Kope and basal Fairview Formations in northern Kentucky and adjacent portions of the 

Cincinnati, Ohio, region and southeastern Indiana; Whetstone Gulf Shale (Upper Ordovician, Maysvillian Stage) in 

northwestern New York.

Studied materials.—University of Cincinnati "cotypes" are UC 1328A (pi. 8, fig. 7), UC 1328B (pi. 8, fig. 6), 

UC 1328C (pi. 8, figs. 4, 8), all listed as coming from "Eden 

Formation at Cincinnati, Ohio"; USNM 468692 (pi. 8, fig. 

5) and 468693 (pi. 8, fig. 9), from the Kope Formation 

exposed just east of Fort Thomas, Campbell County, Ky; 

UC 48259 from the "Eden Shale" at Newport, Campbell 

County, Ky; plus seven unfigured specimens listed as "cotypes" (UC 1328), "Eden Shale" at Cincinnati, Ohio.

Remarks.—Miller (1875) distinguished this species 

on the basis of its medium-sized, gradually expanding 

shell and an "outer shell with transverse lines." Camerae 

were described as shallow, camera! lengths one-fourth to 

one-fifth the diameter of the shell and a siphuncle 

described as excentric in position. Miller indicated that 

the species did not extend more than 300 ft above the 

low-water mark of the Ohio River in the Cincinnati area, 

being collected from an excavation for Columbia Avenue 

at 150 ft above the low-water mark, and at Eden Park, 200 

ft above river level. He indicated that the species was "not 

common by any means" in these strata. "Co-types" of T. 

transversum in the collections of the University of Cincinnati (UC 1328) consist of a number of specimens from 

the "Eden Formation at Cincinnati, Ohio." This collection 

does not contain the partially sectioned specimen figured 

by Miller (1875, fig. 15), although all of these specimens 

are obviously examples of Miller's species. The whereabouts of Miller's figured specimen remains unknown. As 

such, UC 1328C (pi. 8, figs. 4, 8) is here designated the lectotype for T. transversum (Miller). The other specimens 

labeled "co-types" in the University of Cincinnati collections are considered to be paratypes.

A nearly complete, shelled specimen of T. transversum (USNM 468692, pi. 8, fig. 5) and a specimen partially 

covered holoperipherally with encrusting bryozoans 

(USNM 468693, pi. 8, fig. 9) were collected by the writer 

from a thin packstone bed within the claystone and thin 

limestone of the Kope Formation (Upper Ordovician, 

Edenian) exposed at the junction of River Road and State 

Route 8, east of Ft. Thomas and south of the I-275E 

bridge, in Campbell County, Ky. Less complete specimens 

of T. transversum were collected from a claystone bed in 

the Kope Formation exposed 18 m above the road level in 

a roadcut on the north side of Orphanage Road, just west 

of the junction of State Route 17 and I-275E, Kenton 

County, Ky. Here the species was found associated with a 

diverse molluskan fauna that consisted of the nautiloid 

Trocholites faberi (pi. 19, figs. 6-10), several species of
P54 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

gastropods, the monoplacophorans Cyrtolites and Sinuites, pelecypods, and rostroconchs, as well as the brachiopods OnnieUa and Zygospira, and three-dimensional 

specimens of the graptolite Geniculograptus typicalis.

Fragmentary specimens of T. transversum were also 

collected from the overlying claystone and thin limestone 

of the basal Fairview Formation (Upper Ordovician, Edenian and Maysvillian) exposed at a roadcut along the 

south side of 1-74, 2 mi west of Harrison, Dearborn 

County, Ind. In the Cincinnati arch region, T. transversum 

appears to be restricted to the Kope Formation and the 

overlying basal portions of the Fairview Formation 

exposed in adjacent portions of northern Kentucky, 

southwestern Ohio, and southeastern Indiana.

A species collected from the same strata at Cincinnati, Ohio, and described as Orthoceras hindei by James 

(1878) appears to be a preservational phase of T. transversum. These partially replaced, calcite internal molds 

of a small longicone have the same shell morphology as 

better preserved specimens of T. transversum. "Orthoceras" hindei James is here placed in synonymy with T. 

transversum (Miller).

Treptoceras transversum is easily distinguished from 

other Cincinnatian species of Treptoceras on the basis of 

its typically smaller, slender shell, marked by its unique 

transverse ornament, and its small-diameter, subcentral 

siphuncle segments. The species is distinct from similar 

small, slender species of the pseudoceratid Isorthoceras 

in its globular, compressed siphuncle segments compared 

to the depressed, barrel-shaped segments characteristic 

of the latter genus. The distinctive transverse external 

ornament in specimens of T. transversum also readily 

distinguishes it from the longitudinal lirae characteristic 

of /. albersi (Miller and Faber) and the cancellate ornament of /. rogersensis (Foerste) (see pi. 10), both known 

from the Clays Ferry Formation in northern Kentucky.

GENUS MONOMUCHITES WILSON

Type species.—Monomuchites costalis Wilson, 1961, 

p. 23; by original designation; "Leray beds," Rocklandian 

Stage, Middle Ordovician, Ontario.

Description.—Small to medium-sized, moderately to 

rapidly expanding orthoconic longicones, often slightly 

curved adapically; circular in cross section with straight, 

transverse sutures. Cameral lengths from one-fourth to 

one-seventh the diameter of the shell, decreasing with 

ontogeny. Body chamber long; aperture unknown. Shell 

exterior marked by transverse annuli, one annulation per 

cameral chamber. Annuli variably developed, from indistinct rounded to sharply defined elevated; separated by 

shallow, concave interannular spaces. Annuli and interannular spaces marked by transverse growth lines.

Siphuncle moving from supracentral to subcentral in 

position with ontogeny. Segments slightly expanded

within camerae, depressed to compressed in shape; narrow in diameter, from one-fourth to one-sixth the diameter of the shell. Septal necks short, cyrtochoanitic, 

recurved with free brims. Endosiphuncular deposits 

poorly known, consisting of ventral parietal deposits 

developed adapically. Adoralmost cameral deposits consisting of trilobate, botryoidal, ventral-lateral, muraepiseptal deposits and thin, dorsal episeptal deposits.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Blackriveran and Rocklandian), Eastern 

North America (Laurentia).

Remarks.—Wilson (1961) erected this genus for Middle Ordovician annulated longicones with transverse 

growth lines that were previously referred to as species of 

Cycloceras M'Coy by Foerste (1932). True Cycloceras is a 

poorly known Carboniferous form based on an internal 

mold of a body chamber in which even the position of the 

siphuncle is in doubt. Sweet (1964) suggested that until 

better specimens of C. annularis (Fleming), the type species, are discovered, the name Cycloceras should be 

applied only to this species. It is probable, at any rate, that 

these Ordovician species are distinct from these younger 

Carboniferous annulated longicones.

Kobayashi (1927) erected the genus Tofangoceras for 

similar annulated longicones with narrow, expanded 

siphuncle segments from Middle Ordovician (Blackriveran) carbonates in Manchuria and Korea. He did not figure the exteriors of either of the two species that he 

referred to this genus, and his illustrations of the internal 

features of the genus are of a naturally weathered section 

that shows the expanded nature of the siphuncle segments but little else. Tofangoceras, as based on the type 

species, T. pauciannulatum, appears to have a more 

gradually expanding shell than either of the described 

species of Monomuchites, and its external ornament is 

stated to consist of one annulation for every two camerae, 

annuli being more broadly spaced than those in species of 

Monomuchites.

Monomuchites is distinguished from the associated 

annulated orthocerid Gorbyoceras Shimizu and Obata in 

lacking the longitudinal lirae that are characteristically 

developed in representatives of this genus. Similarly, 

Monomuchites can be distinguished from the annulated 

genus Anaspyroceras Shimizu and Obata on the basis of 

its more rapidly expanding shell form and in its lack of 

longitudinal lirae, although this longitudinal ornament is 

not well documented for the type species of Anaspyroceras, A. aneUus (Conrad). Unfortunately, the nature of 

the siphuncle segments is poorly documented for all of 

these annulated longicones. Expanded globular siphuncle 

segments are developed in several species of Monomuchites and in Gorbyoceras. Siphuncle segments in Late 

Ordovician species assigned to Anaspyroceras by Flower 

(1946) are depressed, subtubular in shape.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P55

The genus Monomuchites is apparently restricted to 

Blackriveran to Rocklandian carbonate facies throughout 

Eastern North America, species being known from the 

Watertown Limestone in New York, the "Leray-Rockland 

beds" exposed in the Ottawa region of Ontario and Quebec, the Tyrone Limestone in central Kentucky, and the 

Platteville Group in Illinois or Platteville Formation in 

Minnesota and Wisconsin. Monomuchites was a victim of 

the widespread extinction of nautiloid taxa that occurred 

at the end of the Rocklandian, and no post-Rocklandian 

species is known to the writer. Three species of Monomuchites have been identified in the USGS 6034-CO collection from the upper half of the Tyrone Formation in 

central Kentucky.

More complete and better preserved material is necessary to clarify the relevant morphological features of 

Monomuchites and these other Ordovician annulated longicones. Flower (1962) placed several of these genera in 

the Proteoceratidae, describing Monomuchites as having 

endosiphuncular deposits of the proteoceratid type and 

showing siphuncle segment decompression with ontogeny. He did not, however, indicate the specimens upon 

which these observations were based, nor has such material been illustrated. Until the details of the siphuncle and 

its deposits can be documented for all of these Ordovician 

annulated longicones, they will remain of uncertain affinities. The genus is here retained in the Proteoceratidae, on 

the basis of the rapidly expanding shell form and supracentral position of adapical siphuncle segments, plus proteoceratidlike endosiphuncular deposits in one of the 

species of Monomuchites described below.

MONOMUCHITES CF. M. COSTAHS WILSON, 1961 

Plate 9, figures 16-19

Monomuchites costalis Wilson, 1961, p. 24-25, pi. 5, figs. 

5-5a.

Diagnosis.—Moderately expanding species of Monomuchites distinguished by its narrow-rimmed, transverse 

annuli separated by shallow, concave interannular spaces.

Description.—Small (lengths of up to 14 cm and 

diameters up to 2.0 cm), moderately expanding (apical 

angle 7.5-8 degrees) orthoconic longicones; circular in 

section with straight, transverse sutures. Camera! chambers short, decreasing with ontogeny from one-fourth to 

one-fifth the diameter of the shell. Body chamber 

unknown. Shell exterior marked by low, narrow-rimmed 

transverse annulations, one per camera! chamber. Annuli 

separated by shallow concave interannular spaces typically twice as broad as the annuli. Interannular spaces 

bisected by sutures.

Siphuncle supracentral in position in known portions 

of the shell at SPR values ranging from 0.60 at a diameter 

of 10 mm to 0.53 at a diameter of 19 mm. Segment shape 

poorly known, globular, compressed (SCR=1.33) at shell

diameters between 10 and 15 mm. Segments narrow, 

one-fourth the diameter of the shell at these diameters. 

Septal necks short, recurved, cyrtochoanitic. Endosiphuncular deposits unknown. Camera! deposits 

well-developed adapically, consisting of trilobate, botryoidal, ventrolateral, mural-episeptal deposits and thin, dorsal episeptal deposits at diameters of 10-20 mm. 

Adapically, there is development of a large, subcircular, 

central "boss" that impinges on the ventral surface of the 

siphuncle segment.

Stratigraphic and geographic occurrence.—Upper 

part of the Rocklandian portion of the Tyrone Limestone, 

Inner Blue Grass region of central Kentucky.

Studied material—USNM 158667 (pi. 9, figs. 18,19), 

USNM 158672 (pi. 9, figs. 16, 17), USNM 468705, and 

USNM 468706, all from the USGS 6034-CO collection, Jessamine County, Ky.

Remarks.—This annulated longicone is a rare element in the diverse assemblage of silicified nautiloids 

obtained from the USGS 6034-CO collection in the Tyrone 

Limestone, represented by only four specimens. These 

consist of silicified fragments of phragmocones less than 

2.0 cm in diameter. The narrow-rimmed transverse annuli 

separated by shallow, concave interannular spaces and 

the moderate rate of shell expansion suggest assignment 

of these specimens to the type species of the genus, M. 

costalis Wilson, from the equivalent "Leray beds" in the 

Ottawa, Ontario region. The siphuncle segments preserved in Tyrone specimen USNM 468706 are somewhat 

more expanded than those illustrated for GSC 13844, the 

holotype of this species (Wilson, 1961, pi. 5, fig. 5). Further comparisons with the type material are difficult, as 

the second specimen (GSC 13845) figured by Wilson 

(1961, pi. 5, fig. 6) consists of a larger diameter, more 

adoral section of the shell compared with the Kentucky 

specimens. This writer's studies of more complete specimens of Monomuchites indicate that the external ornament of the shell changes with ontogeny, the annuli 

becoming more closely spaced and the interannular 

spaces decreasing in width. Pending comparisons of a 

larger suite of the Tyrone material with more complete 

specimens of the Canadian species, these Tyrone specimens are only tentatively assigned to M. costalis.

In terms of rate of shell expansion, camera! lengths, 

and siphuncle position and in the number of annuli per 

length of shell, these Tyrone specimens also appear to be 

similar to M. decrescens (Billings), another Canadian species from the Ottawa region. The criteria used by Wilson 

(1961) to distinguish this species from the associated M. 

costalis appear to result from comparisons of different 

ontogenetic stages of the shell. The rate of shell expansion is similar for both species, the only distinction being 

the number of annuli per length of shell: eight annuli in a 

length equal to an adoral diameter of 30 mm in M. costalis
P56 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

versus six annul! in a length equal to an adoral diameter of 

25 mm in M. decrescens (see table 8). Comparisons using 

larger collections of more complete, better preserved 

material are necessary to determine the distinctiveness of 

these two Canadian species.

Monomuchites cf. M. costalis is distinguished from 

the other two species of Monomuchites described here 

from the 6034-CO collection on the basis of its narrowrimmed annulations separated by shallow, concave interannular spaces (pi. 9, figs. 18, 19). Monomuchites obliquum n. sp. is a more gradually expanding (apical angle 6- 

6.5 degrees), slightly curved form with less well defined, 

rounded, and oblique annulations (pi. 9, figs. 5-8). Monomuchites annularis n. sp. is more similar to M. cf. M. costalis in general shell form but differs in its broader, more 

strongly defined annuli and interannular spaces (pi. 9, 

figs. 1, 11). A comparison of the distinctive external ornament used to distinguish these Tyrone species of Monomuchites is presented in figure 17.

MONOMUCHITES ANNULARIS NEW SPECIES

Plate 9, figures 1-3,11-15

Cycloceras cf. C. decrescens (Billings). Foerste, 1932, p.

86, pi. 12, figs. 5A-B, 7 (Foerste, 1933).

Diagnosis.—Moderately expanding, slightly curved 

species of Monomuchites distinguished by its 

well-delineated, elevated, broad transverse annuli separated by broad, flat interannular spaces.

Description.—Medium-sized (up to 40 cm in length 

and shell diameters up to 5.0 cm), moderately expanding 

(apical angle 7-8 degrees) orthoconic longicones, slightly 

endogastrically curved adapically; circular in cross section with straight, transverse sutures. Camera! chambers 

short, decreasing with ontogeny from one-fourth the 

diameter of the shell at diameters of 10 mm or less to 

one-seventh the diameter of the shell at diameters in 

excess of 30 mm. Body chamber poorly known. External 

ornament of strongly defined, broad, elevated transverse 

annuli, one per camera! chamber. Interannular spaces flat, 

broader than annuli except in adoral portions of large 

specimens; marked by transverse growth lines.

Siphuncle supracentral in position in adapical portions of shells 20 mm or less in diameter, moving to a 

more central position at a diameter of 30 mm. Segments 

at these diameters expanded, globular, equiaxial to compressed; diameters typically one-fourth the diameter of 

the shell. Shape of segments unknown in adoral portions 

of the shell greater than 20 mm in diameter. Septal necks 

poorly known; cyrtochoanitic. Endosiphuncular deposits 

unknown. Camera! deposits restricted to adapical portions of the shell 20 mm or less in diameter, consisting of 

massive, trilobate, botryoidal ventrolateral mural-episeptal deposits and dorsal episeptal deposits.

TABLE 8. — Comparison of the morphological features of species 

of Monomuchites from the Middle Ordovician (Rocklandian) 

of Eastern North America

[Data from specimens figured by Wilson (1961) and suites of measured 

specimens from the 6034-CO collection from the Tyrone Limestone 

in central Kentucky. A/D, ratio of number of annuli per length to 

diameter; A/MS, ratio of width of annuli to width of interannular 

space; CL/D, ratio of camera! length to shell diameter, SPR, segment 

position ration; SCR, segment compression ratio; mm, millimeter]

M. M. M- cf- M.

costalis desrescens .' ,. obliquum costalis *

Apical angle, degrees 8 8.5-9 7.5-8 6-6.5

Diameter 35 mm

A/D -

A/IAS -

CL/D -

SPR -

SCR -

Diameter 30 mm

A/D 8

A/IAS 2/2

CL/D .13

SPR -

SCR -

Diameter 25 mm

A/D 6.5 6

A/IAS 2/2.5 2/3 - -

CM) .16 .16

SPR -

SCR -

Diameter 20 mm

A/D - 5 5-6 5-5.5

A/IAS 1.5/3 - 1.5/2.5 3/2

CM) .20 .175 .175 .175

SPR - .55 .5S-.55 .48

SCR .86 .86

Diameter 15 mm

A/D 5

A/IAS - - 1/2.5

CM) .20 - .20 .20

SPR - - .60-.62 .53

SCR 1.0 - 1.33 1.16

Diameter 10 mm

A/D -

A/IAS -

CM) - - .30 -

SPR -

SCR - - 1.33

M. 

annularis

7-8

7

3/2.5

.14

-

-

6.5-7

2.5/3

.15

-

-

5-6

2/3

.16

-

-

5-6

2/3

.175

.55-.60

-

5

1.5/2.5

.20

.60

1.33

4^.5

1/2

.25-.30

.66

1.0
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P57

FIGURE 17.—Comparison of the external ornament characteristic of 

species of Monomuchites from the USGS 6034-CO collection in the 

Tyrone Limestone. A, Monomuchites cf. M. costalis (USNM 158667, 

pi. 9, fig. 18); B, M. annularis (USNM 158674, pi. 9, fig. 11); C, M. 

obliquum (USNM 158653, pi. 9, fig. 5).

Stratigraphic and geographic occurrence.—Upper 

part of the Rocklandian portion of the Tyrone Limestone, 

Inner Blue Grass region of central Kentucky; "Black River 

Formation" (Middle Ordovician), St. Joseph Island, Lake 

Huron, Ontario; Platteville Formation (Middle Ordovician, Rocklandian Stage), Minnesota and Wisconsin, or 

Platteville Group in Illinois.

Studied material—Holotype USNM 158674 (pi. 9, 

fig. 11); paratypes USNM 158630 (pi. 9, fig. 1), 158671 (pi. 

9, fig. 2), 158675, and 158676 (pi. 9, fig. 15); plus studied 

suite USNM 468716, all from the USGS 6034-CO collection 

in the Tyrone Limestone, Jessamine County, Ky.; USNM 

162068 (pi. 9, fig. 14), "Platteville Formation," Dixon, 111.; 

and USNM 25275 (pi. 9, fig. 13), Mineral Point, Wis.

Remarks.—Monomuchites annularis n. sp. is the 

fourth most abundant longiconic nautiloid in the 6034-CO 

collection from the Tyrone Limestone. It is represented in 

this collection by more than 25 silicified specimens 40 

mm or more in length as well as by numerous smaller 

fragments. Specimens consist primarily of adapical portions of phragmocones less than 20 mm in diameter. 

These portions of the shell are less fragile than more 

adoral portions of the phragmocone due to the nearly

complete filling of cameral chambers by cameral deposits, forming a nearly solid shell mass adapically. Unfortunately, septa and connecting rings are poorly preserved, 

their outlines preserved as impressions within the surrounding cameral deposits (pi. 9, fig. 15). More adoral portions of the siphuncle are, as a consequence, largely 

unknown.

Monomuchites annularis is the most abundant of 

the three species of Monomuchites in the 6034-CO collection. It is distinguished from the similar M. cf. M. costalis 

through the development of more strongly delineated, 

broader annuli and interannular spaces (fig. 17). Monomuchites annularis is less similar to M. obliquum n. sp., 

differing from this species in the development of a more 

rapidly expanding shell with more strongly developed 

transverse annuli, compared with the low, rounded, 

oblique annuli in M. obliquum.

Foerste (1932, pi. 12, figs. 5A-B, 7) described and figured Cycloceras cf. C. decrescens (Billings) from the 

"Black River Formation" (Middle Ordovician) exposed on 

St. Joseph Island, Lake Huron. Foerste described these 

specimens (University of Michigan 14419, 144454, and 

144455) as differing from typical Cycloceras decrescens
P58 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

"only in the slightly greater prominence of their annulations." These specimens are similar to the Kentucky specimens of M. annularis in apical angle, the conspicuous 

nature of the annuli, the number and relative dimensions 

of the annuli per shell diameter, and in the globular, 

expanded nature of the siphuncle segments. These similarities indicate that these Canadian specimens are also 

assignable to M. annularis. Monomuchites annularis 

has more prominent transverse annuli and interannular 

spaces plus a less rapidly expanding shell compared with 

the type specimens of M. decrescens (Billings) that are 

figured by Foerste (1932, pi. 12, figs. 1A-C) and by Wilson 

(1961, pi. 5, figs. 7, 8).

Foerste (1932, pi. 12, fig. 4) described and figured 

"Cycloceras sp." from the "Platteville member of the 

Black River Formation" exposed at Minneapolis, Minn. 

Similar specimens from the Platteville Group at Dixon, 111. 

(USNM 162068, pi. 9, fig. 14), and from Mineral Point, Wis. 

(USNM 25275, pi. 9, figs. 12, 13), that were measured as 

part of this study indicate that these annulated Platteville 

specimens are also assignable to M. annularis.

These occurrences ofM. annularis indicate that this 

species was broadly distributed across the shallow-shelf 

areas of eastern Laurentia during Middle Ordovician 

(Rocklandian) times. This widespread distribution as well 

as the similar distributions of associated nautiloid taxa 

(Proteoceras tyronensis, Omnoceras ferecentricuin) 

attest to the uniform, unrestricted shallow-marine shelf 

conditions that existed across much of this area at this 

time.

MONOMUCHITES OBLIQUUM, NEW SPECIES

Plate 9, figures 4-10

Diagnosis.—Gradually expanding, slightly curved 

species of Monomuchites distinguished by its low, 

rounded, oblique annuli and poorly delineated interannular spaces.

Description.—Small (lengths of 18 cm and diameters 

up to 2.0 cm), gradually expanding (apical angle 6-6.5 

degrees) orthoconic longicone, endogastrically curved 

adapically; circular in cross section with straight, transverse sutures. Camera! chambers short, camera! lengths 

ranging from one-fifth to one-sixth the diameter of the 

shell, decreasing with ontogeny. Body chamber unknown. 

Exterior marked by low, indistinct, rounded, oblique 

annuli that slope from the dorsum to the venter in the 

adoral direction. Annuli separated by poorly delineated 

interannular spaces that are narrower than annuli. Five 

and a half annuli present in a length equal to an adoral 

diameter of 20 mm.

Siphuncle supracentral (SPR=0.53) at a diameter of 

15 mm, becoming subcentral with ontogeny (SPR=0.48 at 

a diameter of 20 mm). Siphuncle segments narrow in 

diameter, one-fourth the diameter of the shell at shell

diameters of 12 mm or less. Segments expanded, globular, 

compressed in outline (SCR=1.16) at the same diameter. 

Septal necks cyrtochoanitic, short, recurved, with free 

brims. Endosiphuncular deposits consisting of ventral 

parietal deposits that fuse to form a continuous ventral 

lining adapically. Camera! deposits consisting of botryoidal mural-episeptal deposits more extensively developed 

on the side of the camera! chamber opposite the 

siphuncle.

Stratigraphic and geographic occurrence.—Upper 

part of the Rocklandian portion of the Tyrone Limestone, 

Inner Blue Grass region of central Kentucky.

Studied material.—Holotype USNM 158653 (pi. 9, 

figs. 5-8), paratype USNM 158648 (pi. 9, figs. 9, 10), and 

paratype USNM 158643 (pi. 9, fig. 4), all from the USGS 

6034-CO collection, Little Hickman section A, Jessamine 

County, Ky.

Remarks.—This species is a rare form within the 

6034-CO collection from the Tyrone Limestone, being represented only by the type material. It is, however, distinct 

from associated species of Monomuchites in the slender, 

gradually expanding, endogastrically curved nature of its 

shell and in its low, rounded, poorly delineated oblique 

annulations. No other similar species of Monomuchites 

are known to this writer from equivalent Blackriveran and 

Rocklandian strata elsewhere in North America

The ventral parietal deposits preserved in paratype 

USNM 158648 (pi. 9, fig. 10) are similar to those developed in the previously discussed proteoceratids Proteoceras Flower and Treptoceras Flower. These consist of 

deposits that grow forward, so that the deposit is thickest 

just adoral of the septal neck. These deposits fuse to form 

a continuous ventral lining adapically. As indicated above, 

endosiphuncular deposits are poorly known for most species of Monomuchites, making the phylogenetic affinities 

of this genus uncertain. This specimen of M. obliquum 

supports Flower's assignment of Monomuchites to the 

Proteoceratidae.

FAMILY PSEUDORTHOCERATIDAE FLOWER AND CASTER

Smooth to elaborately ornamented, generally small, 

moderately to rapidly expanding orthoconic longicones 

and cyrtocones; usually circular in cross section with 

straight, transverse sutures. Camera! chambers typically 

short, having cameral lengths from one-fourth to onesixth the diameter of the shell, decreasing with ontogeny. 

Body chambers comparatively short, less than one-fourth 

the total length of the shell, constricted just adapical to 

aperture.

Siphuncle central to subcentral in position; segments 

narrow in diameter, from one-fourth to one-sixth the 

diameter of the shell, typically expanded equiaxial globular or depressed barrel-shaped. Expansion of siphuncle 

segments often localized immediately acyacent to septal
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P59

necks. Septal necks cyrtochoanitic, short, recurved, but 

not typically recumbent, brims equal in length to septal 

necks. Connecting rings thin, homogeneous. Endosiphuncular deposits consisting of annuli that are initiated at the 

septal foramen and grow forward along connecting ring 

walls, eventually fusing to form a continuous lining of uniform thickness. Camera! deposits of the mural-episeptal 

type, lobate, initiated ventrally and laterally prior to development dorsally. Medial mural delta formed in most taxa. 

Initial portions of the shell typically bluntly cone-shaped.

Stratigraphic occurrence.—Middle Ordovician 

(Whiterockian Provincial Series) to Lower Permian 

(Leonardian Provincial Series).

Remarks.—This family constitutes the bulk of the 

superfamily Pseudorthoceratacea and is the dominant 

orthocerid family in the Devonian and later Paleozoic, 

ranging through to the end of the Early Permian. Sweet 

(1964), listed 42 genera as members of this family. Most of 

these taxa, however, are poorly known, based on fragmentary material described primarily by Flower (1939). 

Additional taxa were described by Zhuravleva (1978). 

Dzik (1984) placed many of these taxa in synonymy and 

transferred others to other families, recognizing but six 

genera. This is certainly a case of over zealous lumping of 

taxa but points out the need for extensive restudy and 

revision of the family.

Flower (1939) derived the Pseudorthoceratidae from 

the Geisonoceratidae through Virgoceras Flower, a Middle Silurian (Llandoverian-Ludlovian) genus that had the 

shell morphology of the Geisonoceratidae but having 

endosiphuncular deposits of the pseudorthoceratid type, 

consisting of annuli and parietal deposits that formed 

independent of cameral deposits. Sweet (1964) retained 

Virgoceras in the Geisonoceratidae and indicated that it 

exhibited endosiphuncular deposits similar to later Devonian pseudorthoceratids (Spyroceratinae). He also 

pointed out the presence of a number of cyrtochoanitic 

orthocerids from the early Middle Ordovician, antedating 

Virgoceras by 30-40 m.y. These are Mysterioceras 

Teichert and Glenister, Stereoplasmoceras Grabau, and a 

number of proteoceratids described by Flower (1955b). 

This suggested to Sweet a possibly polyphyletic origin for 

the Pseudorthoceratidae.

Dzik (1984) has also documented cyrtochoanitic 

siphuncle segments and pseudorthoceratid-type endosiphuncular deposits in Clinoceras dens Mascke from Middle Ordovician Llanvirnian (Kunda Stage) strata in the 

Baltic region. As indicated by Dzik, this species, with its 

rapidly expanding phragmocone and short adorally constricted body chamber, is similar to later pseudorthoceratids, in particular, some species of the genus 

Dolorthoceras Miller. These examples suggest that the origin of the Pseudorthoceratidae lies with these Middle 

Ordovician taxa rather than with the Geisonoceratidae.

GENUS ISORTHOCERAS FLOWER

Type species.—Orthoceras sociale Hall, Hall, 1877, p. 

245; designated by Flower, 1962, p. 32-33; Elgin Shale, 

Maysvillian Stage, Upper Ordovician, Iowa.

Description.—Small, slender, gradually to moderately expanding orthoconic longicones; circular in cross 

section with straight, transverse sutures. Cameral chambers short, cameral lengths ranging from one-third to onesixth the diameter of the shell, decreasing with ontogeny. 

Body chamber between one-fifth and one-sixth the total 

length of the shell, constricted just adapical of the aperture. Aperture straight, transverse. Periphract dorsomyarian. Surface ornament of subdued, transverse growth 

lines or raised transverse, longitudinal, or cancellate lirae.

Siphuncle central to subcentral in position having 

segments moving to a more ventral position with ontogeny. Segments narrow, from one-fifth to one-tenth the 

diameter of the shell; only slightly expanded within camerae, forming barrel-shaped segments, of which the maximum diameter is just adapical to septal necks. Septal 

necks cyrtochoanitic, recurved with short, free brims. 

Endosiphuncular deposits initiated as adorally growing 

annuli at septal necks, restricted to adapical portions of 

phragmocones. Adoralmost cameral deposits planar 

mural-episeptal, initiated ventrolaterally prior to their 

development dorsally.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Kirkfieldian Stage) to Upper Ordovician 

(Richmondian Stage), Eastern and Central North America 

(Laurentia).

Remarks.—Flower (1962) erected this genus for 

basically smooth, small, orthoconic longicones distinguished by the development of subcentral siphuncles with 

barrel-shaped segments, cyrtochoanitic septal necks, and 

endosiphuncular deposits consisting of thin parietal 

deposits that are greatly concentrated adapically. Besides 

the type species, /. sociale (Hall) (pi. 10, fig. 15) from the 

Upper Ordovician Maquoketa Formation of Iowa, Flower 

also placed in the genus a number of species from the 

"Cynthiana Limestone" in Kentucky and the middle and 

upper portions of the Trenton Group in New York. These 

latter species consist of a group of small, slender, finely 

ornamented longicones that are the most abundant nautiloids encountered in late Middle Ordovician (Shermanian) carbonates and dark-shale facies in Eastern North 

America, These species are Isorthoceras albersi (Miller 

and Faber) from the Middle Ordovician Point Pleasant 

Tongue of the Clays Ferry Formation in northern Kentucky (pi. 10, figs. 1-9); uGeisonoceras" lineolatus (Hall), 

"G." strigatum (Hall) (pi. 10, fig. 16), "G." strangulatum 

(Hall) (pi. 10, figs. 13, 14), "G" tenuistriatum (Hall), and 

U G." tenuitextum (Hall), all from the Middle Ordovician 

Denley and Dolgeville Limestones in New York. An additional species, Protokionoceras oneidaense (Walcott)
P60 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

from the Upper Ordovician Utica Shale in New York, also 

belongs in Isorthoceras.

Previously, these finely ornamented species have 

been placed in either G&isonoceras Hyatt or Protokionoceras Grabau and Shimer (Ruedemann, 1926; Titus and 

Cameron, 1976). These small, slender, Middle Ordovician 

species are definitely not assignable to either of these two 

genera As indicated above, Geisonoceras, based on 

Orthoceras rivale Barrande from the Silurian of Eastern 

Europe, and Protokionoceras, based on Orthoceras medullare Hall from equivalent Silurian carbonates in the Midwestern United States, both have large, robust, gradually 

expanding shells with deeper cameral chambers, larger 

diameter, slightly expanded dorsal siphuncle segments 

with longer, less recurved septal necks, and annul osiphonate deposits that are continuous and contain massive 

botryoidal episeptal and hyposeptal cameral deposits. 

These small, slender Ordovician species are similar to I. 

sociale (Hall) in gross shell morphology and in details of 

their internal structure, especially siphuncle segment 

shape, septal necks, and the nature of endosiphuncular 

and cameral deposits. The only distinction between these 

taxa is in the nature of the external shell ornament. Isorthoceras sociale has a basically smooth shell marked by 

fine, transverse growth lines (pi. 10, fig. 15). These Middle 

Ordovician species have shells marked by fine, raised, 

longitudinal, transverse, or cancellate lirae. Flower (1962) 

indicated that these more ornate species may eventually 

provide the basis for a separate, allied genus. It is debatable as to whether or not details of shell surface ornament 

constitutes a significant criterion for differentiating 

genus-level nautiloid taxa For the purposes of this paper, 

these more ornate taxa are retained in Isorthoceras.

ISORTHOCERAS ALBERSI (MILLER AND FABER), 1894B

Plate 10, figures 1-9

Orthoceras albersi Miller and Faber, 1894B, p. 140, pi. 8, 

figs. 1-40.

Diagnosis.—Moderately expanding species of Isorthoceras distinguished by an external ornament of fine, 

raised, longitudinal lirae.

Description.—Small (less than 25 cm in length and 

shell diameters up to 2.0 cm), moderately expanding (apical angle 7-8 degrees), orthoconic longicones; circular in 

section with straight, transverse sutures. Cameral lengths 

ranging from one-fourth to one-sixth the diameter of the 

shell, decreasing with ontogeny. Body chamber poorly 

known. Shell exterior marked by distinct, fine, raised, longitudinal lirae.

Siphuncle central in position (SPR=0.50) at shell 

diameters less than 5 mm, becoming more ventral with 

ontogeny having segments subcentral in position 

(SPR=0.33) at shell diameters of 2.0 cm. Segments elongate ovate, not quite twice as long as high, SCR values

averaging between 0.75 and 0.80 (depressed). Segments 

narrow, one-fifth to one-eighth the diameter of the shell, 

decreasing in diameter relative to shell diameter with 

ontogeny. Septal necks cyrtochoanitic, recurved with 

short, free brims. Endosiphuncular deposits unknown. 

Adoralmost cameral deposits consisting of ventrolateral 

mural-episeptal deposits, the deposits completely filling 

cameral chambers in adapical portions of the phragmocone less than 10 mm in diameter.

Stratigraphic and geographic occurrence.—Logana 

Member of the Lexington Limestone (Middle Ordovician, 

Kirkfieldian Stage), Woodford County, Ky.; Grier Limestone Member of the Lexington Limestone (Middle Ordovician, Kirkfieldian and Shermanian Stages), Clark and 

Jessamine Counties, Ky; Shermanian part of the Millersburg Member of the Lexington Limestone, Bourbon 

County, Ky.; and the Shermanian portion of the Point 

Pleasant Tongue of the Clays Ferry Formation, Kenton 

County, Ky.

Studied material.—Syntypes UC 360 (pi. 10, fig. 1) 

and UC 361 (pi. 10, figs. 2, 3), "lower part of the Hudson 

River Group at Ludlow, Kentucky"; MU 447T (pi. 10, fig. 

4), "Point Pleasant Beds" at Cincinnati, Ohio; USNM 

468695 (pi. 10, fig. 7) and 468696 (pi. 10, fig. 8), USGS 

5067-CO collection, Grier Limestone Member; USNM 

468697 (pi. 10, fig. 5) and 468698 (pi. 10, fig. 9), USGS 

5092-CO collection, Logana Member, and USNM 468702 

(pi. 10, fig. 6), USGS 5096-CO collection, Grier Limestone 

Member; plus suites of silicified material: USNM 468699 

from USGS 5067-CO collection, Grier Limestone Member, 

USNM 468700 from USGS 5073-CO collection, Grier Limestone Member; USNM 468701 from USGS 5092-CO collection, Logana Member, USNM 468702 from USGS 5096-CO 

collection, Grier Limestone Member, USNM 468703 from 

USGS 6419-CO collection, Logana Member, and USNM 

468704 from USGS 7353-CO collection, Millersburg 

Member.

Specimen UC 360 (pi. 10, fig. 1) is here designated the 

lectotype of Orthoceras albersi Miller and Faber (1894B). 

Specimen UC 361 (pi. 10, figs. 2, 3) is here designated a 

paralectotype of O. albersi Miller and Faber.

Remarks.—This small, longitudinally marked longiconic nautiloid is the most abundant nautiloid species in 

the various members of the Lexington Limestone in central and northern Kentucky. Specimens of I. albersi constitute 90 percent of the etched nautiloid specimens 

recovered from the USGS 5067-CO collection in the Grier 

Limestone Member (101 out of 114 specimens). The species appears to be most abundant in the deeper water, 

less agitated facies of the Logana Member and Grier Limestone Member within the Lexington Limestone. In these 

facies, I. albersi occurs in association with lesser numbers of the nautiloids Gorbyoceras cf. G. tetreauense (pi. 

12, fig. 3), Polygrammoceras sp. A (pi. 12, figs. 1, 2), and
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P61

AUumettoceras cf. A. tenerum (pi. 20, figs. 19-22), along 

with other mollusks and small, twiglike bryozoans. Isorthoceras albersi is equally abundant in the dark-gray, 

mud-rich limestones of the Point Pleasant Tongue of the 

Clays Ferry Formation in northern Kentucky. In these 

limestones the species occurs in association with rare 

specimens of the large longiconic nautiloid Oraogeisonoceras amplicameratum (Hall) (pi. 3, figs. 1-5) and Trocholites faberi Foerste, other mollusks, and the trilobites 

Flexicalymene and Isotelus.

Isorthoceras albersi is similar to Orthoceras strigatum Hall from the Middle Ordovician (Shermanian) Denley Limestone and equivalents in north-central New York. 

A comparison of these Kentucky specimens with Hall's 

type specimens (AMNH 29691 and 29692) indicates that 

these specimens are similar in general shell morphology 

and in possessing an external ornament of fine, raised, 

longitudinal lirae (compare pi. 10, figs. 5-9 with pi. 10, fig. 

16). The internal features of Hall's species are not known, 

as his material consists of matrix-filled composite molds. 

Ruedemann (1926, pi. 10, fig. 13) figured a sectioned specimen of a closely related species, "Geisonoceras" tenuistriatum (Hall). This specimen reveals narrow, slightly 

expanded siphuncle segments similar to those present in 

/. albersi. The type specimens of/, strigatum differ from 

the Kentucky specimens of /. albersi only in their more 

slender, gradually expanding shells with an apical angle of 

6 degrees versus apical angles of 7 or 8 degrees for /. 

albersi. Pending study of New York material preserving 

the features of the siphuncle segments, the Kentucky 

specimens will remain in /. albersi, although it may eventually be determined that this species is a synonym of /. 

strigatum (Hall), Hall's name having priority. A comparison of the morphological features of /. albersi, L rogersensis, and several of the species described by Hall 

(1847) is presented in figure 18.

ISORTHOCERAS ROGERSENSIS (FOERSTE), 1914A

Plate 10, figures 10-12

Orthoceras rogersensis Foerste, 1914a, p. 143-144, pi. 1,

figs. 17a-b. 

Treptoceras praenuntium Flower, 1942, p. 19, pi. 1, fig. 2.

Diagnosis.—Slender, gradually expanding species of 

Isorthoceras distinguished by an external ornament of 

fine, raised, cancellate lirae.

Description.—Small (lengths of 25 cm having shell 

diameters up to 2.4 cm), slender, gradually expanding 

(apical angle 6.5 degrees) orthoconic longicones; circular 

in section with straight, transverse sutures. Camerae 

short, camera! lengths averaging between one-fifth and 

one-sixth the diameter of the shell, initially decreasing 

with ontogeny, then increasing in length at shell diameters 

in excess of 20 mm. Body chamber unknown. External

5 r-

< - 

O

6 8 10 12 H 16 18 20 

SHELL DIAMETER, IN MILLIMETERS

22

FIGURE 18.—Bivariate plot of camera! length versus shell 

diameter for selected species of Isorthoceras from Middle 

and Upper Ordovician strata in Eastern North America. 

Species are /. albersi from USGS collections in the 

Lexington Limestone (Shermanian) in Kentucky (open 

circles); /. strigatum, syntype AMNH 29692 from the 

Trenton Limestone (Shermanian), New York (solid 

circles); /. rogersensis, syntype USNM 87193A from the 

Clays Ferry Formation in Kentucky (squares); and /. 

sociale, MU 14566 from the Maquoketa Formation 

(Maysvillian), Iowa (triangles).

ornament of fine, raised, longitudinal and transverse lirae, 

equally developed, forming a fine cancellate pattern.

Siphuncle central to subcentral (SPR=0.50-0.46) at 

shell diameters less than 15 mm. Siphuncle segments barrel-shaped, depressed (SCR=0.73-0.85), narrow, one-fifth 

the diameter of the shell. Septal necks cyrtochoanitic, 

recurved, with short, free brims. Endosiphuncular deposits unknown. Mural-episeptal cameral deposits at shell 

diameters of 15 mm or less.

Stratigraphic and geographic occurrence.—Basal 

portion of the Clays Ferry Formation (uppermost Middle 

Ordovician, Shermanian Stage), Harrison and Scott Counties, Ky.

Studied material—Syntypes USNM 87193A (pi. 10, 

figs. 10,11) and USNM 87193B (pi. 10, fig. 12), "Cynthiana 

Limestone" exposed at railroad cut 1 mi north of Rogers 

Gap, 5 mi south of Sadieville, Scott County, Ky; holotype 

of Treptoceras praenuntium Flower (UC 22696), "Cynthiana Limestone," Poindexter Quarry at Cynthiana, Harrison County, Ky; plus uncataloged slabs containing 

specimens from the "Cynthiana Limestone" at Rogers 

Gap, Ky, in the Shideler collection at Miami University.

Specimen USNM 87193A (pi. 10, figs. 10, 11) is here 

designated the lectotype of Orthoceras rogersensis Foerste (1914A). Specimen 87193B (pi. 10, fig. 12) is here designated a paralectotype of O. rogersensis Foerste.

Remarks.—Isorthoceras rogersensis is a locally 

common species in the argillaceous, thin limestone beds 

within the basal Clays Ferry Formation in north-central 

Kentucky. In these strata, /. rogersensis occurs as calcitereplaced or matrix-filled internal molds associated with
P62 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

gastropods, pelecypods, crinoids, inarticulate brachiopods, and the trilobites Flexicalymene and Isotelus. Isorthoceras rogersensis differs from the preceding species, 

I. albersi (Miller and Faber), in being a slightly larger and 

more gradually expanding shell, but is primarily distinguished by its cancellate external ornament compared 

with the distinctive longitudinal ornament of the latter 

species.

Flower (1942) described Treptoceras praenuntium 

from the "Cynthiana Limestone" exposed at Cynthiana, 

Ky. As indicated above, this species is not assignable to 

Treptoceras, as it has narrow, barrel-shaped siphuncle 

segments. This species is similar to /. rogersensis in its 

gradual rate of expansion (apical angle 6.5 degrees), short 

camera! chambers one-sixth the diameter of the shell, 

barrel-shaped, depressed siphuncle segments, and occurrence at the top of the Lexington Limestone in north-central Kentucky. These similarities indicate assignment of 

"Treptoceras" praenuntium to I. rogersensis. Specimens 

of the former species preserving the external shell ornament are necessary to further confirm the affinities of 

these taxa. Unfortunately, "T." praenuntium is known 

only from the holotype, and the bed that was the source 

of this specimen has been quarried away.

Isorthoceras rogersensis is also similar to a species 

described by Hall (1847) as "Endoceras proteiforme variety tenuitextum" from the Middle Ordovician Trenton 

Group exposed at Middleville, N.Y. Comparisons of Hall's 

types (AMNH 29717 and 29718) with the types of /. rogersensis indicate a similar general shell morphology (apical angle 6-7 degrees) and an external ornament of fine 

cancellate lirae. Unfortunately, the internal features of 

Hall's species are unknown. Pending discovery of specimens of/, tenuitextum preserving critical features of the 

siphuncle segments, these species are retained as separate species. As was the case with the previous species, if 

these Kentucky and New York specimens prove to be the 

same, Hall's species name would have priority.

A third species referable to Isorthoceras is known 

from uncommon fragmentary specimens from the Treptoceras duseri shale unit within the "Waynesville biofacies" 

in the Bull Fork Formation (Upper Ordovician, Richmondian) in southwest Ohio (Frey, 1988). This is a small (less 

than 20 cm in length), slender (apical angle 5.5-6.5 

degrees) orthoconic longicone with very short camera! 

chambers (camera! lengths averaging one-seventh the 

diameter of the shell) and narrow, barrel-shaped subcentral siphuncle segments. Endosiphuncular deposits consist of thin parietal deposits. Camera! deposits are muralepiseptal. Although the external ornament of this Richmondian species is unknown, the short camerae typical of 

this species distinguish it from both /. albersi and /. rogersensis. More complete material is needed to more fully 

describe this Richmondian species.

GENUS GORBYOCERAS SHIMIZU AND OBATA

Type species.—Orthoceras gorbyi Miller, 1894, p. 

322; designated by Shimizu and Obata, 1935, p. 4; Saluda 

Formation, Richmondian Stage, Upper Ordovician, 

Indiana.

Description.—Slender, small to medium-sized, gradually to moderately expanding orthoconic longicones that 

adapically may be curved endogastrically. Shells typically 

circular in cross section, laterally compressed in early 

growth stages of some species. Sutures straight, transverse to slightly oblique, sloping from the dorsum to the 

venter in the adapical direction. Camera! chambers short, 

camera! lengths from one-fourth to one-ninth the diameter of the shell, decreasing with ontogeny. Body chamber 

long and slender, contracting toward the aperature in 

some species. Aperture simple, transverse. Periphract 

dorsomyarian. Shell exterior marked by prominent transverse, rounded annuli, oblique in some species; as well as 

fine, raised transverse and longitudinal lirae.

Siphuncle subcentral with expanded segments that 

vary in shape, ranging from depressed barrel-shaped to 

equiaxial globular in outline. Segments narrow, one-fourth 

to one-sixth the diameter of the shell. Septal necks cyrtochoanitic, recurved, but with free brims. Endosiphuncular 

deposits known for a few species, consisting of thin parietal deposits restricted to adapical portions of large individuals. Mural-episeptal camera! deposits adapically.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Rocklandian Stage) to Upper Ordovician 

(Richmondian Stage), North America (Laurentia).

Remarks.—This genus is one of several poorly 

defined annulated longiconic taxa proposed by Shimizu 

and Obata (1935). Their description of Gorbyoceras was 

brief: "(shell) possessing peculiar annulations and distant 

longitudinal striae; the annulations sloping sharply downward and weakening towards the venter." In the same 

paper, they also described HammeUoceras (type species 

Spyroceras hammeUi (Foerste)) as "Externally...somewhat similar to Kionoceras except that it has prominent 

annulations and an ormoceratid siphuncle"; as well 

as Porteroceras (type species Spyroceras porteri 

(Schuchert)), distinguished as being "related to Hammelloceras, differing from it in possessing more prominent 

ornamentation and a sactocerid siphuncle." Gorbyoceras, 

HammeUoceras, and Porteroceras are all annulated longicones with longitudinal lirae, cyrtochoanitic septal necks, 

and expanded siphuncle segments. All three are from 

Upper Ordovician strata in North America Flower (1946) 

and Sweet (1964) both placed these taxa in synonymy, 

with Gorbyoceras having priority.

Flower (1946) described seven species of Gorbyoceras from Upper Ordovician (Richmondian) strata in 

Indiana and Ohio and placed in the genus a number of 

Ordovician species previously referred to as Spyroceras
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P63

Hyatt, a Devonian genus based on Orthoceras crotalum 

Hall. These are "Spyroceras" ferum (Billings) and "S." 

microlineatum Foerste from the Richmondian of Anticosti Island, Quebec; "S." parksi Foerste from the Richmondian Georgian Bay Formation in southern Ontario; 

plus "S." calvini Foerste and "S." perroti (Clarke), both 

from the Maquoketa Formation of Iowa. Other Upper 

Ordovician species assignable to Gorbyoceras are "S." 

geronticum (Foerste and Savage) and G. giganteum Nelson from the Shamattawa and Chasm Creek Limestones 

exposed in the Hudson Bay region of Manitoba Also 

placed in Gorbyoceras are a number of similar forms from 

older Middle Ordovician strata: G. tetreauense Wilson 

from the "Leray-Rockland beds" (Rocklandian) in the 

Ottawa region of Canada and G. iowaense (Foerste) from 

the Decorah Shale (Rocklandian) in Iowa.

The familial affinities of Gorbyoceras are currently 

uncertain. Flower (1962) and Sweet (1964) placed this 

genus in the Proteoceratidae on the basis of its cyrtochoanitic septal necks and occurrence in Ordovician strata. 

The features of the siphuncle segments and the presence 

and types of endosiphuncular deposits developed in species assigned to Gorbyoceras remain largely unknown. No 

species known to this writer have been documented to 

show the siphuncle segment decompression characteristic of the Proteoceratidae. Flower (1946) has illustrated 

siphuncle segments for G. crossi Flower, G. curvatum 

Flower, G. duncanae Flower, and G. hammeUi (Foerste), 

all from the Cincinnatian Provincial Series in the Cincinnati arch region. Gorbyoceras crossi and adoral portions 

of a specimen he referred to as G. hammetti both have 

expanded, globular, equiaxial segments and ventral parietal deposits that appear to be similar to those developed 

in the proteoceratid Treptoceras (Flower, 1946, pi. 1, figs. 

2, 7). Gorbyoceras curvatum (Flower, 1946, pi. 5, fig. 3), 

G. duncanae (Flower, 1946, pi. 1, fig. 1), and adapical portions of G. hammetti illustrated here (pi. 12, fig. 7) exhibit 

less broadly expanded, barrel-shaped segments similar to 

those of the pseudorthoceratid Isorthoceras. The parietal 

deposits evident in the figured specimen of G. hammetti 

also are similar to those documented for various members of the Pseudorthoceratidae. All of the species of Gorbyoceras studied here possess septal necks that are 

cyrtochoanitic with recurved, short, free brims, similar to 

those typical of pseudoceratid genera. As ontogenetic 

decompression has not been demonstrated for any species of Gorbyoceras known to this writer, herein this 

genus is removed from the Proteoceratidae and placed 

with some uncertainty in the Pseudorthoceratidae. Further study may indicate that Gorbyoceras as presently 

known contains two distinct genera, one with expanded, 

globular siphuncle segments that may belong in the Proteoceratidae, and another with depressed, barrel-shaped 

segments that belongs in the Pseudorthoceratidae. Study

of more complete, better preserved material is needed to 

more accurately determine the affinities of the species 

currently assigned to this genus.

GORBYOCERAS GORBYI (MILLER), 1894

Plate 12, figures 12, 13

Orthoceras gorbyi MiUer, 1894, p. 322, pi. 10, fig. 2. 

Orthoceras gorbyi Miller. Cumings, 1908, p. 1037, pi. 52,

fig. 3. 

Spyroceras gorbyi (Miller). Foerste, 1928a, p. 283, pi. 61,

fig. 4. 

Gorbyoceras gorbyi (Miller). Shimizu and Obata, 1935, p.

4. 

Gorbyoceras gorbyi (Miller). Flower, 1946, p. 145, pi. 2,

figs. 9,10; pi. 4, figs. 3, 6, 7.

Diagnosis.—Large, slender, gradually expanding, 

endogastrically curved species of Gorbyoceras distinguished by low, rounded, oblique annuli that slope from 

the dorsum to the venter in an adoral direction, opposite 

the slope of the sutures.

Description.—Long (lengths up to 71.5 cm and shell 

diameters up to 3.2 cm), slender, gradually expanding 

(apical angle 4 degrees) orthoconic longicones, curved 

endogastrically such that the venter is gently convex and 

the dorsum is concave. Shell initially circular in cross section, becoming slightly depressed with ontogeny, then 

becoming more circular again at diameters in excess of 25 

mm. Sutures sloping from the dorsum to the venter in the 

adapical direction, becoming more transverse with ontogeny. Camera! chambers short, camera! lengths decreasing 

with ontogeny, from one-fourth the diameter of the shell 

at a diameter of 20 mm to one-seventh the diameter of the 

shell at diameters greater than 25 mm. Body chamber 

long and tubular, contracting slightly toward the aperture, 

making up at least one-fourth the total length of the shell. 

Aperture poorly known; periphract dorsomyarian. Shell 

exterior marked by low, rounded, oblique annuli that 

slope opposite the direction of the sutures, extending 

from the dorsum to the venter, directed adorally. Annuli 

spaced 4-5 mm apart at diameters in excess of 20 mm. 

Shell marked with alternating sets of coarser and finer 

longitudinal lirae and transverse growth lines that parallel 

the trend of the annuli.

Siphuncle sub central in position, moving to a more 

ventral position with ontogeny; having SPR values of 0.40 

at a diameter of 20 mm and SPR values of 0.28 at a diameter of 32 mm. Siphuncle segments poorly known, 

expanded, globular, equiaxial in known portions of the 

shell 25 mm in diameter. Septal necks cyrtochoanitic, 

short with recurved free brims. Endosiphuncular deposits 

unknown. Camera! deposits mural-episeptal, developed 

adapically at shell diameters of 25 mm or less.

Stratigraphic and geographic occurrence.—Saluda 

Formation (Upper Ordovician, Richmondian Stage),
P64 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

southeastern Indiana and adjacent portions of southwestern Ohio.

Studied material.—Hypotype (MU 397T) figured by 

Flower (1946, pi. 2, figs. 9,10), Shideler Collection, Miami 

University, basal Whitewater Formation, Four-Mile Creek, 

Preble County, Ohio; MU 402T (pi. 12, figs. 12, 13); and 

MU 16050, Bliss Collection, Miami University, "Concrete 

Layer" in the Saluda Formation, Sayers Farm locality, 2 mi 

northwest of Hamburg, Franklin County, Ind. Also studied 

was the holotype of Orthoceras gorbyi Miller (USNM 

64337), which Miller (1894, pi. 10, fig. 2) listed as coming 

from the "Hudson River Group, Franklin County, Indiana."

Remarks.—Gorbyoceras gorbyi is distinguished 

from associated species of Gorbyoceras by its long, slender, endogastrically curved shell marked by low, rounded, 

oblique annuli that are oriented opposite to the obliquely 

curved sutures. The internal features of the species are 

poorly known due to the poor preservation of these features in nautiloids occurring in massive-bedded, micritic 

limestone lithologies in the Saluda Formation. Flower 

(1946) described the siphuncle segments of G. gorbyi as 

globular, similar to those of the genus Treptoceras, with 

short cyrtochoanitic septal necks. He also indicated that 

the external annuli in this species were surpressed on the 

venter of large specimens. This feature is not evident in 

the material studied here, the annuli being developed uniformly dorsally and ventrally.

The associated G. crossi Flower is similar to G. gorbyi in possessing a long, slender shell, circular in section, 

and low, slightly oblique annuli. The annuli in G. gorbyi 

are more strongly developed and more strongly inclined 

than in G. crossi. Transverse, raised lirae are present in G. 

gorbyi and absent in G. crossi. The camerae in G. gorbyi 

are described by Flower (1946) as being shorter than 

those present in G. crossi. The material studied here indicates no significant difference in cameral lengths at comparable diameters, at least in adapical portions of 

phragmocones. The described differences between these 

species may be the result of differences in preservation 

rather than a representation of actual morphological 

differences.

Within the Kentucky-Indiana-Ohio area, G. gorbyi is 

restricted to massive-bedded, fine-grained limestone 

facies that occur above the lower Tetradium biostrome 

within the Saluda Formation. In this facies the species is 

associated with a diverse nautiloid assemblage of G. 

crossi Flower, a large species of Cameroceras, the breviconic ellesmerocerid Cyrtocerina, the oncocerids 

Beloitoceras bucheri Flower (pi. 22, figs. 4, 5), Diestoceras indianense (Miller and Faber) (pi. 22, figs. 6-9), 

andD. shideleri Foerste (pi. 21, figs. 1, 2, 5; pi. 22, figs. 1, 

3), several species of slender oncocerid Manitoulinoceras, and the ascocerid Schuchertoceras prolongatum 

(Foerste). All of these species are preserved as nearly

complete, uncrushed composite molds, often preserving 

the fine external ornament of the shell (pi. 22, figs. 4,5,8). 

This extensive nautiloid fauna was described in part by 

Flower (1946) and represents the peak development of 

the "Arctic" nautiloid fauna in the northern Cincinnati 

arch region.

GORBYOCERAS HAMMELLI (FOERSTE), 1910

Plate 12, figures 4, 6, 7, 10, 11

Orthoceras hammelli Foerste, 1910, p. 74, pi. 1, fig. 4. 

Spyroceras hammeUi (Foerste). Foerste, 1924b, p. 222, pi.

39, fig. 1; pi. 40, fig. 1. 

Hammettoceras hammelli (Foerste). Shimizu and Obata,

1935, p. 6. 

Gorbyoceras hammelli (Foerste). Flower, 1946, p. 151, pi.

1, figs. 2, 3, 9; pi. 2, fig. 5; pi. 3, figs. 1, 4; pi. 4, figs. 1, 2,

5; pi. 5, figs. 4, 9.

Diagnosis.—Small, straight, slender species of Gorbyoceras distinguished by oblique annuli that slope from 

dorsum to venter adorally, the annuli becoming less distinct and spaced further apart with ontogeny.

Description.—Small (lengths up to 30 cm and 

observed shell diameters up to 2.4 cm), slender (apical 

angle 5-6 degrees), orthoconic longicones; circular in section with straight, transverse sutures. Cameral length 

ranging from one-third to one-fifth the diameter of the 

shell, decreasing with ontogeny. Body chamber incompletely known; aperture unknown. Shell exterior marked 

by oblique, rounded annuli that slope from the dorsum to 

the venter in the adoral direction. Annuli prominent, 

spaced 2 mm apart in adapical portions of the shell less 

than 15 mm in diameter; becoming less distinct, low, and 

rounded, spaced 4-5 mm apart in adoral portions of the 

shell greater than 17 mm in diameter. Shell marked by distinct alternating sets of coarse and fine longitudinal lirae 

and intersecting, raised, transverse growth lines that parallel the trend of the annuli.

Siphuncle subcentral in position most of the length of 

the phragmocone, becoming more ventral in position with 

ontogeny, the SPR values ranging from 0.38 (subcentral) 

at a diameter of 9 mm to 0.24 (ventral) at a diameter of 

17mm. Siphuncle segments expanded, roughly barrelshaped in portions of the shell 9 mm or less in diameter, 

becoming more compressed, globular (SCR=1.0, equiaxial) at diameters of 15 mm or greater. Segments unknown 

from more adoral portions of the shell greater than 17 mm 

in diameter. Septal necks cyrtochoanitic, short, recurved, 

with free brims. Endosiphuncular deposits consisting of 

uniformly developed, thin parietal deposits that fuse to 

form a continuous lining with ontogeny; restricted in 

development to adapical portions of the shell less than 15 

mm in diameter. Mural-episeptal cameral deposits welldeveloped in adapical portions of shells less than or equal 

to 15 mm in diameter.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P65

Stratigraphic and geographic occurrence,—Saluda 

Formation and its Hitz Limestone Member (Late Ordovician, Richmondian Stage), Franklin, Ripley, and Jefferson 

Counties, Ind., and adjacent portions of Bedford, Trimble, 

Oldham, and Jefferson Counties in northern Kentucky.

Studied material.—Hypotypes figured by Flower 

(1946), are UC 24165 from the Saluda Formation at 

Canaan, Ind., and 24166 from the Hitz Bed at Madison, 

Ind.; plus MU 408T from the top of the Saluda Formation 

at Versailles, Ripley County, Ind. (pi. 12, figs. 4, 7). Additional material consists of MU 409T (pi. 12, figs. 10, 11) 

and MU 446T (pi. 12, fig. 6), plus numerous small fragmentary specimens, all from the "Hitz Bed" exposed along the 

1-471 roadcut, just north of Madison, Jefferson County, 

Ind. Also studied was the holotype of Orthoceras hammeUi Foerste (USNM 87190), which Foerste (1910, pi. 1, 

fig. 4) listed as coming from "Top of Saluda Bed, Saluda 

Creek, Jefferson County, Indiana."

Remarks.—This species, originally described by Foerste (1910), served as the type species for HammeUoceras 

Shimizu and Obata (1935). Flower (1946) has indicated 

that, as defined by these authors, there are no valid distinctions between the genera Gorbyoceras, HammeUoceras, and Porteroceras. As such, "Orthoceras" hammeUi 

is retained in Gorbyoceras pending further study of these 

annulated longicones. Gorbyoceras hammelli is similar to 

the preceding species, G. gorbyi (Miller), in the development of a slender, longiconic shell and an external ornament of oblique, raised annuli and longitudinal and 

transverse lirae. Both species possess subcentral siphuncles and mural-episeptal camera! deposits. Gorbyoceras 

hammelli is distinct from G. gorbyi in being a smaller 

form with a more rapidly expanding, straight rather than 

gently curved longiconic shell; in possessing oblique 

annuli that are less steeply inclined than those of the type 

species; and in the weaker development of these annuli 

with ontogeny, a feature not evident in G. gorbyi, in which 

the annuli remain prominent the entire length of the shell.

In the "Hitz Bed," G. hammelli occurs as well preserved if often fragmentary specimens in which the external shell, septa, and siphuncle segments are replaced with 

sparry calcite. This coarse spar replacement often 

obscures the details of the internal features of the shell. 

Gorbyoceras hammeUi occurs in the "Hitz Bed" in association with a diverse assemblage of nautiloids: G. crossi 

Flower, the actinocerid Ormoceras hitzi Foerste, the 

breviconic ellesmerocerid Cyrtocerina madisonensis 

(Miller), and a number of small oncocerids currently 

described as species of Oncoceras and Diestoceras. These 

nautiloids occur in association with the sponges Dermatostroma and Stromatocerium, a small solitary rugosan 

coral, rare articulate brachiopods, and a diverse fauna of 

well-preserved gastropods, pelecypods, and ostracodes.

GORBYOCERAS CF. G. TETREAUENSE WILSON, 1961

Plate 12, figure 3

Gorbyoceras tetreauense Wilson, 1961, p. 38, pi. 10, figs.

2-5.

Diagnosis.—Small, slender, rather rapidly expanding, laterally compressed, and endogastrically curved species of Gorbyoceras marked by oblique, low, rounded 

annuli that become less distinct with ontogeny.

Description.—Small (lengths up to 16 cm and shell 

diameters up to 2.0 cm), slender, moderately expanding 

(apical angle 8-8.5 degrees), endogastrically curved longicones with sutures initially straight, transverse; becoming 

slightly oblique with ontogeny, inclined from the dorsum 

to the venter in the adapical direction. Camera! lengths 

ranging from one-fourth to one-fifth the diameter of the 

shell, decreasing with ontogeny. Body chamber incompletely known. Shell marked by raised annuli that are 

transverse initially, becoming slightly oblique with ontogeny, inclined from the dorsum to the venter in the adoral 

direction, opposite the trend of the sutures. Annuli spaced 

2 mm apart at a diameter of 7 mm, and 3 mm apart at a 

diameter of 15 mm. Exterior marked by alternating sets of 

coarse and fine longitudinal lirae.

Siphuncle central (SPR=0.50) at a shell diameter of 8 

mm, becoming subcentral with ontogeny (SPR=0.375 at a 

diameter of 12 mm). Siphuncle segment shape and maximum diameter unknown. Endosiphuncular and camera! 

deposits unknown.

Stratigraphic and geographic occurrence.—Logana 

Member of the Lexington Limestone (Middle Ordovician, 

Kirkfieldian Stage), Woodford and Franklin Counties, Ky.

Studied material.—USNM 468708 (pi. 12, fig. 3) from 

USGS 5092-CO collection, lower part of the Logana Member, Tyrone quadrangle, Woodford County, Ky; USNM 

468707 from USGS 5073-CO collection, upper part of the 

Logana Member, Frankfort East quadrangle, Franklin 

County, Ky; and USNM 468709 from USGS 7791-CO collection, lower part of the Logana Member, Salvisa quadrangle, Woodford County, Ky.

Remarks.—Fragmentary silicified specimens of Gorbyoceras from the Logana Member of the Lexington Limestone exposed in central Kentucky, west and south of 

Lexington, appear to be assignable to G. tetreauense 

described by Wilson (1961) from the "Leray beds" (Middle 

Ordovician, Rocklandian) of the Ottawa region of Quebec. This is indicated by the small, rather rapidly expanding, gently endogastrically curved longiconic shells 

represented in USGS collections. These specimens have 

an external ornament consisting of nearly transverse, 

raised annuli that are spaced increasingly further apart 

with ontogeny, prominent longitudinal lirae, and much 

weaker transverse lirae. The Kentucky specimens are laterally compressed ovate in cross section at diameters of
P66 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

8mm or less, becoming more circular in cross section 

with ontogeny. Wilson (1961) did not describe or illustrate 

a cross-sectional profile of her Canadian type material. 

The Kentucky specimens also exhibit annuli that become 

less strongly developed with ontogeny, similar to the 

younger Cincinnatian species G. hammelli (Foerste). 

This feature is not evident in Wilson's figured specimens. 

Wilson's type material (GSC 1274-75, 1961, pi. 10, figs. 2- 

5) indicates expanded globular segments at shell diameters of 8-12 mm. The nature of the siphuncle segments in 

the Kentucky material remains unknown, although these 

specimens indicate that the siphuncle is central in position at shell diameters of 10 mm or less. Pending better 

documentation of their internal features, these Kentucky 

specimens are only tentatively assigned to G. tetreauense.

Foerste (1910) described Orthoceras (Spyroceras) 

bilineatum-frankfortense from the Curdsville Limestone 

Member of the Lexington Limestone exposed at the Old 

Crow Distillery, southeast of Frankfort, Ky. (USGS locality 

5092-CO). This species was represented by a single composite mold preserving a portion of the shell 35 mm in 

length having a maximum diameter of 15 mm. Foerste's 

figured specimen appears to be distinct from the specimens from the overlying Logana Member in the more 

closely spaced transverse annuli and more gradual rate of 

shell expansion evident in this specimen. More complete 

specimens of the Curdsville species are needed to more 

accurately compare these Kentucky species.

In the shales and thin limestone of the Logana Member, G. cf. G. tetreauense is an uncommon species in comparison with the abundant specimens of the associated 

orthocerid Isorthoceras albersi (Miller and Faber). In the 

USGS 5092-CO collection from the lower part of the 

Logana Member, G. cf. G. tetreauense makes up slightly 

less than 20 percent of the total number of nautiloids 

present. In the USGS 7791-CO collection from the same 

horizon, the species makes up less than 10 percent of the 

identified nautiloid material. In these collections, these 

nautiloids occur with the well-preserved fossil fauna of 

the monoplacophoran Cyrtolites, gastropods, pelecypods, 

and the dalmanellid brachiopod OnnieUa.

ORTHOCERIDA, FAMILY UNCERTAIN 

GENUS ANASPYROCERAS SHIMIZU AND OBATA

Type species.—Orthoceras anettus Conrad, 1843, p. 

334; designated by Shimizu and Obata, 1935, p. 4; "Beloit 

Member, Black River Formation," Blackriveran Stage, 

Middle Ordovician, Wisconsin.

Description.—Small, slender, gradually expanding 

orthoconic longicones, circular in cross section with simple, transverse sutures. Cameral chambers short. Body 

chamber unknown. Shell exterior distinctly marked by 

prominent, rather sharp, narrow, transverse annuli separated by equally deep interannular grooves. One annulus

per camerae; annuli straight or sloping obliquely from the 

dorsum to the venter in the adapical direction. Shell surface marked by fine, raised transverse lirae.

Siphuncle central or subcentral in position, narrow, 

having segments tubular or expanding only very slightly 

within camerae. Septal necks short, orthochoanitic. 

Endosiphuncular and cameral deposits unknown.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Blackriveran Stage) to Upper Ordovician 

(Richmondian Stage), North America (Laurentia).

Remarks.—This genus is another of the annulated 

longiconic taxa proposed by Shimizu and Obata (1935). 

Their description was brief: "This genus is readily distinguished from Spyroceras by its more crowded, stronger 

annulations." Flower (1943), reviewing a number of these 

annulated genera, emended this description to include 

annulated longicones possessing siphuncles that were 

essentially tubular with straight, short, orthochoanitic 

septa! necks. In his study of Cincinnatian cephalopods 

(Flower, 1946), he further included in this genus Upper 

Ordovician species that, in addition to the prominent 

annuli, also possessed alternating prominent and weak 

longitudinal lirae that formed nodelike projections on 

annular surfaces. Earlier Blackriveran species, including 

the type species A. aneUus, appear to lack these longitudinal brae. Much better preserved material, especially specimens preserving the critical features of the siphuncle, is 

necessary to resolve the uncertainty surrounding this 

genus, its morphology, and its affinities to other described 

taxa,

ANASPYROCERAS CF. A. CYLINDRICUM (FOERSTE), 1932 

Plate 12, figure 5

Spyroceras cylindricum Foerste, 1932, p. 97, pi. 11, figs.

3, 6, 7.

"Spyroceras" cylindricum Foerste. Wilson, 1961, p. 35, pi. 

9, figs. 1-3.

Diagnosis.—Slender species of Anaspyroceras distinguished by prominent transverse annuli that slope 

obliquely from the dorsum to the venter in the adapical 

direction having interannular spaces equal in width to 

annuli.

Description.—Small (length less than 30 cm and 

shell diameters up to 1.0 cm), slender (apical angle 3-3.5 

degrees), orthoconic longicones; circular in cross section. 

Sutures and cameral lengths unknown. Body chamber 

unknown. Exterior marked by prominent raised annuli, 

averaging 1 mm in width, separated by interannular 

spaces of equal width. Annuli sloping obliquely from dorsum to venter in the adapical direction.

Siphuncle central in position. Shape of siphuncle segments unknown, segments apparently narrow in diameter. Septal necks unknown. Endosiphuncular deposits and 

cameral deposits unknown.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P67

Stratigraphic and geographic occurrence.—Curdsville Limestone Member of the Lexington Limestone (Middle Ordovician, Kirkfieldian Stage), Curdsville, Ky.

Studied material.—USNM. 48290, "E.G. Ulrich Collection," Curdsville, Ky. (pi. 12, fig. 5). Also studied was 

the holotype of Spyroceras cylindricum Foerste (AMNH 

807B), which Foerste (1932, pi. 11, figs. 3, &-7) listed as 

coming from "Coarse-grained part of the Trenton Formation, Watertown, New York."

Remarks.—The Curdsville Limestone Member specimen illustrated here is similar to several slender, annulated, longiconic nautiloid species distinguished by the 

oblique nature of the annuli. These species are "Spyroceras" arcuoliratum (Hall), "5." cylindricum Foerste, 

both from the "Trenton Limestone" in New York, and "S." 

attumettense Foerste from the "Leray-Rockland beds" in 

the Ottawa, Ontario region. All three species are based on 

fragmentary specimens whose internal features are 

unknown. Foerste (1932-1933) differentiated "S." cylindricum from "S" arcuoliratum on the basis of its less 

rapidly expanding shell, noting that, otherwise, these taxa 

are closely similar. Foerste distinguished "S" attumettense from "5." arcuoliratum by the lesser obliquity 

of the annuli in the former species.

The Kentucky specimen is distinct from "S." attumettense (GSC 6830) in the greater obliquity of the annuli. 

The apical angle of USNM 48290 (3 degrees) is less than 

that of the "5." arcuoliratum (apical angle 5 degrees) and 

indicates placement in "S" cylindricum.

All of these species are similar to the type species of 

Anaspyroceras, which is Orthoceras anettus Conrad, in 

the gradually expanding slender form of the shell and in 

the closely spaced, raised, narrow annulations with narrow, rounded crests. Assignment of the Curdsville specimen to Anaspyroceras is tentative, pending discovery of 

additional specimens that illustrate the morphological 

features of the siphuncle segments of this taxon.

This form is an uncommon species within the Curdsville Limestone Member, known only from the partially 

silicified external mold described and illustrated here. It 

occurs in a coarsely crystalline, fossiliferous grainstone 

associated with echinoderm fragments and an unidentified rhynchonellid brachiopod.

GENUS POLYGRAMMOCERAS FOERSTE

Type species.—Polygrammoceras twenhofeli Foerste, 1928a, p. 263; by original designation; Ellis Bay Formation, Gamachian Stage, Upper Ordovician, Anticosti 

Island, Quebec.

Description.—Medium to large, moderate to rapidly 

expanding orthoconic longicones; circular in section with 

straight, transverse sutures. Cameral chambers short, 

camera! lengths ranging from one-fourth to one-seventh

the diameter of the shell, decreasing with ontogeny. Body 

chamber incompletely known, at least one-fifth the total 

length of the shell; aperture unknown. Periphract dorsomyarian. Shell surface marked by fine to coarse, sharply 

delineated, longitudinal striae.

Siphuncle central in position adapically, becoming 

more ventral with ontogeny. Segments expanded within 

camerae, globular, equiaxial to slightly compressed; narrow in diameter, one-fifth the diameter of the shell. Septal 

necks cyrtochoanitic, short, recurved, with free brims. 

Endosiphuncular deposits unknown. Mural-episeptal 

camera! deposits developed adapically.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Shermanian) to Lower Silurian (Wenlockian 

Series), North America (Laurentia).

Remarks.—Foerste (1928a) erected this genus for 

Ordovician longicones that had an external ornament of 

longitudinal striae, ribs, or bars but that lacked fluting. It 

became common practice to place here any longitudinally 

striated longiconic orthocerid. Troedsson (1932) placed in 

Polygrammoceras a large number of species from the 

lower Middle Ordovician (Llanvirnian) "Orthoceras Limestone" of the Baltic region. All of these species possessed 

longitudinally striated shells, short orthochoanitic septa! 

necks, and subtubular siphuncle segments. All three species of Polygrammoceras described by Foerste (1928a) 

from Anticosti Island, including the type species P. twenhofeli, possess expanded, beadlike siphuncle segments 

and cyrtochoantic septal necks. It is clear that Polygrammoceras should be restricted to longitudinally striated 

shells that possess expanded siphuncle segments similar 

to these Anticosti species. Troedsson's species belong 

elsewhere. One of his species, P. endoceroides Troedsson, 

is the type species for the genus Troedssonella Kobayashi.

The familial affinities of Polygrammoceras remain 

uncertain. The general shell morphology and gross form 

of the siphuncle segments are similar to those of the 

Upper Ordovician proteoceratid Treptoceras Flower. 

Unfortunately, neither complete sectioned specimens of 

Polygrammoceras nor endosiphuncular deposits are 

known. In the absence of evidence of ontogenetic siphuncle segment decompression and the presence of proteoceratid endosiphuncular deposits, this genus cannot be 

placed with certainty in the Proteoceratidae. Sweet 

(1964) placed Polygrammoceras in the subfamily Kionoceratinae within the Orthoceratidae. The features of the 

siphuncle segments in the type species of Polygrammoceras clearly are not those of a member of the Orthoceratidae. As is indicated above, the subfamily 

Kionoceratinae is a largely artificial grouping of taxa. Longitudinal ornament of the type present in Polygrammoceras evolved a number of times in the Ordovician and 

Silurian in a number of different orthocerid lineages.
P68 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

POLYGRAMMOCERAS SP. A

Plate 12, figures 1, 2

Diagnosis.—Moderately expanding species of Polygrammoceras distinguished by its external ornament of 

narrow, longitudinal striae separated by smooth interspaces that are twice as broad as the striae.

Description.—Medium-sized (lengths of 30 cm and 

shell diameters up to 3.0 cm), moderately expanding (apical angle 7 degrees) orthoconic longicone; circular in 

cross section with straight, transverse sutures. Camera! 

lengths ranging from one-fourth to one-seventh the diameter of the shell, decreasing with ontogeny. Shell surface 

marked by narrow, longitudinal grooves incised at 1-mm 

intervals in specimens 20-30 mm in diameter. The intervening areas smooth, twice as broad as the striae.

Siphuncle central in position (SPR=0.50) at diameters less than 10 mm, becoming subcentral with ontogeny 

(SPR=0.428 at diameters of 15 mm). Siphuncle segments 

expanded, globose, changing with ontogeny from equiaxial (SCR=1.00) at shell diameters less than 10 mm, to 

slightly compressed (SCR=1.20) at diameters of 15 mm, to 

equiaxial in adoral portions of the shell at diameters in 

excess of 25 mm. Septal necks cyrtochoanitic, recurved, 

with free brims in tangential sections. Endosiphuncular 

deposits unknown. Camera! deposits consisting of 

mural-episeptal deposits that are lobate, botryoidal ventrally with a medial ventral mural delta. Deposits welldeveloped in adapical portions of shell less than 15 mm in 

diameter.

Stratigraphic and geographic occurrence.—Grier 

Limestone Member and Strodes Creek Member of the 

Lexington Limestone (Shermanian-Edenian), Clark 

County, Ky

Studied material.—Incomplete phragmocone, 135 

mm in length, (USNM 468710; pi. 12, figs. 1, 2) and additional fragmentary silicified material from the USGS 

5067-CO collection, Grier Limestone Member, Ford, Clark 

County, Ky; USNM 468729, Strodes Creek Member, roadcut Route 89, 5 mi east of Winchester, Clark County, Ky.

Remarks.—This species is based primarily on silicified material described above from the Grier Limestone 

Member in Clark County, Ky. An external mold of a similar 

longitudinally striated longiconic nautiloid impressed on 

the base of a stromatoporoid coenosteum (USNM 468729) 

was also collected by the writer from the higher Strodes 

Creek Member of the Lexington Limestone, also in Clark 

County, Ky. The distinctive, longitudinally incised external 

ornament and relatively shallow camerae, coupled with 

the expanded, globular siphuncle segments (pi. 12, figs. 1, 

2) preserved in the Grier Limestone Member material 

indicate placement in the genus Polygrammoceras Foerste as based on the type species P. twenhofeli Foerste

from Upper Ordovician strata exposed on Anticosti 

bland, Quebec.

This writer has elected not to erect a new species on 

the basis of this material at this time due to the lack of 

abundant, well-preserved specime.ns representative of the 

species as well as the limited knowledge of the important 

morphological features of the type species and other previously described species of Polygrammoceras. The Lexington Limestone species is distinct from the type species 

P. twenhofeli Foerste in possessing narrower striae with 

broader interspaces in contrast to the broader striae with 

narrow interspaces described for the Upper Ordovician 

type species (Foerste, 1928a). It is distinct from P. ettisensis Foerste (1928a) from the Ellis Bay Formation (Upper 

Ordovician, Gamachian) on Anticosti Island, in possessing flat, indistinct "ribs" compared with the more prominent, rounded longitudinal "ribs" characteristic of the 

Canadian form. Comparisons with the third species 

described by Foerste from the Ellis Bay Formation on 

Anticosti Island, P. latolineatum Foerste (1928a), are difficult to make due to a lack of specimens at comparable 

diameters, the Lexington Limestone species being represented by specimens less than 30 mm in diameter and P. 

latolineatum being known from more adoral sections of 

the phragmocone greater than 35 mm in diameter.

In the 5067-CO collection from the Grier Limestone 

Member, the species occurs in association with abundant 

specimens of the small orthocerid Isorthoceras albersi 

(Miller and Faber) (pi. 10, figs. 5, 6), plus the univalves 

Cyrtolites and Lophospira, and the pelecypods Deceptrix 

and Modiolodon. Polygrammoceras sp. A can be distinguished from the associated /. albersi in being a larger 

form with an ornament of incised longitudinal grooves in 

constrast to the raised longitudinal lirae characteristic of 

the latter species. Additionally, siphuncle segments in P. 

sp. A are expanded and globular in outline, in contrast to 

the depressed, barrel-shaped segments in /. albersi. Isorthoceras albersi is about 10 times more abundant than 

Polygrammoceras sp. A in these collections.

Species of the genus Treptoceras are similar in general shell morphology, siphuncle segment position and 

shape, and camera! length at comparable diameters. They 

can be distinguished from Polygrammoceras only if the 

exterior ornament of the shell is preserved, as Treptoceras lacks the distinctive incised longitudinal striae characteristic of P. sp. A.

POLYGRAMMOCERAS? CF. P. SP. A

Plate 11, figures 1-3

Diagnosis.—Very large, moderately expanding 

orthoconic longicone with subcentral, slightly expanded 

siphuncle segments one-sixth to one-eighth the diameter 

of the shell, decompressing with ontogeny; moderately 

long, suborthochoanitic septa! necks.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P69

Description.—Large (known portions of the shell 

indicating lengths up to 1.13 m and a maximum observed 

shell diameter of 9.0 cm), moderately expanding (apical 

angle 7 degrees) orthoconic longicone; circular in cross 

section with straight, transverse sutures. Cameral chambers short, cameral lengths ranging from one-sixth the 

diameter of the shell at a diameter of 70 mm to one-ninth 

the diameter of the shell at a diameter of 90 mm. Body 

chamber unknown. Shell exterior unknown.

Siphuncle subcentral in position for the known 

length of the shell, having a SPR value of 0.33 at a diameter of 70 mm to a value of 0.28 at a diameter of 90 mm. 

Segments slightly expanded, compressed (SCR=1.10) 

adapically at a diameter of 70 mm, becoming equiaxial 

(SCR=1.00), plano-convex at a diameter of 90 mm. 

Siphuncle segments narrow, diameter ranging from onesixth the diameter of the shell adapically, to slightly less 

than one-eighth the diameter of the shell adorally; segments decompressing with ontogeny. Septal necks moderately long, suborthochoanitic both dorsally and ventrally. 

No endosiphuncular or cameral deposits are present in 

preserved portion of the phragmocone.

Stratigraphic and geographic occurrence.—Strodes 

Creek Member of the Lexington Limestone (Edenian), 

Winchester region, Clark County, Ky.

Studied material.—USNM 468694 (pi. 11, figs. 1-3) 

from the USGS 7310-CO collection.

Remarks.—This form is represented by a single, very 

large fragment of a phragmocone from the Strodes Creek 

Member of the Lexington Limestone. The specimen is a 

well-preserved, calcite-replaced internal mold that has 

been sectioned dorsoventrally to reveal the Siphuncle segments. This specimen consists of 21 camerae and is compressed laterally as the result of sediment compaction. 

Indications are that the original shell cross section was 

circular. The siphuncle segments and some of the camerae are filled with a fine-grained matrix of blue-gray, calcareous mudstone that weathers to a buff yellow. A 

majority of the camerae are, however, filled with coarse, 

sparry calcite (pi. 11, fig. 1). A number of the septa are 

fractured, especially in the section of the shell between 75 

and 80 mm in diameter. This fracturing is probably due to 

postdepositional compaction of the shell and the enclosing sediments.

The affinities of this specimen are difficult to determine due to the incomplete nature of this specimen and 

the lack of additional material preserving more adapical 

portions of the phragmocone. The large size of this specimen makes it difficult to compare with any other orthocerid from the Ordovician of the Cincinnati arch region. 

The only comparable species in terms of shell diameter is 

Ordogeisonoceras amplicameratum (Hall) from the 

Shermanian part of the Point Pleasant Tongue of the 

Clays Ferry Formation in northern Kentucky. This species

is, however, distinct from USNM 468694 in having a more 

gradually expanding shell and deeper camerae at comparable diameters, a more excentric, dorsally located 

siphuncle, and orthochoanitic rather than suborthochoanitic septal necks.

The suborthochoanitic septal necks, lack of cameral 

or endosiphuncular deposits, and adoral decompression 

of siphuncle segments all indicate that this fragmentary 

specimen represents the adoral end of a very large orthocerid. Similar morphological features have been observed 

in much smaller specimens of the proteoceratid Treptoceras Flower (pi. 5, figs. 1, 7). This suggests that the 

468694 specimen might represent the adoral end of an 

enormous species of Treptoceras. Species of Treptoceras 

are currently unknown from strata older than Late Ordovician (Edenian), although uOrmoceras" lindsleyi Foerste 

and Teichert (1930) from the Shermanian part of the Cannon Limestone in central Tennessee looks like Treptoceras.

As indicated above, comparably sized specimens of 

Treptoceras and Polygrammoceras cannot easily be differentiated unless the external shell is preserved. Treptoceras is basically a smooth-shelled form, in contrast to 

Polygrammoceras, which has a distinctive external ornament of sharply incised longitudinal striae. Specimens of 

Polygrammoceras sp. A have been collected from both 

the Grier Limestone Member and Strodes Creek Member 

of the Lexington Limestone in Clark County, Ky, the 

Strodes Creek Member in the same county being the 

source of the 468694 specimen. Polygrammoceras latolineatum Foerste from the Upper Ordovician Ellis Bay 

Formation on Anticosti Island approaches the USNM 

468694 specimen in size, represented by an adapical portion of the phragmocone at least 40 cm in length and up to 

6.0 cm in diameter. This, in conjunction with the occurrence of Polygrammoceras sp. A in the Strodes Creek 

Member in the Winchester region, suggests that this large 

fragmentary specimen may be an internal mold of the 

adoral end of a large species of Polygrammoceras rather 

than a species of Treptoceras. No specimens of Treptoceras have been collected from the Strodes Creek Member in this area by the writer. More complete material 

from these strata preserving the adapical portions of the 

phragmocone and the external shell surface is needed in 

order to more fully determine the affinities of this interesting specimen.

POLYGRAMMOCERAS? SP. B

Plate 12, figures 8, 9

Diagnosis.—Small, slender, gradually expanding longiconic orthocone marked by broadly spaced, narrow longitudinal furrows about one-fourth as wide as the 

intervening smooth spaces.
P70 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

Description.—Small (15 cm in length and shell diameters up to 1.3 cm), slender, gradually expanding (apical 

angle 5.5 degrees) orthoconic longicone; circular in cross 

section with straight, transverse sutures. Sutures poorly 

defined, camera! lengths one-sixth the diameter of the 

shell at a shell diameter of 10 mm. Body chamber 

unknown. Shell exterior marked by broadly spaced (1 mm 

apart), narrow, longitudinal, sharply defined squared-off 

furrows about one-fourth as wide as the intervening 

smooth spaces.

Siphuncle central in position adapically (SPR=0.50 at 

a diameter of 10 mm). Nature of siphuncle segments 

unknown. Septal necks unknown. Endosiphuncular and 

cameral deposits unknown.

Stratigraphic and geographic occurrence.—Upper 

Rocklandian part of the Tyrone Limestone, Jessamine 

County, Ky.

Studied material.—USNM 468711 (pi. 12, figs. 8, 9) 

from the silicified USGS 6034-CO collection, Little Hickman section A, Jessamine County, Ky.

Remarks.—This form is known from a single fragment of a portion of a phragmocone, 35 mm in length, 

from the USGS 6034-CO collection from the Tyrone Limestone. The external ornament, consisting of sharply 

defined, squared-off longitudinal grooves separating 

broader, flat interspaces, is very similar to that described 

for species of Polygrammoceras by Foerste. The critical 

features of the siphuncle segments are, however, 

unknown for this specimen, making its placement in Polygrammoceras uncertain. In an unpublished manuscript, 

Flower placed this Kentucky specimen with a group of 

small, slender, longitudinally marked longicones he 

placed previously (Flower, 1952) in Kionoceras, Hyatt. 

These species occur in the Ordovician, ranging from the 

Chazyan to the Shermanian. Flower expressed doubt that 

these forms were related to typical Silurian Kionoceras, 

which he described as being much larger species with 

expanded siphuncle segments. Additional material preserving the key features of the siphuncle segments are 

necessary to further determine the affinities of this 

species.

GENUS RICHMONDOCERAS NEW GENUS

Type species.—Richmondoceras brevicameratum, n. 

sp.; designated here; Saluda Formation and upper part of 

the Bull Fork Formation, Richmondian Stage, Upper 

Ordovician, Indiana and Ohio.

Description.—Medium to large, slender, gradually 

expanding orthoconic longicones; circular in section with 

straight, transverse sutures. Cameral chambers short, 

cameral lengths decreasing with ontogeny. Body chamber 

long and tubular, at least one-fifth the total length of the 

shell, aperture unknown. Periphract dorsomyarian. Shell 

exterior unknown, apparently smooth.

Siphuncle midventral in position the length of the 

phragmocone. Siphuncle segments greatly expanded 

within camerae having segment diameter decompressing 

with ontogeny from one-third to one-sixth the diameter of 

the shell. Segments highly compressed, the length of the 

phragmocone. Septal foramina broad, averaging half the 

total diameter of the siphuncle segment. Septal necks cyrtochoanitic and recumbent dorsally and ventrally in more 

adapical portions of the phragmocone; septal neck, highly 

curved and short with free brims adorally in large specimens. Connecting rings thin, adnate adapically and ventrally to free part of the septa. Endosiphuncular deposits 

greatly retarded in their development, consisting of thin 

adapical parietal deposits. Episeptal and hyposeptal 

cameral deposits restricted to adapical portions of 

phragmocone.

Stratigraphic and geographic occurrence.—Upper 

Ordovician (Richmondian Stage) strata in East-Central 

North America (Laurentia).

Remarks.—This genus is erected for medium to 

large, gradually expanding orthoconic longicones possessing short camerae and midventral siphuncles with 

greatly expanded, compressed segments and the limited 

development of both endosiphuncular and cameral 

deposits. The genus is currently represented only by the 

type species Richmondoceras brevicameratum n. sp., 

which is restricted in its occurrence to upper Richmondian strata in southeastern Indiana and southwestern 

Ohio.

The affinities of Richmondoceras are uncertain. The 

recumbent cyrtochoanitic septal necks and ontogenetic 

decompression of siphuncle segments are features common to the order Actinocerida. The greatly retarded 

development of endosiphuncular deposits is, however, 

distinctly unlike members of this order, and the thin parietal deposits evident in specimens of R. brevicameratum 

are more similar to those occurring in members of the 

order Orthocerida. At least one orthocerid family, the Proteoceratidae, also exhibits siphuncle segment decompression with ontogeny and the development of parietal 

endosiphuncular deposits (pi. 13, figs. 7, 8). The uniformly 

developed recumbent septal necks and broad septal 

foramina in Richmondoceras are, however, not typical of 

members of the Proteoceratidae. Siphuncle segments are 

similar to those illustrated (Sweet, 1964) for members of 

the Greenland oceratidae, a problematic group of lower 

and middle Paleozoic orthocerids. Richmondoceras 

seems to lack the thin endosiphuncular linings that are 

described as being characteristic of this group. Until a 

larger suite of more complete specimens of Richmondoceras is collected and studied, the affinities of this 

genus will remain uncertain. Its known shell morphology 

is sufficiently distinct from other Cincinnatian longiconic 

nautiloids to warrant the erection of a new genus.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P71

Etymology.—The genus gets its name from its occurrence in Richmondian strata exposed in southeastern 

Indiana and southwestern Ohio.

RICHMONDOCERAS BREVICAMERATUM NEW SPECIES

Plate 13, figures 1-8

Diagnosis.—Medium to large, slender, gradually 

expanding orthoconic longicone distinguished by its short 

camerae, expanded, compressed, midventral siphuncle 

segments, and weak development of both endosiphuncular and camera! deposits.

Description.—Medium to large (up to 73.5 cm in 

length and 6.5 cm in diameter), slender, gradually expanding (apical angle 6 degrees) orthoconic longicone; circular in section with straight, transverse sutures. Camera! 

chambers short having camera! lengths decreasing with 

ontogeny from one-sixth the diameter of the shell at a 

shell diameter of 20 mm to one-ninth the diameter of the 

shell at a shell diameter of 40 mm. Adoralmost septa in 

large specimens becoming approximate with ontogeny. 

Body chamber long, tubular, at least one-fifth the total 

length of the shell. Aperture unknown. Shell exterior 

apparently smooth.

Siphuncle position ranging from subcentral 

(SPR=0.40) at shell diameters of 20 mm or less, to midventral (SPR=0.25) at shell diameters of 50 mm. Siphuncle 

segments greatly expanded the length of the phragmocone, ranging from highly compressed (SCR=3.0) at a 

shell diameter of 25 mm to compressed (SCR=1.25) at a 

diameter of 50 mm. Segment diameter ranging from onethird the diameter of the shell at shell diameters of 20 mm 

or less to slightly less than one-sixth the diameter of the 

shell at a diameter of 50 mm. Septa! foramina broad, the 

length of the siphuncle, ranging from nearly one-half to 

two-thirds the maximum diameter of the siphuncle. Septal necks cyrtochoanitic, short, recumbent most of the 

length of the phragmocone. Brims becoming free in 

adoral portions of the shell, 45-50 mm in diameter. Connecting rings adnate ventrally to both adapical and adoral 

septa at diameters of 35-40 mm; adnate ventrally to only 

the adapical septum at diameters greater than 45 mm. 

Endosiphuncular deposits consisting of small annuli and 

thin, ventral parietal deposits observed in portions of the 

phragmocone 15 mm or less in diameter. Camera! deposits consisting of hyposeptal and episeptal deposits occurring at shell diameters of 40 mm or less.

Stratigraphic and geographic occurrence.—Saluda 

Formation (Upper Ordovician, Richmondian Stage) and 

its equivalents exposed in Ripley County, Ind., and Preble 

County, Ohio; upper part of the Bull Fork Formation 

(Richmondian), Clinton County, Ohio.

Studied material.—Holotype MU 398T (pi. 13, figs. 1, 

3, 4) from the Whitewater Formation along Laugherty 

Creek, north of Versailles, Ripley County, Ind.; paratype

MU 399T (pi. 13, fig. 2), Saluda Formation along Four-Mile 

Creek, Preble County, Ohio; plus paratypes MU 400T, a 

suite of specimens from the uppermost Bull Fork Formation at the Cowan Lake spillway, Wilmington, Clinton 

County, Ohio (pi. 13, figs. 5-8).

Remarks.—This species is represented by a limited 

number of specimens from the fine-grained limestones of 

the Saluda Formation in southeastern Indiana These 

specimens consist of isolated adoral portions of large 

individuals, often with attached portions of the body 

chamber (pi. 13, figs. 1, 2). Richmondoceras brevicameratum is, however, most abundant in the interbedded blue 

clay shale and thin fossiliferous wackestone of the uppermost Bull Fork Formation exposed in the vicinity of Wilmington, Clinton County, Ohio. Specimens typically consist 

of incomplete matrix-filled, occasionally calcite-replaced 

internal molds representing portions of the phragmocone 

and isolated, often crushed body chambers (pi. 13, figs. 5- 

8). Specimens from the Cowan Lake locality are often 

covered with holoperipheral encrustations of the sponge 

Dermatostroma. These specimens occur in association 

with similarly preserved specimens of the orthocerid 

Treptoceras, the endocerid Cameroceras, and rare specimens of the large oncocerid Diestoceras (pi. 21, fig. 4). 

This low-diversity nautiloid fauna occurs in mud-rich 

facies deposited in shallow-marine, mud-bottom environments that supported thickets of small, twiglike ramose 

bryozoans. Also abundant are the orthid brachiopod 

Hebertella, the pelecypods Ischyrodonta, Pseudocolpomya, and Caritodens, the large asaphid trilobite Isotelus, and large numbers of the ornate ostracode 

Drepanetta richardsoni.

Richmondoceras brevicameratum can be distinguished from the externally similar, slender, gradually 

expanding longiconic orthocerid Treptoceras fosteri 

(Miller) (pi. 6, figs. 4, 5, 7, 8) by its more expanded, 

broader diameter siphuncle segments. In southwestern 

Ohio, specimens of T. fosteri are most common near the 

base of the "Liberty biofacies" in the Bull Fork Formation, 

whereas specimens of R. brevicameratum appear to be 

restricted to the uppermost portions of the same formation. A comparison of the morphological features of R. 

brevicameratum and T. fosteri is presented in figure 19.

Richmondoceras brevicameratum is a locally common species characteristic of upper Richmondian shallow-marine facies across the northern periphery of the 

Kentucky-Indiana-Ohio region. Currently, the species is 

known only from fragmentary specimens that, however, 

allow for a composite reconstruction of almost the entire 

shell greater than 15 mm in diameter. A larger suite of 

more complete specimens preserving the adapical portions of the phragmocone, the siphuncle segments, and 

their internal features are needed to more fully determine 

the systematic affinities of this species and this genus.
P72 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

6 i-

_j^ 3 

< ^

QC =!

LU ^ 2

10 20 30 40 50 

SHELL DIAMETER, IN MILLIMETERS

60

9i 2 

en B

0 10 20 30 40 50 

SHELL DIAMETER, IN MILLIMETERS

FIGURE 19.—Bivariate plots of camera! length versus shell 

diameter, A, and siphuncle diameter versus shell 

diameter, B, for specimens of Richmondoceras 

brevicameratum (circles) and Treptoceras fosteri 

(triangles) from the upper part of the Bull Fork 

Formation in southwestern Ohio. Specimens of R. 

brevicameratum from locality OH-10, Clinton County, 

Ohio. Specimens of T. fosteri from locality OH-7, 

Warren County, Ohio, and locality OH-11, Clinton 

County, Ohio. Note the uniformly larger siphuncle 

diameters typical of specimens of R. brevicameratum.

Etymology.—The species name denotes the uniformly short nature of the camera! chambers, which run 

the length of the phragmocone in this form.

SUBCLASS ENDOCERATOIDEA TEICHERT

Medium-size to very large (up to 6 m in length) orthoconic longicones and, less commonly, brevicones, both 

with large tubular, generally ventral siphuncles. Septal 

necks may be short in primitive forms, becoming elongate 

holochoanitic or macrochoanitic in younger taxa. Connecting rings primitively thick, becoming thin, lining the 

inner surfaces of septal necks in younger forms. Buoyancy regulation via calcareous ballast in the form of telescoping inverted cones (endocones) concentrated in the 

apical portions of the siphuncle and pierced by a narrow, 

open endosiphuncular tube. Cameral deposits absent.

Stratigraphic range.—Lower Ordovician to Lower 

Silurian.

ORDER ENDOCERIDA TEICHERT

Features of the subclass.

Stratigraphic range.—Lower Ordovician to Lower

Silurian.

FAMILY ENDOCERATIDAE TEICHERT

Straight, large to extremely large longiconic shells 

having large ventral siphuncles that are generally from 

one-third to two-thirds the diameter of the shell. Septal 

necks holochoanitic or macrochoanitic with thin connecting rings that form linings on the inner surfaces of septal 

necks. Apical portions of the siphuncle inflated in some 

forms, occasionally filling the entire apical portion of the 

shell. Endosiphuncular structures generally consisting of 

the endosiphuncular tube and simple blades.

Stratigraphic range.—Lower Ordovician (upper 

Ibexian Provincial Series) to Lower Silurian (Wenlockian 

Series).

Remarks.—Flower (1955a) noted some of the problems surrounding the classification and identification of 

members of this group. The fragmentary nature of most 

described species results in a lack of knowledge of the 

morphology of the entire shell, leading to a profusion of 

names, each representing a particular portion of the same 

organism. Equally problematic is the tendency for the 

endosiphuncles to be completely recrystallized during 

diagenesis, often obliterating the critical structures 

within. These critical structures are the shape and form of 

the endocones, the position and cross-sectional shape of 

the endosiphuncular tube, and the number and configuration of radial plates, termed "blades." The conservative 

nature of members of this family also make classification 

and identification difficult, most taxa being long ranging 

and exhibiting similar, simple endosiphuncular structures. All of these problems plague the present study, 

especially the diagenetic alteration of the endosiphuncle 

and the fragmentary nature of most endoceratid material, 

leading to the tentative identification of most of these 

specimens.

Endocerids have not previously been described from 

the Middle Ordovician High Bridge Group and the Lexington Limestone in Kentucky and equivalent strata in Tennessee. Large endocerids have been described in a 

general sense from the overlying Cincinnatian Provincial 

Series in the area. Flower (1946) presented a review of 

the described taxa from the region. Most of these specimens have traditionally been referred to one of several 

large species of "Endoceras" described by Hall (1847) 

from late Middle Ordovician (Shermanian) strata in New 

York. A majority of these species are currently inadequately known. The morphology of the best known of 

these species, Endoceras proteiforme Hall, is discussed 

below.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P73

GENUS CAMEROCERAS CONRAD

Type species.—Cameroceras trentonense Conrad, 

1842, p. 267, by original designation; Trenton Limestone, 

Shermanian Stage, Middle Ordovician, New York.

Description.—Large to extremely large (up to 6 m in 

length) orthoconic longicones with circular to slightly 

depressed cross sections and straight, transverse sutures. 

Slight ventral lobe developed in some species. Camera! 

chambers typically short, from one-fourth to one-tenth 

the diameter of the shell, the camera! length decreasing 

with ontogeny relative to shell diameter. Body chamber 

large, up to one-third the total length of the shell; aperture 

simple, transverse. Periphract dorsomyarian. Shell exterior smooth. Dorsum marked by longitudinal color bands.

Siphuncle large, tubular, diameter up to 60 percent 

the diameter of the shell adorally; typically ventral in position, less commonly removed from the ventral shell margin. Septal necks holochoanitic; foramina broad, equal to 

the maximum width of siphuncle tube. Connecting rings 

narrow, extending from the tip of one septal neck adapically to that of the next. Endocones simple; endosiphuncular tube narrow, circular to depressed, elliptical in 

cross section, central to ventral in position. Number and 

configuration of endosiphuncular blades poorly known, 

reported to consist of three blades. Apical end of the 

siphuncle gradually tapering to an acute apex, well 

marked to the apical tip by septal "annuli." Siphuncle is a 

little more than one-third the diameter of the shell at this 

point.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Whiterockian Provincial Series) to Lower Silurian (Wenlockian Series), Laurentia, Baltica, Siberian 

Platform.

Remarks.—There has been much confusion concerning the relationship of this genus, based on the apical end 

of a large endocerid from the Trenton Limestone (Middle 

Ordovician) of New York, and the genus Endoceras Hall, 

which is based on more adoral portions of a large 

endocerid from the same strata. A good discussion of 

these taxa was presented by Flower (1955a). It has been 

suggested by a number of authors that Cameroceras trentonense Conrad, the type species of Cameroceras, was 

the apical end of one of the large endocerid species 

described by Hall in 1847. Since Conrad's genus was 

described in 1842, his name would have priority over 

Endoceras Hall, which would become a junior synonym 

of Cameroceras. Hall, however, did not designate a type 

species for his genus. Subsequently, Miller (1889) designated Endoceras annulatum Hall as the type species of 

Endoceras. This species differs from other large endocerids from the Trenton Limestone in possessing an annulated exterior. These annulated species, placed in the 

genus Cyclendoceras by Grabau and Shinier (1910), are 

properly referred to as true Endoceras Hall. Similar large

endocerids with smooth shell exteriors are currently 

placed in the genus Cameroceras Conrad.

Flower (written commun., 1981) indicated that 

Endoceras is most typical of the Lowville and Black River 

Limestones in New York, where it is uncommon in 

younger (Kirkfieldian and Shermanian) strata. The genus 

is also widespread in the Platteville Formation or Group 

(Blackriveran and Rocklandian) of the upper Mississippi 

valley region and in the Upper Ordovician Red River Formation and its equivalents in Western and Arctic North 

America Cameroceras is the common large endocerid in 

the Trenton Group (Kirkfieldian and Shermanian) in New 

York and adjacent states, and in younger Cincinnatian 

strata in Eastern North America (Frey, 1989). Gil (1988) 

has described and illustrated what appear to be the earliest representatives of Cameroceras from the early Middle 

Ordovician (Whiterockian) Juab Limestone of Utah.

The critical internal features of the siphuncle are 

poorly documented for Cameroceras. Conrad's (1842) 

original description of the genus was brief: "Straight, 

siphuncle marginal; longitudinal septum, forming a roll or 

involution with the margin of the siphuncle." Foerste 

(1924b) described Cameroceras, based on C. trentonense, 

as having short, rapidly tapering oblique endocones, the 

straight ventral part being in contact with the ventral wall 

of the siphuncle and the endocones being asymmetrical 

about the central axis of the siphuncule, thicker dorsally 

than ventrally. He described the endocones of Endoceras 

proteiforme Hall as being long, few in number, free from 

contact with the siphuncle wall, and symmetrical about 

the central axis of the siphuncle. Flower (1955a) 

described the siphuncular structure in E. proteiforme as 

consisting of endocones, neither short nor widely spaced, 

the endosiphuncular tube circular in section, situated 

close to the ventral wall of the siphuncle. The latter is the 

condition described for Cameroceras by Foerste. Flower 

reiterated the suggestion by Sardeson (1930) that Cameroceras trentonense and the various Trenton Group species of Endoceras described by Hall were different 

portions of the same nautiloid. Flower noted that endosiphuncular blades were not clearly preserved in these 

forms due to coarse recrystallization of the siphuncle. In 

the same paper, however, he illustrated (Flower, 1955a, 

fig. 2J) a cross section stated to represent the endosiphuncular structure typical of several Trenton Group species of "Endoceras." In these species the endosiphuncular 

tube is highly elliptical and supported by three blades. In 

his review of Chazyan and Mohawkian endocerids, 

Flower (1958) described the endosiphuncular tubes of 

several species of uEndoceras" (=Cameroceras of this 

report) as being depressed, elliptical in cross section, terminating in the ventral half of the siphuncle. Flower 

(1958) also indicated that Cyclendoceras Grabau and 

Shinier (=true Endoceras) consists of large, straight shells
P74 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

with variably developed, raised, transverse annuli and 

large siphuncle situated close to the ventral margin of the 

shell. Septal necks were described as being holochoanitic; 

endocones subcircular, terminating in a central endosiphuncular tube. Endosiphuncular blades were not known 

for the genus nor was the apical end of the siphuncle, 

although Flower speculated that the apical end in this 

genus was of the Nanno type, inflated apically to fill the 

apical end of the shell. Recent collections of specimens of 

Endoceras from the Upper Ordovician Beaverfoot Formation in British Columbia have confirmed this speculation. 

More recent descriptions of these later Ordovician 

Endoceratidae are limited. Gil (1988) described and illustrated three species of Cameroceras from Whiterockian 

strata in Utah, some forms of which have slightly compressed cross sections and simple endocones that terminate in either centrally or ventrally positioned 

endosiphuncular tubes. Blades could not be distinguished 

due to coarse recrystallization. Frey (1983, 1988) 

described and figured Cameroceras cf. C. inaequabile 

(Miller) from the Upper Ordovician (Richmondian) of the 

Cincinnati area. This species is known from isolated 

recrystallized siphuncles and complete, if extensively 

crushed, shells up to 1 m in length, which include the 

body chamber and apical end of the shell. The siphuncle 

is large, situated close to the ventral margin of the shell, 

constituting 30 percent of the diameter of the shell at the 

apex and expanding to nearly 60 percent the diameter of 

the shell at adoral diameters in excess of 80 mm. Septal 

necks are holochoanitic. Endocones are somewhat 

retarded in their development, consisting of long, thin 

cones that terminate in a central endosiphuncular tube 

that becomes depressed, elliptical in cross section adapically. Clearly, better preserved, more complete material is 

critical to developing a more rigorous definition of Cameroceras as well as other members of the Endoceratidae.

CAMEROCERAS ROWENAENSE NEW SPECIES

Plate 14, figures 1,2; figure 21A

Diagnosis.—Moderately expanding species of Cameroceras distinguished by a siphuncle that is removed 

from the ventral margin of the shell adorally and which 

has a subcentral endosiphuncular tube whose axis is situated midway between the center and the venter.

Description.—Medium-sized (portions of phragmocone up to 70 cm in length and shell diameters up to 8.0 

cm), moderately expanding (apical angle 7.5-8 degrees) 

orthoconic longicones; circular to slightly depressed in 

cross section with straight, transverse sutures. Cameral 

chambers short, cameral lengths one-sixth the diameter 

of the shell at a diameter of 55 mm and one-ninth the 

diameter of the shell at a shell diameter of 75 mm. Body 

chamber unknown. Shell exterior basically smooth, 

marked by fine transverse growth lines.

Siphuncle large and tubular, removed from the ventral margin of the shell by a distance of 4-7 mm in shell 

sections that are 50-75 mm in diameter. Siphuncle makes 

up from one-third to slightly over half the total diameter 

of the shell, increasing in diameter relative to shell diameter with ontogeny. Siphuncle circular in cross section 

adapically, becoming depressed in section adorally, 

slightly wider than high. Septal necks holochoanitic. 

Mural portions of septa extending one-third to one-half 

the length of the cameral chamber. Connecting rings 

short, forming thin linings on the inside of septal necks. 

Endocones present at shell diameters up to 55 mm. Cones 

asymmetrical and having endosiphuncular tube subcentral; axis of tube situated nearly midway between the center and the venter. Dorsal endocone thickness roughly 

twice the thickness of ventral portions. Apical end of 

siphuncle unknown.

Stratigraphic and geographic occurrence.—Leipers 

Limestone (Upper Ordovician, Maysvillian Stage part), 

Cumberland River valley and tributary streams, Russell 

County, Ky. Older fragmentary material from the "Cynthiana Limestone" at Cynthiana, Ky, in the Shideler Collection at Miami University may also be assignable to this 

species.

Studied material.—Holotype MU 266T (pi. 14, figs. 1, 

2) and four paratypes (MU 267T, A-D), plus several other 

less complete, fragmentary specimens, Shideler Collection location number 3.51 B2, exposures along the Cumberland River, opposite Belk Island, near Rowena, Ky.

Remarks.—The type specimens of C. rowenaense 

were discovered among specimens stored in the vault at 

the Department of Geology, Miami University, Oxford, 

Ohio. Stored with the specimens were several USNM 

labels written by A.F. Foerste, listing these specimens as 

co-types A-63M and A-63N. The name applied to these 

specimens by Foerste was Endoceras rowenaense. These 

specimens were apparently awaiting description by Foerste when he died in the late 1930's. Foerste's proposed 

name is retained here for this species.

Cameroceras rowenaense is most similar to one of 

several species described by Hall (1847) as Endoceras 

proteiforme. Hall's specimens were from the Trenton 

Limestone (Middle Ordovician, Shermanian) at Middleville, N.Y. Hall did not designate type specimens for E. 

proteiforme. Foerste (1924b) indicated that typical E. 

proteiforme was represented by material Hall illustrated 

on his plates 48-50, 53, and 57. Foerste selected the original of figure 4 on plate 48 as the lectotype of the species 

and listed the specimens figured on plate 49 as "co-types." 

Foerste's figures and text indicate that he placed two distinct forms under the name E. proteiforme. The lectotype 

and a "co-type," both at the AMNH, are gradually expanding longicones (apical angle 6 degrees) with dorsally 

located endosiphuncular tubes (Foerste, 1924b, pi. 21,
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P75

figs. 1, 3; pi. 22, fig. 1; pi. 23, fig. LB). A second "co-type" 

(also at the AMNH) is a more rapidly expanding specimen 

(apical angle 8.5 degrees) with a ventrally located endosiphuncular tube (Foerste, 1924b, pi. 21, fig. 2; pi. 23, fig. 2). 

This latter form is the same figured by Flower (1958, pi. 

60, fig. 6) and identified by him as E. proteiforme from the 

"Denmark Member of the Sherman Fall Limestone" at 

Trenton, N.Y. The rapid expansion of shells of this type is 

similar to that illustrated for specimens of Cameroceras 

trentonense Conrad (AMNH 815; Hall, 1847, pi. 56, figs. 

4a-c; Foerste, 1924b, pi. 24, figs. 1, 2A-E) from the same 

strata. The more rapidly expanding forms with ventral 

endosiphuncular tubes are placed here in C. trentonense 

Conrad, and the more gradually expanding species with 

dorsal endosiphuncular tubes are retained in C. proteiforme (Hall). Endoceras magniventrum Hall (1847, pi. 53, 

fig. LB) is thought to represent the adoral portion of a 

large specimen of C. trentonense and is placed in synonymy with this species.

Cameroceras rowenaense is most similar to the species identified here as C. trentonense Conrad, both taxa 

having moderate to rapidly expanding shells (apical 

angles 8-9 degrees) and a siphuncle with asymmetrical 

endocones that have ventrally located endosiphuncular 

tubes. Cameroceras rowenaense differs from C. trentonense in possessing a smaller diameter siphuncle (onethird the diameter of the shell at a diameter of 50 mm) 

that is subcentral in position (SPR=0.30) compared with 

the broader (half the diameter of the shell), nearly midventral (SPR=0.26) siphuncle present in C. trentonense at 

the same diameter. The endosiphuncular tube in C. rowenaense is also removed from the ventral margin of the 

siphuncle, compared with its more marginal position in C. 

trentonense at the same diameter. A comparison of the 

cross sections of these two species at a diameter of 55 

mm is presented in figure 20. In addition, the camerae in 

C. rowenaense are somewhat shorter than those of C. 

trentonense at the same shell diameters. A comparison of 

cameral lengths relative to shell diameter for these two 

species is presented in figure 21. A silicified siphuncle 

from USGS collection 4073-CO in the Grier Limestone 

Member of the Lexington Limestone at Tyrone, Woodford 

County, Ky., may be assignable to C. trentonense (USNM 

468712, pi. 14, figs. 3, 4).

Cameroceras rowenaense is also similar to C. 

inaequabile (Miller) from younger Richmondian strata in 

the Kentucky-Indiana-Ohio area in its rate of shell expansion, the relative diameter of the siphuncle to the diameter of the shell, and the short length of cameral chambers. 

It is distinct from C. inaequabile in the more central position of the siphuncle and more ventral position of the 

endosiphuncular tube in C. rowenaense (compare figs. 

2QA and 20C7). A comparison of the morphological feaB

FIGURE 20.—Scale drawings comparing cross-sectional 

features of species of Cameroceras from Middle and 

Upper Ordovician strata in Eastern North America, Sections all from specimens 55-60 mm in diameter. 

A, Cameroceras rowenaense, MU 266T, Leipers Limestone (Maysvillian), Rowena, Ky.; B, C. trentonense, figured by Flower (1958, pi. 60, fig. 6), Sherman Fall 

Limestone, Trenton Falls, New York; C, C. inaequabile, 

MU 171, Bull Fork Formation, Warren County, Ohio.

tures of all three of these species of Cameroceras is presented in table 9.

Cameroceras rowenaense is distinguished from the 

large endoceratid described here from the Bull Fork Formation in Bath County, Ky. (pi. 14, figs. 5, 6) in its more 

rapid rate of shell expansion and in the macrochoanitic 

septal necks observed in the latter species. These elongate septal necks are distinct from the holochoanitic septal necks characteristic of C. rowenaense and other more 

typical species of Cameroceras.

As indicated above, C. rowenaense is currently 

known from the Leipers Limestone exposed in the valley 

of the Cumberland River in Russell County, Ky. Specimens 

typically consist of incomplete calcite-replaced internal 

molds representing portions of the phragmocone between 

50 and 75 mm in diameter and often holoperipherally 

encrusted by the bryozoan AtactoporeUa. These specimens occur in an olive-colored fossiliferous wackestone 

that weather slight gray. The limestone contains large 

algal oncolites (see pi. 14, fig. 1) and is extensively bioturbated. Associated species are a small, geniculate species 

of the brachiopod Rafinesqina, the elongate, compressed 

pelecypod Orthodesma, trilobites, and ostracodes. A list 

of associated nautiloid taxa can be found in the work of 

Flower (1946).
P76 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

15

10

50 60 70

SHELL DIAMETER, IN MILLIMETERS

80

50 r

40

20

B

50 60 70

SHELL DIAMETER, IN MILLIMETERS

80

FIGURE 21.—Bivariate plots of camera! length versus shell 

diameter, A, and siphuncle diameter and shell diameter, B, 

for species of Cameroceras from the Ordovician of New 

York and Kentucky. Species are C. rowenaense (triangles) 

from the Leipers Limestone, Rowena, Ky. (MU 266T and 

267T), and C. trentonense (circles) from the Trenton 

Limestone, Middleville, N.Y. (Hall, 1847).

CAMEROCERAS? SP.

Plate 14, figures 5, 6

Diagnosis.—Large, gradually expanding endoceratid known from adoral portions of the phragmocone and 

distinguished by short camera! chambers one-tenth the 

diameter of the shell, a dorsally depressed siphuncle that 

constitutes two-thirds the total diameter of the shell, and 

septal necks that are macrochoanitic.

Description.—Large (phragmocone estimated to 

have been up to 1 m in length at a maximum observed 

shell diameter of 8.2 cm), gradually expanding (apical 

angle 6 degrees) orthoconic longicone; circular to slightly 

depressed in cross section with straight, transverse 

sutures. Camera! chambers short having camera! lengths 

ranging from one-eighth to one-tenth the diameter of the 

shell at shell diameters between 70 and 80 mm. Body 

chamber unknown. Shell exterior essentially smooth, 

marked by numerous closely spaced, fine, transverse 

growth lines.

Siphuncle large and tubular, removed from the ventral shell margin by a distance of 7-9 mm. Siphuncle

TABLE 9.—Comparison of the morphological features of the 

Middle Ordovician (New York) and Upper Ordovician species 

of Cameroceras from the Cincinnati arch region of Kentucky, 

Indiana, and Ohio

[Data from specimens of C. trentonense figured by Hall (1847), type 

specimens of C. rowenaense (MU 266T, 267T), and specimens of C. 

inaequabile from the T. duseri shale in Warren County, Ohio (MU 

17165). CL/D, ratio of camera! length to shell diameter; SPR, siphuncle segment position ration; SD/D, ratio of siphuncle diameter to 

shell diameter; EP, endosiphuncle tube position within siphuncle; 

mm, millimeter]

Feature C. trentonense C. rowenaense

C. 

inaequabile

Apical angle, degrees 

Diameter 50-55 mm

8.5-9 7.5-8 7-8

CL/D

SPR

SD/D

EP

.18

.26

.56

Ventral

.12

.30

.36

Midway

between

center and

venter.

.14

.22

.22

Center

depressed ovate in section, wider than high, becoming 

more flattened dorsally with ontogeny. Siphuncle constitutes two-thirds the total diameter of the shell at shell 

diameters of 70-80 mm. Septal necks long, macrochoanitic, their distal ends extending 2-3 mm beyond the 

adoral face of the adjacent adapical septum, and overlapping for this distance. Connecting rings absent 

Endocones unknown. Nature of endosiphuncular structures unknown. Apical end of siphuncle unknown.

Stratigraphic and geographic occurrence.—Upper 

part of the Bull Fork Formation (Upper Ordovician, Richmondian Stage), Bath County, Ky.

Studied material.—USNM 468713 (pi. 14, figs. 5, 6) 

from the Bull Fork Formation, 50 ft below the contact 

with the Drakes Formation, exposed at a roadcut at the 

junction of 1-64 and State Route 36, Owingsville, Ky.

Remarks.—This species is represented by the adoral 

portion of a large endoceratid, 125 mm in length and from 

70 to 80 mm in diameter. The specimen has the general 

attributes of a species of Cameroceras, the most abundant endoceratid in Upper Ordovician strata exposed in 

the Kentucky-Indiana-Ohio area. This species, however, is 

distinct from all other specimens of Cameroceras known 

to the writer, in the nature of its septal necks, which are 

macrochoanitic rather than holochoanitic, as is typical of 

other members of the genus. Other endoceratids with 

macrochoanitic septal necks are Hudsonoceras Flower, 

Kutorgoceras Balashov, Protovaginoceras Ruedemann, 

and Wittiamsoceras Flower, all genera that are restricted
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P77

to lower Middle Ordovician strata in North America, Baltic Europe, and portions of Soviet Asia. The affinities of 

this Kentucky specimen remain tentative, pending the discovery of more complete specimens, especially specimens preserving the critical apical portions of the 

siphuncle, providing knowledge of the endocones and 

other endosiphuncular structures.

GENUS VAGINOCERAS HYATT

Type species.—Endoceras multitubulatum Hall, 

1847, p. 59; designated by Hyatt, 1884, p. 266; Black River 

Limestone, Blackriveran Stage, Middle Ordovician, New 

York.

Description.—Large orthoconic longicones of circular to slightly depressed cross section with straight, transverse sutures. Shell surface essentially smooth. Nature of 

body chamber unknown.

Siphuncle large, tubular, about one-third the diameter of the shell, situated slightly removed from the ventral 

shell margin. Siphuncle slightly wider than high in cross 

section, no ventral flattening. Septal necks holochoanitic, 

internally lined with thick connecting rings. Endocones 

compressed to cuneate in cross section, having two vertical endosiphuncular blades. Endosiphuncular tube central in position, compressed or cuneate in cross section. 

Siphuncle gradually tapering to an acute apex, not 

strongly inflated adapically

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Blackriveran to Kirkfieldian Stages), North 

America (Laurentia) and Baltic Europe.

Remarks.—Flower (1955a) provides a good description of this genus. He pointed out that, on the basis of 

gross shell morphology alone, there are no significant differences between this genus and Cameroceras Conrad. 

The only differences noted were in the shape and structure of the endocones and endosiphuncular tube, which 

are depressed, elliptical in Cameroceras and compressed 

and cuneate in Vaginoceras. Another distinction is in the 

nature of the endosiphuncular blades. Vaginoceras has 

two vertical blades, and Cameroceras was stated by 

Flower (1955a) to have one vertical blade and two oblique 

blades. Although the apical end of the siphuncle of Vaginoceras was known from only one poorly preserved specimen, Flower described it as being very similar to that of 

Cameroceras. He indicated that the annuli on isolated 

siphuncles would be less evident in their development 

compared with those of Cameroceras due to the thicker 

connecting rings in Vaginoceras. Unless endosiphuncular 

structures are preserved, it is evident that distinguishing 

these two genera would be difficult, if not impossible.

Vaginoceras is stated by Flower to be characteristic 

of Blackriveran and Rocklandian nautiloid faunas in Eastern North America but absent from the underlying 

Chazyan and overlying Shermanian strata. In these Blackriveran strata, Vaginoceras is associated with less abundant species of Endoceras Hall. Cameroceras becomes 

the dominant large endoceratid in younger Shermanian 

and Richmondian rocks in the same region. For the purposes of this paper, poorly preserved, large endoceratids 

from the High Bridge Group in central Kentucky are 

placed in Vaginoceras. Similarly preserved material from 

younger Middle and Late Ordovician strata in the area will 

be placed in Cameroceras.

VAGINOCERAS SP. A

Plate 15, figures 1-4; 8-12

Diagnosis.—Slender, gradually expanding species of 

Vaginoceras, distinguished by an external shell marked 

by narrow, raised, transverse bands and possessing only a 

slightly inflated siphuncle apex marked by low but distinct septal annuli.

Description.—Medium to large (estimated shell 

lengths up to 90 cm and maximum observed shell diameters of 6.5 cm), gradually expanding (apical angle 5.5 

degrees) orthoconic longicones; circular in section with 

straight, transverse sutures. Camera! chambers short, 

camera! lengths averaging one-seventh the diameter of 

the shell at shell diameters of 45-55 mm. Body chamber 

tubular, at least one-sixth the total length of the shell. 

Shell exterior marked by indistinct, narrow, raised transverse bands 1-2 mm in width.

Siphuncle large, tubular, one-third the diameter of 

the shell at shell diameters of 45-55 mm. Siphuncle 

removed from ventral shell margin by a distance of 5 mm 

(SPR=0.265, nearly midventral). Septal necks holochoanitic, connecting rings unknown. Adapical portions of 

siphuncle slender, tubular (10 mm in diameter), circular 

in cross section, expanding adapically to a maximum 

diameter of 13 mm at 10-20 mm adoral of the siphuncle 

apex. Apex acute, apical tip narrowly rounded. Apical end 

marked by low, rounded "septal annuli," 4-5 mm wide, 

sloping from the dorsum to the venter in the adoral direction, annuli becoming obsolete ventrally. Adapically, 

endosiphuncular structures are the dorsal and ventral vertical blades and a compressed, central endosiphuncular 

tube 1 mm in diameter that extends to the very tip of the 

apex.

Stratigraphic and geographic occurrence.—Upper 

part of the Rocklandian portion of the Tyrone Limestone 

(Middle Ordovician), Jessamine County, Ky

Studied material.—USNM 158668 (pi. 15, figs. 1-4), 

USNM 158652 (pi. 15, figs. 8-10), USNM 468714 (pi. 15, 

figs. 11, 12), plus a suite of four additional specimens 

(USNM 468715), all from the USGS 6034-CO collection, 

Little Hickman section A, Jessamine County, Ky. Additional material consists of a silicified siphuncle (MU 

29868) from the Tyrone Limestone at High Bridge, Ky.
P78 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

Remarks.—This endoceratid is represented in the 

silicified USGS 6034-CO collection by a single camerated 

portion of the phragmocone and attached portions of the 

body chamber, 23 cm in total length, diameters of 45-65 

mm (USNM 158668 (pi. 15, figs. 1-4), plus a number of 

apical portions of the siphuncle (pi. 15, figs. 8-12). It is 

thought that these fragmentary specimens represent a single endocerid species, although intervening portions of 

the shell are not known. The adoral portion of the phragmocone might just as easily be assigned to Cameroceras 

because the endosiphuncular structures are not preserved in this specimen. The apical ends of the siphuncle, 

while having the external shape of Cameroceras, preserved some key diagnostic features of Vaginoceras: dorsal and ventral vertical blades with a narrow diameter and 

a compressed central endosiphuncular tube. This Tyrone 

Limestone material demonstrates clearly that the apical 

ends of the siphuncle in Vaginoceras are, as suggested by 

Flower, of the Cameroceras type, slightly expanding and 

then tapering to an acute tip and having camerae extending adapically to the very apex of the siphuncle.

Comparisons with other described species of Vaginoceras are difficult due to the incomplete nature of the 

Kentucky material and the equally incomplete nature of 

other published species. Flower (1955b) recognized only 

two species in Vaginoceras: the type species V multitubulatum (Hall) and V. longissimum (Hall), both from the 

Black River Limestone in New York. Both species are 

known from isolated siphuncles that contained 

endocones. Troedsson (1926, pis. 3-5) described and figured a number of fragmentary siphuncles he assigned to 

Hall's species and to uVaginoceras species indeterminate I 

and II," all from the basal Cape Calhoun Formation (Middle Ordovician, Blackriveran) in northern Greenland. Species he referred to as uEndoceras species indeterminate I" 

(Troedsson, 1926, pi. 5, figs. 3, 4; pi. 6, fig. 2) and#. proteiforme Hall (Troedsson, pi. 6, fig. 2) are also from the 

basal portion of the Cape Calhoun Formation and also 

appear to be species of Vaginoceras. The latter species is 

represented by a portion of the phragmocone 14 cm in 

length and 6.5 cm in diameter and having camera! lengths 

one-ninth the diameter of the shell.

The preserved Tyrone Limestone material is more 

closely comparable with Vaginoceras sp. described by 

Stait (1988, pi. 2, figs. 10,11) from the Lourdes Formation 

(Middle Ordovician, upper Blackriveran) exposed in 

western Newfoundland. The figured portion of the phragmocone measures 70 mm in length and has a gradual rate 

of shell expansion, camera! lengths averaging one-sixth 

the diameter of the shell, and siphuncle diameters roughly 

one-third the diameter of the shell, both at shell diameters 

of 50 mm.

Sweet (1958) described and figured Vaginoceras sp. 

from the Middle Ordovician "Cephalopod Shale" in Norway. His figured specimen (Sweet, 1958, fig. 3; pi. 1, fig. 4) 

represented a portion of the phragmocone that ranged 

from 32 to 35 mm in diameter. Camera! lengths ranged 

from one-fifth to one-seventh the diameter of the shell. 

The apical angle is 6.5 degrees. No comparable material at 

these shell diameters is present in the 6034-CO collection 

from Kentucky.

VAGINOCERAS SP. B

Plate 15, figures 5-7

Diagnosis.—Slender, gradually expanding section of 

siphuncle, circular in cross section, having centrally 

located compressed cuneate endosiphuncular tube and 

dorsal and ventral vertical blades.

Description.—Slender, gradually expanding (apical 

angle 4 degrees), tubular section of siphuncle 9.0 cm in 

length, adoral diameter 20 mm and adapical diameter 17 

mm. Siphuncle tube circular in cross section. Adorally 

with a laterally compressed tube 8 mm wide and 16 mm 

high that tapers rapidly adapically to a point separating 

dorsal and ventral vertical blades. Siphuncle surface 

smooth, no evidence of "septal annuli."

Stratigraphic and geographic occurrence.—Basal 

Curdsville Limestone Member of the Lexington Limestone 

(Middle Ordovician, Kirkfieldian Stage), Frankfort area, 

Franklin County, Ky.

Studied material.—USNM 468718 (pi. 15, figs. 5-7) 

from the USGS 5072-CO collection, Old Crow Distillery, 

Frankfort East B section.

Remarks.—Little can be inferred from this specimen 

beyond that the preserved endosiphuncular structures 

indicate that it is a species of Vaginoceras. The preserved 

portion of the siphuncle cannot be compared with the 

more adoral and adapical sections known for the preceding Tyrone Limestone species of Vaginoceras. The more 

gradual rate of expansion suggests this siphuncle may 

come from a more slender species of Vaginoceras, distinct from the Tyrone Limestone form. This specimen is 

significant in that it extends the range of Vaginoceras into 

the Kirkfieldian.

GENUS TRIENDOCERASYLOWER

Type species.—Triendoceras montrealense Flower, 

1958, p. 453, by original designation; "Chazy Beds," 

Chazyan Stage, Middle Ordovician, Quebec.

Description.—Large, gradually expanding orthoconic longicones that are slightly depressed in cross section. Venter broadly rounded, no conspicuous midventral 

flattening. Sutures straight, transverse, camera! lengths 

uniformly short in known portions of the phragmocone. 

Body chamber unknown. Shell surface apparently 

smooth.

Siphuncle situated at the ventral shell margin, tubular, enlarging with ontogeny from diameters one-third the
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P79

diameter of the shell adapically to one-half the diameter 

of the shell adorally. Siphuncle depressed ovate in cross 

section, wider than high. Septal necks holochoanitic with 

thin, narrow connecting rings. Endocones short. Endosiphuncular tube having the cross sectional shape of an 

isosceles triangle, and having the broad, slightly rounded 

convex base close to the dorsal wall and the apex 

directed ventrally. Endosiphuncular tube situated dorsally 

within the siphuncle. Apical end of the siphuncle 

unknown.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Chazyan) to Upper Ordovician (Edenian? 

Stage), Eastern North America (Laurentia).

Remarks.—This genus is based on two rather poorly 

preserved fragmentary phragmocones described from an 

early Middle Ordovician limestone unit in Quebec 

(Flower, 1958). Flower's diagnosis of the genus centered 

on the triangular shape of the endosiphuncular tube in 

these specimens, although he failed to illustrate them. 

Specimens were described as being otherwise "typical 

Endoceratidae," similar to Cameroceras and Vaginoceras 

in all other characteristics. Because the endocones were 

replaced with sparry calcite in the type species, there is 

no evidence of the pattern of the endosiphuncular blades 

in this genus.

Flower (1958) also referred to this genus a form 

known primarily from isolated siphuncles that are not 

uncommon in the Upper Ordovician (Edenian) Kope Formation in the Cincinnati, Ohio-Covington, Ky, area. These 

specimens typically consist of "speiss," the preserved 

mud-infilling of the endocones, the rest of the siphuncle 

and the phragmocone being largely unknown. This form 

is tentatively placed in Triendoceras here and is 

described below.

1RIENDOCERAS? DAVISI, NEW SPECIES

Plate 16, figures 1-5

Diagnosis.—Large-diameter, rapidly expanding infillings of the siphuncle that have a distinctive subtriangular 

cross section adapically, having the acute angle directed 

ventrally and the broadly rounded base located dorsally.

Description.—Known primarily from large (up to 40 

cm in length and diameters up to 4.0 cm), isolated molds 

of the siphuncle and endosiphuncular tube (speiss). 

These consist adapically of rapidly expanding (apical 

angle 8-9 degrees), narrow-diameter infillings of the 

endosiphuncular tube that expand from a narrow tube 3 

mm in diameter to a diameter of 35 mm at a length of 80 

mm. Subtriangular cross-sectional shape of endosiphuncular tube at these diameters, having the venter forming 

an acute angle and the dorsum being more broadly 

rounded. Siphuncle infilling becoming more gradually 

expanding (apical angle 4 degrees) adorally, the remainder of the length of the siphuncle. Cross-sectional shape

adorally becoming circular. Adoral portions of the siphuncle bear impressions of the connecting rings; raised rings 

2-3 mm wide that slope from the dorsum to the venter 

in the adoral direction, indicating a ventrally located 

siphuncle.

A portion of the phragmocone, 40 mm in length and 

50 mm in width, indicates cameral lengths at this diameter of one-fifth the diameter of the shell and the presence 

of holochoanitic septal necks. Remainder of the phragmocone and body chamber unknown.

Stratigraphic and geographic occurrence.—Edenian 

part of the Kope Formation (Upper Ordovician), Cincinnati, Ohio, area and ac^acent portions of northern 

Kentucky.

Studied material—Holotype MU 410T (pi. 16, fig. 1) 

and paratype MU 412T (pi. 16, fig. 4) both from the Kope 

Formation at the Orphanage Road locality, Kenton 

County, Ky; paratype MU 41 IT (pi. 16, fig. 2) from the 

same formation at Cincinnati, Hamilton County, Ohio; 

paratype MU 413T (pi. 16, fig. 5) Shideler locality 1.23A8; 

and paratype MU 414T (pi. 16, fig. 3) from the "Fulton 

Beds" at Moscow, Clermont County, Ohio. Numerous 

additional fragments from the Kope Formation in the 

greater Cincinnati area of Ohio and Kentucky were also 

studied.

Remarks.—This species is known primarily from 

matrix infillings of the siphuncle and endosiphuncle tube, 

often referred to as "speiss." Only a single fragment of the 

phragmocone preserving portions of several cameral 

chambers (pi. 16, fig. 4) and the septal necks was available for study. More adoral portions of these infillings 

commonly preserve impressions of the connecting rings, 

consisting of narrow rings 2-3 mm wide that encircle the 

siphuncle and slope from the dorsum to the venter in the 

adoral direction (pi. 16, fig. 1). The features of the phragmocone and endosiphuncle are otherwise unknown. Figure 22 illustrates the relation between the preserved 

speiss and the endosiphuncular structures of the siphuncle. One interesting phenomenon associated with these 

infillings of the siphuncle is the black coating that often 

covers the speiss, possibly indicative of a high organic 

content (conchiolin?) in the enclosing endocones (pi. 16, 

fig. 1).

This writer has elected to erect a new species for this 

form on the bases of the distinctive subtriangular cross 

section of adapical portions of the speiss, the rapidly 

expanding nature of the internal molds, and the restricted 

occurrence of siphuncles of this type to the Kope Formation in the greater Cincinnati region of southwestern Ohio 

and northern Kentucky. Siphuncles assigned to this species cannot be confused with those of any other endoceratid from Upper Ordovician strata in this region. 

Triendocerast davisi is the most commonly encountered 

nautiloid within the Kope Formation in the Cincinnati-
P80 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

FIGURE 22.—Diagrammatic drawing of the siphuncular structure 

in Triendoceras^ davisi. Based on holotype (MU 410T) from 

the Kope Formation, Ft. Mitchell, Ky. (see pi. 16, fig. 1). 

A, Section through adoral portion of siphuncle, circular in 

cross section; B, section through medial portion of siphuncle 

tube, initiation of more triangular cross section; C, adapical 

terminus of endosiphuncular tube with triangular cross 

section. xO.65.

Covington area. It occurs primarily in thin packstone beds 

in association with crinoids, bryozoans, the brachiopods 

Sowerbyella and Zygospira, and the trilobite 

Cryptolithus.

The distinctive subtriangular cross section of the 

endosiphuncular tube in Triendoceras? davisi is similar

to that described by Flower (1958) for the Middle Ordovician (Chazyan) endoceratid Triendoceras. The acute 

angle in cross sections of these Kope endosiphuncular 

tubes is directed ventrally, consistent with Flower's 

description of these features in his specimens of Triendoceras. The affinities of this Edenian species remain 

uncertain, pending discovery of more complete specimens preserving critical portions of the phragmocone as 

well as further study of the type species of Triendoceras 

Flower.

Etymology.—This species is named in recognition of 

the contributions of Richard A. Davis, a fellow student of 

the nautiloid cephalopods and of the paleontology of the 

Ordovician of the Cincinnati, Ohio, region.

SUBCLASS ACTINOCERATOIDEA 1EICHERT

Medium to large orthoconic or slightly curved cyrtoconic longicones, usually depressed in cross section with 

large subcentral or midventral, less commonly marginal, 

siphuncles. Siphuncle segments broadly expanded within 

camerae, diameters commonly between one-third and 

two-thirds the diameter of the shell. Septal necks cyrtochoanitic, often recumbent. Buoyancy regulation provided by calcareous ballast in the form of massive 

endosiphuncular deposits that form in and around a 

branching endosiphuncular vascular system, consisting of 

a central canal, radial canals, and perispatia. Camera! 

deposits typically well developed. Apical end of shell 

short, blunt, terminating in a large, cap-shaped initial segment that covers the apex of the shell.

Stratigraphic range.—Lower Ordovician to middle 

Carboniferous.

ORDER ACTINOCERIDA1EICHERT

Characters of the subclass.

Stratigraphic range.—Lower Ordovician to middle 

Carboniferous.

FAMILY ACTINOCERATIDAE SAEMAN

Large, straight, generally fusiform shells with blunt 

apices, slightly to greatly depressed in cross section, having straight transverse or slightly sinuous sutures. Siphuncle segments large, subcentral to ventral in position, 

segments strongly expanded within camerae. Segments 

often decompressing with ontogeny. Septal necks long 

with comparatively short brims. Endosiphuncular canals 

well developed, of the curved type; remainder of the 

siphuncle filled with endosiphuncular deposits consisting 

of coalesced annulosiphonate deposits. Cameral deposits 

consisting of both episeptal and hyposeptal deposits.

Stratigraphic range.—Middle Ordovician (Blackriveran Stage) to Lower Silurian (Llandoverian Series).
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P81

GENUS ACTINOCERAS BRONN

Type species.—Actinoceras bigsbyi Bronn, 1837, p. 

97, by original designation; Black River Formation, Blackriveran Stage, Middle Ordovician, Thessalon Island, Lake 

Huron, Ontario.

Description.—Large (up to 1 m in length), robust, 

straight to slightly endogastrically curved, rapidly 

expanding fusiform shells; subcircular to moderately 

depressed in cross section with sutures that slope slightly 

in the adapical direction from the dorsum to the venter. 

Camerae short, camera! lengths decreasing with ontogeny. Phragmocone rather short, body chamber nearly onethird the length of the shell, contracting toward the aperture. Maximum shell diameter at the junction of the body 

chamber and the phragmocone. Aperture straight, transverse, open. Shell exterior smooth.

Siphuncle large having maximum diameters up to 

one-half to three-fourths the diameter of the shell. Segments subcentral to midventral in position, having the 

ventral connecting ring in contact with the ventral shell 

wall in many species. Siphuncle typically moving from the 

venter to a more central position with ontogeny. 

Segments strongly expanded within camerae, highly 

compressed in shape. Segments decompressing with 

ontogeny to form equiaxial or depressed globular segments. Septal necks long, recurved, but not recumbent, 

with relatively short brims. Massive endosiphuncular 

deposits consisting of fused annulosiphonate deposits 

that fill most of the siphuncle, leaving a narrow central 

canal and curved, radial, lateral canals in the adapical portions of large individuals. Well developed episeptal and 

hyposeptal camera! deposits.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Blackriveran) to Lower Silurian (Llandoverian), North America, Baltic Europe, and Siberia.

Remarks.—Flower (1957a) divided this genus into a 

number of generalized "species groups." Members of his 

uActinoceras ruedemanni Group" were characterized as 

having straight fusiform shells with depressed cross sections and flattened venters. Sutures have broad ventral 

lobes, and siphuncle segments are large and broadly 

expanded in early stages, becoming smaller in diameter 

with ontogeny. Segments are sinuate in outline, the curve 

of the septal neck being as broadly rounded as the 

expanded portions of the segment (see fig. 23). In 

Flowers "A. centrale Group" were species with closely 

spaced septa, broad, short siphuncles, and the outline of 

the segment more broadly rounded than the contracted 

area at the septal neck. Species assigned to his "A. 

paquettense Group" are described as being essentially 

breviconic; short phragmocones with rarely more than 20 

camerae, compared with the 30-40 present in species 

belonging to the two previous groups. Members of the "A. 

winstoni Group" have slender shells, circular in section,

that are slightly curved adapically. Segments are also narrower in diameter for a much greater length of the siphuncle compared with other species groups.

The first three of Flower's species groups are characteristic of Middle Ordovician (Blackriveran and Rocklandian) carbonate facies exposed in portions of Eastern and 

Central North America It is in these strata that Actinoceras reaches its apogee in terms of abundance and diversity. Members of the A. winstoni Group occur in younger, 

Middle Ordovician (Kirkfieldian and Shermanian) strata 

and are much less abundant than their Blackriveran progenitors. Flower also described two additional species 

groups from younger (Shermanian to Richmondian) carbonates in Western and Arctic North America. These are 

the "A. simplicem Group," characterized by species with 

broad, evenly rounded siphuncle segments in early stages 

having the siphuncle remaining large and ventral with 

ontogeny, but the expansion of the segments within the 

camerae becoming reduced. The largely Upper Ordovician "A. anticostiense Group" is distinguished by siphuncle segments that show a long, tubular adoral region and a 

short adapical region, in which segment expansion is 

abruptly concentrated. The septa have long septal necks 

that terminate in very short brims that are abruptly 

recurved. Flower (1968a) reviewed the early evolution of 

actinocerids.

Species of Actinoceras described from the Kentucky 

Blue Grass region are "Leurorthoceras" altopontense Foerste and Teichert and Actinoceras libanum Foerste and 

Teichert from the Camp Nelson Limestone (Middle Ordovician, Blackriveran); A. altopontense Foerste and 

Teichert, A. arcanum Foerste and Teichert, A. bigsbyi 

Bronn, A. jessaminense Foerste and Teichert, and A. kentuckiense Foerste and Teichert, all from the Tyrone 

Limestone (Middle Ordovician, Rocklandian); and A. 

curdsviUense Foerste and Teichert from the Curdsville 

Limestone Member of the Lexington Limestone (Middle 

Ordovician, Kirkfieldian). Kentucky species of Actinoceras from the Tyrone Limestone are all members of 

Flower's A. ruedemanni Group. Actinoceras curdsvillense from the Lexington Limestone appears to be a member of the A. centrale Group on the basis of its narrowly 

rounded, nearly recumbent septal necks and shallow 

camerae. Most of these Kentucky species of Actinoceras 

were described from fragmentary portions of the phragmocone. This, coupled with a lack of extensive collections of individuals, makes accurate species comparisons 

difficult, especially in light of the pronounced ontogenetic 

changes that are typical of this genus. Species of Actinoceras described below are those that are able to be recognized from additional material collected in the central 

Kentucky region by U.S. Geological Survey and Kentucky 

Geological Survey field crews.
P82 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

ACTINOCERAS ALTOPONTENSE FOERSTE AND TEICHERT, 1930

Plate 16, figure 6; plate 17, figures 6-10

Actinoceras altopontense Foerste and Teichert, 1930, p. 

225, pi. 35, figs. L4-C; pi. 56, fig. 1.

Diagnosis.—Rapidly expanding species of Actinoceras with comparatively short camerae and broadly 

expanded, highly compressed siphuncle segments, in 

which the length of the connecting ring is nearly twice 

that of the septal necks; segments in contact with the ventral shell margin most of the length of the shell.

Description.—Medium-sized (phragmocone lengths 

in excess of 35 cm and shell diameters of up to 7.2 cm), 

rapidly expanding (apical angle 10.5-11.5 degrees) orthoconic longicones, depressed circular in cross section and 

having the venter more flattened than the dorsum, causing sutures to slope from the dorsum to the venter in the 

adapical direction. Sutures forming a broad ventral lobe. 

Cameral chambers short, cameral lengths ranging from 

one-fifth to one-sixth the diameter of the shell, decreasing 

with ontogeny. Body chamber unknown. Shell exterior 

smooth.

Siphuncle subcentral (SPR=0.28-0.33) for the length 

of the siphuncle and having ventral portions of the connecting rings in contact with the ventral shell margin. 

Siphuncle segments highly compressed (SCR=3.7-2.5), 

decompressing only slightly with ontogeny. Segments 

broad, having diameters ranging from two-thirds the 

diameter of the shell at diameters of 30 mm or less, to 

one-half the diameter of the shell adorally In dorsal-ventral profile, connecting rings twice as long as the length of 

the septal necks. Septal necks long, cyrtochoanitic, 

recurved, with short free brims. Siphuncle segments with 

well-developed annulosiphonate deposits that delineate a 

broad, central canal having numerous fine, curved radial 

canals. Cameral deposits not observed in known portions 

of the shell, 30-50 mm in diameter.

Stratigraphic and geographic occurrence.—Upper 

part of the Rocklandian portion of the Tyrone Limestone 

(Middle Ordovician), in the vicinity of the Kentucky River, 

Jessamine County, Ky.

Studied material.—Holotype, USNM 82196, from the 

Tyrone Limestone at High Bridge, Ky; USNM 158640 (pi. 

16, fig. 6), USNM 158641 (pi. 17, figs. 8, 9), 158642 (pi. 17, 

fig. 10), 158646 and 158648, all silicified material from 

USGS collection 6034-CO, Tyrone Limestone, Little Hickman section A, Sulfur Wells, Ky.

Remarks.—Actinoceras altopontense is most similar 

to a group of Blackriveran and Rocklandian species of 

Actinoceras distinguished by their large, rapidly expanding shells and by their broadly expanded siphuncle segments that are typically in contact with the ventral shell 

margin and that consist of connecting rings whose lengths 

are nearly twice the lengths of the septal necks (fig. 23).

Actinoceras altopontense differs from the associated A. 

kentuckiense Foerste and Teichert in its consistently 

shorter camerae at comparable shell diameters, the more 

ventral position of the siphuncle, higher segment compression ratios at the diameters studied, and in the narrower diameter of segments relative to shell diameter at 

comparable diameters. Actinoceras glenni Foerste and 

Teichert from equivalent strata at Nashville, Tenn., is similar to A. kentuckiense and differs from A. altopontense in 

the same manner. Actinoceras ruedemanni Foerste and 

Teichert, from the Black River Formation at Watertown, 

N.Y., is a more slender form (apical angle 9 degrees), having longer camerae and more compressed, broader 

siphuncle segments at shell diameters less than 45 mm. 

Actinoceras beloitense (Whitfield) from the Platteville 

Formation and equivalents in the upper Mississippi valley 

is similar to A. altopontense in the ventral position of the 

siphuncle, but differs from the Kentucky species in its 

longer camerae and lower SCR values. Siphuncle segment 

diameters relative to shell diameter are similar in early 

stages of growth, but segment diameters in A. beloitense 

become narrower with ontogeny. A comparison of the 

morphological features of a number of these species of 

Actinoceras from Middle Ordovician strata in North 

America is presented in table 10.

Actinoceras altopontense and A. kentuckiense 

appear to be equally common within the USGS 6034-CO 

collection, but the sample size is too small to determine 

this relationship with any certainty. Identifiable phragmocone fragments of both species are uncommon in this collection, and disarticulated siphuncle segments referable 

to species of Actinoceras are abundant. These segments 

often preserve impressions of the fine radial canals typical of members of this genus (pi. 17, figs. 6, 7).

ACTINOCERAS KENTUCKIENSE FOERSTE AND TEICHERT, 1930

Plate 17, figures 1-5

Actinoceras kentuckiense Foerste and Teichert, 1930, p. 

244, pi. 32, figs. L4-LB; pi. 33, fig. 1; pi. 57, fig. 3.

Diagnosis.—Rapidly expanding species of Actinoceras with comparatively long camerae and broadly 

expanded, highly compressed siphuncle segments, in 

which the lengths of the connecting rings are nearly twice 

the length of the septal necks; segments not in contact 

with the ventral shell margin in adoral portions of shell.

Description.—Medium-sized (phragmocone lengths 

of at least 30 cm and shell diameters up to 6.0 cm), rapidly 

expanding (apical angle 10-11 degrees) orthoconic longicone; depressed in cross section such that sutures slope 

from the dorsum to the venter in the adapical direction, 

forming a shallow ventral lobe. Cameral chambers comparatively long, cameral lengths ranging from one third to 

one fourth the diameter of the shell, decreasing with
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P83

SNL PS 

I

RC

-SPR

FIGURE 23.—Important morphological features used to 

distinguish species of the genus Actinoceras from 

Middle Ordovician strata in Eastern North America, 

CC, central canal; RC, radial canals; PS, perispatia; CL,

cameral length; SL, segment length; SNL, length of septal 

neck; SPR, segment position ratio; and SCR, segment 

compression ratio.

ontogeny. Body chamber unknown. Shell exterior 

smooth.

Siphuncle subcentral the known length of the phragmocone (SPR=0.28-0.40). Siphuncle segments not in contact with ventral shell margin at diameters greater than 45 

mm. Segments highly compressed (SCR=2.3-2.9) at shell 

diameters of 35-45 mm, compression ratio decreasing 

slightly with ontogeny. Segments broad, diameters threefourths the diameter of the shell at shell diameters less 

than 40 mm, decreasing to one- half the diameter of the 

shell adorally, indicative of segment decompression with 

ontogeny. In dorsal-ventral section, length of connecting 

rings nearly twice the length of septal necks. Septal necks 

cyrtochoanitic, broadly recurved, long, with short, free 

brims. Well developed annulosiphonate deposits, having 

the radial vascular system typical of the genus. Hyposeptal cameral deposits weakly developed in phragmocone 

sections less than 35 mm in diameter.

Stratigraphic and geographic occurrence.—Upper 

part of the Rocklandian portion of the Tyrone Limestone 

(Middle Ordovician), in the vicinity of the Kentucky River, 

Jessamine County, Ky.

Studied material.—Holotype USNM 82237 from the 

Tyrone Limestone at High Bridge, Ky.; plus USNM 158670 

(pi. 17, figs. 1,2,4, 5), 158647 (pi. 17, fig. 3), and 468720, all 

silicified material from the Tyrone Limestone, USGS 6034- 

CO collection, Little Hickman section A, Sulfur Wells, Ky.

Remarks.—The differences between A. kentuckiense 

and the associated A. altopontense were listed in the

previous description of that species. Although general 

morphological features are similar, phragmocones can be 

distinguished by the longer camerae of A. kentuckiense at 

comparable shell diameters. A. kentuckiense is most similar to A. glenni Foerste and Teichert from the Tyrone 

Limestone in central Tennessee, in that both species have 

rapidly expanding shells and comparatively long camerae. 

Actinoceras kentuckiense differs from A. glenni in possessing broader, more highly compressed siphuncle segments at comparable shell diameters (table 10). 

Actinoceras kentuckiense differs from A. ruedemanni 

Foerste and Teichert from Blackriveran strata in New 

York in being a broader, more rapidly expanding shell having more highly compressed segments at diameters of 50 

mm and less compressed segments at diameters less than 

45 mm. Actinoceras kentuckiense is distinct from A. 

beloitense (Whitfield) from Blackriveran strata in Wisconsin and insular portions of Lake Huron in possessing more 

centrally located, more highly compressed siphuncle segments. Actinoceras kentuckiense is similar to the type 

species of Actinoceras, A. bigsbyi Bronn, in that adoral 

siphuncle segments are removed from the ventral shell 

margin. It differs from this species in being a more rapidly 

expanding form with longer camerae at comparable shell 

diameters. Ontogenetic siphuncle decompression also is 

much more extensive in A. bigsbyi, the segment diameters being slightly less than two-thirds the diameter of the 

shell at a diameter of 35 mm and less than one-third the 

diameter of the shell at diameter of 45 mm.
P84 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

TABLE 10.—Comparisons of the morphological features of selected Middle Ordovician (Blackriveran 

and Rocklandian) species of Actinoceras, showing variation in rate of shell expansion, cameral 

length, siphuncle position, siphuncle segment shape, and siphuncle diameter relative to shell 

diameter

[Data from silicified material from Tyrone Limestone in Kentucky and specimens illustrated by Foerste and 

Teichert (1930). CL/D, ratio of cameral length to shell diameter; SPR, siphuncle segment position ratio; SCR, 

siphuncle segment compression ration; SD/D, ratio of siphuncle diameter to shell diameter; NA, not applicable; mm, millimeter]

Feature A. altopontense A. kentuckiense A. gtenni A. ruedemanni A. beloitense

Apical angle, degrees

Diameter 50 mm

CL/D

SPR

SCR

SD/D

Diameter 45 mm

CM)

SPR

SCR

SD/D

Diameter 40 mm

CM)

SPR

SD/D

Diameter 35 mm

CM)

SPR

SCR

SD/D

10.5

.18

.28

2.88

.52

.20

.31

3.125

.55

.20

.325

.625

.20

.285

2.85

.57

11

.24

.34

2.33

.56

.24

.40

2.70

.66

.25

.35

.725

.285

.37

2.60

.74

12

.22

.30

2.27

.50

.22

.28

2.65

.58

.25

NA

.50

.285

.34

2.30

.65

9

.22

.30

1.80

.40

.20

.33

3.00

.60

.21

.36

.675

.228

.37

3.25

.74

10.5

.26

.26

1.46

.38

.27

.29

1.66

.44

.25

.275

.55

.257

.257

2.20

.57

ACTINOCERAS CURDSVILLENSE FOERSTE AND TEICHERT, 1930

Plate 17, figure 11

Actinoceras curdsvittense Foerste and Teichert, 1930, p. 

240, pi. 39, figs. 2A-B] pi. 56, fig. 9.

Diagnosis.—Species of Actinoceras distinguished by 

its very short camerae and peculiar short, highly 

recurved, nearly recumbent septal necks.

Description.—Medium-sized (estimated phragmocone length of at least 26 cm and shell diameters of up to 

4.0 cm), rapidly expanding (apical angle 10 degrees) species of Actinoceras; circular in cross section, with essentially straight, transverse sutures that form a weakly 

developed ventral lobe. Cameral chambers short, cameral 

lengths one-seventh to one-eighth the diameter of the 

shell, decreasing with ontogeny. Body chamber unknown. 

Shell exterior apparently smooth.

Siphuncle midventral in position at a diameter of 40 

mm and having siphuncle segments in contact with the 

ventral shell margin. Segments for known portions of the

phragmocone (from 32 to 40 mm in diameter) are very 

highly compressed (SCR=4.0) and broadly expanded, constituting from two-thirds to one-half the diameter of the 

shell, decreasing in relative diameter with ontogeny. Septal necks short, highly curved, nearly recumbent, with 

brims as long or longer than necks. Endosiphuncular vascular system unknown. Cameral deposits consisting of 

well developed hyposeptal deposits.

Stratigraphic and geographic range.—Curdsville 

Limestone Member of the Lexington Limestone (Middle 

Ordovician, Kirkfieldian Stage), Blue Grass region of 

north-central Kentucky.

Studied material—Holotype USNM 48425 (pi. 17, 

fig. 11), a silicified fragment of the phragmocone; 

Curdsville, Ky.

Remarks.—This species is an apparently uncommon 

form in the Curdsville Limestone Member of the Lexington Limestone, known only from the holotype, a natural 

section of a fragment of the phragmocone 50 mm in
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P85

length. Although this species is known only from this one 

specimen, the preserved features indicate a distinctive 

morphology characterized by the very short length of the 

camerae, highly compressed, broad siphuncle segments, 

and peculiar recurved, nearly recumbent nature of the 

short septal necks. These features distinguish this species 

from any other species of Actinoceras known to the 

writer. As indicated above, this species appears to belong 

in Flower's "A. centrale Group," as indicated by its short 

camerae and short, broad siphuncle segments. It represents a Blackriveran "relict" that survived the Rocklandian extinction event to persist into the Kirkfieldian. 

Actinoceras is not known from the overlying Ordovician 

section exposed in the Kentucky-Indiana-Ohio area.

FAMILY ORMOCERATIDAE SAEMAN

Generally straight, medium-sized (less than 1 m in 

length) orthoconic longicones with circular to slightly 

depressed cross sections and straight, transverse sutures. 

Camerae typically short. Body chambers poorly known. 

Shell exteriors smooth or ornamented with longitudinal 

ribs or lirae.

Siphuncles subcentral to midventral in position. Segments rather narrow in diameter for this order, making up 

one-third or less the diameter of the shell. Segments globular to spheroidal, compressed to slightly depressed or 

equiaxial in outline. Septal necks cyrtochoanitic, typically 

short, with short brims, recumbent or free. Endosiphuncular deposits consisting of coalescing annulosiphonate 

deposits and simple endosiphuncular vascular systems 

consisting of a central canal and radial canals that are 

straight, generally at right angles to the central canal. 

Cameral deposits well developed, consisting of both 

hyposeptal and episeptal deposits.

Stratigraphic range.—Middle Ordovician (Whiterockian) to Middle Devonian (Eifelian).

GENUS ORMOCERAS STOKES

Type species.—Ormoceras bayfieldi Stokes, 1840, p. 

709; by original designation; Manistique Formation, Middle Silurian, Michigan.

Description.—Medium-sized, moderately to rapidly 

expanding orthoconic longicones; circular to slightly 

depressed in section with straight, transverse sutures. 

Cameral chambers short, with camera! lengths decreasing 

with ontogeny. Body chamber unknown. Shell exterior 

smooth.

Siphuncle subcentral in position having segments 

becoming more central in position with ontogeny. Segments broad, typically one-third the diameter of the shell, 

moderately to highly compressed; becoming more compressed with ontogeny. Siphuncle segments do not demonstrate segment decompression with ontogeny. Septal 

necks cyrtochoanitic, with short necks and brims; necks

strongly recurved, but free, not recumbent. Connecting 

rings thin, homogeneous; adapical portions of rings typically adnate both dorsally and ventrally to adjacent septa 

having the adoral portions of rings free. Endosiphuncular 

deposits consisting of coalescing annulosiphonate deposits and a vascular system consisting of straight radial 

canals situated at right angles to the central canal. Well 

developed hyposeptal and episeptal camera! deposits.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Chazyan Champlainian Provincial Series) to 

Early Silurian (Llandoverian Series); worldwide.

Remarks.—This genus has become a receptacle for a 

variety of small to medium-sized Ordovician and Silurian 

longiconic actinocerids with rather narrow, globular to 

compressed siphuncle segments. A brief investigation of 

some of the better known species assigned to this genus 

indicates that more than one genus-level taxon is contained in Ormoceras as it is currently defined (Teichert 

and others, 1964). At least three genus-level taxa can be 

recognized within Ormoceras at this time.

Flower (1957a) erected Adamsoceras for Middle 

Ordovician (Whiterockian) forms with thick, layered connecting rings and a recticular vascular canal system. In 

addition, species assigned to Adamsoceras are gradually 

expanding longicones (apical angle 4-5 degrees) with 

siphuncle segments only one-fifth to one-fourth the diameter of the shell and SCR < 1.5. Cameral length appears to 

increase with ontogeny in species assigned to this genus. 

Younger, more typical Middle Ordovician (Blackriveran) 

to Early Silurian (Llandoverian) species of Ormoceras, 

including the type species O. bayfieldi, have more rapidly 

expanding shells (apical angle 7-9 degrees) and broader, 

more highly compressed siphuncle segments (SCR=1.75- 

2.0), diameters averaging one-third the diameter of the 

shell. Connecting rings are thin and homogeneous, consisting of simple, straight radial canals. Based on these 

criteria, Adamsoceras Flower appears to be distinct from 

Ormoceras based on O. bayfieldi Stokes.

A third taxon, Sactoceras Hyatt, based on Orthoceras 

richteri Barrande from the Upper Silurian (Ludlovian) of 

Czechoslovakia, also has been placed in synonymy with 

Ormoceras Stokes. Sactoceras richteri is a medium-sized 

(phragmocone lengths up to 45 cm and shell diameters up 

to 5.5 cm), moderately expanding (apical angle 7-7.5 

degrees) orthoconic longicone that is slightly curved 

endogastrically adapically. Camerae are short, decreasing 

with ontogeny from one-fifth to one-seventh the diameter 

of the shell. The siphuncle is in a central position for the 

length of the shell. Siphuncle segments are globular, 

slightly compressed having SCR values less than 1.33, and 

diameters from one-fourth to one-seventh the diameter of 

the shell. Endosiphuncular deposits consist of annulosiphonate deposits that fuse ventrally to form parietal 

deposits adapically. There is little evidence of a well-
P86 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

developed actinocerid type of vascular system, and perispatia are lacking. Dzik (1984), citing the absence of radial 

structure in the endosiphuncular deposits of these species, went as far as to remove Sactoceras from the Actinocerida, placing it in the Sactoceratidae within the order 

Orthocerida. The type species of Sactoceras appears to be 

distinct from Ormoceras in terms of siphuncle diameter 

relative to shell diameter, in segment compression, and in 

the nature of the endosiphuncular deposits. As such, 

Sactoceras appears to be a valid genus distinct from 

Ormoceras and may not, as suggested by Dzik, belong in 

the Actinocerida. The Kentucky material described here 

belongs to the complex of species that includes O. bayfieldi and constitutes true Ormoceras.

ORMOCERAS FERECENTRICUM FOERSTE AND TEICHERT, 1930

Plate 18, figures 1-7

Ormoceras ferecentricum Foerste and Teichert, 1930, 

p. 289, pi. 49, figs. 2A-B] pi. 58, fig. 10.

Diagnosis.—Moderately expanding species of 

Ormoceras with short camerae and a subcentral siphuncle with broad, highly compressed segments that average 

one-third the diameter of the shell.

Description.—Small to medium-sized (known portions of phragmocone up to 30 cm in length and 3.5 cm in 

diameter), moderately expanding (apical angle 7 degrees) 

orthoconic longicones, circular in cross section with 

straight, transverse sutures. Camera! chambers short, 

cameral lengths decreasing with ontogeny from one-third 

to one-seventh the diameter of the shell. Body chamber 

unknown. Shell exterior smooth.

Siphuncle subcentral in position the length of the 

phragmocone, moving to a more central position with 

ontogeny. Siphuncle segments have SPR values of 0.30 at 

diameters of 15-20 mm and 0.40 at diameters in excess of 

30 mm. Segments broad and highly compressed 

(SCR= 1.5-2.0) the length of the siphuncle, segment diameters one-third the diameter of the shell. Segments 

becoming more compressed with ontogeny. Endosiphuncular deposits consisting of annulosiphonate deposits and 

a vascular system of radial canals at right angles to the 

central canal. Adoralmost cameral deposits consisting of 

episeptal deposits.

Stratigraphic and geographic occurrence.—Upper 

part of the Rocklandian portion of the Tyrone Limestone 

(Middle Ordovician), in the vicinity of the Kentucky River, 

Jessamine County, Ky.

Studied material.—Holotype USNM 82214 (pi. 18, 

figs. 1-3), High Bridge, Ky.; plus silicified portions of the 

phragmocone from the USGS 6034-CO collection: USNM 

158639 (pi. 18, figs. 4-6) and 468721 (pi. 18, fig. 7), from 

the Little Hickman section A, south of Sulfur Wells, Ky.

Remarks.—As indicated above, O. ferecentricum 

belongs to Ormoceras, in a narrow sense, by virtue of its

shallow camerae and broad, highly compressed, subcentral siphuncle segments. It is most similar to a group of 

Middle and Upper Ordovician species from North America. This group lists O. aUumettense (Billings) from the 

"Leray-Rockland beds" (Middle Ordovician, Rocklandian) in the Ottawa region of Ontario and Quebec, O. cannonense Foerste and Teichert from the Shermanian part 

of the Cannon Limestone (Middle Ordovician) of central 

Tennessee, and O. dartoni Flower from the Upper Ordovician Second Value Dolomite of New Mexico.

Ormoceras ferecentricum is most similar to O. aUumettense (Billings), differing from this species only in its 

slightly less rapidly expanding shell (apical angle 7 

degrees compared with 8-8.5 degrees) and the more central position of the siphuncle in the Kentucky species at 

comparable diameters. Larger collections of both species 

may indicate that these species represent regional variants of the same species, the observed morphological differences falling within the range of intraspecific variation. 

A comparison of the morphological features of these two 

species of Ormoceras is presented in figure 24.

Ormoceras ferecentricum is distinct from O. cannonense Foerste and Teichert in the much shorter camerae typical of the latter species, the cameral lengths 

averaging one-eighth the diameter of the shell compared 

with average cameral lengths one-fifth the diameter of the 

shell in the Kentucky species. Comparisons between O. 

ferecentricum and O. dartoni Flower are difficult due to 

the fact that the holotype and only known specimen of 

O.dartoni is represented by a section of phragmocone 

40-50 mm in diameter, larger than any known fragment of 

O. ferecentricum.

At both the High Bridge and Sulfur Wells localities, O. 

ferecentricum is an uncommon species associated with 

more abundant specimens of the actinocerids Actinoceras altopontense Foerste and Teichert (pi. 16, fig. 6) and 

A. kentuckiense (pi. 17, figs. 1-5). At both localities, O. 

ferecentricum is represented by incomplete portions of 

the phragmocone and isolated siphuncle segments. It 

occurs in the 6034-CO collection in association with the 

diverse nautiloid fauna that is listed in table 1.

GENUS DEIROCERAS HYATT

Type species.—Orthoceras python Billings, 1857, 

p. 335; designated by Hyatt, 1884; Trenton Limestone, 

upper Shermanian Stage, Middle Ordovician, Ontario.

Description.—Medium-sized, gradually expanding 

orthoconic longicones; circular in cross section with 

straight transverse sutures. Cameral chambers moderately long, cameral lengths ranging from one-third to twofifths the diameter of the shell. Body chambers unknown. 

Shell exterior poorly known; some species apparently 

smooth, other forms with faint longitudinal fluting.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P87

_ A

10 20 30 

SHELL DIAMETER, IN MILLIMETERS

40

10

B

10 20 30 

SHELL DIAMETER, IN MILLIMETERS

40

FIGUEE 24.—Bivariate plots of camera! length versus shell 

diameter, A, and siphuncle diameter versus shell 

diameter, B, for Middle Ordovician species of Ormoceras 

from Eastern North America. Species are O. 

ferecentricum (USNM 82214, 158639, 468721), Tyrone 

Limestone, Kentucky, (circles); O. attumettense (GSC 

1265) "Leray-Rockland beds," Quebec (triangles); and O. 

cannonense (USNM 82232), Cannon Limestone, central 

Tennessee (squares).

Siphuncles in midventral position for the length of 

the shell. Siphuncle segments typically from one-third to 

one-fourth the diameter of the shell; segments expanded 

ovate, globular, depressed in shape, longer than wide. 

Septal necks comparatively long, cyrtochoanitic, with 

necks gently curved, free, no areas of adnation. Endosiphuncular deposits consisting of annulosiphonate deposits and simple, straight radial canals set perpendicular to 

narrow central canal. Camera! deposits well developed, 

adorally consisting of episeptal and hyposeptal deposits.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Blackriveran) to Upper Ordovician (Edenian 

Stage), Eastern North America.

Remarks.—This genus is known primarily from 

poorly preserved fragmentary steinkerns and isolated 

siphuncles of late Middle Ordovician (Shermanian) to 

early Late Ordovician (Edenian) Age in Eastern and Central North America. Deiroceras, including the type species 

D. python Billings, is especially characteristic of the dark 

limestones of the Cobourg Formation in Ontario and adjacent portions of New York. Foerste and Teichert (1930) 

illustrated a number of species from coeval platform carbonates in Kentucky, Missouri, and Tennessee. Older 

Blackriveran species are D. kindlei Foerste, D. 

paquettense Foerste, D. pertinax (Billings), and D. 

scofieldi Foerste, all from Middle Ordovician carbonates 

exposed in the upper Mississippi valley and the Ottawa 

region of Ontario and Quebec.

Flower (1957a) pointed out the close similarity in 

terms of the siphuncle between the presumed smoothshelled genus Deiroceras and the longitudinally fluted 

genus Troedssonoceras Foerste, both of which occur in 

the Catheys Formation of central Tennessee. Flower suggested that these two genera might prove to be one and 

the same. Shell exteriors are unknown for most described 

species of Deiroceras, as well as the type species. Deiroceras pertinax (Billings) and an unnamed species of the 

genus illustrated by Flower (1957, pi. 11, fig. 7) from 

upper Middle Ordovician limestones in Quebec both 

exhibit indications of a longitudinally fluted shell similar 

to that of Troedssonoceras. Troedssonoceras is currently 

known from upper Middle Ordovician (Shermanian) 

through upper Ordovician (Maysvillian) strata exposed in 

central Tennessee, the Cumberland River valley in southcentral Kentucky, and the Cincinnati region of southwestern Ohio and adjacent portions of northern Kentucky. For 

the purposes of this paper, these taxa are retained as separate genera, pending the discovery of better preserved 

specimens of Deiroceras retaining the external shell. Deiroceras is interesting in that it was one of the few Blackriveran genera that survived the Rocklandian crisis to 

undergo a second radiation of species in the Shermanian 

and Edenian.

DEIROCERAS CURDSVILLENSEfOERSTE AND TEICHERT, 1930

Plate 18, figures 8, 9

Deiroceras curdsvittense Foerste and Teichert, 1930, 

p. 294, pi. 47, figs. 3A-B; pi. 58, fig. 6.

Diagnosis.—Slender, gradually expanding species of 

Deiroceras, cameral lengths averaging one-third the diameter of the shell and depressed siphuncle segments midventral to ventral in position.

Description.—Medium-sized (lengths of up to 30 cm 

and observed shell diameters of 3.0 cm), slender,
P88 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

gradually expanding (apical angle 6 degrees) orthoconic 

longicones; circular in section with straight transverse 

sutures. Camera! chambers comparatively long, having 

cameral lengths averaging one-third the diameter of the 

shell, decreasing slightly with ontogeny. Body chamber 

unknown. Shell exterior apparently smooth.

Siphuncle midventral to ventral in position, becoming more ventral with ontogeny. Siphuncle segments 

depressed, globular (SCR=0.70-0.88), showing no indication of siphuncle segment decompression with ontogeny. 

Segment diameters from slightly less than one-third to 

one-fourth the diameter of the shell. Connecting rings 

appear to have been thin and homogeneous. Septal necks 

cyrtochoanitic, long, with free brims. Endosiphuncular 

deposits unknown. Cameral deposits consisting of muralepiseptal deposits dorsally.

Stratigraphic and geographic occurrence.—Curdsville Limestone Member of the Lexington Limestone (Middle Ordovician, Kirkfieldian Stage), central Kentucky Blue 

Grass region.

Studied material—Holotype USNM 48221 (pi. 18, 

fig. 8) from Curdsville, Ky. A number of silicified shell 

fragments including USNM 468723 (pi. 18, fig. 9) from the 

USGS 5100-CO collection, Little Hickman section B, Jessamine County, Ky.

Remarks.—This species is known only from a limited 

number of fragmentary specimens; collectively they make 

up a section of shell roughly 10 cm in length having shell 

diameters of 21 to 30 mm. All specimens studied were 

coarsely silicified internal molds that have been sectioned 

to expose the siphuncle. Siphuncle segments have been 

recrystallized, destroying any evidence of endosiphuncular structure. Comparison with other described species of 

Deiroceras is limited due to the incomplete and limited 

amount of material in collections.

In terms of general shell morphology, D. curdsvillense is most similar to the coeval species D. paquettense 

Foerste, D. pertinax (Billings), andD. kindlei Foerste, all 

from the Middle Ordovician (Blackriveran and Rocklandian) strata in the Ottawa, Ontario, region. Deiroceras 

paquettense is a more slender form having an apical angle 

of 4 degrees. Deiroceras pertinax is another slender form 

(apical angle 5 degrees), in which the outer shell is 

marked by a number of faint, raised longitudinal ribs. Its 

internal structure is poorly known, but cameral lengths 

approximate those of D. curdsvillense. The Kentucky species is most similar to D. kindlei, the specifics of the camerae and siphuncle segments in the holotype of D. kindlei 

matching up almost exactly with the Curdsville Limestone 

Member material. The holotype (GSC 14418) of D. kindlei 

differs from the holotype of D. curdsvillense only in its 

slightly more rapid rate of shell expansion: 7 degrees 

compared with 6 degrees in the Kentucky specimens. Further study may indicate that these species are the same,

with D. kindlei Foerste having priority. Deiroceras persiphonatum (Flower), represented by a single known specimen (UC 22695) from the upper part of the Lexington 

Limestone at Cynthiana, Ky, differs from D. curdsvillense 

in being a more slender shell (apical angle 5 degrees), 

having somewhat shorter cameral lengths at comparable 

shell diameters. Deiroceras curdsvillense is evidently an 

uncommon form within the Curdsville Limestone Member, associated with a low-diversity nautiloid fauna that 

consists of Actinoceras curdsvillense Foerste and 

Teichert (pi. 17, fig. 11), Anaspyroceras cf. A. cylindricum (Foerste) (pi. 12, fig. 5), and poorly preserved specimens of the endocerids Cameroceras and Vaginoceras.

GENUS ORTHONYBYOCERAS SHIMIZU AND OBATA

Type species.—Ormoceras? covingtonense Foerste 

and Teichert, 1930, p. 288; designated by Shimizu and 

Obata, 1935, p. 7; Maysvillian Stage; Upper Ordovician, 

Kentucky.

Description.—Medium-sized, moderately to rapidly 

expanding orthoconic longicones; circular to slightly 

depressed in cross section with straight, transverse 

sutures. Camerae short, with cameral lengths typically 

from one-fourth to one-sixth the diameter of the shell, 

decreasing in length with ontogeny. Body chamber incompletely known. Shell exterior smooth.

Siphuncle subcentral to midventral in position, 

becoming more ventral with ontogeny. Siphuncle segments expanded, compressed in outline, segment diameters from one-third to one-fourth the diameter of the shell. 

Septal necks cyrtochoanitic, short, with recumbent brims. 

Connecting rings thin, adnate dorsally to both adoral and 

adapical septa; not adnate ventrally to adapical surface of 

adoral septum. Endosiphuncular deposits well developed, 

consisting of dorsal annuli developed more or less symmetrically around septal necks and more massive ventral 

annulosiphonate deposits that thicken adapical of the 

septal necks. Broad central canal having dorsal radial 

canals approaching connecting rings at the midpoint of 

the segment, while ventrally, canals enter in the adoral 

half of segment. Adoralmost cameral deposits consisting 

of discrete episeptal and hyposeptal deposits, which are 

more strongly developed ventrolaterally.

Stratigraphic and geographic occurrence.—Upper 

Ordovician (Maysvillian-Richmondian Stages), Eastern 

North America.

Remarks—The nomenclatural history of this genus is 

described in part in the preceding remarks concerning the 

orthocerid genus Treptoceras. As demonstrated by 

Aronoff (1979), Orthonybyoceras is an actinocerid and 

distinct from the associated orthocerid Treptoceras. 

Although the two genera are externally similar, Orthonybyoceras differs from Treptoceras in the possession of 

short, recumbent septal necks both dorsally and ventrally,
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P89

in the development of true perispatia between annulosiphonate deposits, and in the possession of more compressed, ovate siphuncle segments that increase in height 

with ontogeny, in contrast to the heart-shaped segments 

in Treptoceras, which decompress during ontogeny (compare pi. 5, figs. 1-4 with pi. 18, figs. 10,14, 17).

Orthonybyoceras does not fit neatly into any of the 

existing families of the Actinocerida, Orthonybyoceras 

differs from other members of the Ormoceratidae in possessing short, recumbent septal necks dorsally and ventrally and in the development of connecting rings that are 

adnate to septal surfaces. It differs from most members 

of the Armenoceratidae in possessing well developed 

camera! deposits, simple radial canal systems, and comparatively narrow diameter siphuncle segments. Orthonybyoceras is similar to members of the Wutinoceratidae in 

particulars of the siphuncle segments, their position, and 

the nature of the septal necks. It is distinct from these 

genera, however, in possessing thin, homogeneous connecting rings and a simple radial canal system. It is probable that Orthonybyoceras represents an "advanced" 

member of the Wutinoceratidae as suggested by Aronoff 

(1979). However, pending a more thorough restudy of the 

Actinocerida, Orthonybyoceras is retained here in the 

Ormoceratidae, following Teichert (in Teichert and others, 1964).

As currently recognized, Orthonybyoceras is known 

only from the type species, O. dyeri (Miller) from the 

Upper Ordovician (Maysvillian) of northern Kentucky and 

adjacent portions of Indiana and Ohio. Teichert and 

Glenister (1953) described a second species of Orthonybyoceras, O. tasmanense, from lower Middle Ordovician 

strata exposed in Tasmania, Aronoff (1979) removed this 

species from the genus due to the ontogenetic decrease in 

siphuncle diameter present in this species. He transferred 

it to "Nybyoceras" paucicubiculatum Teichert and 

Glenister, also from Middle Ordovician limestones 

exposed in Tasmania. Flower (1957a) and Stait (1984) 

placed this species in Wutinoceras Flower on the basis of 

the bifurcating radial canals. If these assignments are 

accepted, then the genus Orthonybyoceras is known only 

from the type species from the Upper Ordovician of the 

Cincinnati arch region.

ORTHONYBYOCERAS DYERI (MILLER), 1875 

Plate 18, figures 10-17

Orthoceras dyeri Miller, 1875, p. 125, Fig. 11.

Orthoceras dyeri Miller. Miller, 1880, p. 236, pi. 7, fig. 7.

Ormoceras? covingtonense Foerste and Teichert, 1930, p.

288, pi. 45, figs. 2A-B; pi. 58, fig. 9.

Orthonybyoceras covingtonense (Foerste and Teichert).

Shimizu and Obata, 1935, p. 7, 8.

Orthonybyoceras covingtonense (Foerste and Teichert).

Teichert and Glenister, 1953, p. 223.

Orthonybyoceras covingtonense (Foerste and Teichert). 

Teichert, 1964, p. K214, Fig. 151,la. 

Orthonybyoceras covingtonense (Foerste and Teichert). 

Aronoff, 1979, p. 106-109, figs. 2D, 3A-C.

Diagnosis.—Small to medium-sized, rather rapidly 

expanding orthoconic longicone with compressed, subcentral siphuncle segments one-third to one-fourth the 

diameter of the shell; short recumbent septal necks, and 

thin connecting rings adnate dorsally to adjacent septa.

Description.—Small to medium-sized (phragmocones at least 25 cm in length and up to 4.3 cm in diameter), rapidly expanding (apical angle 8.5-10 degrees) 

orthoconic longicones; circular to slightly depressed in 

cross section with straight transverse sutures. Camerae 

short having cameral lengths ranging from one-fifth to 

one-seventh the diameter of the shell, decreasing in 

length with ontogeny relative to shell diameter. Body 

chamber poorly known, at least one-fifth the total diameter of the shell. Periphract dorsomyarian. Shell exterior 

smooth.

Siphuncle subcentral most of the length of the shell 

(SPR=0.40-0.285), becoming more ventral in position 

with ontogeny. Siphuncle segments expanded, compressed, the SCR values ranging from 1.3 at shell diameters of 25 mm to 1.7 at diameters of 35 mm. Segments 

from one-third to one-fourth the diameter of the shell, 

decreasing slightly in diameter with ontogeny. Septal 

necks short, with recumbent brims. Connecting rings 

thin, homogeneous, adnate to either adoral or adapical 

septa dorsally; ventrally adnate to adapical septa or not 

adnate at all. Dorsal endosiphuncular deposits consisting 

of annuli developed more or less symmetrically about the 

septal necks; deposits more asymmetrical ventrally, consisting of annulosiphonate deposits that are much thicker 

in development in the region adoral to septal necks. Perispatia well developed. Dorsal radial canals intersect the 

connecting ring wall at midpoint of segment. Ventrally, 

radial canals intersect connecting ring wall in adoral half 

of segment. Cameral deposits consisting of episeptal and 

hyposeptal deposits that, adorally, are more heavily developed ventrolaterally.

Stratigraphic and geographic occurrence.—Fairview Formation and Grant Lake Limestone and equivalents in northern Kentucky and adjacent portions of the 

Cincinnati, Ohio, region; lower part of the Bull Fork Formation, southeastern Indiana,

Studied material.—Holotype of Orthoceras dyeri, 

MCZ 3403 (pi. 18, figs. 13, 15, 16), Cincinnati, Ohio; 

holotype of Ormoceras? covingtonense Foerste and 

Teichert, USNM 48258 (pi. 18, figs. 14,17), Covington, Ky; 

hypotype of O. dyeri, UC 351, Corryville Member of the 

Grant Lake Limestone, Cincinnati, Ohio; specimens 

labeled "co-types" of O. dyeri, UC 352A (pi. 18, fig. 11), 

352B (pi. 18, fig. 12), and 352C, labeled "Maysville-
P90 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

Corryville, Cincinnati, Ohio; UC 31380" (pi. 18, fig. 10), 

"Waynesville biofacies" in the Bull Fork Formation, Weisburg, Ind; and numerous uncataloged specimens.

Remarks.—Comparisons of the holotype of 

Ormocerasffl covingtonense Foerste and Teichert 

(USNM 48258) with the holotype (MCZ 3403), hypotype 

(UC 351), and "co-types" of Orthoceras dyeri Miller (UC 

352A-C) indicate that these specimens are all the same 

species. All of these specimens occur in the same strata in 

the greater Cincinnati region of southwestern Ohio and 

northern Kentucky and all are rapidly expanding longicones with relatively short camerae and compressed, subcentral siphuncle segments one-third to one-fourth the 

diameter of the shell. As indicated in the species synonymy, Orthoceras dyeri was the first published name given 

to this species (Miller, 1875) and has priority over 

Ormoceras? covingtonense (Foerste and Teichert, 1930).

Orthonybyoceras dyeri is the only species currently 

recognized as assignable to the genus Orthonybyoceras 

Shimizu and Obata. Species previously assigned to the 

genus (Teichert and Glenister, 1953) have been transferred to other genera by subsequent workers (Flower, 

1957a; Aronoff, 1979; Stait, 1984). As indicated in the previous discussions of the genus Treptoceras Flower, these 

two taxa are internally distinct and are members of different orders. Treptoceras is by far the more abundant taxon 

in the Ordovician strata exposed in the Kentucky-IndianaOhio region. In this area, Orthonybyoceras dyeri is 

locally common in the Fairview Formation and in the 

overlying Corryville Member of the Grant Lake 

Formation.

A specimen (UC 31380, pi. 18, fig. 10) listed as coming from the "Waynesville Formation" (Upper Ordovician, 

Richmondian Stage) exposed at Weisburg, Ind., also 

appears to be assignable to Orthonybyoceras. Comparisons with other specimens of Orthonybyoceras dyeri are 

difficult due to the incomplete nature of the "Waynesville" 

specimen, but the sectioned phragmocone fragment is 

similar to O. dyeri in the rate of shell expansion and in 

the diameter and shape of siphuncle segments. It differs 

from Maysvillian specimens of O. dyeri in the shorter 

length of its camerae and in the more central position of 

its siphuncle at comparable shell diameters. The affinities 

of this specimen remain unclear pending the discovery of 

more complete specimens of this form from these 

younger strata.

SUBCLASS NAUTILOIDEA AGASSIZ

Breviconic, cyrtoconic, and coiled nautiloids with 

generally small diameter, primitively subtubular siphuncles having orthochoanitic or cyrtochoanitic septal necks 

and connecting rings of varying thickness. Periphract ventromyarian; hyponomic sinus variably developed, but

typically present ventrally. Buoyancy regulation achieved 

through the development of short phragmocones coupled 

with large body chambers having the large volume of visceral mass and thick shell counteracting the small volume 

of gas-filled phragmocone; or by planispiral coiling of the 

shell, bringing the center of buoyancy directly over the 

center of mass, these centers being fixed in their relative 

position within the coil. This subclass is thought to represent a phylogenetic sequence from the primitive, evolutely coiled Tarphycerida through breviconic and 

cyrtoconic Oncocerida, to the involutely coiled Nautilida. 

This is the dominant nautiloid subclass in the postDevonian.

Stratigraphic range.—Lower Ordovician to 

Holocene.

ORDER TARPHYCERIDA FLOWER

Primitive coiled nautiloids with evolutely coiled gyroconic or serpenticonic shells of variable whorl section 

and simple transverse or slightly curved sutures. Body 

chambers typically long, extending from one-half to one 

complete whorl in length, mature portions often slightly 

to greatly divergent from earlier coiled portions. Ventromyarian periphract and a well developed hyponomic sinus. 

Siphuncle varies in position, consisting of depressed, 

elongate tubular segments with orthochoanitic septal 

necks and thick connecting rings in primitive forms; cyrtochoanitic septal necks and thin, homogeneous rings in 

younger forms. Stability offered by the coiled shell morphology offset to some degree by length of body chamber, 

generating some rotational instability. This is countered 

by the divergence of the final one-quarter to one-half 

whorl of the body chamber. Modified apertures in some 

younger taxa.

Stratigraphic range.—Lower Ordovician to Middle 

Devonian.

SUBORDER TARPHYCERINA FLOWER

Gyrocones and serpenticones with simple septa, 

including both depressed and compressed forms. Siphuncles vary in position with orthochoanitic septal necks and 

thick, layered connecting rings.

Stratigraphic range.—Lower Ordovician (Ibexian 

Provincial Series) to Upper Silurian (Ludlovian Series).

FAMILY TROCHOLTTIDAE CHAPMAN

Subglobular to discoidal nautilicones with three to 

five or more, gradually expanding, dorsally impressed 

whorls, typically depressed in cross section. Sutures simple transverse, or forming broad ventral lobes; camerae 

short. Shell sculpture varies in development, usually consisting of imbricating growth lamellae that form deep ventral sinuses. Strong ribs and periodic constrictions of the 

shell developed in some taxa.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P91

Siphuncles dorsal in position, marginal or dorsal of 

the center except in initial volution, where they may be 

central or ventral in position. Siphuncle segments tubular, 

narrow in diameter, usually less than one-fourth the diameter of the shell. Septal necks short, orthochoanitic. Connecting rings typically thick, but becoming thin and 

homogeneous in some taxa,

Stratigraphic range.—Lower Ordovician (Ibexian 

Provincial Series) to Upper Silurian (Ludlovian Series).

GENUS TROCHOLFTES CONRAD

Type species.—Trocholites ammonius Conrad, 1838, 

p. 118; by original designation; Trenton Limestone, Shermanian Stage, Middle Ordovician, New York.

Description.—Small, generally less than 10 cm in 

diameter, gradually expanding nautilicones, subdiscoidal 

in shape, having five or more volutions and a body chamber one-half to three-fourths of a volution in length that 

does not diverge from preceding whorls. Whorl section 

depressed, broadly reniform; dorsal part of whorl has 

shallow impressed zone. Umbilicus wide; umbilical perforation small.

Siphuncle tubular, narrow in diameter, segment 

diameters from one-fifth to one-sixth the diameter of the 

whorl; dorsal or subdorsal in position at all stages of 

growth. Septal necks short, orthochoanitic. Connecting 

rings thin, thickening adorally with ontogeny. Surface 

sculpture consisting of fasciculate growth lines or bands 

and raised ribs that form ventral sinuses.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Chazyan) to Upper Ordovician (Maysvillian 

Stage), North America, Baltic Europe, Iberian Peninsula.

mOCHOLITES FABERI TOERSTE, 1929C

Plate 19, figures 6-10

Trocholites faberi Foerste, 1929c, p. 323, pi. 63, 

figs. IA-D.

Diagnosis.—Rather large species of Trocholites distinguished by its subdued external ornament of fine, 

oblique growth lines, strongly depressed whorl profile, 

and dorsal location of the Siphuncle.

Description.—Gradually expanding, evolute nautilicones consisting of four to five whorls in close contact 

with one another; shell up to 9.0 cm in diameter and 

whorls up to 3.0 cm in diameter. Whorls reniform, 

depressed in cross section, nearly twice as wide as high. 

Shallow, concave, dorsal impressed zone, having venter 

convex, broadly rounded. Whorl profile becoming less 

depressed with ontogeny. Camera! chambers ranging 

from one-third to one-half the height of the whorl. Sutures 

essentially straight, transverse initially, becoming more 

sinuous with ontogeny marked by development of a shallow ventral lobe and ventrolateral saddles. Body chamber 

makes up one-half of a whorl, in contact with previous

whorl its entire length and contracting at the aperture. 

Aperture marked by a deeply incised, narrow, U-shaped 

hyponomic sinus, 7 mm deep at an adoral diameter of 2.5 

cm. Aperture sloping adorally from the venter, then curving back adapically at the dorsum. Shell exterior marked 

by fine, weakly developed, sinuous growth lines that 

slope obliquely from the dorsum to the venter in the 

adapical direction. Growth lines marking a broad sinus 

ventrally.

Siphuncle tubular, located nearly at the dorsal margin 

of the whorl. Siphuncle diameter slightly less than onethird the diameter of the shell at a shell height of 13 mm. 

Septal necks and nature of connecting rings unknown.

Stratigraphic and geographic occurrence.—Shermanian part of the Clays Ferry Formation, to Upper Ordovician (Edenian Stage), north-central Kentucky; Point 

Pleasant Tongue of the Clays Ferry Formation and the 

overlying Kope Formation; Covington, Ky., area and adjacent portions of Cincinnati, Ohio, region.

Studied material.—USNM 468724 (pi. 19, figs. 6, 7), 

468725 (pi. 19, figs. 8, 9), and 468726 (pi. 19, fig. 10) from 

the Kope Formation at Orphanage Road roadcut, Ft. 

Mitchell, Kenton County, Ky.; plus additional material 

including UC 46011, an impression from the same locality 

as above; UC 8138, labeled T. planorbiformis from the 

Cincinnati, Ohio, area; and UC 24476, a large shelled specimen (7.7 cm in diameter) and an incomplete portion of a 

body chamber, listed from the Vaupel Collection, "Southgate Member [Kope Formation] exposed at the Big 4 RR 

cut at Sadieville, Scott County, Kentucky." Other specimens of Trocholites studied are UC 1483, labeled T. 

ammonius Conrad from the Trenton Group, Trenton 

Falls, N.Y.; UC 8139, labeled T. circularis from the "Hudson River Group," Cincinnati, Ohio; UC 24475, labeled T. 

dyeri from the Carley Collection, "Trenton Limestone," 

Cincinnati, Ohio; and MU 29869, labeled T. ammonius, 

Trenton Limestone, New York. The location of the holotype of Trocholites faberi (Foerste, 1929C, pi. 58, fig. lac) is unknown at the present time.

Remarks.—Specimens of Trocholites from the 

greater Cincinnati region of Kentucky and Ohio have been 

placed in a number of species over the course of the past 

century. Examples are the type species, T. ammonius 

Conrad, T. planorbiformis Conrad, T. circularis Miller 

and Dyer, T. minisculus Miller and Dyer, T. dyeri Hyatt, 

and T. faberi Foerste. The specimens studied as part of 

this investigation, a majority of which are from the Edenian part of the Kope Formation (Upper Ordovician) in 

northern Kentucky, appear to be most similar to T. faberi 

Foerste. This is indicated by the large size of most specimens (in excess of 6.0 cm in diameter), the depressed 

whorl profile, and the weakly developed external ornament of fine, irregular, oblique growth lines preserved in
P92 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

most specimens. Unfortunately, none of the studied material preserves evidence of the structure of the siphuncle.

Trocholites ammonius Conrad was originally 

described (Conrad, 1838) from the middle part of the 

Trenton Limestone (Middle Ordoviciaii, Shermanian) of 

New York. Emmons (1842) and Hall (1847) remarked that 

this species also occurs in the equivalent black shale 

facies (=Canajoharie Shale). Ruedemann (1926) indicated 

that the species ranges up into the overlying Utica Shale 

(Upper Ordovician) in the same area. Foerste (1929c) distinguished T. ammonius from T. faberi on the basis of the 

smaller size of/, ammonius, the more central position of 

the siphuncle, and its distinctive surface ornament of 

alternating coarse and fine, raised, transverse lamellose 

ribs and lirae that give the shell surface a peculiar netlike 

appearance. This distinctive external shell ornament has 

not been observed in specimens of Trocholites from the 

Cincinnati area.

Trocholites faberi is similar to a variety of T. ammonius described by Ruedemann (1926) as T. ammonius 

var. major from the Utica Shale at Holland Patent, N.Y. 

These specimens were described as consisting of five 

whorls and attaining a larger diameter than typical T. 

ammonius, as well as possessing deeper camerae and 

lacking evidence of the coarse external ornament (Ruedemann, 1926, pi. 17, figs. 1-3). The position of the siphuncle 

was unknown. These specimens appear to be more similar to the Kentucky material from the Kope Formation.

The second species of Trocholites described by Conrad from the Ordovician strata in New York, T. planorbiformis from the Pulaski Formation (Upper Ordovician, 

Maysvillian), was distinguished by Hall (1847) and Ruedemann (1926) from T. ammonius primarily on the basis of 

its surface ornament. This ornament was described as 

consisting of oblique, raised, transverse and revolving longitudinal lines, forming a distinct cancellate pattern. The 

prominent, raised, longitudinal lirae described as being 

characteristic of this species have not been observed in 

any of the studied specimens of Trocholites from the Cincinnati-Covington area. Specimens of Trocholites preserving the outer shell and surface ornament are rare in the 

Kope Formation and equivalents in the greater Cincinnati 

area. Specimens preserving the siphuncle are equally 

uncommon. Both of these factors make further comparisons with these New York species difficult.

The remainder of the species of Trocholites 

described from the Cincinnati region are poorly known, 

and the locations of the type specimens of T. circularis, 

T. dyeri, T. faberi, and T. minisculus are unknown. Comparisons of these various species are, as a result, difficult. 

Assignment of the Kope material to T. faberi is tentative, 

pending further study of these various species and discovery in the Kope Formation of specimens of Trocholites 

that preserve the siphuncle.

At the Orphanage Road locality (KY-1), specimens of 

T. faberi occur as uncommon matrix-filled internal molds 

in a meter-thick claystone bed. The species is associated 

with similarly preserved specimens of the orthocerid 

Treptoceras transversum (Miller) and a diverse fauna of 

mollusks, consisting of pleurotomariacean snails, the 

monoplacophorans Cyrtolites and Sinuites, rostroconchs, and pelecypods (Frey, 1987b). Additional associated fauna are the brachiopods Onniellla and Zygospira, 

twiglike bryozoans, and three-dimensional specimens of 

the graptolite Geniculograptus typicalis.

SUBORDER BARRANDEOCERINA FLOWER

Cyrtocones, gyrocones, serpenticones, and torticones with primitively tubular, empty, orthochoanitic, 

thin-walled siphuncles that vary in position but are usually central or ventral; many derived taxa have cyrtochoanitic septal necks and inflated siphuncle segments.

Stratigraphic range.—Middle Ordovician to Middle 

Devonian.

FAMILY PLECTOCERATIDAE HYATT

Coiled barrandeocerinids having comparatively 

broad, tubular, midventral siphuncles and short orthochoanitic septal necks and thin, structureless connecting 

rings. Differing from ancestral tarphyceratids primarily in 

the nature of the connecting rings: thin in the Plectoceratidae; thick, layered in the Tarphyceratidae.

Stratigraphic range.—Middle Ordovician (Chazyan 

Stage) to Middle Silurian (Wenlockian Series).

GENUS PLECTOCERAS HYATT

Type species.—Nautilus jason Billings, 1859, p. 464; 

designated by Hyatt, 1884, p. 268; Mingan Formation, 

Chazyan Stage, Middle Ordovician, Mingan Islands, 

Quebec.

Description.—Comparatively large (up to 20 cm in 

diameter), robust serpenticones consisting of three or 

four volutions with initial whorls in contact; fairly rapidly 

expanding, the dorsal-ventral diameter doubling in one 

volution. Umbilical perforation large. Initial whorls somewhat depressed, subcircular, the venter slightly flattened 

and dorsum with a shallow impressed zone, sides 

rounded. Later whorls becoming compressed, subquadrate. Camerae short, the sutures initially straight, developing shallow lateral lobes with ontogeny. Mature body 

chambers free, less than one-half a volution in length. 

Aperture has a deep hyponomic sinus ventrally. Surface of 

shell marked by strong costae that curve obliquely in an 

adapical direction from the dorsum to the venter and 

swing back ventrally, forming V-shaped elevations. Parallel to costae are coarse transverse lirae. Costae more conspicuous ventrolaterally, becoming obsolete dorsally.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P93

Siphuncle near the ventral margin of the shell, 

removed from it by a distance equal to one-sixth the diameter of the shell. Siphuncle tubular, having diameters 

between one-eighth and one-fifth the diameter of the 

shell. Septal necks orthochoanitic, short, straight. Connecting rings thin, homogeneous.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Chazyan to Rocklandian Stages), Eastern and 

Arctic North America (Laurentia).

PLECTOCERAS CF. P. CARLETONENSE FOERSTE, 1933

Plate 19, figures 1-3

Plectoceras carletonense Foerste, 1933, p. 123, pi. 36, 

fig. 1.

Diagnosis.—Species of Plectoceras distinguished by 

its depressed whorl profile and an external ornament consisting of weakly developed ventrolateral costae.

Description.—Species incompletely known, represented by fragmentary specimens. These consist of a portion of the inner whorl expanding from 18 to 21 mm in 

diameter in a length of 50 mm. Whorl profile depressed, 

18 mm in width and 15 mm high at the adapical end. Venter broadly rounded with a very shallow dorsal impressed 

zone, although much of the dorsal portion of the whorl 

has been lost. Camerae short, cameral lengths averaging 

one-sixth the diameter of the shell at diameters of 18-21 

mm. Inner whorl in contact with outer whorl ventrally. 

Shell exterior marked by indistinct, raised costae spaced 

3 mm apart, sloping obliquely in the adapical direction 

from the dorsum to the venter. Costae most distinct ventrolaterally. Costae forming broadly rounded V-shaped elevations ventrally. Siphuncle 2.5-3.0 mm in diameter, 

situated less than 1 mm from ventral shell margin.

Other fragments representing portions of the body 

chamber, including part of the aperture. Aperture disjunct 

from earlier whorls, the lateral portions curving sharply 

forward from venter and then curving sharply back at dorsum. Exterior marked by nearly flat, indistinct costae 4 

mm wide, spaced 8 mm apart having intervening irregular, 

fine growth lines.

Stratigraphic and geographic occurrence.—Upper 

part of the Rocklandian portion of the Tyrone Limestone 

(Middle Ordovician), vicinity of the Kentucky River gorge, 

Jessamine County, Ky.

Studied material.—USNM 158651 (pi. 19, figs. 1-3) 

and additional fragmentary specimens, all silicified material from the USGS 6034-CO collection, Little Hickman 

section A, Sulfur Well, Ky.

Remarks.—The silicified Tyrone Limestone material 

described here, although fragmentary, preserves enough 

of the morphology of the shell to indicate placement of 

these specimens in the genus Plectoceras Hyatt. This is 

indicated by the ventral position of the Siphuncle, the 

depressed whorl profile, the short camerae, and the

FIGURE 25.—Reconstruction of the entire shell of the 

coiled tarphycerid Plectoceras cf. P. carletonense 

from the upper part of the Tyrone Limestone, 

Jessamine County, Ky. Based on fragmentary 

silicified specimens from the USGS 6034-CO 

collection (see pi. 19, figs. 1-3). xO.65.

raised costae forming a V-shaped pattern ventrally. A 

reconstruction of a complete specimen of this species 

based on this fragmentary material (fig. 25) indicates a 

specimen at a maximum diameter of 13.0 cm.

The Tyrone specimens are most similar to P. carletonense Foerste from the "Black River Formation" (Leray 

beds) exposed in the Ottawa region of Ontario. Both species possess depressed, subrectangular whorl sections 

that are wider than high, have inner whorls that are in 

contact but not strongly impressed dorsaUy, and have 

siphuncles situated very close to the ventral shell margin. 

Costae in both forms are weakly developed, compared 

with other described species of Plectoceras, being most 

distinct ventrolaterally. More complete material from the 

Tyrone Limestone is needed to further compare these 

species.

The Tyrone material is less similar to P. robertsoni 

(Hall), another dorsaUy depressed species of Plectoceras 

from the Middle Ordovician (Blackriveran and Rocklandian) Platteville Formation in Wisconsin and Platteville 

Group in Illinois. It differs from this species in that the 

inner whorls of the Platteville form have a distinct dorsal 

impressed zone that appears to be lacking in the Kentucky material. The costae in specimens of P. robertsoni 

figured by Foerste (1932, pi. 36, figs. 2A-D, 3A-B) are also 

much more strongly developed than is evident in the Kentucky specimens.
P94 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

In a similar manner, the Tyrone species is distinct 

from P. halli (Foord) described from Middle Ordovician 

strata exposed at Lorette, Quebec. This is another species 

of Plectoceras with a depressed whorl profile and strongly 

developed ventrolateral costae (pi. 19, figs. 4, 5). Further 

study may indicate that this species is a synonym of P. 

robertsoni (Hall).

The Tyrone species of Plectoceras is less similar to 

other described species of Plectoceras, such as the type 

species, P. jasoni (Billings) from Middle Ordovician 

(Chazyan) strata in New York and Quebec, P. undatum 

(Conrad) from the Watertown Limestone (Blackriveran 

and Rocklandian) in New York, and P occidentalis (Hall) 

from the Platteville Group (Blackriveran and Rocklandian) in Illinois. This group of species is distinct from the 

preceding group, as well as the Tyrone form, in having 

whorls that are more circular in profile and that become 

disjunct at an earlier ontogenetic stage than the dorsalventrally depressed species described above. Additionally, Pjasoni and P occidentalis possess costae that are 

much more strongly developed than is evident in the 

Tyrone species.

Study of the described species currently assigned to 

the genus Plectoceras Hyatt has indicated that the genus 

can be divided into two major groups. One group is of 

generally smaller diameter species that have the whorls in 

contact most of the length of the shell, giving the whorls a 

depressed cross section having a variably developed dorsal impressed zone. A second group, including the type 

species, consists of generally larger shells in which the 

whorls become disjunct at an earlier stage of development, giving the whorls a more circular cross section and 

typically lacking a dorsal impressed zone. Flower (1984) 

proposed splitting up Plectoceras along similar lines, 

although he noted there is such gradation in this respect 

that he regarded these groups as making up one genus. He 

differentiated Plectoceras instead on the basis of the more 

quadrate whorl and flattened venter typical of most 

younger (Blackriveran) species in contrast to the rounded 

venter typical of the type species, P jasoni from older 

Chazyan strata in New York and Quebec. Pending further 

study of the genus, all of these species, as well as the 

Tyrone form, are retained here in Plectoceras.

ORDER ONCOCERIDA FLOWER

Primitively compressed, exogastric cyrtocones and 

brevicones with short camerae and simple, transverse or 

slightly curved sutures. Younger taxa are rapidly or gradually expanding longiconic cyrtocones, orthocones, torticones, gyrocones, and nautilicones, some depressed in 

section with endogastric curvature. Body chambers typically large; apertures primitively simple with a ventral 

hyponomic sinus; later forms developing bizarre contracted apertures. Periphract ventromyarian. Siphuncle

ventral of center, segments generally narrow in diameter, 

but may become large and inflated. Septal necks suborthochoanitic or cyrtochoanitic; connecting rings typically 

thin but may thicken with ontogeny, producing actinosiphonate deposits. Major means of buoyancy regulation is 

the large volume of visceral mass and shell material relative to the phragmocone. Actmosiphonate deposits may 

have served a hydrostatic function, controlling the volume of cameral fluids in the phragmocone.

Stratigraphic range.—Middle Ordovician to lower 

Carboniferous.

FAMILY ONCOCERAHDAE HYATT

Rapidly to gradually expanding exogastric cyrtocones, brevicones, and longiconic cyrtocones; compressed in section and having straight transverse sutures 

that tend to become more curved with ontogeny, sloping 

adorally from the dorsum to the venter. Camerae typically 

short, cameral length decreasing with ontogeny. Body 

chamber large, contracting toward the aperture. Aperture 

simple, open, marked by a variously developed ventral 

hyponomic sinus. Shell exteriors typically smooth but 

may be marked by strong transverse costae or crenulate 

frills.

Siphuncle ventral of center, often located close to 

ventral shell margin. Segments empty, depressed, tubular 

in early stages, becoming expanded, scalariform to heartshaped in later stages. Septal necks suborthochoanitic initially, becoming cyrtochoanitic with ontogeny. Connecting rings thin. Actinosiphonate deposits develop in some 

younger taxa.

Stratigraphic range.—Middle Ordovician (Chazyan 

Stage) to Upper Silurian (Ludlovian Series).

GENUS ONCOCERAS HALL

Type species.—Oncoceras constrictum Hall, 1847, p. 

197; by original designation; Trenton Limestone, Shermanian Stage, Middle Ordovician, New York.

Description.—Small, exogastrically curved brevicones, compressed in cross section having the venter 

more narrowly rounded than dorsum. Greatest diameter 

of the shell typically located just adapical of the body 

chamber, so that the dorsal shell outline is initially concave, becoming broadly convex at junction with body 

chamber, then slightly concave at the aperture. Ventral 

shell outline remaining broadly convex the length of the 

shell. Cameral chambers short, cameral length decreasing 

with ontogeny. Sutures straight, transverse, sloping with 

ontogeny from the dorsum to the venter in the adoral 

direction. Body chamber short but broad, contracting 

toward the aperture. Aperture marked by a variously 

developed hyponomic sinus ventrally and a shallow sinus 

dorsally. Periphract ventromyarian. Shell exterior essentially smooth in most species, marked by fine transverse
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P95

growth lines and a color pattern of transverse bands that 

completely encircle the shell.

Siphuncle small in diameter, located close to the ventral shell margin. Segments subtubular adapically, becoming more expanded with ontogeny to form ovoid to 

scalariform segments adorally. Septal necks short, 

recurved, cyrtochoanitic. Connecting rings thin, homogeneous. Segments devoid of deposits.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Chazyan Stage) to Upper Ordovician (Gamachian Stage), North America (Laurentia).

Remarks.—Flower (1946) gives an excellent synopsis of this genus and its Stratigraphic and geographic distribution, and a discussion of its relationships with the 

genera Beloitoceras Hyatt and Neumatoceras Foerste. 

Oncoceras differs from Beloitoceras in being a less compressed, more rapidly expanding shell. Beloitoceras lacks 

the well-developed gibbosity characteristic of Oncoceras, 

namely, its evenly concave dorsal profile and a weak convexity in the lower half of the body chamber. These distinctions may, however, be blurred in early stages of 

growth and in the development of transitional species 

that share features common to both genera. Beloitoceras 

is the dominant form in earlier Chazyan and Blackriveran 

strata, Oncoceras becomes more prevalent in younger 

Shermanian to Maysvillian rocks. Flower (1946) 

described Oncoceras as a more advanced, "phylogeronitic" version of Beloitoceras. Curiously, both genera are 

equally represented in younger Richmondian strata in the 

Cincinnati region.

Flower (1946) described the closely related genus 

Neumatoceras Foerste as being a less well established 

genus, based on species that attain an extreme in the convexity of the shell just adapical to the body chamber. This 

genus is most typical of Shermanian to Richmondian 

strata that are part of the areally extensive carbonate platform facies that were deposited over much of Western 

and Arctic North America during this time. Species 

grouped in this genus were thought to represent the end 

product of the evolutionary sequence described above for 

Beloitoceras and Oncoceras. The differences between 

Neumatoceras and Oncoceras lie chiefly in the areas of 

size and the degree of shell convexity, vaguely defined 

characters to use to distinguish these genera. Flower further pointed out the possible effects of taphonomy. He 

replicated a cast of a typical specimen of Oncoceras and 

then, simulating the effects of sediment compaction, flattened the cast, resulting in a typical Neumatoceras. As a 

result of these observations, he suggested placing Neumatoceras in synonymy with Oncoceras as a junior 

synonym.

ONCOCERAS MAJOR NEW SPECIES

Plate 19, figures 11-15

Diagnosis.—Large species of Oncoceras distinguished by the lack of a constricted area adapical of the 

aperture and by its distinctive external ornament of 

coarse transverse costae.

Description.—Comparatively large (estimated 

lengths of 12.5 cm and a maximum observed shell diameter of 4.3 cm), broadly inflated, rapidly expanding (apical 

angle 25 degrees), exogastric brevicone. Lateral shell profile uniformly convex ventrally, dorsum slightly convex 

adorally such that the maximum shell diameter is at the 

juncture between the phragmocone and the body chamber. Compressed-ovate in cross section, height to width 

ratio 1.16 at a shell height of 30 mm and 1.22 at a shell 

height of 43 mm. In cross section the dorsum is broadly 

rounded, the venter narrowly rounded, almost angular. 

Sutures nearly straight, transverse, becoming slightly 

oblique in adoralmost portions of the phragmocone, sloping from the dorsum to the venter in adoral direction. 

Camera! chambers short, camera! lengths ranging from 

one-eighth to one-eleventh the diameter of the shell at 

shell diameters from 30 to 40 mm. Body chamber inflated 

but laterally compressed, contracting slightly towards the 

aperture. Aperture open, subtriangular, broadly rounded 

dorsally, the venter narrowly rounded, marked by a shallow V-shaped hyponomic sinus. Periphract ventromyarian. Shell surface marked by fine, incised, transverse 

striae between broad, 1-2 mm wide, raised convex costae 

of varying width and prominence. Costae transverse dorsally, curving ventrally to delineate a shallow V-shaped 

sinus.

Siphuncle situated at the ventral shell margin, the 

siphuncle 5 mm in diameter at a shell diameter of 30 mm. 

Opening for siphuncle in adoralmost septum broad, 9 mm 

in diameter. Segment shape unknown. Nature of septal 

necks unknown.

Stratigraphic and geographic occurrence.—Upper 

part of the Rocklandian portion of the Tyrone Limestone 

(Middle Ordovician), vicinity of the Kentucky River, Jessamine County, Ky.

Studied material—Holotype USNM 158665 (pi. 19, 

figs. 11-15), USGS 6034-CO collection, Little Hickman 

section A, Sulfur Well, Ky.

Remarks.—This writer is hesitant to erect a new species on the basis of a single specimen, but this specimen 

is quite distinct from all other species of Oncoceras. Diagnostic of O. major is its large size, on which Flower 

(unpublished notes) remarked that the species is "The 

largest species of Oncoceras known to me." He stated further that "forms of comparable size have not been found 

in the eastern United States or Canada." Its coarse external ornament of broad, raised, transverse costae is equally
P96 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

distinctive, not being described or figured for any other 

species of Oncoceras known to this writer. Additional 

diagnostic features are the convex dorsal outline of the 

shell coupled with the lack of a strong constricted area 

adapical of the aperture.

Oncoceras major is most similar to a group of primarily Middle Ordovician species of Oncoceras characterized by a distinctly convex dorsal outline at the juncture 

of the phragmocone with the body chamber. These species are the type species O. constrictum Hall, from Rocklandian to Shermanian strata exposed in New York and 

adjacent portions of Canada; O. coUinsi Foerste, O. scalariforme Wilson, and O. tetreauviUense Foerste, all from 

the "Leray beds" exposed in the Ottawa, Ontario region; 

and O. douglassi (Clarke) from the Shermanian Prosser 

Limestone in Minnesota. Oncoceras major differs from 

the first three species in its larger size, distinctive transverse external ornament, and lack of a well-developed 

constriction adapical of the aperture, the latter being a 

feature common to all three of these species of Oncoceras. Oncoceras major also is a more inflated, more dorsally convex species compared with O. coUinsi and O. 

scalariforme. The Kentucky specimen is more similar to 

O. tetreauviUense and O. douglassi in inflation and dorsal 

convexity but differs from both in its coarse transverse 

surface markings.

Oncoceras major is less similar to Upper Ordovician 

species of Oncoceras described by Flower (1946) from 

the Cincinnati arch region. These Cincinnatian species, 

consisting of O. arlandi Flower from the Leipers Limestone in Kentucky, O. deliculatum Flower from the Bull 

Fork Formation in southwestern Ohio, and O. madisonense Flower from the Hitz Limestone Member of the 

Saluda Formation at Madison, Ind., all lack the obvious 

dorsal convexity and coarse transverse ornament characteristic of O. major.

As indicated above, O. major is apparently a rare element of the diverse, abundant nautiloid fauna present in 

the USGS 6034-CO collection from the upper part of the 

Tyrone Limestone hi central Kentucky. There it is associated with abundant specimens of the baltoceratid Cartersoceras shideleri (pi. 1, figs. 1-6), the orthocerids 

Pojetoceras jloweri (pi. 2, figs. 1-9) and Proteoceras 

tyronensis (pi. 4, figs. 1-7), the actinocerids Actinoceras 

altopontense, A. kentuckiense (pi. 17), and Ormoceras 

ferecentricum (pi. 18, figs. 1-7), the endocerid Vaginoceras sp. A (pi. 15, figs. 1-4), uncommon specimens of the 

tarphycerid Plectoceras cf. P. carletonense (pi. 19, figs. 1- 

3), and the oncocerids Beloitoceras cf. B. huronense (pi. 

20, figs. 3-6), Maelonoceras cf. M. praematurum (pi. 20, 

figs. 7-12), and Laphamoceras cf. L. scofieldi (pi. 20, figs. 

13-18).

ONCOCERAS SP.

Plate 20, figures 1, 2

Diagnosis.—Small, rapidly expanding species of 

Oncoceras, having exterior marked by fine, raised transverse lirae.

Description.—Incomplete, fragmentary specimens 

indicate a comparatively small (estimated lengths of 85 

mm and a maximum observed shell diameter of 26 mm), 

rapidly expanding (apical angle 30 degrees), exogastrically curved brevicone having venter broadly convex and 

the dorsum concave adapicaUy at shell heights of 10 mm, 

becoming straight to slightly convex adorally at shell 

heights of 15-25 mm. Shell compressed ovate in cross 

section, the height to width ratio being 1.11 at a shell 

height of 10 mm and 1.18 at a shell height of 20 mm. Camerae short, with cameral lengths increasing from oneeighth to one-sixth the diameter of the shell at shell 

heights from 15 to 23 mm, and then decreasing to oneninth the diameter of the shell at a shell height of 25 mm. 

Body chamber incompletely known, inflated, making up 

roughly one-third the total length of the shell. Aperture 

unknown. Periphract ventromyarian. Shell surface 

marked by fine (0.5 mm wide), raised, transverse lirae 

that delineate a shallow V-shaped ventral sinus.

Siphuncle located at the ventral margin, narrow in 

diameter, one-ninth the diameter of the shell at a shell 

diameter of 25 mm. Segments scalariform, broader 

adorally than apically. Segments empty. Septal necks 

unknown.

Stratigraphic and geographic occurrence.—Grier 

Limestone Member of the Lexington Limestone (Middle 

Ordovician, Kirfieldian to Shermanian), Jessamine 

County, Ky.

Studied material.—USNM 468732 (pi. 20, fig. 1) and 

468731 (pi. 20, fig. 2), both fragmentary silicified specimens from USGS 4879-CO and 4883-CO collections from 

exposures along Antioch Church Road, Valley View section C, Valley View, Ky.

Remarks.—The fragmentary nature of the material 

makes comparisons with other described species of 

Oncoceras difficult. Especially critical is the lack of any 

specimens preserving the dorsal outline of the adoral portion of the shell and adjacent portions of the body chamber. Additionally, no specimens available to this writer 

preserve the aperture of the body chamber. More complete material is necessary to further the affinities of 

these specimens.

In the Grier Limestone Member, Oncoceras sp. is an 

uncommon species found in association with a number of 

specimens of an unidentified large, smooth, orthoconic 

longicone (Treptoceras?^. Other faunal associates are 

well-preserved specimens of the pleurotomariacean
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P97

gastropods Clathrospira and Lophospira, plus a number 

of small orthid, strophomenid, and atrypid brachiopods.

GENUS BELOITOCERAS fOERSTE

Type species.—Oncoceras pandion Hall, 1861, p. 45; 

designated by Foerste, 1924b, p. 244; Platteville Limestone, Blackriveran Stage, Middle Ordovician, Wisconsin.

Description.—Small to moderate in size (rarely up to 

20 cm in length and 7.5 cm in diameter), strongly curved, 

exogastric brevicones that are ovate in cross section, 

becoming more compressed with ontogeny. Maximum 

shell diameter situated within the adapical one-half to 

two-thirds of the body chamber; shell only slightly 

inflated. Dorsal outline of shell typically concave for its 

entire length. Ventral margin broadly convex. Sutures 

straight and transverse adapically, sloping from the dorsum to the venter in the adoral direction with ontogeny. 

Cameral chambers short, cameral lengths ranging from 

one-fifth to one-eighth the diameter of the shell, increasing with ontogeny until onset of maturity. Body chamber 

short, laterally compressed; well-developed hyponomic 

sinus ventrally; shallow sinus dorsally. Periphract ventromyarian. Shell smooth or with fine, raised transverse 

ribs.

Siphuncle small in diameter, located close to the ventral shell margin. Segments subtubular adapically, becoming expanded, elongate ovate adorally. Septal necks, 

adapically short, suborthochoanitic, becoming more 

recurved, cyrtochoanitic, with ontogeny. Connecting rings 

thin, homogeneous. Segments empty. Cameral deposits 

described for some species.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Chazyan Stage) to Upper Ordovician (Gamachian Stage); North America and Baltic Europe.

Remarks.—As indicated in the previous discussion 

of Oncoceras, Beloitoceras forms the primitive stock from 

which Oncoceras andNeumatoceras were later derived in 

the Middle Ordovician. It differs in its typical form from 

these related genera in being a more laterally compressed, strongly curved shell that lacks the dorsal convexity in adoral portions of the shell that is typical of 

specimens of the latter two genera. Beloitoceras is the 

dominant oncocerid in Chazyan and Blackriveran strata 

in Eastern and Central North America, becoming less 

important in succeeding upper Middle Ordovician (Kirkfieldian to Shermanian) and lower Upper Ordovician 

(Edenian) strata. The genus has a resurgence of speciation in the Richmondian, being widespread across both 

Arctic and East-Central North America,

As noted by Flower (1946), the genus currently 

embraces more species than Oncoceras and Neumatoceras combined. Flower (1946) divided the genus into a 

number of "species groups," based primarily on the 

nature of the dorsal outline of the shell. He noted that

these groups graded into one another, and therefore, he 

did not formally recognize these groups as distinct taxa,

BELOITOCERAS AMOENUM (MILLER), 1879 

Plate 21, figure 3; plate 22, figure 2

Cyrtoceras amoenum Miller, 1879, p. 105, pi. 3, fig. 8. 

Cyrtoceras amoenum Miller. James, 1886, p. 247. 

Cyrtoceras amoenum Miller. Cumings, 1908, p. 1027, 

pi. 49, fig. 1.

Beloitoceras amoenum (Miller). Flower, 1946, p. 272, 

pi. 32, figs. 15,17; pi. 34, figs. 4, 5; pi. 37, fig. 9; pi. 38, fig. 6; 

pi. 42, figs. 2, 5.

Diagnosis.—Relatively large, elongate, slender species of Beloitoceras, the greatest shell diameter just 

adapical of the body chamber, an essentially straight dorsum, and sutures that, with ontogeny, become strongly 

oblique, sloping adorally from the dorsum to the venter.

Description.—Size large for genus (estimated 

lengths up to 12.0 cm and observed shell diameters up to 

3.8 cm); rapidly expanding (apical angle 22-26 degrees), 

exogastric brevicones whose dorsal outline is concave 

adapically, becoming nearly straight or slightly convex 

with ontogeny, having the maximum shell diameter just 

adapical of body chamber. Venter broadly convex for the 

length of the shell. Shell cross section ovate adapically, 

becoming more compressed adorally with ontogeny. 

Sutures straight, transverse adapically, becoming strongly 

oblique with ontogeny, sloping adorally from the dorsum 

to the venter. Cameral chambers short, cameral length 

decreasing with ontogeny from one-sixth to one-ninth the 

diameter of the shell at diameters of 15-25 mm, then 

increasing adorally from one-ninth to one-seventh the 

diameter of the shell at diameters greater than 25 mm. 

Adoralmost septa becoming approximate in larger specimens, cameral lengths reduced to one-twentieth the diameter of the shell. Body chamber short, one-fifth the total 

length of the shell, highly compressed, tapering toward 

aperture. Aperture marked by well-developed ventral 

hyponomic sinus and shallow dorsal sinus. Shell exterior 

marked by coarse tranverse lirae.

Siphuncle located at ventral margin. Segments narrow, diameters one-eighth to one-ninth the diameter of 

the shell; slightly expanded, depressed ovate in outline. 

Structure of septal necks and connecting rings unknown.

Stratigraphic and geographic occurrence.—Upper 

Ordovician (Richmondian Stage); Whitewater Formation 

in southeastern Indiana, upper part of the Bull Fork Formation in southwestern Ohio.

Studied material.—Holotype UC 106, Whitewater 

Formation, Richmond, Ind.; hypotypes Earlham College 

nos. 7744 and 14953, Whitewater Formation, Richmond, 

Ind.; USNM 468668 (pi. 21, fig. 3), upper part of the Bull 

Fork Formation, Dayton, Ohio; and USNM 468669 (pi. 22, 

fig. 2), Whitewater Formation, Richmond, Ind.
P98 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

Remarks.—This species is a common form in the 

rubbly bedded, fossiliferous limestones of the Whitewater 

Formation exposed in the vicinity of Richmond, Wayne 

County, hid. It usually occurs as poorly preserved internal 

molds associated with a diverse fauna of orthid and rhynchonellid brachiopods, ramose trepostome bryozoans, 

the coral Grewingkia canadense, pelecypods, and other 

mollusks. Figured specimen USNM 468668 (pi. 21, fig. 3) 

was collected from the interbedded, thin, fossiliferous 

packstone and shale in the upper part of the Bull Fork 

Formation exposed in north Dayton, Montgomery County, 

Ohio. The species is apparently a rare form in these strata, 

where it is associated with ramose trepostome bryozoans, 

the rugosan coral Grewingkia canadense, and the rhynchonellid brachiopod Hiscobeccus capax.

Flower (1946) commented that, on the basis of having the maximum shell diameter adapical of the body 

chamber, this species could be placed in the genus Oncoceras. The adorally compressed shell and the concave 

dorsal margin, however, indicate assignment of the species to Beloitoceras. Beloitoceras amoenum is most similar to B. cumingsi Flower, from equivalent fine-grained 

limestones of the Saluda Formation in southeastern Indiana and adjacent portions of western Ohio. Both species 

have adorally compressed shells that have their maximum 

diameter just adapical of the body chamber, straight dorsums, and sutures that slope adorally from the dorsum to 

the venter. Beloitoceras cumingsi differs from B. amoenum in being a smaller, more rapidly expanding shell. 

Beloitoceras amoenum is also similar to B. magisterium 

Foerste, a somewhat larger species from the Vaureal Formation (Gamachian) on Anticosti Island, Quebec. Similar 

in size to B. amoenum is B. whitneyi (Hall) from the 

Maquoketa Formation in Iowa. This species, however, differs from B. amoenum in possessing a more slender, 

longer phragmocone and longer body chamber. Beloitoceras amoenum differs from B. bucheri Flower (pi. 22, 

figs. 4, 5) from the Saluda Formation in being a larger, 

more inflated species with deeper camerae and sutures 

that slope from the dorsum to the venter adorally.

BELOITOCERAS BUCHERTYLOVfER, 1946 

Plate 22, figures 4, 5

Beloitoceras bucheri Flower, 1946, p. 283, pi. 39, fig. 6.

Diagnosis.—A slender, highly compressed species of 

Beloitoceras distinguished by its slight curvature, nearly 

straight dorsum, and very short camerae.

Description.—Medium-sized (estimated lengths up 

to 11.0 cm and observed diameters up to 3.0 cm), slender 

(apical angle 19-20 degrees), exogastric cyrtocone. Dorsal outline nearly straight adorally, the maximum shell 

diameter occurring at the junction of phragmocone and 

body chamber. Venter gently convex for the length of the 

shell. Shell cross section compressed ovate, the shell

height exceeding the width for the entire length of the 

shell. Sutures straight, transverse. Cameral chambers very 

short, cameral length decreasing with ontogeny from oneeighth the diameter of the shell adapically to one-eleventh 

the diameter of the shell adorally. Body chamber long, in 

excess of one-fourth the length of the shell, compressed 

tubular, sides subparallel, contracting slightly at the aperture. Aperture has well-developed V-shaped ventral 

hyponomic sinus and very shallow dorsal sinus. Shell 

marked by closely spaced, raised transverse lirae.

Siphuncle located at ventral shell margin. Segment 

diameters narrow, one-seventh the diameter of the shell. 

Structure of septal necks and connecting rings unknown.

Stratigraphic and geographic occurrence.—Upper 

Ordovician (Richmondian Stage), Bull Fork Formation in 

southwestern Ohio; Saluda Formation in southeastern 

Indiana.

Studied material.—Holotype MU 437T, "lower 

Whitewater Beds," near Winchester, Adams County, Ohio; 

MU 433T (pi. 22, figs. 4, 5) and MU 29865, both from the 

"Concrete layer" (Bliss, 1984) at the top of the Saluda Formation, Hamburg, Franklin County, hid.

Remarks.—Flower (1946) distinguished this species 

from all other Cincinnatian species of Beloitoceras on the 

basis of its "slender form, very short camerae, and relatively slight curvature." The species previously was 

known only from the holotype, a somewhat flattened 

internal mold preserving the body chamber and adoral 

portions of the phragmocone. Several better preserved, 

calcite-replaced specimens of a slender Beloitoceras (pi. 

22, figs. 4, 5) have been collected from the "Concrete 

layer," a 1-ft (0.3-m) thick micritic limestone bed that 

occurs at the top of the Saluda Formation in portions of 

Franklin County, hid. The slender, compressed, only 

slightly curved shell shape and short camerae in these 

specimens suggest placement of these specimens in 

Flower's species, hi this massive limestone bed, B. 

bucheri occurs associated with a diverse nautiloid fauna 

that consists of Gorbyoceras gorbyi (Miller) (pi. 12, figs. 

12,13), Cameroceras sp., the ascoceroid Schuchertoceras 

prolongatum Flower, the large oncocerids Diestoceras 

indianense (Miller and Faber) (pi. 22, figs. 6-9) and D. 

shideleri (pi. 22, figs. 1,3), and several species of the slender oncocerid Manitoulinoceras. This fauna is unique in 

terms of both its diversity and the complete nature of 

many of the preserved shells.

Beloitoceras bucheri is probably most similar to B. 

ohioense Flower, a slender, compressed species of 

Beloitoceras from the equivalent Whitewater Formation 

in Indiana and the upper part of the Bull Fork Formation 

in southwestern Ohio. It differs from this species in lacking the obliquity of the adoral sutures and deeper camerae 

characteristic of B. ohioense and similar species like B. 

amoenum and B. cumingsi. Beloitoceras bucheri differs
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P99

from the associated slender, compressed oncocerid Oonoceras fennemani Flower in its greater shell height and 

more strongly curved shell form.

BELOITOCERAS CF. B. HURONENSE (BILLINGS), 1865

Plate 20, figures 3-6

Cyrtoceras huronense Billings, 1865, p. 176, figs. 158A-B. 

Beloitoceras huronense (Billings). Foerste, 1932, 1933, 

p. 100, pi. 30, figs. 3A-C.

Beliotoceras huronense (Billings). Wilson, 1961, p. 84, 

pi. 32, figs. 3,4.

Diagnosis.—Small, compressed species of Beloitoceras with a short body chamber whose dorsal outline is 

only slightly concave.

Description.—Small (estimated lengths of up to 6.0 

cm and observed shell diameters up to 1.7 mm), slender 

(apical angle 15.5 degrees), exogastrically curved brevicone, the dorsum slightly concave in outline adorally, 

more strongly concave adapically at shell diameters less 

than 10 mm. Venter uniformly convex for the length of the 

shell. Shell circular in cross section at shell diameters less 

than 10 mm, becoming more compressed adorally with 

ontogeny. Sutures adapically straight, transverse; becoming slightly oblique with ontogeny, sloping from the dorsum to the venter in the adoral direction. Camerae short, 

cameral lengths ranging from one-fifth to one-sixth the 

diameter of the shell, decreasing slightly with ontogeny. 

Body chamber short, one-fifth the total length of the shell, 

laterally compressed, the maximum shell diameter just 

adoral to the juncture of the phragmocone and the body 

chamber. Aperture marked by a shallow dorsal sinus. Ventral portions of aperture not preserved. Shell exterior 

essentially smooth, marked by fine transverse growth 

lines.

Siphuncle located at the ventral shell margin. Segments small in diameter, shape unknown. Structure of 

septal necks and connecting rings unknown.

Stratigraphic and geographic occurrence.—Upper 

part of the Rocklandian part of the Tyrone Limestone 

(Middle Ordovician), vicinity of the Kentucky River, Jessamine County, Ky.

Studied material.—USNM 158666 (pi. 20, figs. 3,4, 6) 

and 468733 (pi. 20, fig. 5), plus a suite of fragmentary silicified specimens (USNM 468729), all from the USGS 6034- 

CO collection, Little Hickman section A, Sulfur Well, Ky.

Remarks.—Specimens of Beloitoceras from the 

USGS 6034-CO collection in the Tyrone Limestone consist 

of incomplete, fragmentary silicified material, one specimen consisting of the adoral portion of the phragmocone 

and the attached body chamber (pi. 20, figs. 3, 4, 7) and a 

second specimen consisting of the adoral part of the 

phragmocone (pi. 20, fig. 5). The remainder of the specimens of Beloitoceras from this collection consist of 

numerous adapical portions of the phragmocone 5 mm or

less in diameter. As no complete phragmocones are 

known for any of the various oncocerids present in the 

6034-CO collection, the identity of these latter specimens 

is uncertain. The strong curvature of the small adapical 

portions of shells suggests placement in either Beloitoceras huronense or in Laphamoceras cf. L. scofieldi (pi. 

20, figs. 13-18), as both O. major (pi. 19, figs. 11-15) and 

Maelonoceras cf. M. praematurum (pi. 20, figs. 7-12) are 

less strongly curved, rapidly expanding forms. These 

small adapical specimens may also be assignable, in part, 

to the genus Loganoceras Foerste. Larger diameter portions of the shell recognizable as belonging to Loganoceras have not, however, been observed in the 6034-CO 

collection.

The fragmentary specimens of Beloitoceras from the 

6034-CO collection appear to be most similar to B. huronense (Billings) from the Middle Ordovician (Rocklandian) 

limestones exposed on St. Joseph Island in Lake Huron. 

The Kentucky material and the types of Billing's species 

(GSC 1297) are similar in the small size of the shell, the 

short body chamber, the laterally compressed adoral 

cross section, and the minimum concavity of the dorsal 

profile of the adoral portion of the shell. The Kentucky 

material appears to differ from B. huronense in the more 

dorsally produced shape of the body chamber and the 

lack of shell contraction at the aperture.

Beloitoceras cf. B. huronense differs from the type 

species of Beloitoceras, B. pandion (Hall), and from B. 

janesviUense Foerste, both from the Platteville Formation 

in Wisconsin, in being a smaller, more laterally compressed, less inflated species. It appears to be distinct 

from similar small, laterally compressed Middle Ordovician species like B. clochense Foerste, B. houghtoni 

(Clarke), and B. isodorum (Billings) in having a less 

strongly concave dorsal shell outline and possessing a 

shorter body chamber. More complete specimens of the 

Kentucky species are needed to more fully determine the 

affinities of the species and the identity of the small adapical shell fragments common in the 6034-CO collection.

GENUS MAELONOCERAS HYATT

Type species.—Phragmoceras praematurum Billings, 1860, p. 173; designated by Hyatt, 1884, p. 280; 

"Cloche Island beds," Rocklandian Stage, Middle Ordovician, Ontario.

Description.—Relatively small, slender, inflated exogastric cyrtocones with a distinctive subtriangular cross 

section, the dorsum wide, nearly flat, and the venter more 

narrowly rounded, subangular. Venter broadly convex in 

lateral profile, the dorsal outline subparallel, slightly concave. Sutures transverse, slightly oblique, sloping from 

dorsum to venter in the adoral direction. Cameral chambers short; septa thin, flat. Body chamber short, inflated, 

having the maximum diameter of the shell occurring just
P100 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

adapical of the aperture. Aperture distinctive, pearshaped, constricted laterally by two rounded lateral, 

visorlike projections such that the ventral portion of the 

aperture is restricted to a narrow hyponomic sinus. Dorsal portion of aperture broad, open.

Siphuncle small in diameter, situated at the ventral 

shell margin. Segment shape unknown. Structure of septal necks and connecting rings unknown.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Rocklandian Stage), East-Central North 

America (Laurentia).

Remarks.—This poorly known genus was originally 

based on Phragmoceras praematurum Billings, known 

from a single body chamber from Rocklandian strata 

("Cloche Island beds") exposed on Cloche Island, in Lake 

Huron, Ontario. This species was selected as the type species for the genus Maelonoceras by Hyatt. The genus was 

distinguished on the basis of its distinctive pear-shaped 

aperture and subparallel dorsal and ventral shell margins. 

Foerste initially used this name for the group of compressed cyrtocones he later (Foerste, 1924b) placed in his 

new genus Beloitoceras. Maelonoceras was then 

restricted in scope to include only the type species, M. 

praematurum. The Kentucky specimens described here 

are the only other examples of the genus known to this 

writer.

Maelonoceras is distinct from Beloitoceras in being a 

more inflated, less compressed form adorally that is also 

less strongly curved. In this respect, the genus is more 

similar to Oncoceras. It differs from Oncoceras in being 

concave in dorsal outline, in contrast to the pronounced 

convexity of this portion of the shell in Oncoceras. 

Maelonoceras differs from both Beloitoceras and Oncoceras in its distinctive, partially visored, pear-shaped aperture and in the development of the maximum shell 

diameter just adapical of the aperture.

MAELONOCERAS CF. M. PRAEMATURUM (BILLINGS), 1860

Plate 20, figures 7-12

Phragmoceras praematurum Billings, 1860, p. 173,

fig. 19.

Maelonoceras praematurum (Billings). Hyatt, 1884,

p. 280.

Maelonoceras billingsi Foerste, 1924a, p. 244, pi. 39,

figs. 5a-c.

Maelonoceras praematurum (Billings). Flower, 1946,

p. 288, figs. 11X-Y.

Diagnosis.—Small, slender, only slightly exogastrically curved cyrtocone, subtriangular in cross section, the 

maximum shell diameter just adapical of the distinctive, 

pear-shaped aperture.

Description.—Small (estimated lengths up to 8.0 cm 

observed diameters up to 2.1 cm), slender, inflated (apical 

angle 20 degrees), exogastric cyrtocones. Venter gently

convex in outline the length of the shell; dorsum subparallel to venter, slightly concave. Shell cross section roughly 

heart-shaped; dorsum wide, flattened; venter narrowly 

rounded, nearly angular. Shell height equal to shell width. 

Sutures straight, transverse adapically, becoming slightly 

inclined adorally, sloping from the dorsum to the venter in 

the adoral direction at diameters of 20 mm. Camera! 

chambers short, cameral lengths averaging one-ninth the 

diameter of the shell at diameters of 15-17 mm. Body 

chamber short, inflated, about one-sixth the estimated 

length of the shell, the ventral and dorsal margins straight, 

subparallel. Maximum shell diameter is just adapical of 

the aperture. Aperture pear-shaped, having rounded visorlike lateral projections that constrict the aperture ventrolaterally, defining a narrowly rounded, distinct hyponomic 

sinus. Aperture broadening dorsally, subtriangular, open. 

Shell surface marked by fine, faint transverse growth 

lines.

Siphuncle small in diameter, situated at ventral shell 

margin. Segment shape unknown. Structure of septal 

necks and connecting rings unknown.

Stratigraphic and geographic occurrence.—Upper 

half of the Rocklandian part of the Tyrone Limestone 

(Middle Ordovician), vicinity of the Kentucky River, Jessamine County, Ky.

Studied material.—USNM 158649 (pi. 20, figs. 7, 8, 

11,12) and 468735 (pi. 20, figs. 9,10), both silicified specimens from USGS 6034-CO collection, Little Hickman section A, Sulfur Well, Ky.

Remarks.—Maelonoceras cf. M. praematurum is an 

uncommon species within the diverse assemblage of nautiloids identified from the 6034-CO collection. Comparisons between the Kentucky specimens and the figures of 

the type specimen of M. praematurum (Foerste, 1924a, 

pi. 39, figs. 5a-c) are difficult as the Canadian specimen is 

known only by a single body chamber. This appears to be 

quite similar to the body chamber described and illustrated here (pi. 20, figs. 9,10) from the Tyrone Limestone. 

Better, more complete specimens of both species are necessary to further determine the affinities of the Kentucky 

material. This material does suggest, however, that 

Maelonoceras is a valid genus, distinctive from similar 

Middle Ordovician oncocerids.

GENUS LAPHAMOCERAS FOERSTE

Type species.—Cyrtoceras tenuistriatum Hall, 1877, 

p. 243; designated by Foerste, 1933, p. 76; Platteville Limestone, Blackriveran Stage, Middle Ordovician, Wisconsin.

Description.—Small, rapidly expanding, strongly 

curved exogastric brevicones that are subcircular in cross 

section adapically, dorsum and venter equally rounded; 

becoming depressed in section with ontogeny, the venter 

more narrowly rounded than dorsum. Sutures straight, 

transverse adapically, becoming inclined, sloping from
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P101

dorsum to venter adorally. Camera! chambers short. Body 

chamber short, open; venter marked by variably developed hyponomic sinus. Shell surface marked by numerous, closely spaced, raised, narrow, low transverse 

lamellae; occasionally marked by small nodes, but not 

crenulate or with extensive development of frills.

Siphuncle close to venter, consisting of narrow, subtubular, depressed segments that expand only slightly 

within camerae. Septal necks short, weakly recurved, 

suborthochoanitic. Segments empty.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Blackriveran Stage) to Late Ordovician 

(Richmondian Stage); East-Central North America 

(Laurentia).

Remarks.—Foerste (1933) originally erected this 

genus for species of ZitteUoceras Hyatt that possessed 

transverse, linear ornament but lacked the prominent 

crenulate frills characteristic of more typical ZitteUoceras. These species are Laphamoceras tenuistriatum 

(Hall) and L. scofieldi Foerste, both from the Middle 

Ordovician (Blackriveran) Platteville Formation of Wisconsin and Minnesota, Flower (1946) described ZitteUoceras russelli from the Upper Ordovician (Richmondian) 

of southwest Ohio and noted that this species was very 

similar to described species of Laphamoceras in general 

shell shape and in the nature of the external ornament, 

but possessed faintly crenulate short frills. He suggested 

that, based on its external ornament, Z. russelli was gradational between Laphamoceras and ZitteUoceras and 

that such subdivision of these species was artificial. 

Sweet (1964) followed suit and placed Laphamoceras as a 

synonym of ZitteUoceras. Upon study of the various species placed in ZitteUoceras, it was observed that species 

placed in Laphamoceras, as well as "Z." russelli, are distinct from other members of ZitteUoceras, including the 

type species Z. haUianum (D'Orbigny), in possessing a 

more adorally depressed, more rapidly expanding, and 

more strongly curved shell. These morphological differences, independent of the nature of the shell ornament, 

seem to be significant enough to warrant resurrecting 

Laphamoceras as a separate genus distinct from 

ZitteUoceras.

Both Laphamoceras and ZitteUoceras are most abundant in the Middle Ordovician (Blackriveran to Rocklandian) Platteville Formation and its equivalents in the 

upper Mississippi valley and the Ottawa-St. Lawrence 

Lowland in Ontario and Quebec, represented by 8 of the 

15 described species. Younger "Trenton" species consist 

of only the type species of ZitteUoceras, Z. haUianum, 

from the lower part of the Trenton Group in New York. No 

members of either genus are known from lower Upper 

Ordovician (Edenian and Maysvillian) strata in North 

America. In Upper Ordovician strata, Laphamoceras and 

ZitteUoceras are known only from Richmondian rocks in

the Cincinnati area, represented by Laphamoceras russeUi (Flower) and five additional species of ZitteUoceras 

(Flower, 1946). The other described Upper Ordovician 

species is Z. costatum Teichert from the Drummock 

Group (Ashgillian) of Girvan, Scotland.

LAPHAMOCERAS CF. L. SCOFIELDI FOERSTE, 1932

Plate 20, figures 13-18

Cyrtoceras billingsi Clarke, 1897, p. 806, pi. 60, fig. 10. 

Laphamoceras scofieldi Foerste, 1932, pi. 27, fig. 5; 1933, 

p. 77.

Diagnosis.—Rather small, rapidly expanding, 

strongly curved species of Laphamoceras with an external ornament of transverse lamellae.

Description.—Rather small (lengths estimated to be 

up to 8.0 cm and observed shell diameters up to 2.5 cm), 

rapidly expanding (apical angle 28 degrees), strongly 

curved exogastric cyrtocones; shell remaining strongly 

curved the length of the shell. Cross section adapically 

circular, becoming depressed ovate with ontogeny such 

that the shell has a height to width ratio of 0.88 at a shell 

height of 15 mm. Dorsum and venter evenly rounded. 

Sutures sloping obliquely from the dorsum to the venter 

in the adoral direction. Camera! chambers short, camera! 

lengths averaging between one-seventh and one-eighth 

the diameter of the shell. Body chamber incompletely 

known, aperture unknown. Shell exterior marked by fine, 

transverse, raised lamellae, not crenulated, spaced 1 mm 

apart at a shell diameter of 18 mm. Preserved surface 

markings indicate a broad, shallow, V-shaped, ventral 

hyponomic sinus.

Siphuncle diameter small, one-seventh the diameter 

of the shell at a shell diameter of 13 mm, located at the 

ventral shell margin. Segments short, only slightly 

expanded, subtubular. Septal necks and structure of connecting rings unknown.

Stratigraphic and geographic occurrence.—Upper 

part of the Rocklandian part of the Tyrone Limestone 

(Middle Ordovician), vicinity of the Kentucky River, 

Jessamine County, Ky.

Studied material.—USNM 158654 (pi. 20, figs. 16-18) 

and 158663 (pi. 20, figs. 13-15), plus USNM 158655, 

158664, and four uncataloged specimens, all from the 

USGS 6034-CO collection, Little Hickman section A, 

Sulfur Well, Ky.

Remarks.—The Kentucky specimens from the 6034- 

CO collection, in terms of shell size, extent of shell curvature, and rate of shell expansion, are similar to the holotype of L. scofieldi Foerste (University of Minnesota, 

no.207) illustrated by Foerste (1932, pi. 27, fig. 5). Flower 

(unpublished notes) stated that the Kentucky specimens 

differed from this specimen in being much more rapidly 

expanding shells distinguished by the development of 

paired ventrolateral nodes adapically. Comparisons of the
P102 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

Kentucky material with Foerste's illustration indicate similar rates of shell expansion. The nodes described by 

Flower appear to be adventitious, associated with irregular sponge encrustations on these shells. The surface 

ornament is evident in only two of the Kentucky specimens, USNM 158655 and 158663 (pi. 20, figs. 13-15) and 

appears similar to that of the holotype. As is the case with 

many of these Tyrone species, a more definitive assignment of these specimens awaits the discovery of more 

complete material preserving the distinctive surface 

markings of this genus.

Laphamoceras scofieldi is distinct from the type species, L. tenuistriatum (Hall) from the Platteville Formation in Wisconsin, in being a much more rapidly 

expanding, more strongly curved shell. Similarly, L. 

scofieldi is a more strongly curved form compared with L. 

russelli (Flower) from the "Waynesville Formation" (Late 

Ordovician, Richmondian) in southwestern Ohio. The 

apparent curvature of the "Waynesville" specimen may, 

however, be the result of postdepositional compaction of 

the enclosing shale rather than being a true representation of the shell's original shape. There is evidence of 

dorsal-ventral crushing of the holotype and only known 

specimen (Flower. 1946, pi. 27, figs. 1-3).

Laphamoceras cf. L. scofieldi, while being an 

uncommon species in the 6034-CO collection, is the second most abundant oncocerid species identified from this 

collection, second to specimens of Beloitoceras cf. B. 

huronense. It is represented by 10 incomplete portions of 

the phragmocone, all greater than 10 mm in diameter. A 

number of these specimens are encrusted by nodose holoperipheral encrustations of the problematic sponge 

Demnatostroma.

FAMILY TRIPTEROCERATIDAE FLOWER

Straight to faintly exogastric longicones with 

depressed cross sections; flattened venter with dorsum 

broadly rounded to slightly keeled. Cross sections vary 

from depressed ovate to subtriangular. Sutures forming 

broad lobes dorsally and ventrally. Body chambers broad, 

tubular, apertures open. Paired weak sinuses dorsallaterally and a broad, shallow sinus ventrally. Shells 

smooth, marked with transverse growth lines, or less 

commonly, longitudinally fluted.

Siphuncles close to venter, separated from it by a distance equal to diameter of the siphuncle. Siphuncles narrow in diameter, from less than one-tenth to nearly onequarter the diameter of the shell. Segments typically subtubular, depressed, twice as long as high. Septal necks 

short, orthochoanitic to cyrtochoanitic. Segments empty.

Stratigraphic range.—Middle Ordovician (Chazyan 

Stage) to Upper Ordovician (Richmondian Stage).

Remarks.—Flower erected this family for a group of 

rather poorly known, typically rapidly expanding

orthoconic longicones distinguished by the development 

of a depressed, planoconvex shell cross section. In this 

family are the genera AUumettoceras Foerste, Tripteroceras Hyatt, Tripterocerina Foerste, and Rasmussenoceras Foerste. AUumettoceras is the oldest member of the 

family, occurring in Chazyan and Blackriveran strata in 

eastern North America, and is distinct from the other genera in this group in being a less rapidly expanding form, 

and having a less depressed cross section and globular, 

expanded siphuncle segments. Tripteroceras is a more 

rapidly expanding, highly depressed form with a strongly 

flattened venter and overlaps with AUumettoceras in the 

Blackriveran and then becomes most abundant in 

younger Kirkfieldian and Shermanian carbonates in the 

same region. Tripterocerina from the Bighorn Dolomite 

in Wyoming (Upper Ordovician) is similar in morphology 

to Tripteroceras except for the development of longitudinal fluting on the shell's dorsal exterior. Rasmussenoceras, a large, rapidly expanding, highly depressed shell, is 

known from Upper Ordovician carbonates of the Cape 

Calhoun Formation in Greenland (Troedsson, 1926) and 

from the rubbly limestones of the Whitewater Formation 

(Richmondian) in Indiana and Ohio (Flower, 1946). The 

latter genera are distinct from Alumettoceras in the possession of narrow, tubelike siphuncle segments and orthochoanitic septal necks. The variation hi shell morphology 

and, especially, in the nature of the siphuncle segments 

suggests that this family is an artificial grouping of independently derived, ventrally flattened Middle and Upper 

Ordovician "flatfish" nautiloids.

The Tripteroceratidae have traditionally been placed 

in the Oncocerida on the basis of the ventral position of 

the siphuncle and the lack of cameral or endosiphuncular 

deposits. A logical origin for this family can be found in 

the primitive, longiconic Graciloceratidae, the probable 

ancestral stock for all succeeding Ordovician oncocerid 

families. Dzik (1984) removed the Tripteroceratidae from 

the Oncocerida and placed it in the Orthocerida, presumably on the basis of the orthoconic shell form of its members. However, an orthoconic shell morphology occurs 

several times within the Oncocerida, namely within the 

Tripteroceratidae in the Ordovician, the Jovellanidae in 

the Silurian, and the Tripleuroceratidae in the Devonian. 

The possession of an orthoconic shell morphology alone 

does not seem be sufficient cause to remove the Tripteroceratidae to the Orthocerida, and here they are retained, 

in the Oncocerida.

GENUS ALLUMETTOCERAS FOERSTE

Type species.—Tripteroceras paquettense Foerste, 

1924a, p. 233; designated by Foerste, 1926, p. 311; "LerayRockland beds," Rocklandian Stage, Middle Ordovician, 

Ontario.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P103

Description,—Small, rather rapidly expanding, 

orthoconic to slightly exogastric longicones, depressed 

ovate in cross section, with the dorsum broadly convex, 

not keeled; venter only slightly flattened, lateral margins 

narrowly rounded. Sutures sinuate, forming broad dorsal 

and deeper ventral lobes and lateral saddles. Cameral 

chambers short. Body chamber long; aperture open, not 

constricted. Shell exterior basically smooth, marked by 

fine transverse growth lines.

Siphuncle situated at or near the ventral shell margin. 

Siphuncle segments expanded, globose, nearly equiaxial 

with height equal to the length. Septal necks short, 

slightly recurved, cyrtochoanitic. Cameral and endosiphuncular deposits apparently absent.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Chazyan to Kirkfieldian Stages), East-Central 

North America (Laurentia).

Remarks.—As indicated above, Allumettoceras differs from other members of the Tripteroceratidae in possessing a less depressed, less angular cross section and in 

the development of expanded, equiaxial siphuncle segments whose diameters average one-fourth the diameter 

of the shell. The nature of the siphuncle segments in many 

taxa assigned to these genera is unknown. Specimens of 

Tripteroceras cf. T. planocovexum (Hall) and Rasmussenoceras variable Flower studied by the writer indicate 

the presence of narrow, tubular siphuncles less than onetenth the diameter of the shell. The morphological differences between Allumettoceras and the other members of 

the Tripteroceratidae are probably sufficient to remove 

this genus from the family. The affinities of this genus, 

however, remain unknown pending discovery of more 

complete material preserving key internal structures of 

adapical portions of the shell. This writer has elected to 

retain it in the Tripteroceratidae at this time.

Dzik (1984) made Allumettoceras a junior synonym 

of Tripteroceras. For the reasons discussed above, this is 

totally erroneous and indicates a lack of knowledge of the 

morphological features of these two taxa. They are distinct genera and probably do not even belong in the same 

family.

ALLUMETTOCERAS CF. A. TENERUM (BILLINGS), 1860

Plate 20, figures 19-22

Orthoceras tener Billings, 1860, p. 174.

Allumettoceras tenerum (Billings). Foerste, 1932, p. 124,

pi. 13, figs. 1A-B.

Allumettoceras tenerum (Billings). Wilson, 1961, p. 77,

pi. 30, figs. 13-16.

Diagnosis.—A rather slender, moderately expanding 

species of Allumettoceras, camera! lengths averaging oneninth the diameter of the shell.

Description.—Small (estimated lengths of up to 16.0 

cm with shell diameters of up to 2.4 cm), moderately

expanding (apical angle 7.5-8 degrees), orthoconic longicones; depressed ovate hi cross section, the dorsum more 

convex than venter. Venter strongly flattened adapically, 

becoming more convex with ontogeny. Shell becoming 

slightly more depressed with ontogeny, the height to 

width ratios ranging from 0.71 at a height of 7 mm and 

0.65 at a height of 20 mm. Sutures somewhat sinuous, having shallow dorsal and ventral lobes and lateral saddles. 

Cameral chambers short, camera! lengths one-ninth the 

diameter of the shell at a shell diameter of 22 mm. Body 

chamber incompletely known, at least one-sixth the total 

length of the shell; smooth, continuous with the phragmocone. Aperture open, no evidence of a ventral hyponomic 

sinus, consisting of ventral and dorsal lobes and lateral 

sinuses. Shell exterior smooth.

Siphuncle situated at ventral shell margin. Segment 

diameter nearly one-third the height of the shell at a shell 

height of 11 mm. Segments expanded, spherical hi shape, 

equiaxial. Structure of septal necks and connecting rings 

unknown.

Stratigraphic and geographic occurrence.—Lower 

part of the Logana Member of the Lexington Limestone 

(Middle Ordovician, Kirkfieldian), exposed in Jessamine 

and Woodford Counties, Ky.

Studied material.—Incomplete silicified specimens 

USNM 468738 and 468670 (pi. 20, figs. 19, 21, 22) from the 

USGS 6419-CO collection, Wilmore quadrangle, Jessamine 

County, Ky, and USNM 468739 (pi. 20, fig. 20) from the 

USGS 4865-CO collection, Tyrone quadrangle, Woodford 

County, Ky; plus additional uncataloged shell fragments 

from both localities.

Remarks.—The Kentucky material described here 

consists of fragmentary silicified portions of the phragmocone that, collectively, indicate a depressed longicone 

16.0 cm hi total length. Comparisons with other described 

species of Allumettoceras are complicated by the incomplete, fragmentary nature of most of the figured type 

specimens, often consisting of an internal mold of the 

body chamber and a few attached adoral camerae. The 

Kentucky specimens are less rapidly expanding compared 

with the type species of the genus, A. paquettense Foerste, as well as A. josephium Foerste, both from Blackriveran and Rocklandian strata in Ontario. Both of these latter 

species have apical angles of 13 degrees compared with 

values of 7.5-8 degrees for the Kentucky specimens. Similarly, the Logana Member specimens are less expanded 

than A. huronense Foerste from the "Black River Formation" on St. Joseph Island, Lake Huron (apical angle 11 

degrees). In terms of the rate of shell expansion, the 

Logana material is most similar to A. carletonense Foerste 

and A. tenerum (Billings), both from Blackriveran and 

Rocklandian strata in Ontario. Both of these species have 

apical angles of 8 degrees. Allumettoceras carletonense is 

based on an isolated body chamber. AUumettoceras
P104 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

tenerum is known from the adapical portion of the phragmocone. The incomplete specimens from the Logana 

Member compare more favorably with A. tenerum in 

camera! depth and cross sectional shape, the ventral portion of the shell increasing in convexity with ontogeny. A 

complete restudy of this genus is needed to better define 

the known species of AUumettoceras and to more accurately determine the affinities of the Kentucky specimens. 

These specimens from the Logana Member of the Lexington Limestone are the youngest members of the genus 

(Middle Ordovician, Kirkfieldian) currently known to this 

writer.

Within the Logana Member, the species is a rare form 

found associated with the more abundant phragmocones 

of the small orthocerid Isorthoceras albersi (Miller and 

Faber). Other associated fauna consists of rare fragments 

of a small species of Trocholites, and abundant, well-preserved specimens of the univalved mollusks Lophospira, 

Liospira, and Sinuites, and the small pelecypod 

Deceptrix.

FAMILY DIESTOCERATIDAE FOERSTE

Straight to endogastrically curved, compressed brevicones with inflated body chambers that more or less contract toward the aperture, where a ventral hyponomic 

sinus is well developed. Sutures transverse or slightly 

sloping adorally from the venter to the dorsum. 

Periphract ventromyarian.

Siphuncle situated close to the ventral shell margin. 

Segments typically expanded, scalariform to subquadrate, 

with cyrtochoanitic septal necks. Segments possessing 

discrete, rather irregular actinosiphonate deposits.

Stratigraphic range.—Middle Ordovician (Blackriveran Stage) to Upper Ordovician (Gamachian Stage).

GENUS DIESTOCERAS FOERSTE

Type species.—Gomphoceras indianense Miller and 

Faber, 1894b, p. 137; designated by Foerste, 1924b, p. 262; 

Saluda Formation, Richmondian Stage, Upper Ordovician, Indiana

Description.—Typically large (up to 30 cm in length), 

straight to faintly endogastrically curved, rapidly expanding brevicones that commonly reach their greatest diameter close to the base of the body chamber. Slightly 

compressed in cross section, the venter more narrowly 

rounded than the dorsum. Sutures typically transverse or 

sloping slightly adorally from the venter to the dorsum. 

Cameral chambers short, cameral lengths typically 

decreasing with ontogeny. Body chamber large, inflated, 

contracting toward the aperture. Aperture marked by a 

well-developed, broad, ventral hyponomic sinus. 

Periphract ventromyarian, the well-developed basal zone 

marked by short, longitudinal buttresses. Shell exterior

marked by variably developed, raised, transverse growth 

lines.

Siphuncle situated close to the ventral shell margin. 

Segments broadly expanded adorally, the Siphuncle segments one-fifth to one-fourth the diameter of the shell. 

Segments compressed ovate to subquadrate in outline. 

Septal necks short and abruptly recurved, cyrtochoanitic. 

Connecting rings thin and homogeneous except near septal foramen. Rings broadly adnate to adjacent adoral 

septa dorsally, but free ventrally. Rings adnate to adapical 

septa both dorsally and ventrally. Adoral segments of 

large individuals have irregularly developed deposits consisting initially of annulosiphonate deposits that then give 

rise to irregular calcareous processes that extend adapically from septal necks.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Blackriveran Stage) to Upper Ordovician 

(Gamachian Stage), North America and Baltic Europe.

Remarks.—Flower (1946) reviewed the morphological features and history of this genus and pointed out that 

it is probably overly broad in its scope. The critical features of the siphuncle are unknown for the majority of 

species currently assigned to the genus. This is particularly true of Middle Ordovician taxa placed in the genus. 

These consist of small, slender, atypical species compared with younger members of the genus, and include 

the type species, D. indianense (Miller and Faber) from 

Richmondian strata in the Cincinnati arch region.

Diestoceras is a prominent member of the so-called 

"Arctic" fauna, for which a number of large, characteristic 

species are described from Upper Ordovician carbonate 

facies in Wyoming, Manitoba, Quebec, the Canadian Arctic archipelago, and northern Greenland. The genus 

occurs in the Kentucky-Indiana-Ohio region in middle and 

upper Richmondian strata, being most abundant along 

with other "Arctic" nautiloid taxa in the Saluda and Whitewater Formations in southeastern Indiana and adjacent 

portions of western Ohio. The bulk of the figured specimens of Diestoceras from these strata come from a single 

locality in the "Lower Whitewater Formation" along Little 

Four-Mile Creek, near Oxford, Preble County, Ohio. Here, 

several species of Diestoceras have been identified associated with hundreds of specimens of the coiled nautiloid 

Characteroceras baeri (Meek) and many other, less common oncocerids (Flower, 1946, 1957b). The genus is also 

known from the equivalent, more clastic-rich Bull Fork 

Formation exposed in Montgomery and Clinton Counties 

in southwestern Ohio.

Foerste (1924b) and Flower (1946) identified five 

species of Diestoceras from these strata in Indiana and 

Ohio; all being large, essentially straight brevicones differentiated primarily on the basis of the shape and size of the 

body chamber and the relative length of cameral chambers. Unfortunately, most Cincinnatian species of
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P105

Diestoceras are preserved as matrix-filled internal molds 

in argillaceous limestones, many of these specimens 

showing evidence of postdepositional deformation due to 

sediment compaction. This makes comparisons of body 

chamber shape and cross section difficult. Curiously, 

specimens of Diestoceras in the Bull Fork and Saluda Formations often consist of just the body chamber with a few 

attached camerae. This complicates comparisons of specimens based on length of individual camera! chambers. 

Larger suites of more complete, uncrushed specimens are 

necessary to more fully determine the distinctiveness of 

these different species of Diestoceras described from the 

Cincinnati arch region.

DIESTOCERAS INDIANENSE (MILLER AND FABER), 1894B

Plate 22, figures 6-9

Gomphoceras indianense Miller and Faber, 1894b, p. 137,

pi. 7, figs. 3-5.

Gomphoceras indianense Miller and Faber. Cumings,

1908, p. 1030, pi. 19, figs. 4r-4B.

Diestoceras indianense (Miller and Faber). Foerste,

1924b, p. 263, pi. 25, figs. 1A-B; pi. 26, figs. 1A-B, 2A-B.

Diestoceras indianense (Miller and Faber). Flower, 1946,

p. 482, pi. 36, figs. 1-3; pi. 41, figs. 10,11.

Diagnosis.—Large, slightly endogastrically curved 

species of Diestoceras having the maximum shell diameter at the base of the body chamber, camera! lengths oneseventh to one-ninth the diameter of the shell at shell 

diameters greater than 35 mm, and compressed, subquadrate siphuncle segments adorally.

Description.—Large (estimated lengths of up to 14.0 

cm and shell diameters up to 6.0 cm), rapidly expanding 

(apical angle 34-38 degrees), exogastrically curved, 

inflated brevicone; compressed ovate in cross section, the 

venter more narrowly rounded than the dorsum. Venter 

slightly concave adapically, becoming slightly convex 

adorally. Dorsum convex the length of the shell. Maximum shell diameter at base of body chamber. Adapically, 

sutures inclined slightly from the venter to dorsum; 

straight transverse adorally. Camera! chambers short, 

camera! lengths from one-seventh to one-ninth the diameter of the shell at diameters greater than 35 mm. Adoralmost two to three septa approximate at shell diameters of 

55 mm or more. Body chamber inflated, the dorsal and 

ventral margins subparallel, straight, contracting adorally 

toward aperture. Body chamber length roughly threefourths its maximum diameter. Aperture subtriangular, 

open and broadly rounded dorsally; constricted and narrowly rounded ventrally, forming a distinct hyponomic 

sinus. Shell exterior marked by closely spaced, narrow, 

raised transverse growth lines that slope ventrally to 

define a shallow, V-shaped sinus.

Siphuncle slightly removed from ventral shell margin. Siphuncle segments broad, expanded, subquadrate

adorally, segment diameters one-fifth the diameter of the 

shell. Segments compressed, SCR values of 1.40 at shell 

diameters between 35 and 50 mm. Septa! necks short, 

strongly recurved, cyrtochoanitic. Connecting rings not in 

contact with ventral shell margin, thin and homogeneous. 

Rings adnate to adoral septum both dorsally and ventrally. 

Endosiphuncular deposits developed adorally, consisting 

of flat, longitudinal radial plates projecting adapically 

from septal necks into siphuncle segments.

Stratigraphic and geographic occurrence.—Saluda 

Formation (Upper Ordovician, Richmondian Stage), 

southeastern Indiana; and equivalent portions of the "Liberty" and "Lower Whitewater biofacies" within the Bull 

Fork Formation in southwestern Ohio.

Studied material.—MU 431T (pi. 22, fig. 8) and 432T 

(pi. 22, figs. 6, 7, 9), both from the Saluda Formation at 

Hamburg, Franklin County, Ind.; MU 29866 from the 

"Saluda tongue" exposed north of Camden, Preble 

County, Ohio; MU 29867 from the "Saluda tongue" 

exposed on Talawanda Creek, just north of Oxford, Butler 

County, Ohio; Hypotype UC 24480 of Flower (1946, pi. 36, 

fig. 6), and hypotype of Foerste (1924b, pi. 25, figs. 1A-B), 

both from the "Saluda tongue" at Little Four-Mile Creek, 

McDills Mills, Preble County, Ohio.

Also studied was the holotype of Gomphoceras indianense (University of Chicago 8818), which Miller and 

Faber (1894B, pi. 7, figs. 3-5) reported as coming from 

"Upper part of the Hudson River Group, Versailles, 

Indiana."

Remarks.—Contrary to Flower's (1946) remarks, the 

holotype of Gomphoceras indianense resides in the 

Faber collection at the Field Museum of Natural History, 

Chicago, Illinois. It is cataloged under the University of 

Chicago, Walker Museum number 8818. Flower noted that 

the specimen came from the Saluda Formation. Foerste 

(1924b) and Flower (1946) described and illustrated a 

number of specimens they referred to this species, all of 

which were from the Charactoceras baeri bed in the 

"Lower Whitewater Formation" along Little Four-Mile 

Creek, just north of Oxford, in Preble County, Ohio 

(Flower, 1957b). This unit is now believed to be a tongue 

of the Saluda Formation that extends eastward into the 

Bull Fork Formation from southeastern Indiana into ach'acent portions of western Ohio (J. Marak, Miami University, oral commun.). The two specimens of D. indianense 

illustrated here (pi. 22, figs. 6-9) are from the "Concrete 

layer," a 12-in (0.3-m) thick, resistant micritic limestone 

bed that overlies the coralliferous zone of the Saluda Formation in portions of Franklin County, Ind. These specimens consist of a fairly complete, uncrushed internal 

mold (pi. 22, figs. 6, 7, 9) and a similar specimen preserving some of the external shell that is crushed dorsally (pi. 

22, fig. 8). These specimens are also of interest in that 

they preserve a blackened pigment around the aperture of
P106 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

TABLE 11.—Comparisons of the morphological features of 

species of the oncocerid Diestoceras from Upper Ordovician 

strata in the Cincinnati arch region

[Data from specimens listed in text, mm, millimeter]

Feature D. indlanense D. shidelwi D. eos

Apical angle from 34-40 30-35 

venter, degrees.

Location of At base of Midlength of

maximum body body

diameter. chamber. chamber.

Aperture shape Triangular Triangular

Cameral length at 5.5-7 6-7.5 

55-mm 

diameter, mm.

Cameral length at 4-7 6-8 

40-mm 

diameter, mm.

Siphuncle Subquadrate Compressed 

segment shape. ovate.

Adapicai Yes Yes 

endo gastric 

curvature.

45-48

1-2 cm adoral 

of base of 

body 

chamber.

Compressed 

ovate.

5.5-6

5.5-6

Compressed 

ovate.

No

the shell. Flower (1964b, pi. 1, figs. 6-11) observed a similar phenomenon in oncocerids from the Middle Ordovician of Quebec. This pigmentation is thought to represent 

the "black layer," a blackened area located at the aperture 

border and inside the shell margin all around the aperture 

that has been observed in specimens of Nautilus (Stenzel, 1964).

Foerste (1924b) distinguished D. indianense from 

associated species of Diestoceras primarily on the basis 

of the position of the area of maximum shell diameter 

within the shell. This was described as being located at 

the base of the body chamber in D. indianense and "at a 

point distinctly above the base of the living chamber" in 

D. eos (Hall and Whitfield) and "at the mid-height of the 

living chamber" in the holotype of/), shideleri Foerste.

Flower (1946) described D. indianense as a shell 

with "a rather short living chamber; little contracted 

adorally." He also noted that the phragmocone, adapically, 

was distinctly concave ventrally and strongly convex dorsally, its sutures spaced "moderately close" together. Diestoceras eos was described as "a larger form with living 

chamber nearly symmetrical, contracting more strongly 

towards the aperture," the shell being most inflated just 

adoral of the base of the body chamber. Diestoceras 

shideleri was described as being a large form with a body 

chamber comparable in length to D. eos but being less 

inflated and contracting only slightly toward the aperture.

Flower also noted that D. shideleri had a "phragmocone 

with exceptionally deep camerae; early part curved as in 

D. indianense"

Study of the few more or less complete specimens of 

Diestoceras available to this writer (JV=15) indicate significant variation within individual specimens assigned to 

these species in terms of body chamber dimensions and 

cameral lengths. Specimens currently assigned to D. indianense have the maximum shell diameter at the base of 

the body chamber and body chambers whose lengths are 

roughly three-fourths or less their adapical diameters. 

Length to diameter ratios for body chambers of specimens of D. indianense studied range from 0.58 to 0.86, 

averaging 0.78. Cameral lengths in specimens assigned to 

D. indianense were 4-7 mm (average 5.25) at a diameter 

of 40 mm and 5.5-7 mm (average 6.2 mm) at a diameter of 

55mm.

Specimens currently assigned to D. shidelen-i have 

the maximum shell diameter roughly at a point midlength 

on the body chamber, and body chamber lengths are 

roughly equal to the adapical diameter of the body chamber. Adapically, cameral lengths in specimens of D. shideleri tend to be greater than those of typical D. indianense 

at the same diameter. There is, however, some overlap 

between specimens assigned to these two species.

Diestoceras eos is less well represented in collections, and the holotype (OSU 38082) is flattened due to 

compaction of the enclosing shaly limestone, making the 

dimensions of its original shell uncertain. Diestoceras eos 

appears to be distinguishable from D. indianense in 

being a more rapidly expanding species, the maximum 

shell diameter some distance adoral to the base of the 

body chamber and lacking any indications of endogastric 

curvature. Diestoceras eos also has a compressed ovate 

aperture compared to the broader, strongly triangular 

apertures present in D. indianense and D. shideleri. 

Comparison of the apertures of these three species of 

Diestoceras is illustrated in figure 26. Both D. eos and D. 

shideleri have more rounded, compressed ovate siphuncle segments compared with the subquadrate, scalariform 

segments in D. indianense. Comparisons of some of the 

morphological features used to distinguish these three 

species of. Diestoceras are presented in table 11.

Diestoceras attenuatum Flower is known only from 

the holotype (UC 24524) from the "Lower Whitewater 

Formation" at Little Four-Mile Creek, just north of 

Oxford, in Preble County, Ohio. This species is a much 

more gradually expanding, slender form compared with 

D. indianense. Likewise, D. waynesvillense Flower is 

known only from the holotype (MU 446T) from the middle 

of the "Waynesville Formation" at Oldenburg, Franklin 

County, Ind. This species appears to be a smaller version 

of/), eos (Hall and Whitfield) and differs from D. indianense in the same manner.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P107

FIGURE 26.—Drawings of the apertures of species of Diestoceras from 

Richmondian strata in the Cincinnati arch region. The drawings are based 

on internal molds. The outer line in each figure is the shape of the rilling of 

the body chamber. The inner line is the shape of the aperture. All figures xl. 

A, Apertural view of Diestoceras indianense (Miller and Faber), drawing 

based on specimen MU432T, Saluda Formation, Hamburg, Indiana, B, 

Apertural view of D. shideleri Foerste, drawing based on specimen 

MU430T, Saluda Formation, Hamburg, Indiana. C, Apertural view of D. eos 

(Hall and Whitfield), drawing based on specimen MU382T, lower 

Whitewater Formation, Talawanda Creek, Oxford, Ohio. All xO.65.

Flower (1946) describes D. indianense as being similar, especially in the shape of the siphuncle segments, to 

D. scalare Foerste from the Richmondian Vaureal Formation on Anticosti Island, Quebec. The other Cincinnati 

arch species of Diestoceras, as well as D. indianense, are 

more laterally compressed adorally compared with a 

number of large, highly inflated, bulbous species of Diestoceras described from coeval or slightly older (Edenian) 

carbonate facies in northern Greenland (Cape Calhoun 

Formation), the Hudson Bay region (Shammattawa and 

Nelson Limestones), the lakes region of southern Manitoba (Red River Formation), and Wyoming (Bighorn Formation and its Lander Sandstone Member).

DIESTOCERAS SHIDELERI FOERSTE, 1924B

Plate 21, figures 1, 2, 5; plate 22, figures 1, 3

Diestoceras shideleri Foerste, 1924b, p. 266, pi. 27, figs.

1A-B.

Diestoceras shideleri Foerste. Flower, 1946, p. 407, pi. 38,

figs. 1, 8.

Diagnosis.—Large, slightly exogastrically curved 

species of Diestoceras having the maximum shell diameter at the midpoint of the body chamber, camera! lengths 

one-fifth to one-ninth the diameter of the shell at shell

diameters greater than 35 mm, and compressed ovate 

siphuncle segments adorally.

Description.—Large (estimated lengths up to 18.0 

cm and shell diameters of up to 7.7 cm), exogastrically 

curved brevicone, compressed ovate in cross section, the 

venter more narrowly rounded than the dorsum. Venter 

slightly concave adapically, becoming strongly convex 

adorally. Dorsum convex the length of the shell. Maximum shell diameter near the midpoint of the body chamber. Sutures adapically slightly inclined from the venter to 

the dorsum in the adapical direction; becoming straight, 

tranverse adorally. Cameral chambers of moderate length, 

the cameral lengths ranging from one-fifth to one-ninth 

the diameter of the shell at shell diameters in excess of 35 

mm, decreasing with ontogeny. Adoralmost two or three 

septa approximate in specimens having phragmocone 

diameters in excess of 60 mm. Body chamber inflated, not 

laterally compressed. Venter and dorsum both gently convex; chamber expanding to its midlength, then contracting toward the aperture. Body chamber length roughly 

equal to maximum diameter. Aperture subtriangular, 

open, broadly rounded dorsally; more narrowly rounded 

ventrally, forming a distinct hyponomic sinus. Shell exterior marked by low, indistinct, rounded transverse costae
P108 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

that slope towards the venter, marking a shallow V-shaped 

sinus.

Siphuncle located at ventral shell margin. Siphuncle 

segments broad, expanded, compressed ovate, with diameters nearly one-third the diameter of the shell adorally at 

shell diameters in excess of 55 mm. Segments highly compressed adorally, SCR values of 3.2 at a shell diameter of 

55 mm. Septal necks strongly recurved, cyrtochoanitic. 

Connecting rings in contact with ventral shell margin, thin 

and homogeneous. Rings adnate dorsally to adoral septum and ventrally to adapical septum. Endosiphuncular 

deposits developed adorally, consisting of flat, longitudinal radial plates projecting from septal necks adapically 

into siphuncle segments.

Stratigraphic and geographic occurrence.—Saluda 

Formation (Upper Ordovician, Richmondian Stage), 

southeastern Indiana; and Saluda Tongue within the Bull 

Fork Formation in portions of Butler and Preble Counties, Ohio.

Studied material.—MU 429T (pi. 21, figs. 1, 2) from 

the "Concrete layer" just above the Tetradium zone 

within the Saluda Formation, Route 101, just north of 

Brookville, Franklin County, Ind.; MU 430T (pi. 21, fig. 5; 

pi. 22, figs. 1, 3), same horizon exposed just north of Hamburg, Franklin County, Ind.; hypotypes MU 442T (Flower, 

1946, pi. 38, fig. 1) and UC 24508 (Flower, 1946, pi. 38, fig. 

8), both from the "Saluda tongue," Little Four-Mile Creek, 

Preble County, Ohio; and MU 14078 from the rubbly facies 

in the Whitewater Formation at Route 725, just north of 

Camden, Preble County, Ohio.

Also studied was the holotype of Diestoceras shideleri (USNM 81286) Foerste (1924B, pi. 27, Figs. 1A-B), 

which he listed as coming from the "basal part of the 

Whitewater Member of the Richmond near Oxford, Ohio."

Remarks.—Comparisons between D. shideleri and 

the associated D. indianense (Miller and Faber) are presented in the previous description of that species. The 

important distinctions between these species are in the 

relative shape and dimensions of the body chamber. 

These distinctions and the common association of both 

species together in the same beds exposed at a number of 

localities suggests that these morphological differences 

could be the result of sexual dimorphism. This feature has 

been recognized in several species of living Nautilus 

(Stenzel, 1964; Saunders and Spinoza, 1978; Ward, 1987), 

the mature males having a broader aperture and body 

chamber to accommodate the male sexual organs (spadix). Oncocerids are believed to belong to the same evolutionary group as the Nautilida (Flower, 1955d), and sexual 

dimorphism had been suggested previously for other 

members of the order (Ruedemann, 1921). The smaller, 

less inflated body chambers currently assigned to D. 

indianense may represent female individuals, the larger, 

more inflated body chambers of D. shideleri being the

males. Large collections of relatively well-preserved, 

undistorted specimens of both species need to be studied 

in order to further validate sexual dimorphism in this 

genus.

Comparisons between D. shideleri and D. eos (Hall 

and Whitfield) are more difficult due to the deformed 

nature of the holotype of D. eos and the lack of well-preserved museum material referable to this species. These 

taxa are similar, both in being large species and in having 

the maximum diameter of the body chamber at a point 

adoral of the base of the body chamber. Siphuncle segments in both species also appear to be compressed ovate 

rather than subquadrate as in D. indianense. Flower 

(1946) indicated that D. eos is a more rapidly expanding 

species that lacks the endogastric curvature characteristic of D. shideleri and has a body chamber that contracts 

more strongly toward the aperture. The limited number of 

specimens of D. eos available to this writer also indicate 

that D. eos has a shorter body chamber relative to chamber diameter, more comparable with that characteristic of 

D. indianense.

DIESTOCERAS EOS (HALL AND WHTTFIELD), 1875

Plate 21, figure 4

Gomphoceras eos Hall and Whitfield, 1875, p. 100, pi. 3,

fig. 5.

Diestoceras eos (Hall and Whitfield). Foerste, 1924b,

p. 265, pi. 28, figs. 1A-B.

Diestoceras eos (Hall and Whitfield). Flower, 1946, p. 403,

pi. 34, figs. 1, 6; pi. 35, fig. 9; pi. 37, fig. 10; pi. 38, fig. 7;

pi. 39, fig. 10.

Diagnosis.—Large, inflated, somewhat bulbous species of Diestoceras having the maximum shell diameter 

just adoral of the base of the body chamber and possessing a short, rapidly expanding phragmocone that lacks 

any clear indication of endogastric curvature.

Description.—Large (estimated lengths of up to 12.0 

cm and shell diameters up to 7.4 cm), rapidly expanding 

(apical angle 45-48 degrees), orthoconic brevicones, the 

venter and dorsum both concave adapically, nearly symmetrical; becoming more inflated with ontogeny such that 

the venter adorally becomes more convex than dorsum. 

Cross section compressed ovate adapically, the venter 

more narrowly rounded than the dorsum; becoming 

inflated, nearly circular in cross section adorally. Maximum shell diameter just adoral of the base of the body 

chamber. Sutures straight, transverse. Camera! chambers 

short, camera! lengths ranging from one-sixth to onetenth the diameter of the shell at diameters in excess of 30 

mm, decreasing with ontogeny. Adoralmost two or three 

septa become approximate at diameters in excess of 60 

mm. Body chamber length roughly three-fourths the maximum diameter of the shell; chamber inflated, roughly circular in cross section, the maximum shell diameter
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P109

situated just adoral of the base, then contracting evenly 

toward the aperture. Aperture compressed ovate, the venter more narrowly rounded than the dorsum, delineating a 

ventral hyponomic sinus. External ornament of raised, 

fine, closely spaced transverse growth lines.

Siphuncle located at ventral shell margin, the segments adorally expanded, their diameters nearly onefourth the diameter of the shell. Segments highly 

compressed ovate, the SCR values being 2.85 at a shell 

diameter of 54 mm. Septal necks strongly recurved, cyrtochoanitic. Connecting rings thin, in contact with ventral 

shell wall. Rings adnate to adoral septum dorsally and to 

adapical septum ventrally Endosiphuncular deposits 

developed adorally, consisting of flat, radial plates projecting adapically from the septal necks into the segment.

Stratigraphic and geographic occurrence.—Upper 

part of the Bull Fork Formation (Upper Ordovician, Richmondian Stage) in southwestern Ohio and equivalent portions of the Saluda Formation, southeastern Indiana.

Studied material—Holotype OSU 3082 (Hall and 

Whitfield, 1875, pi. 3, fig. 5; Foerste, 1924b, pi. 28, figs. 1AB; Flower, 1946, pi. 34, fig. 6), "Whitewater beds" at Dayton, Montgomery County, Ohio; hypotype MU 382T (Foerste, 1924b, pi. 26, figs. 1A-B; Flower, 1946, pi. 34, fig. 6), 

"Lower Whitewater Formation" at Talawanda Creek, near 

Oxford, in Preble County, Ohio; hypotype MU 440T (Foerste, 1924b, pi. 27, fig. 2; Flower, 1946, pi. 39, fig. 10), 

Saluda Formation, Madison, Jefferson County, Ind.; hypotype UC 24500 (Flower, 1946, pi. 37, fig. 10), "Lower 

Whitewater beds," Little Four-Mile Creek, near Oxford, 

Ohio; and USNM 468730 (pi. 21, fig. 4) and MU 15905, both 

from the DrepaneUa richardsoni zone in the upper part 

of the Bull Fork Formation, Cowan Lake spillway, near 

Wilmington, Clinton County, Ohio.

Remarks.—As indicated in the preceding descriptions of D. indianense and D. shideleri, comparisons 

between these species and D. eos are difficult due to the 

flattened, distorted condition of Hall and Whitfield's type 

specimen. However, study of hypotype MU 382T, a wellpreserved, undistorted internal mold preserving all of the 

body chamber and most of the phragmocone, indicates 

that D. eos is a valid taxon, distinct from these associated 

species of Diestoceras. Diestoceras eos differs from D. 

indianense and D. shideleri in lacking any indication of 

endogastric curvature of the shell and in possessing a laterally compressed ovate aperture, compared with the 

strongly triangular apertures typical of these other two 

species (fig. 26). Additionally, D. eos differs from D. indianense in having the maximum shell diameter some distance adoral of the base of the body chamber and having 

broader, more highly compressed siphuncle segments 

compared with the narrower, subquadrate segments 

present in D. indianense at the same shell diameters. 

Diestoceras eos differs from D. shideleri in possessing a

shorter body chamber relative to shell width and having 

shorter camera! lengths at comparable diameters. The differences between these Cincinnati arch species of Diestoceras are summarized in table 11.

Diestoceras eos is most similar to D. waynesvillense 

Flower from the underlying Waynesville "biofacies" in the 

Bull Fork Formation at Oldenburg, Ind. Detailed comparison between these species is difficult due to the poor 

preservation of the holotype (MU 446T) and only known 

specimen of D. waynesvillense. The general outline of the 

shell is, however, very similar to that of D. eos and additional specimens of this species are needed to further 

determine the affinities.

Diestoceras eos is more similar to the large species of 

Diestoceras described from slightly older and coeval carbonates in the Western United States and Canada than 

eitherD. indianense or D. shideleri. The "Arctic" species, 

like D. BOS, are more inflated, nearly hemispherical forms, 

the flanks evenly convex, lacking any indication of endogastric curvature. These species, consisting of D. gibbosum Foerste, D. nobile (Whiteaves), and D. whiteaves 

Foerste from the Red River Formation in Manitoba, and 

D. staufferi Foerste from the Maquoketa Formation in 

Minnesota, all tend to be more inflated than D. eos, possessing greater apical angles and shorter body chambers.

In the Cincinnati arch region, specimens identified as 

D. eos have been collected from the Saluda Formation in 

southeastern Indiana, a tongue of the Saluda Formation 

extending into the Bull Fork Formation in Preble and Butler Counties, Ohio, and in the upper portions of the Bull 

Fork Formation at Dayton and near Wilmington, in southwestern Ohio. Well-preserved, undistorted specimens are, 

unfortunately, rather rare, the species being typically represented by distorted matrix-filled molds or isolated body 

chambers.

FAMILY VALCOUROCERATTDAE FLOWER

Typically small, slender, gradually to rapidly expanding exogastric cyrtocones. Cross sections varying with 

ontogeny from compressed ovate adapically to depressed 

ovate to subtriangular adorally, the venter more narrowly 

rounded than the dorsum, often being subangular. Sutures 

sloping adorally from the dorsum to the venter. Broad 

lobe developed dorsally in some taxa. Camera! chambers 

typically very short, camera! lengths decreasing with 

ontogeny. Body chambers short relative to phragmocone 

length. Apertures open, variably developed ventral 

hyponomic sinus. Shells smooth or marked by fine, raised 

growth lines.

Siphuncle located near ventral shell margin, consisting of expanded ovate segments that typically become 

larger in diameter and more compressed with ontogeny. 

Septal necks cyrtochoanitic; recurved with short free 

brims. Connecting rings becoming thickened with
P110 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

ontogeny, generating complex actinosiphonate deposits 

consisting of radial, platelike processes that converge 

inward but fail to meet in the center of the segment.

Stratigraphic range.—Middle Ordovician (Chazyan 

Stage) to Upper Ordovician (Richmondian Stage); currently known only from North America (Laurentia).

Remarks.—The Valcouroceratidae were defined by 

Flower (1946) as a group of typically slender, exogastric 

cyrtocones with ventral cyrtochoanitic siphuncles. They 

were differentiated from the Oncoceratidae by the presence of actinosiphonate deposits within the siphuncle. 

The oldest known genus, Valcouroceras Flower from 

Chazyan strata in New York, is remarkable for the dramatic changes in morphology that the shell undergoes 

with ontogeny (Flower, 1946, fig. 14). Shell cross sectional 

shape changes from highly compressed ovate adapically 

to broad, depressed subtriangular adorally, then contracting to compressed ovate at the aperture. The siphuncle 

segments initially are slender, subtubular with thin connecting rings; becoming more expanded, compressed 

heart-shaped adorally, the connecting rings thickening 

with ontogeny, leading to the development of thick actinosiphonate deposits in adoralmost segments of large specimens. Early slender, subtubular adapical segments with 

suborthochoanitic septal necks are similar to those developed at the same stage of growth in the Oncoceratidae 

and in some members of the Tripteroceratidae, suggesting 

io Flower (1946) a common origin for all three families in 

the early Middle Ordovician.

Younger members of the family retain the same 

sequence of morphologic changes with ontogeny that are 

characteristic of Valcouroceras, the shells being compressed ovate adapically, becoming depressed, subtriangular with venter subangular with ontogeny. These 

younger taxa, consisting of Augustoceras Flower, Kindleoceras Foerste, and ManitouLinoceras Foerste, tend to 

be more depressed, slender forms compared with the 

adorally inflated shells typical of Valcouroceras.

Small, fragmentary silicified specimens assignable to 

the family occur in the USGS 6034-CO collection from the 

upper part of the Tyrone Limestone (Middle Ordovician, 

Rocklandian) in central Kentucky. These specimens may 

be assignable to either Valcouroceras or Manitoulinoceras, but not enough of the shell is preserved to be diagnostic of either genus. The family is best represented in 

Upper Ordovician strata in the Cincinnati arch region 

where Flower (1946) has described four species of 

Augustoceras, four species of Kindleoceras, and seven 

species of Manitoulinoceras. Within these Cincinnatian 

strata, members of this family are most abundant in the 

Leipers Limestone (Edenian and Maysvillian) in southcentral Kentucky and in younger carbonates in the Saluda 

and Whitewater Formations (Richmondian) in southeastern Indiana

GENUS AUGUSTOCERAS FLOWER

Type species.—Augustoceras shideleri Flower, 1946, 

p. 343; by original designation; Leipers Limestone, 

(Maysvillian part), south-central Kentucky.

Description.—Small, slender, somewhat fusiform 

cyrtocones; shell initially rapidly expanding, then becoming more gradually expanding, tubular with ontogeny. 

Venter convex and dorsum concave the length of the 

shell. Shell cross section rounded subtriangular, the dorsum flattened and venter subangular. Sutures oblique, 

sloping adorally from the dorsum to the venter. Cameral 

chambers very short, length decreasing with ontogeny. 

Body chamber short, slightly inflated adapically, contracting slightly toward aperture. Aperture open, inclined 

adorally from dorsum to venter, the ventral hyponomic 

sinus weakly developed. Shell exterior marked by closely 

spaced, fine, raised growth lines.

Siphuncle situated near ventral shell margin; segments small in diameter (averaging one-eighth the diameter of the shell), slightly expanded within camerae, 

scalariform. Segments becoming more compressed, 

broader in diameter with ontogeny. Septal necks short, 

strongly recurved, cyrtochoanitic. Connecting rings 

slightly thickened. Segments occupied by actinosiphonate 

deposits originating from connecting ring wall and consisting of longitudinal plates that, in cross section, consist 

of numerous radially disposed rays extending inward 

from the connecting ring wall. Deposits thickening 

adorally with ontogeny.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Shermanian Stage) to Upper Ordovician 

(Maysvillian Stage); Ohio valley, central Kentucky, and 

central basin of Tennessee.

Remarks.—Augustoceras is distinct from other members of the Valcouroceratidae in its slender, fusiform shell 

shape and the restriction of the ontogenetic changes in 

the siphuncle segments to the earliest adapical portions 

of the shell. The latter results in the presence of 

expanded, cyrtochoanitic siphuncle segments and actinosiphonate deposits over much of the length of the phragmocone. The genus also differs from the more primitive 

Minganoceras and Valcouroceras in the development of a 

shallow hyponomic sinus, a feature absent in these older 

Middle Ordovician taxa

Cincinnatian species of Kindleoceras Foerste and 

Manitoulinoceras Foerste differ from Augustoceras in 

having the development of actinosiphonate deposits 

restricted to adoral portions of the shell adjacent to the 

body chamber. Additionally, Kindleoceras has a more pronounced subtriangular cross section and both Kindleoceras and Manitoulinoceras have a more slender, 

gradually expanding shell compared with known species 

of Augustoceras. As indicated above, in the Cincinnati 

arch region, Augustoceras is best known from the
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION Pill

Maysvillian Leipers Limestone in south-central Kentucky, 

whereas species of Kindleoceras and Manitoulinoceras 

are known from younger Richmondian strata in southeastern Indiana and adjacent portions of southwestern 

Ohio.

Known occurrences of Augustoceras consist of fragmentary specimens from the Catheys Formation in central Tennessee and the Strodes Creek Member of the 

Lexington Limestone in northern Kentucky (Middle 

Ordovician, Shermanian). Poorly preserved specimens 

from the Edenian part of the Kope Formation (Upper 

Ordovician) in the Cincinnati, Ohio, region may also 

belong in this genus. Augustoceras is represented by 

abundant, well-preserved, calcite-replaced specimens 

from the Maysvillian part of the Leipers Limestone (Upper 

Ordovician, Maysvillian) in the Cumberland River valley 

in south-central Kentucky (pi. 20, figs. 23-27). Flower 

(1946) differentiated four species from these strata. Cyrtoceras vallandighami Miller, a poorly known species 

from the Maysvillian part of the Fairview Formation (Late 

Ordovician) at Cincinnati, Ohio, might also be a species of 

Augustoceras.

Augustoceras, along with the actinocerid Troedssonoceras Foerste and the large discosorids Faberoceras 

Flower and Antiphragmoceras Foerste, was endemic to 

the southern Cincinnati arch region in the Middle and 

Late Ordovician and is characteristic of Flower's "Austral" 

fauna This indigenous nautiloid fauna, as well as the 

orthocerid Treptoceras Flower and the endocerid Cameroceras Conrad, alternates with immigrant "Boreal" taxa 

derived from coeval carbonate facies in Western and Arctic North America throughout the Upper Ordovician 

strata exposed in the Kentucky-Indiana-Ohio area 

(Flower, 1946,1976).

AUGUSTOCERAS SHIDELERI FLOWER, 1946 

Plate 20, figures 23-27

Augustoceras shideleri Flower, 1946, p. 432, pi. 13, figs. 

1-10; pi. 19, fig. 14; pi. 20, figs. 1-7.

Diagnosis.—Large species of Augustoceras distinguished by the nearly tubular nature of the adoral portion 

of the shell and its comparatively deep camerae and rapid 

rate of shell expansion adapically.

Description.—Small (estimated lengths of up to 11.6 

cm and shell diameters of up to 2.7 cm), slender (apical 

angle 18-22 degrees), exogastrically curved, fusiform cyrtocones. Shell initially rapidly expanding up to diameters 

of 20 mm, then becoming more gradually expanding with 

ontogeny. Venter strongly convex the length of the shell; 

dorsum concave. Shell cross section compressed ovate at 

diameters of 15 mm or less, venter more narrowly 

rounded than dorsum; section gradually becoming more 

depressed, the dorsum slightly flattened and venter more 

angular at diameters greater than 15 mm. Shell height

roughly equal to width much of the length of the shell. 

Sutures sloping adorally from dorsum to venter; very shallow dorsal lobe developing adorally. Camera! chambers 

short, camera! lengths ranging from one-fifth to one-eleventh the diameter of the shell, decreasing with ontogeny. 

Body chamber comparatively short, slightly less than onefifth the total length of the shell; slightly inflated adapically, then contracting adorally toward aperture. Aperture 

open, the lateral flanks oblique, sloping forward from dorsum to venter. Dorsum broadly rounded, marked by shallow V-shaped ventral hyponomic sinus. Shell surface 

having crowded, fine, raised transverse growth lines that 

slope dorsally and ventrally, delineating a shallow lobe 

and ventral sinus.

Siphuncle located close to the ventral shell margin, 

separated from it by a distance equal to the diameter of 

the siphuncle segment. Segments narrow in diameter, 

averaging one-seventh the diameter of the shell. Segments 

slightly expanded, scalariform, wider adorally than adapically, SCR values being 0.90-1.10 (nearly equiaxial to 

slightly compressed) at shell diameters of 13.5-17 mm. 

Segments adnate adorally to adjacent septum. Septal 

necks short, cyrtochoanitic, more strongly recurved dorsally than ventrally. Connecting rings thickened much of 

the length of the phragmocone, producing well developed 

actinosiphonate deposits that thicken adorally. Deposits 

consisting of longitudinal plates that in cross section 

show 12-17 variably developed radial rays that project 

inward from the connecting ring wall but do not meet in 

the center.

Stratigraphic and geographic occurrence.—Leipers 

Limestone (Upper Ordovician, Maysvillian part); vicinity 

of the Cumberland River valley, south-central Ky

Studied material.—Holotype UC 24290 (Flower, 

1946, pi. 18, figs. 2-4), paratype UC 24292 (Flower, 1946, 

pi. 18, figs. 5-9), paratype MU 435T, and topotype MU 

428T (pi. 20, figs. 23-27), all from the Tetradium biostrome in the Leipers Limestone exposed along the banks 

of the Cumberland River at Belk Island, near Rowena, Ky.

Remarks.—Flower (1946) distinguished A. shideleri 

from associated species of Augustoceras on the basis of 

its larger size and the deeper camerae and more rapid rate 

of shell expansion evident in adapical portions of the 

phragmocone. Comparisons of studied specimens of A. 

shideleri with Flower's types of A. medium Flower (UC 

28284) and A. minor Flower (UC 24287) indicate that 

these differences can be used to differentiate these species. Additionally, overlays of the shell outlines of these 

specimens indicate that both of these species are much 

more gently curved compared with typical specimens of 

A. shideleri.

Augustoceras shideleri is more similar to A. commune Flower in the curvature of the shell and in the rate 

of shell expansion of the adapical portion of the shell
P112 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

(both 18-23 degrees). Camera! lengths in portions of the 

shell 15 mm in diameter tend to be shorter in specimens 

of A. commune. The holotype of A. commune (MU 448T) 

indicates that the maximum size attained by this species 

was approximately 10.0 cm, a maximum observed diameter being 2.0 cm; somewhat less than the maximum size 

observed in A. shideleri (up to 11.6 cm in length and 2.5 

cm in diameter). Further study of large suites of more 

complete specimens is needed to determine the relation 

between these two similar species, associated in taxa. 

Flower (1946) indicated that in the Leipers Limestone, A. 

commune was the most abundant species of Augustoceras and, in fact, the most abundant nautiloid present in 

the Tetradium biostrome.

GENUS MANITOULINOCERAS FOERSTE

Type species.—Cyrtoceras lysander Billings, 1865, p. 

161; designated by Foerste, 1924a, p. 230; Meaford Formation, Richmondian Stage, Upper Ordovician, Manitoulin 

Island, Ontario.

Description.—Small to medium-sized, slender exogastric cyrtocones, the shell moderately to rapidly 

expanding adapically, becoming more gradually expanding, almost tubular adorally with ontogeny. Shell nearly 

straight to strongly curved; venter typically convex the 

length of the shell, dorsum concave. Cross section 

depressed ovate, the dorsum more flattened than the venter. Venter rounded or subangular. Sutures weakly crenulate; straight, transverse adapically, becoming oblique 

with ontogeny, sloping from dorsum to venter. Dorsum 

with shallow lobe adorally. Cameral chambers very short, 

cameral lengths decreasing with ontogeny. Body chambers short, nearly tubular, not contracting towards aperture. Aperture open, marked by a broad shallow sinus 

dorsally and a shallow V-shaped hyponomic sinus ventrally Shell surface marked by closely spaced, fine, transverse growth lines.

Siphuncles located at or near ventral shell margin; 

narrow in diameter, averaging one-fifth the diameter of 

the shell. Segments expanded, spherical to compressed 

ovate in shape; broad at the septal foramen relative to 

segment length. Septal necks short, recurved, cyrtochoanitic. Connecting rings thickening adorally, producing 

irregularly developed actinosiphonate deposits.

Stratigraphic and geographic occurrence.—Middle 

Ordovician (Blackriveran? Stage) to Upper Ordovician 

(Richmondian Stage); Eastern and Central North America 

(Laurentia).

Remarks.—Manitoulinoceras is evidently a longranging genus that has been reported from strata as old as 

Blackriveran in age by Foerste (1933). Flower (1946) 

noted, however, that older Middle Ordovician species 

assigned to the genus were atypical, consisting of forms 

that were too narrow in section and (or) more rapidly

expanding than is typical of younger members of the 

genus, including the type species. He indicated that the 

oldest well-established species assignable to the genus 

was M. wykoffense Foerste from the Prosser Limestone 

(Middle Ordovician, Shermanian) of Minnesota. Undescribed typical specimens of. Manitoulinoceras from Middle Ordovician (Rocklandian and Kirkfieldian) strata in 

Quebec indicate, however, that the genus goes back at 

least to the Rocklandian. The bulk of the described species of Manitoulinoceras are from younger Late Ordovician (Richmondian) strata in the Cincinnati arch region of 

Kentucky-Indiana-Ohio and adjacent portions of southern 

Ontario.

In contrast to the preceding genus, specimens of 

Manitoulinoceras from the Cincinnati region typically 

consist of matrix-filled internal molds in which the septal 

necks and connecting ring walls are not preserved. As a 

result, with the exception of several molds from the 

Saluda Formation in southeastern Indiana (Flower, 1946, 

pi. 23, figs. 7-9), actinosiphonate deposits are not known 

for most of these species of Manitoulinoceras from the 

Cincinnati arch region. Curiously, well-preserved, calcitereplaced specimens of M. tenuiseptum (Faber) and M. 

wiUiamsae Flower from the Treptoceras duseri shale 

unit sectioned by the author lacked any evidence of actinosiphonate deposits (Frey, 1983, pi. 19, fig. 3).

Within the Cincinnati arch region, the earliest occurrence of Manitoulinoceras is M. tenuiseptum (Faber) 

and M. wiUiamsae Flower in the "Treptoceras duseri 

Shale" within the Bull Fork Formation (lower Richmondian) in southwestern Ohio (Flower, 1946; Frey, 1983, 

1989). I have found a number of incomplete internal 

molds of Manitoulinoceras in several other trilobite-bearing claystone beds higher up in the Bull Fork section in 

the same area. The genus, however, is most abundant in 

younger Richmondian carbonate facies, where M. moderatum Flower and M. gyroforme Flower occur in the 

micritic limestones of the Saluda Formation in southeastern Indiana and western Ohio and M. moderatum, M. 

erraticum Flower, and M. ultimum Flower occur in the 

various facies of the overlying Whitewater Formation in 

same area, Manitoulinoceras gyroforme Flower is 

described here from the uppermost Bull Fork Formation 

(Richmondian) exposed near Fairborn, Greene County, 

Ohio.

MANITOULINOCERAS GYROFORME FLOWER, 1946

Plate 20, figures 28, 29

Manitoulinoceras gyroforme Flower, 1946, p. 382, pi. 21, 

figs. 12-14.

Diagnosis.—Small species of Manitoulinoceras distinguished by its strongly curved shell and highly 

depressed cross section.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P113

Description.—Small (estimated lengths of up to 11.0 

cm and shell diameters up to 2.0 cm), moderately expanding (apical angle of 10 degrees), strongly exogastrically 

curved cyrtocones with a strongly convex venter and concave dorsum. Shell cross section depressed ovate, becoming more depressed in section with ontogeny at a height 

to width ratio averaging 0.86 for shell heights of 12-20 

mm. Dorsum only slightly more flattened than venter. 

Sutures slightly crenulate, sloping adorally from dorsum 

to venter with the development of a broad, shallow dorsal 

lobe. Cameral chambers short, camera! lengths ranging 

from one-seventh to one-tenth the diameter of the shell, 

decreasing with ontogeny. Body chamber depressed, 

tubular, slightly less than one-fifth the total length of the 

shell. Aperture poorly known; open with a shallow dorsal 

lobe and sloping obliquely from dorsum to venter. Shell 

exterior marked by closely spaced, fine, raised growth 

lines.

Siphuncle located at ventral shell margin; segments 

expanded, compressed ovate, slightly greater than oneseventh the diameter of the shell; SCR values of 1.16-1.50 

(compressed) at shell widths of 19-22 mm. Structure of 

septal necks and connecting rings unknown.

Stratigraphic and geographic occurrence.—"Saluda 

tongue" within the upper part of the Bull Fork Formation 

(Upper Ordovician, Richmondian Stage), Butler County, 

Ohio; uppermost Bull Fork Formation (late Richmondian), Greene County, Ohio.

Studied material.—Holotype MU 436T (Flower, 

1946, pi. 21, figs. 12-14), Saluda Formation at Indian 

Creek, 5 mi west of Oxford, Ohio; USNM 468719 (pi. 20, 

figs. 28, 29), Bull Fork Formation, railroad cut at Wright 

Memorial, Fairborn, Greene County, Ohio.

Remarks.—Manitoulinoceras gyroforme is apparently a rare species in Richmondian strata exposed in the 

Cincinnati arch region, currently known from only two 

specimens: the holotype from the "Saluda" tongue near 

Oxford, Butler County, Ohio, and the specimen illustrated 

here from the uppermost Bull Fork Formation in Greene 

County, Ohio. This species is readily distinguished from 

all other species of Manitoulinoceras on the basis of the 

strong curvature of the shell and the more or less equally 

depressed venter and dorsum over the length of the shell. 

The most abundant species of Manitoulinoceras in these 

strata, M. moderatum Flower, is a larger, more gently 

curved, slender cyrtocone that is most common in the 

micritic limestones of the Saluda Formation in adjacent 

portions of southeastern Indiana.

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P120 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

APPENDIX: LOCALITY REGISTER

During the geologic mapping of the State of Kentucky 

by the Kentucky and U.S. Geological Surveys, Ordovician 

fossils were collected from nearly 1,100 localities. Pojeta 

(1979) listed 317 of these localities from which Ordovician fossils were collected and studied. Below is a list of 

18 USGS localities from which some of the fossils studied 

for this report were collected. The localities are arranged 

sequentially by collection number assigned to each in the 

USGS register of Cambrian and Ordovician (CO) localities. The following abbreviations are used in this locality 

listing: C.n., collection number; G.I., geographic locality; 

E, formation; S.p., stratigraphic position; Q.n., 7.5 min 

quadrangle name; S.n., section name. Not all localities 

have information in all categories.

U.S. Geological Survey Localities

C.n. - 4073-CO.

G.I. - 0.75 mi east of Milner, Ky, turn right (southwest)

on Shyrock Ferry Road. Continue down road

about 1 mi to top of section.

E - Grier Limestone Member, Lexington Limestone. 

S.p. - 148 ft above the base of the Curdsville Limestone

Member, Lexington Limestone. 

Q.n. - Tyrone, Ky. 

S.n. - Tyrone A.

C.n. - 4865-CO.

G.I. - U.S. Route 62 at crossing of Kentucky River; from 

east side of Blackburn Memorial Bridge, take 

side road north 0.1 mi to railroad cut exposure.

E - Logana Member, Lexington Limestone.

S.p. - Lower 12 ft of Logana Member.

Q. n.- Tyrone, Ky

S.n. - Tyrone C, or Ky. Utilities Plant.

C.n. - 4879-CO.

G.I. - Road exposures between Trinity Church and 

Antioch Church, southwest quadrant, Valley 

View quadrangle, Kentucky, 1 mi southwest of 

northern termination of Kentucky Route 595 at 

Kentucky River.

E - Grier Limestone Member, Lexington Limestone.

S.p. - 43-45 ft above base of section.

Q.n. - Valley View, Ky.

S.n. - Valley View C (Antioch Church Road).

C.n. - 4883-CO.

G.I. - Same as for 4879-CO.

E - Grier Limestone Member, Lexington Limestone.

S.p. - 60.5 ft above base of section.

Q.n.- Valley View, Ky.

S.n. - Valley View C (Antioch Church Road).

C.n. - 5067-CO.

G.I. - Hillside pasture exposure on west side of U.S. 

Route 227, 0.4 mi south of intersection of 

Ford-Hampton Road and U.S. 227, north of Ford, 

Ky.

E - Grier Limestone Member, Lexington Limestone.

S.p. - 140 ft above the top of the Tyrone Limestone.

Q.n.- Ford, Ky.

C.n. - 5072-CO.

G.I. - Immediately behind Old Crow Distillery, northern 

bluff of Glenns Creek Road, 0.7 mi west of intersection with Hanley Lane.

E - Lower part of the Lexington Limestone; mostly 

basal Curdsville Limestone Member, but with 

some float blocks of Logana Member in the 

sample.

Q.n. - Frankfort East, Ky.

S.n. - Frankfort East B.

C.n. - 5073-CO.

G.I. - Northwest of Old Crow Distillery on first sharp

north bend of Glenns Creek Road, 0.9 mi west of

intersection with Hanley Lane. 

E - Upper part of the Logana Member, Lexington

Limestone.

S.p. - Just below 4-ft-thick dalmanellid coquina. 

Q.n. - Frankfort East, Ky. 

S.n. - Frankfort East B.

C.n. - 5092-CO.

G.I. - From east side of Blackburn Memorial Bridge 

crossing Kentucky River, take first road north 

towards Kentucky Utilities Plant; section in railroad and road exposures.

E - Logana Member, Lexington Limestone.

S.p. - 10-12 ft above base of Logana Member.

Q.n. - Tyrone, Ky.

S.n. - Tyrone C, or Ky. Utilities Plant.

C.n. - 5096-CO.

G.I. - Just before ferry crossing Tates Creek Road and 

Kentucky River, take road west toward Daniel 

Boone YMCA Camp; collection from near top of 

northern bluff of Kentucky River, 0.4 mi southeast of YMCA Camp, in abandoned railroad bed.

E - Grier Limestone Member, Lexington Limestone.

Q.n. - Valley View, Ky.

C.n. - 5100-CO.

G.I. - Crisman Mill Road, 0.2 mi west of Hickman Creek

crossing. 

E - Lower part of Curdsville Limestone Member,

Lexington Limestone.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P121

Q.n. - Little Hickman, Ky. 

S.n. - Little Hickman B.

C.n. - 6034-CO.

G.I. - Section on New Watts Mill Road, 0.1 mi southwest

of intersection with Kentucky Route 39. 

F. - Tyrone Limestone. 

S.p. - 112 ft above the base of section. 

Q.n. - Little Hickman, Ky. 

S.n. - Little Hickman A.

C.n. - 6127-CO.

G.I. - Southernmost tributary of Landing Run, 2,000 ft 

east of intersection of U.S. Route 3IE and 

Kentucky Route 46, between Balltown and 

Culvertown, Ky.

F. - Rowland Member, Drakes Formation.

Q.n. - New Haven, Ky

C.n. - 6419-CO.

G.I. - 1.4 mi east of Wilmore, Ky, 500 ft north of main

road. 

F - Lower part of the Logana Member, Lexington

Limestone. 

Q.n. - Wilmore, Ky.

C.n. - 7310-CO.

G.I. - 1700 ft east of Kentucky Route 89, 1.5 mi southeast

of Winchester, Ky.

F. - Strodes Creek Member, Lexington Limestone. 

Q.n. - Winchester, Ky.

C.n. - 7328-CO.

G.I. - Roadcut along Maple Street, Winchester, Ky; 2.6 mi

north of 1-64.

F. - Strodes Creek Member, Lexington Limestone. 

Q.n. - Austerlitz, Ky

C.n. - 7353-CO.

G.I. - 1 mi northeast of junction of Cook Road and Lair

Road in stock pond. 

F. - Lower tongue of Millersburg Member, Lexington

Limestone. 

Q.n. - Shawhan, Ky

C.n. - 7471-CO.

G.I. - Section along road to U.S. Route 25, 0.4 mi west of

Sadieville, Ky

F - Clays Ferry Formation. 

S.p. - 97 ft above base. 

Q.n. - Sadieville, Ky.

C.n. - 7791-CO.

G.I. - Road exposure on west side of Kentucky River at

bridge crossing Central Kentucky Parkway on

northern side of parkway. 

F. - Lower part of the Logana Member, Lexington

Limestone.

S.p. - 35 ft above Tyrone Limestone-Lexington Limestone

contact.

Q.n. - Salvisa, Ky 

S.n. - Salvisa B.

Non-USGS Collections

C.n. - KY-1.

G.I. - Roadcut on north side of Orphanage Road (State 

Route 371), 0.25 mi west of intersection with 

Kentucky Route 17, just north of I-275E, Fort 

Mitchell, Kenton County, Ky.

F. - Kope Formation.

S.p. - Clay shale bed 54 ft above the road level.

Q.n. - Covington, Ky.

C.n. - KY-2.

G.I. - Road exposures at junction of Kentucky Routes 8 

and 445, below and just west of I-275E bridge 

over Ohio River, Fort Thomas, Campbell County, 

Ky

F - Kope Formation.

S.p. - Talus blocks at base of exposure.

Q.n. - Newport, Ky.

C.n. - KY-3.

G.I. - 0.5 mi north of I-275E at intersection of Taylor Mill 

Pike (Kentucky Route 16) and Riedlin (Mason) 

Road, southeast roadcut at curve in road, Forest 

Hills, Kenton County, Ky.

F. - Upper part of the Kope Formation and basal Fairview Formation.

S.p. - Thin packstone bed 12 ft above Kope FormationFairview Formation contact.

Q.n. - Covington, Ky

C.n. - KY-4.

G.I. - Belk Island in the Cumberland River, near Rowena,

Russell County, Ky. (Shideler locality 3.5 IB; now

flooded by Lake Cumberland). 

F - Leipers Limestone.

S.p. - Tetradium biostrome exposed along river bank. 

Q.n. - Jamestown, Ky.

C.n. - KY-5.

G.I. - Road exposure south of 1-64 at exit ramp to Kentucky Route 60, 1 mi southeast of Owingsville, 

Bath County, Ky.

F. - Upper part of Bull Fork Formation.

S.p. - 50 ft below contact with Preachersville Member of 

the Drakes Formation.

Q.n. - Colfax, Ky.
P122 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

C.n. - IND-1.

G.I. - Streambank exposures along Harveys Branch of

Salt Creek, just north of Oldenburg, Franklin

County, Ind.

F. - Bull Fork Formation. 

S.p. - Upper 25 ft of the "Waynesville biofacies" and

lower 15 ft of the "Liberty biofacies." 

Q.n. - Batesville, Ind.

C.n. - IND-2.

G.I. - Exposures on the west bank of the spillway for 

Brookville Lake, just west of Brookville Dam 

Road and north of Indiana Route 101, north of 

Brookville, Franklin County, Ind.

F. - Bull Fork Formation.

S.p. - "Waynesville and Liberty biofacies."

Q.n. - Whitcomb, Ind.

C.n. - IND-3.

G.I. - Road exposure on the west side of Indiana Route

101 at the north end of the valley at the crest of

Garr Hill, 5.0 mi north of Brookville, Franklin

County, Ind. 

F. - Tongue of the Saluda Formation and overlying

Whitewater Formation. 

S.p. - Tetradium biostrome and overlying shales and

micritic limestone beds. 

Q.n. - Whitcomb, Ind.

C.n. - IND-4.

G.I. - Streambank exposures along Bull Fork of Salt 

Creek at the Sayers Farm, 2 mi northeast of Hamburg, Franklin County, Ind.

F - Saluda Formation.

S.p. - "Concrete Layer," 18-in-thick resistant micritic 

limestone bed 15 ft above the Tetradium biostrome.

Q.n. - Clarksburg, Ind.

C.n. - IND-5.

G.I. - Road exposure on the south side of Indiana Route 

50 at the east edge of Versailles, Ripley County, 

Ind.

F. - Saluda Formation.

S.p. - Slabby micritic limestone beds above the main Tetradium biostrome.

Q.n. - Milan, Ind.

C.n. - IND-6.

G.I. - Road exposures near the top of the hill along U.S. 

Route 421, 3.1 mi north of the intersection with 

Indiana Route 56 in Madison, Jefferson County, 

Ind.

F. - Saluda Formation and its Hitz Limestone Member.

Q.n. - Madison-West, Ind.

C.n. - IND-7.

G.I. - Road exposures on both sides of U.S. Route 27,1.0

mi south of Richmond, Wayne County, Ind. 

F - Whitewater Formation. 

S.p. - Upper 30 ft of the rubbly facies of the Whitewater

Formation (Rhynchotrema dentatum zone). 

Q.n. - Richmond, Ind.

C.n. - OH-1.

G.I. - Stream exposures along West Fork, west of Mill 

Creek, just above dairy and concrete retaining 

wall, near Cumminsville, western Cincinnati, 

Hamilton County, Ohio.

F - Kope Formation.

Q.n. - Cincinnati-West, Ohio.

C.n. - OH-2.

G.I. - Road exposures on the east side of Ohio Route 125 

in the Whiteoak Creek valley, 0.8 mi west of junction with U.S. Route 68 in Georgetown, Brown 

County, Ohio.

F. - Fairview Formation.

Q.n. - Higginsport, Ohio-Ky.

C.n. - OH-3.

G.I. - Streambank exposures along Taylors Creek, near

Dent, Hamilton County, Ohio (Shideler locality

1.22A27).

F. - Fairview Formation. 

S.p. - Basal 15 ft. 

Q.n. - Addyston, Ohio.

C.n. - OH-4.

G.I. - Stonelick Creek, just south of Route 131 bridge,

2 mi west of Newtonsville, Clermont County,

Ohio.

F. - Grant Lake Formation.

S.p. - Corryville Member of the Grant Lake Formation. 

Q.n. - Newtonsville, Ohio.

C.n. - OH-5.

G.I. - North side of Conrail Railroad tracks, 500 ft south

of 1-75 and south of Maud, Butler County, Ohio. 

F. - Grant Lake Formation. 

S.p. - Mount Auburn Member of the Grant Lake

Formation. 

Q.n. - Glendale, Ohio.

C.n. - OH-6.

G.I. - Road exposure on the west side of U.S. Route 42, 2

mi northeast of Waynesville, Warren County,

Ohio.

F - "Waynesville biofacies" in the Bull Fork Formation. 

S.p. - Treptoceras duseri shale unit. 

Q.n. - Waynesville, Ohio.
MIDDLE AND UPPER ORDOVICIAN NAUTILOID CEPHALOPODS, CINCINNATI ARCH REGION P123

C.n. - OH-7.

G.I. - Excavation for spillway (now under water) at junction of Caesars Creek and Flat Fork Creek, plus 

exposures along emergency spillway of Caesars 

Creek Lake, off Clarksville Road, Warren County, 

Ohio.

F - "Waynesville and Liberty biofacies" in the Bull Fork 

Formation.

S.p. - Section from Treptoceras duseri shale unit to the 

upper Thaerodonta clarksvittensis zone.

Q.n. - Oregonia, Ohio.

C.n. - OH-8.

G.I. - Streambank exposures along the north and south 

forks of Harpers Run at the Whip-Poor-Will Girl 

Scout Camp, south of Stout Road and west of 

Middleboro Road, Warren County, Ohio.

F. - "Waynesville biofacies" in the Bull Fork Formation.

S.p. - Treptoceras duseri shale unit.

Q.n. - Oregonia, Ohio.

C.n. - OH-9.

G.I. - Streambank exposures along Stony Hollow, 1,000 ft

north of Todds Fork, just north of Clarksville,

Clinton County, Ohio.

F. - "Waynesville biofacies" in the Bull Fork Formation. 

S.p. - Treptoceras duseri shale unit. 

Q.n. - Clarksville, Ohio.

C.n. - OH-10.

G.I. - Exposures on the north side of spillway at Cowan

Lake, just west of the Ohio Route 730 bridge, 5

mi southwest of Wilmington, Clinton County,

Ohio.

F. - Bull Fork Formation. 

S.p. - Upper 40 ft of the formation just below contact

with Preachersville Member of the Drakes

Formation. 

Q.n.- Clarksville, Ohio.

C.n. - OH-11.

G.I. - Small road exposure at junction of U.S. Route 22

and Ohio Route 380, just west of Todds Fork,

Clinton County, Ohio.

E - "Liberty biofacies" in the Bull Fork Formation. 

Q.n. - Clarksville, Ohio.

C.n. - OH-12.

G.I. - Railroad exposure on the north edge of Wright

Brothers Memorial Park, just south of Ohio

Route 444 and Huffman Dam, Greene County,

Ohio.

F. - Bull Fork Formation. 

S.p. - Upper part of the Bull Fork Formation 45 ft below

contact with Preachersville Member of the

Drakes Formation. 

Q.n. - Fairborn, Ohio.

C.n. - OH-13.

G.I. - Small stream flowing southwest into the Stillwater 

River at Cricket Holler Boy Scout Camp, northwest of Dayton, Montgomery County, Ohio.

F. - Bull Fork Formation.

Q.n. - Dayton-North, Ohio.

C.n. - OH-14.

G.I. - Stream exposures along Collins Run, 0.25 mi

upstream and north of Pffeifer Park, 1.5 mi south

of the Oxford, just west of U.S. Route 27, Butler

County, Ohio. 

E - "Waynesville and Liberty biofacies" in the Bull Fork

Formation. 

S.p. - "Waynesville biofacies" from the "Trilobite shale

unit" to the contact with the overlying "Liberty

biofacies." 

Q.n.- Millville, Ohio.

C.n. - OH-15.

G.I. - Addisons Creek, southeast flowing tributary of

Four-Mile Creek, just south of the spillway for

Acton Lake, 3 mi north of Oxford, Butler County,

Ohio.

E - Bull Fork Formation. 

S.p. - Upper 15 ft of the "Waynesville biofacies" and the

lower 30 ft of the "Liberty biofacies." 

Q.n.- Oxford, Ohio.

INDEX

P125

Page

Abstract....................................................................... 1

Acknowledgments....................................................^

Actinoceras .............................................................. 81

altopontense ..................................................... 82

curdsvittense.................................................... 84

kentuckiense .................................................... 82

Actinoceratidae........................................................80

Actinoceratoidea............................................... 23,80

Actinocerida.............................................................80

albersi, Isorthoceras............................................... 60

Attumettoceras cf. A. tenerum............................. 103

altopontense, Actinoceras...................................... 82

amoenum, Betoitoceras.......................................... 97

amplicameratum, Ordogeisonoceras ............ 38,39

Anaspyroceras cf. A cylindricum ....................... 66

annularis, Monomuchites..................................... 56

apical angle............................................................... 24

Arctic nautiloid fauna....................................... 10,19

Ashlock Formation....................................................9

Augustoceras ......................................................... 110

commune........................................................ Ill

B

Baltoceratidae................................. ...................... ...27

Bardstown Member, Drakes Formation ................. 9

Barrandeocerina...................................... ........... .....92

Beloitoceras............................ .................................. 97

amoenum ......................................................... 97

huronense, cf. B. .............................................. 99

Black River Group................................................... 12

Black River Formation............................................ 12

Blackriver nautiloid fauna................................ 10, 12

Brannon Member, Lexington Limestone ................ 8

Brassfield Limestone............................................... 20

brevicameratum, Richmondoceras. ..................... 71

bucheri, Beloitoceras .............................................. 98

Bull Fork Formation ............................................. 5, 9

byrnesi, Treptoceras ............................................... 51

Galloway Creek Limestone....................................... 9

camera! deposits...................................................... 24

camera! length.......................................................... 24

Camemceras............................................................ 73

rowenaense ...................................................... 74

sp.......................................................................76

trentonense....................................................... 76

Camp Nelson Limestone, High Bridge Group........ 6

cartetonense, Plectoceras cf. P. .............................. 93

Cartersoceras...................................................... .....28

popei..................................................................30

shideleri............................................................ 28

Catheys Formation....................................................9

central canal............................................................. 81

Page

Champlainian Provincial Series, Middle

Ordovician........................................................ 5, 6

Cincinnatian nautiloid fauna.................................. 10

Cincinnatian Provincial Series, Upper

Ordovician........................................................ 4,8

Cincinnati arch.......................................................... 4

cincinnatiensis, Treptoceras................................ 52

clarksvittensis, Pleurorthoceras ........................... 37

Clays Ferry Formation.......................................... 5,8

commune, Augustoceras...................................... Ill

costalis, Monomuchites cf. Jlf................................ 55

cross-sectional shape (shell)................................. 24

Cumberland Formation............................................ 9

Cumberland sag..................................................... 5, 9

Curdsville Limestone Member, Lexington

Limestone............................................................. 7

curdsviUense, Actinoceras..................................... 84

curdsvittense, Deiroceras ...................................... 87

cylindricum, Anaspyroceras cf. A. ...................... 66

Cynthiana Limestone.............................................. 16

D

davisi, Triendoceras(T).......................................... 79

Decorah Shale/Decorah Group.............................. 13

Deicke Bentonite Bed....................................... 12,15

Deicke volcanic event............................................. 15

Deiroceras curdsvittense ....................................... 86

Diestoceras............................................................. 104

eos................................................. ................... 108

indianense ..................................................... 105

shideleri ......................................................... 107

Diestoceratidae...................................................... 104

Dillsboro Formation.............................................. 5, 9

Distribution and Faunal Affinities of 

Ordovician Nautiloids in the Cincinnati 

Arch Region....................................................... 10

Drakes Formation..................................................... 9

duseri, Treptoceras................................................. 46

dyeri, Ortkonybyoceras......................................... 89

E

Edenian Nautiloid Fauna........................................ 16

Edenian Stage, Upper Ordovician........................... 8

Ellesmerocerida....................................................... 27

Endoceratidae.......................................................... 72

Endoceratoidea................................................. 23, 72

Endocerida............................................................... 72

endosiphuncular deposits................................ 24, 28

eos, Diestoceras..................................................... 108

Euorthoceras ........................................................... 46

faberi, Trocholites ................................................... 90

Fairview Formation.............................................. 5,9

ferecentricum, Ormoceras..................................... 86

floweri, Pojetoceras ................................................ 35

fosteri, Treptoceras ................................................ 48\

Page

6

Galena shelf............................................................... 4

Gamachian Stage, Upper Ordovician.................... 20

Geisonoceras rivale................................................ 39

Geisonoceratidae.................................................... 38

gorbyi, Gorbyoceras .............................................. 63

Gorbyoceras............................................................. 62

gorbyi............................... ................................. 63

hammetti.......................................................... 64

tetreauense....................................................... 65

Grant Lake Formation/Grant Lake Limestone.. 5,9 

Grier Limestone Member, Lexington

Limestone............................................................. 7

gyroforme, Manitoulinoceras............................. 112

H

hatti, Plectoceras..................................................... 94

hammetti, Gorbyoceras.......................................... 64

High Bridge Group, Middle Ordovician.............. 4,6

Hitz Limestone Bed................................................... 5

huronense, Beloitoceras cf. B................................ 99

indianense, Diestoceras...................................... 105

Introduction............................................................... 2

Isorthoceras............................................................. 59

o»erai............................................................... 60

rogersensis....................................................... 61

sociote............................................................... 61

strangulatum .................................................. 59

strigatum......................................................... 61

Jessamine dome........................................................ 5

K

kentuckiense, Actinoceras..................................... 82

Kirkfieldian Stage, Middle Ordovician.................... 5

Kope Formation..................................................... 5,8

Laphamoceras cf. L. sco/ieldi.............................. 101

Late Ordovician Extinction Event......................... 20

Leipers Limestone........................................... 5,9,19

Leray-Rockland beds, Middle Ordovician............ 12

Lexington Limestone........................................ 4,5,6

Lexington platform............................................... 3,4

Locality Register.................................................... 120

Logana Member, Lexington Limestone............ 7, 99

M

Maelonoceras cf. M.praematurum.................... 100

major, Oncoceras.................................................... 95

Manitoulinoceras gyroforme.............................. 100
P126 CONTRIBUTIONS TO THE ORDOVICIAN PALEONTOLOGY OF KENTUCKY AND NEARBY STATES

Maysville Group, Upper Ordovician........................ 3

Maysvillian and Early Richmondian Nautiloid 

Faunas................................................................. 17

Maysvillian Stage, Upper Ordovician.................. 8, 9

Michelinoceratidae.................................................. 33

Middle Ordovician Champlainian Provincial

Series Lithostratigraphy in Kentucky............... 6

Middle to Late Richmondian Nautiloid Fauna..... 19

Millersburg Member, Lexington Limestone ........... 8

Millbrig Bentonite Bed............................................ 15

Millbrig volcanic event............................................ 15

Monomuchites ......................................................... 54

annularis ......................................................... 56

costaliscf.......................................................... 55

obliquum.......................................................... 58

Mud Cave bentonite bed........................................... 6

murrayi, Murrayoceras cf. M. .............................. 31

Murrayoceras cf. M. murrayi ............................... 31

N

Nautiloid Biostratinomy......................................... 21

Nautiloid Classification.......................................... 23

Nautiloidea.........................................................23, 90

Nautiloid Fauna of the Cincinnatian

Provincial Series................................................ 16

Nautiloid Fauna of the Leipers Limestone....... 5,19

Nautiloid Fauna of the Lexington

Limestone................................................. 5,15,16

Nautiloid Fauna of the Tyrone Limestone........ 5,10

Nautiloid Taphonomy.............................................. 21

Non-silicifiedNautiloids.........................................22

O

obliquum, Monomuchites......................................58

Oncoceras................................................................. 94

major.................................................................95

sp.......................................................................96

Oncoceratidae..........................................................94

Oncocerida............................................................... 94

Ordogeisonoceras amplicameratum............. 38,39

Ordovician Lithostratigraphy in the

Cincinnati Arch Region....................................... 4

Oregon Formation, High Bridge Group.................. 6

Ormocerasferecentricum......................................86

Ormoceratidae......................................................... 85

Orthoceras regularis .............................................. 34

Orthoceratidae.........................................................33

Orthoceratoidea.................................................23,27

Orthocerida........................................................ 23,32

Orthonybyoceras dyeri .......................................... 89

Pencil Cave bentonite bed.................................. 6,12

Page 

Platteville Formation/Group, Middle

Ordovician.......................................................... 12

Plectoceras ............................................................ ...92

cartetonense, cf. P ........................................... 93

Plectoceratidae. ....................................................... 92

Pleurorthoceras ....................................................... 36

clarksvillense.... ................................... ............ 37

seUcirkense ....................................................... 37

Point Pleasant Tongue, Clays Ferry

Formation............. ........................................ ..8, 33

Pojetocerasfloweri ........................................... 35, 38

Polygrammoceras .... ............................................ ...67

sp. A, cf. .PC?).......................................... 68

sp. B...................................................................69

popei, Cartersoceras. .............................................. 30

praematurum, Maelonoceras cf. M. ................... 100

Preachersville Member, Drakes Formation ........... 9

Proteoceras tyronensis..... ...................................... 43

Proteoceratidae .................................................... ...41

Pseudoceratidae . ..................................................... 58

Q

Queenston delta.........................................................3

R

radial canal(s)..........................................................81

References Cited................................................... 113

Regional Ordovician Paleogeographic Setting...... 3

regularis, Orthoceras ............................................. 34

Richmondian nautiloid fauna................................. 10

Richmondian Stage, Upper Ordovician.............. 8, 9

Bichmondoceras brevicameratum....................... 71

rivale, Geisonoceras............................................... 39

Rocklandian Nautiloid Extinction......................... 12

Rocklandian Stage, Middle Ordovician.................. 5

rogersensis, Isorthoceras....................................... 61

rowenaense, Cameroceras..................................... 74

Rowland Member, Drakes Formation..................... 9

Saluda Dolomite Member, Drakes Formation..... 10

Saluda Formation...................................................... 5

scofieldi, Laphamoceras cf. L. ........................... 101

Sebree trough......................................................... 4, 7

segment compression ratio (SCR)........................ 24

segment height.........................................................24

segment length.........................................................24

segment position ratio (SPR)................................. 24

selkirkense, Pleurorthoceras................................. 37

shell ornament......................................................... 24

shideteri, Augustoceras ....................................... Ill

shideteri, Cartersoceras......................................... 28

Page 

shideteri, Diestoceras........................................... 107

SilicifiedNautiloids................................................. 22

siphuncle segment measurements........................ 24

sociale, Isorthoceras............................................... 61

Species Problem in Nautiloid Systematics.......... 23

strangulatum, Isorthoceras .................................. 59

strigatum, Isorthoceras......................................... 61

Strodes Creek Member, Lexington Limestone...... 8

Systematic Descriptions......................................... 24

Systematic Paleontology........................................ 27

Taconic Landmass................................................. 3,8

Tanglewood bank...................................................... 8

Tanglewood Limestone Member, Lexington

Limestone............................................................. 8

Tarphycerida............................................................ 90

Tarphycerina............................................................ 90

tenerum, Attumettoceras cf. A. ........................... 103

tetreauense, Gorbyoceras cf. G. ............................ 65

transversum, Treptoceras...................................... 53

trentonense, Cameroceras..................................... 76

Trenton Group, Middle Ordovician....................... 16

Trenton nautiloid fauna.......................................... 10

Trenton shelf..............................................................4

Treptoceras ..............................................................44

byrnesi.............................................................. 51

cincinnatiensis............................................... 52

duseri................................................................ 46

fosteri................................................................ 48

transversum.................................................... 53

Triendoceras(T) davisi........................................... 79

Tripteroceratidae................................................... 102

Trocholitesfaberi.................................................... 91

Trocholitidae............................................................ 90

Tyrone Limestone, High Bridge Group............... 5,6

tyronensis, Proteoceras ......................................... 43

U

Upper Ordovician Cincinnatian Provincial 

Series Lithostratigraphy..........................

Vaginoceras ............................................................. 77

sp. A.................................................................. 77

sp. B.................................................................. 78

Valcouroceratidae................................................. 109

W

Watertown Limestone......................................... 6, 13

Whitewater Formation........................................... 10
PLATES 1-22

Contact photographs of the plates in this report are available, at cost, from U.S. Geological Survey 

Library, Federal Center, Denver, Colorado 80225.
PLATE 1

FIGURES 1-6, 11. Cartersoceras shideleri Flower, 1964a (p. 28).

1, 2, 4, 5. Lateral, dorsal (xl), adoral, and adapical (x2) views of silicified 

phragmocone. Tyrone Limestone (Rocklandian), USGS 6034-CO. 

USNM 158631. 

3. Dorsal natural section exposing siphuncle rod (xl). Same

collection as figure 1 above. USNM 158627. 

6. Dorsal natural section exposing siphuncle rod (xl). Same

collection as figure 1 above. USNM 158633. 

11. Thin section (x3) of a partially silicified phragmocone. Same

collection as figure 1 above. USNM 468656. 

7-10. Cartersoceras popei new species (p. 30).

7, 9. Dorsal views (x2, xl) of silicified portion of phragmocone

preserving siphuncular rod. Note dorsal groove. Same collection 

as figure 1 above. Holotype USNM 158625. 

8. Dorsal view of more adoral portion of phragmocone (xl). Same

collection as figure 1 above. Paratype USNM 468664. 

10. Dorsal view showing siphuncular rod preserving expanded 

outline of siphuncle segments x2. Note dorsal groove. Same 

collection as figure 1 above. USNM 158624. 

12-17. Murrayoceras cf. M. murrayi (Billings), 1857 (p. 31).

12,13. Dorsal and ventral views of nearly complete silicified

phragmocone (xl). Same collection as figure 1 above. USNM

468674.

14, 15. Dorsal and adapical views (xl.5) of silicified specimen exposing 

siphuncular rod. Same collection as figure 1 above. USNM

468675.

16. Dorsal view of silicified specimen exposing siphuncular rod 

(xl.5). Same coUection as figure 1 above. USNM 468672.

17. Dorsal view of weathered silicified specimen exposing siphuncle 

(xl.5). Same coUection as figure 1 above. USNM 468673.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 1

CARTERSOCERAS AND MURRAYOCERAS
PLATE 2

FIGURES 1-9. Pojetoceras floweri new species (p. 35).

1,9. Dorsal-ventral section of phragmocone, venter to right (x3.5, xl). Note

camera! deposits and thin ventral parietal deposits adapically. Tyrone

Limestone (Rocklandian), USGS 6034-CO. Holotype USNM 468676. 

2,3. Adoral and exterior views of silicified paratype (xl). Same collection

as figure 1 above. Paratype USNM 468677. 

4, 6. External and adapical views of more adapical section of phragmocone

(xl). Same collection as figure 1 above. Paratype USNM 468678. 

5. External view of silicified adapical portion of phragmocone (xl). Same

collection as figure 1 above. Paratype USNM 468679.

7. Incomplete fragment of phragmocone revealing camera! deposits 

(xl.5). Same collection as figure 1 above. Paratype USNM 468681.

8. Exterior of silicified adapical portion of phragmocone (xl). Same

collection as figure 1 above. Paratype USNM 468683. 

10-15. Pleurorthoceras clarksvillense (Foerste), 1924b (p. 37).

10. Ventral view of an internal mold showing impressions of cameral 

deposits (xl). Bull Fork Formation (Richmondian), Addisons Creek, 

near Oxford, Ohio (locality OH-15). MU 269T.

11. Nearly complete specimen holoperipherally encrusted by the bryozoan 

Spatiopora (xl). Bull Fork Formation (Richmondian), Harveys 

Branch, Oldenburg, Ind. (locality IND-1). MU 444T.

12. Naturally weathered internal mold of phragmocone exposing

siphuncle (xl). Bull Fork Formation (Richmondian), near Blanchester, 

Ohio. Holotype USNM 48255.

13-15. Dorsal-ventral sections through adoral and adapical portions of a 

nearly complete phragmocone (xl), illustrating siphuncle segments 

and adapical development of cameral deposits. Same collection as 

figure 10 above. Same specimen illustrated by Flower (1962). MU 268T.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 2

POJETOCERAS AND PLEURORTHOCERAS
PLATE 3

FIGURES 1-8. Ordogeisonoceras amplicameratum (Hall), 1847 (p. 40).

1-3. Dorsal-ventral sections exposing siphuncle (xl) and adoral view (xl), 

venter on right. "Trenton Limestone," Ludlow, Ky. Syntype of 

Orthoceras ludlowense Miller and Faber, UC 6457.

4, 5,8. Dorsal-ventral sections of a more adapical portion of phragmocone 

(xl) with magnified view of adapical piece showing camera! deposits 

and siphuncle segments (x2), venter to right. Kope Formation 

(Edenian), Cincinnati, Ohio. UC18229.

6, 7. Exterior and adapical view of partially shelled internal mold (xl) 

showing faint longitudinal lirae and dorsal position of siphuncle. 

Trenton Limestone (Shermanian), Middleville, N.Y. Lectotype AMNH 

29688. 

9,10. Geisonoceras rivale (Barrande), 1866 (p. 39).

Adoral view and dorsal-ventral section showing siphuncle and camera! 

deposits (xl), venter on left. Middle Silurian, Czechoslovakia, From Barrande 

(1866, pi. 209, figs. 2,10).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 3

ORDOGEISONOCERAS AND GEISONOCERAS
PLATE 4

FIGURES 1-7. Proteoceras tyronensis (Foerste), 1912 (p. 43).

1-3. Dorsal and lateral (xl) and magnified ventral view exposing siphuncle 

(x2) of a silicified phragmocone. Tyrone Limestone (Rocklandian), 

USGS 6034-CO. USNM 158629. 

4. Adapical view of phragmocone showing cross section of

endosiphuncular deposits (xl). Same collection as figure 1 above. 

USNM 468687. 

5, 7. Dorsal and adapical views (xl) of weathered silicified specimen

exposing cameral deposits. Same collection as figure 1 above. USNM 

468689. 

6. Dorsal view of silicified specimen exposing cameral deposits (xl). Same

collection as figure 1 above. USNM 468688. 

8-12. Treptoceras duseri (Hall and Whitfield), 1875 (p. 46).

8-10. Dorsal and adapical views (xl.25) of adoral piece and dorsal-ventral 

section of adapical piece exposing siphuncle segments (xl.25), venter 

on right. "Hudson River Group," Waynesville, Ohio. Holotype UCal 

34325.

11. Dorsal-ventral section of adoral portion of phragmocone (xl), venter on 

left. Fairview Formation (Maysvillian), Dent, Ohio (locality OH-3). MU 

29766.

12. Dorsal-ventral section of a fragmentary specimen (xl), venter on right. 

Fairview Formation (Maysvillian), Taylor Mill, Ky. (locality KY-3). USMN 

468727.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 4

PROTEOCERAS AND TREPTOCERAS
PLATE 5

FIGURES 1-6. Treptoceras duseri (Hall and Whitfield), 1875 (p. 46).

Dorsal-ventral sections through a nearly complete phragmocone (xl.25) plus a 

magnified view of adapical pieces showing endosiphuncular deposits (x2.5), 

venter on left. "Treptoceras duseri Shale," Bull Fork Formation 

(Richmondian), Warren County, Ohio (locality OH-8). MU 417T. 

7-9. Treptocerasfosteri (Miller), 1875 (p. 48).

7, 9. Dorsal-ventral section of a nearly complete phragmocone (xl) and

magnified view of adapical end showing endosiphuncular deposits (x2), 

venter on left. Same collection as figure 1 above. MU 418T. 

8. Dorsal-ventral sections of less complete phragmocone (xl), venter on 

right. "Richmond Group," Clinton County, Ohio. Lectotype UC 356.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 5

TREPTOCERAS
PLATE 6

FIGURES 1-5, 7, 8. Treptoceras fosteri (Miller), 1875 (p. 48).

1. Exterior of specimen preserving much of the body chamber (xl). 

"Treptoceras duseri Shale," Bull Fork Formation (Richmondian), 

Waynesville, Ohio Gocality OH-6). MU 419T.

2. Dorsal-ventral section of slightly crushed phragmocone (xl), 

venter on right. Bull Fork Formation (Richmondian), Oldenburg, 

Ind. (locality IND-1). UC 28389.

3. Dorsal view of shelled specimen preserving dorsal color bands 

(xl.5). Same collection as figure 1 above. MU 276T.

4. Internal mold preserving much of the body chamber (xl). "Liberty 

biofacies" in the Bull Fork Formation (Richmondian), Caesars 

Creek Lake, Ohio (locality OH-7). MU 420T.

5, 7. Adoral and adapical views of phragmocone showing position of 

siphuncle (xl). "Treptoceras duseri Shale," Bull Fork Formation 

(Richmondian), Clarksville, Ohio Gocality OH-9). MU 421T. 

8. Internal mold of phragmocone (xl). "Liberty biofacies" in Bull Fork 

Formation (Richmondian), Clinton County, Ohio (locality OH-11). 

MU422T. 

6. Treptoceras byrnesi (Miller), 1875 (p. 51).

Dorsal-ventral section through phragmocone revealing siphuncle 

segments (xl), venter on left. Grant Lake Formation (Maysvillian), 

Clermont County, Ohio Gocality OH-4). MU 11035.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 6

TREPTOCERAS
PLATE 7

FIGURES 1-8. Treptoceras cincinnatiensis (Miller), 1875 (p. 52).

1. Large specimen consisting of phragmocone and complete body 

chamber (xl). "Treptoceras duseri Shale," Bull Fork Formation 

(Richmondian), Clarksville, Ohio (locality OH-9). MU 423T. 

2,3, 5. Dorsal exterior, adoral view, and dorsal-ventral section revealing

siphuncle segments (xl). Upper Ordovician, "hills behind Cincinnati, 

Ohio." Holotype MCZ 3404. 

4,6, 7. Dorsal-ventral section (xl), magnified view of apical end showing

endosiphuncular deposits (x2), and adapical view showing position of 

siphuncle (xl). "Treptoceras duseri Shale," Bull Fork Formation 

(Richmondian), Warren County, Ohio (locality OH-8). MU 426T. 

8. Dorsal-ventral section of a nearly complete phragmocone (xl), venter 

on left. Same collection as figure 4 above. MU425T.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 7
PLATE 8

FIGURES 1-3. Treptoceras cincinnatiensis (Miller), 1875 (p. 52).

1. Mold of body chamber holoperipherally encrusted by bryozoan 

Spatiopora (xl). "Liberty biofacies" in Bull Fork Formation 

(Richmondian), Brookville, Ind. (locality IND-2). MU 427T.

2. Dorsal-ventral section through incomplete phragmocone exposing 

siphuncle (xl), venter on left. "Liberty biofacies" in Bull Fork Formation 

(Richmondian), Oxford, Ohio Qocality OH-14). MU 425T.

3. Internal mold of a large phragmocone weathered to expose siphuncle 

adapically (xl). "Waynesville biofacies" in Bull Fork Formation 

(Richmondian), Oxford, Ohio Qocality OH-14). MU 443T. 

4-9. Treptoceras transversum (Miller), 1875 (p. 53).

4,8. Dorsal-ventral section exposing siphuncle showing camera! and parietal 

deposits (xl) and a magnified view of the same (x2). Kope F6rmation 

(Edenian), Cincinnati, Ohio. Lectotype UC 1328C.

5. Nearly complete shelled phragmocone showing transverse external 

ornament (xl). Kope Formation (Edenian), Ft. Thomas, Ky. (locality 

KY-2). USNM 468692.

6. Dorsal-ventral section through phragmocone exposing siphuncle (xl). 

Same collection as figure 4 above. Paratype UC 1328B.

7. Shelled fragment of phragmocone showing transverse ornament (xl).

Same collection as figure 4 above. Paratype UC 1328A. 

9. Adorally crushed phragmocone holoperipherally encrusted by bryozoa

(xl). Same collection as figure 5 above. USNM 468693.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 8
PLATE 9

FIGURES 1-3,11-15. Monomuchites annularis new species (p. 56).

I,3. Exterior and adapical view of large silicified specimen, crushed 

adorally (xl). Tyrone Limestone (Rocklandian), USGS 6034-CO. 

Paratype USNM 158630.

2. Dorsal view of naturally sectioned silicified specimen showing 

distinctive cameral deposits (x2). Same collection as figure 1 

above. Paratype USNM 158671.

II. Lateral view (xl) of exterior of silicified specimen showing 

slight curvature of shell, crushed adorally. Same collection as 

figure 1 above. Holotype USNM 158674.

12,13. Adoral and lateral views (xl) of internal mold of large specimen. 

Platteville Limestone (Rocklandian), Mineral Point, Wis. USNM 

25275.

14. Internal mold of a nearly complete specimen showing faint shell 

curvature (xl). Platteville Limestone (Rocklandian), Dixon, 111. 

USNM 162068.

15. Natural dorsal-ventral section through silicified specimen (xl) 

showing supracentral siphuncle and cameral deposits, venter to 

left. Same collection as figure 1 above. Paratype USNM 158676. 

4-10. Monomuchites obliquum new species (p. 58).

4. Adoral view (xl.5) of silicified specimen showing cameral 

deposits. Same collection as figure 1 above. Paratype USNM 

158643.

5-8. Dorsal, ventral, lateral, and adapical views (xl) of silicified 

specimen showing oblique annuli and central position of 

siphuncle. Same collection as figure 1 above. Holotype USNM 

158653. 

9,10. Ventral view of exterior (xl) and dorsal view exposing

siphuncle and ventral parietal deposits (xl). Same collection as 

figure 1 above. Paratype USNM 158648. 

16-19. Monomuchites cf. M. costalis Wilson, 1961 (p. 55).

16,17. Adoral and dorsal views of small silicified fragment (xl). Same

collection as figure 1 above. USNM 158672.

18,19. Adoral and lateral views of small silicified fragment (xl). Same 

collection as figure 1 above. USNM 158667.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 9

MONOMUCHITES
PLATE 10

FIGURES 1-9. Isorthoceras atoersi (Miller and Faber), 1894b (p. 60).

1. Shelled exterior showing longitudinal ornament (xl). "Trenton

Limestone," Ludlow, Ky. Lectotype UC 360.

2, 3. Dorsal-ventral section exposing siphuncle and cameral deposits (xl) 

and magnified view of same (x2), venter to left. Same collection as 

figure 1 above. Paralectotype UC 361.

4. Tangential section through adapical portion of phragmocone revealing 

siphuncle and cameral deposits (xl.5). Point Pleasant Tongue of Clays 

Ferry Formation (Shermanian), Cincinnati, Ohio. MU 447T.

5. Silicified exterior showing longitudinal ornament (xl). Logana

Member, Lexington Limestone (Kirkfieldian), USGS 5092-CO. USNM 

468697.

6. Adoral view (xl.5) showing subcentral siphuncle. Grier Limestone 

Member, Lexington Limestone (Shermanian), USGS 5096-CO. USNM 

468702.

7. Silicified exterior showing longitudinal ornament (xl.5). Grier

Limestone Member, Lexington Limestone (Shermanian), USGS 5067- 

CO. USNM 468695.

8. Silicified exterior exposing part of siphuncle (xl.5). Same collection 

as figure 7 above. USNM 468696.

9. Silicified exterior showing longitudinal ornament (xl.5). Same

collection as figure 5 above. USNM 468698. 

10-12. Isorthoceras rogersensis (Foerste), 1914 (p. 61).

10, 11. Shelled exterior showing cancellate ornament (xl) and exfoliated 

venter showing cameral chambers (xl). "Rogers Gap Limestone" 

(Edenian?), Rogers Gap, Ky. Lectotype USNM 87193A.

12. Naturally weathered section exposing siphuncle segments and 

cameral deposits (xl), venter on left. Same collection as figure 10 

above. Paralectotype USNM 87193B. 

13,14. Isorthoceras strangulatum (Hall), 1847 (p. 59).

13. Shelled internal mold of body chamber (xl). Trenton Limestone 

(Shermanian), Middleville, N.Y. Syntype AMNH 29714.

14. Partially shelled internal mold with body chamber and much of 

phragmocone (xl). Same collection as figure 13 above. Syntype 

AMNH 29715.

15. Isorthoceras sociale (Hall), 1862 (p. 59).

Internal mold with body chamber and much of phragmocone (xl) and 

fragments of shell showing growth line. "Orthoceras" coquina in Elgin Member, 

Maquoketa Formation (Maysvillian), Graf, Iowa. MU 14566.

16. Isorthoceras strigatum (Hall), 1847 (p. 59).

Partially shelled internal mold of phragmocone and body chamber showing 

longitudinal ornament (xl). Compare with figures 1-9. Same collection as 

figure 13 above. Syntype AMNH 29692.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 10

ISORTHOCERAS
PLATE 11

FIGURES 1-3. Polygrammoceras? cf. P. sp A (p. 68).

Dorsal-ventral section revealing siphuncle, portion of lateral exterior, and 

adapical view showing siphuncle position in large calcite-replaced specimen 

(xl). Strodes Creek Member, Lexington Limestone (Shermanian), USGS 7310- 

CO.USNM 468694.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 11

POLYGRAMMOCERAS ?
PLATE 12

FIGURES 1,2. Polygrammoceras sp. A (p. 68)

Dorsal and ventral views of silicified specimen (xl) showing longitudinal 

ornament and globular siphuncle segments. Grier Limestone Member, 

Lexington Limestone (Shermanian), USGS 5067-CO. USNM 468710. 

3. Gorbyoceras cf. G. tetreauense Wilson, 1961 (p. 65)

Lateral view of silicified specimen (xl.5) showing slight curvature of shell 

and external ornament. Logana Member, Lexington Limestone 

(Kirkfieldian), USGS 5092-CO. USNM 468708. 

4, 6, 7,10,11. Gorbyoceras hammetti (Foerste), 1910 (p. 64).

4, 7. Exterior of adoral portion of shelled phragmocone (xl) and 

tangential section through adapical piece of the same specimen 

showing siphuncle segments (x2). Saluda Formation (Richmondian), 

Versailles, Ind. (locality IND-5). MU 408T.

6. Section through calcite-replaced phragmocone showing siphuncle 

segments (xl). Hitz Limestone Member of the Saluda Formation 

(Richmondian), Madison, Ind. (locality IND-6). MU 446T. 

10,11. Calcite-replaced phragmocone and adapical view (xl). Same

collection as figure 6 above. MU 409T. 

5. Anaspyroceras cf. A. cylindricum (Foerste), 1932 (p. 66).

External mold showing oblique annuli and slender shell form (xl). 

Curdsville Limestone Member, Lexington Limestone (Kirkfieldian), 

CurdsvUle, Ky. USNM 48290. 

8, 9. Polygrammoceras'? sp. B (p. 69).

Lateral exterior showing longitudinal furrows and adapical view showing 

central position of siphuncle (xl.5). Tyrone Limestone (Rocklandian), USGS 

6034-CO. USNM 468711. 

12,13. Gorbyoceras gorbyi (Miller), 1894 (p. 63).

Lateral and ventral views of a nearly complete internal mold of a large 

phragmocone showing oblique annuli and slender, slightly curved shell 

(xO.8). Saluda Formation (Richmondian), Hamburg, Ind. (locality IND-4). 

MU 402T.
U.S. GEOLOGICAL SURVEY

PROFESSIONAL PAPER 1066-P PLATE 12

POLYGRAMMOCERAS, ANASPYROCERAS, AND GORBYOCERAS
PLATE 13

FIGURES 1^8. Richmondoceras brevicameratum new species (p. 71).

1,3,4. Internal mold showing most of body chamber and adoral portions of 

phragmocone (xl), adapical view showing subcentral position of 

siphuncle (xl), and dorsal-ventral section through attached 

phragmocone revealing siphuncle segments (xl). Saluda Formation 

(Richmondian), Laugherty Creek, near Versailles, Ind. Holotype MU 

398T.

2. Internal mold of adoral portion of large phragmocone showing 

approximate septa (xl). Saluda Formation (Richmondian), Oxford, 

Ohio. Paratype MU 399T.

5. Tangential section of adoral portion of phragmocone revealing 

siphuncle segments (xl). Upper part of the Bull Fork Formation 

(Richmondian), Clinton County, Ohio (locality OH-10). MU 400T(A).

6. Dorsal-ventral section exposing siphuncle segments (xl). Same

collection as figure 5 above. MU 400T(B).

7, 8. Dorsal-ventral section through adapical portion of phragmocone 

showing siphuncle segments (x2) and a magnified view of the same 

showing annulosiphonate deposits and cameral deposits. Same 

collection as figure 5 above. MU 400T(C).
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 13

RICHMONDOCERAS
PLATE 14

FIGURES 1, 2. Cameroceras rowenaense new species (p. 74).

Dorsal-ventral and adapical view of calcite-replaced specimen showing 

siphuncle structure and position (xl). Leipers Limestone (Maysvillian), 

Rowena, Ky. (locality KY-4). Holotype MU 266T.

3, 4. Cameroceras cf. C. trentonense Conrad, 1842 (p. 75).

Adoral and lateral views of silicified siphuncle showing location of 

endosiphuncular tube and rate of expansion (xl). Grier Limestone 

Member, Lexington Limestone (Shermanian), USGS 4073-CO. USNM 

468712.

5, 6. Cameroceras? sp. (p. 76).

Adoral view showing depressed cross section of siphuncle (xl) and 

tangential section revealing large-diameter siphuncle and 

macroholochoanitic septal necks (xl). Upper part of the Bull Fork 

Formation (Richmondian), Owingsville, Ky. (locality KY-5). USNM 468713.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 14

CAMEROCERAS
PLATE 15

FIGURES 1-4, 8-12. Vaginoceras sp. A (p. 77).

l-4.Lateral exterior, dorsal-ventral section, adoral, and adapical views 

of a large silicified specimen (xl). Note faint, raised transverse 

ornament on exterior and siphuncle diameter and position. Tyrone 

Limestone (Rocklandian), USGS 6034-CO. USNM 158668. 

8-10.Lateral (xl), dorsal (xl), and adoral (xl.5) views of the apical end 

of a silicified siphuncle revealing endosiphuncular blades typical of 

genus. Same collection as figure 1 above. USNM 158652. 

11,12.Dorsal and lateral views (xl) of apical end of a silicified siphuncle.

Same collection as figure 1 above. USNM 468714. 

5-7. Vaginoceras sp. B (p. 78).

Lateral, adoral, and adapical views (xl) of silicified portion of siphuncle 

revealing endosiphuncular blades typical of genus. Curdsville Limestone 

Member, Lexington Limestone (Kkkfieldian), USGS 5072-CO. USNM 

468718.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 15

VAGINOCERAS
PLATE 16

FIGURES 1-5. Triendoceras? davisi new species (p. 79).

1. Ventral view of infilling of large siphuncle showing impressions of narrow 

connecting rings and initially rapid expansion of tube (xO.8). Kope 

Formation (Edenian), Ft. Mitchell, Ky. (locality KY-1). Holotype MU 410T.

2. Ventral view of adapical infilling of siphuncle showing rapid expansion of 

endosiphuncular tube (xl). Kope Formation (Edenian), Cincinnati, Ohio 

(locality OH-1). Paratype MU 411T.

3. Cross section through infilling of siphuncle tube showing subtriangular 

shape, venter up (xl). "Fulton Shale" (Edenian), Moscow, Ohio. Paratype 

MU414T.

4. Portion of phragmocone preserving several camera! chambers (xl). Same 

collection as figure 1 above. Paratype MU 412T.

5. Lateral view of infilling of siphuncle tube (xl). Kope Formation (Edenian),

Cincinnati, Ohio. Paratype MU 413T. 

6. Actinoceras altopontense Foerste and Teichert, 1930 (p. 82).

Lateral view of a large silicified phragmocone revealing cameral chambers and 

rapid rate of sheU expansion (xl). USGS 6034-CO. USNM 158640.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 16

TRIENDOCERAS (?) AND ACT1NOCERAS
PLATE 17

FIGURES 1-5. Actinoceras kentuckiense Foerste and Teichert, 1930 (p. 82).

1, 2,4, 5. Adoral (xl), dorsal (xO.8), dorsal-ventral section (xl), and adapical 

views (xl) of a large silicified specimen. Note septal necks and the 

vascular canal system evident in dorsal-ventral adapical section. 

Tyrone Limestone (Rocklandian), USGS 6034-CO. USNM 158670. 

3. Large silicified portion of phragmocone exposing siphuncle 

segments and camerae (xl). Same collection as figure 1 above. 

USNM 158647. 

6-10. Actinoceras altopontense Foerste and Teichert, 1930 (p. 82).

6. Adapical view of silicified siphuncle segment showing central canal 

and impressions of radial canals (xl). Same collection as figure 1 

above. USNM 158658.

7. Adapical view of more adoral siphuncle segment showing decreased 

diameter of central canal and impressions of radial canals (xl). 

Same collection as figure 1 above. USNM 158657. 

8, 9. Adapical and dorsal views of silicified specimen exposing siphuncle

(xl). Same collection as figure 1 above. USNM 158641. 

10. Large silicified specimen exposing siphuncle (xl). Same collection

as figure 1 above. USNM 158642. 

11. Actinoceras curdsvillense Foerste and Teichert, 1930 (p. 84).

Dorsal view of natural section of silicified mold (xl). Note highly recurved, 

short septal necks. Curdsville Limestone Member, Lexington Limestone 

(Kirkfieldian), Curdsville, Ky. Holotype USNM 48425.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 17

"*

ACTINOCERAS
PLATE 18

FIGURES 1-7. Ormoceras ferecentricum Foerste and Teichert, 1930 (p. 86).

1-3. Adoral, ventral, and adapical views (xl) of silicified specimen

exposing siphuncle. Tyrone Limestone (Rocklandian), High Bridge, 

Ky. Holotype USNM 82214.

4-6. Ventral, adoral, and lateral views (xl) of adapical portion of 

silicified phragmocone exposing siphuncle. Tyrone Limestone 

(Rocklandian), USGS 6034-CO. USNM 158639.

7. Nearly complete silicified phragmocone (xl). Same collection as

figure 4 above. USNM 468721. 

8, 9. Deiroceras curdsviUense Foerste and Teichert, 1930 (p. 87).

8. Dorsal-ventral section of silicified specimen exposing siphuncle 

(xl), venter on left. Curdsville Limestone Member, Lexington 

Limestone (Kirkfieldian), CurdsviUe, Ky. Holotype USNM 48221.

9. Dorsal-ventral section of silicified specimen exposing siphuncle 

(xl), venter on left Curdsville Limestone Member, Lexington 

Limestone (Kirkfieldian), USGS 5100-CO. USNM 468723. 

10-17. Orthonybyoceras dyeri (Miller), 1875 (p. 89).

10. Dorsal-ventral section exposing siphuncle (xl.25), venter on left. 

"Waynesville biofacies" in Bull Fork Formation (Richmondian), 

Weisburg, Ind. UC 31380.

11. Tangential section exposing siphuncle and annulosiphonate

deposits (xl). Fairview Formation (Maysvillian), Cincinnati, Ohio.

UC 352A. 

12. Dorsal-ventral section exposing siphuncle and annulosiphonate

deposits (xl). Fairview Formation (Maysvillian), Cincinnati, Ohio.

UC 1330A. 

13,15,16. Adapical, adoral, and dorsal-ventral section (xl) of adoral portion

of phragmocone. Upper Ordovician, "hills behind Cincinnati,

Ohio." Holotype MCZ 3403. 

14,17. Lateral exterior of internal mold and dorsal-ventral section (xl) of

the same, exposing siphuncle segments and deposits (xl).

"Maysville Group" (Maysvillian), Covington, Ky. Holotype of

Ormoceras'? covingtonense Foerste and Teichert, 1930. USNM

48258.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 18

ORMOCERAS, DEIROCERAS, AND ORTHONYBYOCERAS
PLATE 19

FIGURES 1-3. Plectoceras cf. P. carletonense Foerste, 1933 (p. 93).

Lateral, ventral, and dorsal views of silicified inner whorl showing ventral 

sinus and camerae (xl). Tyrone Limestone (Rocklandian), USGS 6034-CO. 

USNM 158651. 

4, 5. Plectoceras hatti (Foord), 1891 (p. 94).

4. Apertural view showing depressed subquadrate whorl profile (xl). Label 

states "Trenton, near Lorette, Quebec." Flower collection, uncataloged.

5. Lateral view of a large specimen showing development of lateral costae

and fine oblique growth lines (xl). Same collection as figure 4 above. 

6-10. Trocholitesfaberi Foerste, 1929c (p. 91).

6, 7. Lateral and ventral views (xl) of a large specimen with complete body 

chamber. Note U-shaped hyponomic sinus. Kope Formation (Edenian), 

Ft. Mitchell, Ky. (locality KY-1). USNM 468724.

8,9. Fragmentary specimen preserving part of body whorl and inner whorl 

(xl). Adoral view of outer whorl (xl). Same collection as figure 6 above. 

USNM 468725. 

10. Small, slightly deformed internal mold with body chamber and

phragmocone (xl). Same collection as figure 6 above. USNM 468726. 

11-15. Oncoceras major new species (p. 95).

Dorsal, ventral, lateral, apertural, and adapical views (xl) of a silicified 

specimen preserving complete body chamber and most of phragmocone. Note 

distinctive transverse costae. Tyrone Limestone (Rocklandian), USGS 6034- 

CO. Holotype USNM 158665.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 19

:*-,!

11 ^ ^> ^^^^fc^wr?— ~' ^^^H^^^H ^ *^ ^»- - - --TV*- - -^^^^^^^^^

PLECTOCERAS, TROCHOLITES, AND ONCOCERAS
PLATE 20

FIGURES 1, 2. Oncoceras sp. (p. 96)

1. Adapical view of silicified specimen (xl) showing cross-sectional 

shape and position of siphuncle. Grier Limestone Member, 

Lexington Limestone (Shermanian), USGS 4879-CO. USNM 

468732.

2. Dorsal view of adapical portion of phragmocone (xl) showing 

external ornament of fine transverse growth lines. Grier 

Limestone Member, Lexington Limestone (Shermanian), USGS 

4883-CO. USNM 468731. 

3-6. Beloitoceras cf. B. huronense (Billings), 1865 (p. 99).

3,4, 6. Dorsal, lateral, and apertural views of small silicified specimen 

(xl) preserving most of body chamber. Tyrone Limestone 

(Rocklandian), USGS 6034-CO. USNM 158666. 

5. Lateral view of part of phragmocone (xl.5). Same collection as

figure 3 above. USNM 468733. 

7-12. Maelonoceras cf. M. praematurum (Billings), 1860 (p. 100).

7, 8,11,12. Apertural (venter down), adapical, dorsal, and lateral views (xl) 

of silicified specimen with incomplete aperture. Same collection 

as figure 3 above. USNM 158649. 

9,10. Apertural (venter down) and lateral views of complete body

chamber (xl). Same collection as figure 3 above. USNM 468735. 

13-18. Laphamoceras cf. L. scofieldi Foerste, 1932 (p. 101).

13-15. Dorsal, lateral, and ventral views of a small silicified specimen 

(x2) showing external ornament and sponge(?) encrustations. 

Same collection as figure 3 above. USNM 158663. 

16-18. Lateral and dorsal views of silicified specimen (xl) showing 

strong curvature of shell. Same collection as figure 3 above. 

USNM 158654. 

19-22. Allumettoceras cf. A. tenerum (Billings), 1860 (p. 103).

19. Adapical view (xl) showing depressed cross section and ventral 

siphuncle. Logana Member, Lexington Limestone (Kirkfieldian), 

USGS 6419-CO. USNM 468738.

20. Adoral view of a smaller specimen (xl) showing depressed cross 

section and expanded siphuncle segments. Logana Member, 

Lexington Limestone (Kirkfieldian), USGS 4865-CO. USNM 

468739.

21, 22. Lateral and dorsal views (xl) of most complete phragmocone 

observed. Same collection as figure 19 above. USNM 468640. 

23-27. Augiistoceras shideleri Flower, 1946 (p. 111).

Ventral, dorsal, adoral, adapical, and lateral views of a nearly complete 

specimen preserving body chamber (xl). Leipers Limestone (Maysvillian), 

Rowena, Ky. (locality KY-4). MU 428T. 

28, 29. Manitoulinoceras gyroforme Flower, 1946 (p. 112).

Ventral and lateral views of an internal mold of phragmocone (xl) showing 

short camerae, marginal expanded siphuncle segments, and strong shell 

curvature. Upper part of the Bull Fork Formation (Richmondian), Fairborn, 

Ohio (locality OH-12). USNM 468719.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 20

ONCOCERAS, BELOITOCERAS, MAELONOCERAS, LAPHAMOCERAS 

ALLUMETTOCERAS, AUGUSTOCERAS, AND MANITOULINOCERAS
PLATE 21

FIGURES 1,2, 5. Diestoceras shideleri Foerste, 1924b (p. 107).

1,2. Ventral and lateral views of a large, nearly complete specimen

preserving all of the body chamber and much of the phragmocone (xl). 

Note slight endogastric curvature of shell adapically. Saluda Formation 

(Richmondian), north of Brookville, Ind. (locality IND-3). MU 429T. 

5. Ventral view of internal mold of body chamber showing welldeveloped hyponomic sinus (xl). Saluda Formation (Richmondian), 

Hamburg, Ind. (locality IND4). MU 430T.

3. Beloitoceras amoenum (Miller), 1879 (p. 97).

Lateral view of nearly complete internal mold preserving body chamber 

(xl). Bull Fork Formation (Richmondian), Dayton, Ohio (locality OH-13). 

USNM 468668.

4. Diestoceras eos (Hall and Whitfield), 1875 (p. 108).

Lateral view of internal mold of body chamber (xl), venter to right Upper 

part of the Bull Fork Formation (Richmondian), Clinton County, Ohio 

(locality OH-10). USNM 468730.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 21

> ^

DIESTOCERAS AND BELOITOCERAS
PLATE 22

FIGUEES 1,3. Diestoceras shideleri Foerste, 1924b (p. 107).

Lateral and apertural views of body chamber showing general dimensions and 

subtriangular aperture shape (xl). Saluda Formation (Richmondian), 

Hamburg, Ind. (locality IND^). MU 430T. 

2. Beloitoceras amoenum (Miller), 1879 (p. 97).

Lateral view of internal mold of nearly complete phragmocone with attached 

body chamber (xl). Whitewater Formation (Richmondian), Richmond, Ind. 

(locality IND-7). USNM 468669. 

4, 5. Beloitoceras bucheri Flower 1946 (p. 98).

Ventral and lateral views of a nearly complete, shelled specimen (xl). Note 

slender phragmocone and fine transverse ornament. Same collection as figure 

1 above. MU433T. 

6-9. Diestoceras indianense (Miller and Faber), 1894 (p. 105).

6, 7, 9. Apertural, lateral, and ventral views of a nearly complete internal 

mold, including body chamber (xl). Note triangular aperture. Same 

collection as figure 1 above. MU 432T. 

8. Ventral view of a partially shelled specimen showing ventral

hyponomic sinus and external growth lines (xl). Same collection as 

figure 1 above. MU 431T.
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1066-P PLATE 22

DIESTOCERAS AND BELOITOCERAS

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