R. LANGENHEIM

STATE OP ILLINOIS

WILLIAM G. STRATTON, Governor

DEPARTMENT OP REGISTRATION AND EDUCATION

VERA M. BINKS, Director

DIVISION OP THE

STATE GEOLOGICAL SURVEY

JOHN C. PRYE, Chief URBANA

REPORT OF INVESTIGATIONS 199

CONODONTS FROM THE CHESTER SERIES IN THE TYPE AREA OF SOUTHWESTERN ILLINOIS

CARL B. REXROAD

PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS

URBANA, ILLINOIS 1957

STATE OF ILLINOIS

WILLIAM G. STRATTON, Governor

DEPARTMENT OF REGISTRATION AND EDUCATION

VERA M. BINKS, Director

DIVISION OF THE

STATE GEOLOGICAL SURVEY

JOHN C. FRYE, Chief URBANA

REPORT OF INVESTIGATIONS 199

CONODONTS FROM THE CHESTER SERIES IN THE TYPE AREA OF SOUTHWESTERN ILLINOIS

BY

CARL B. REXROAD

PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS

URBANA, ILLINOIS

February 1957

ORGANIZATION

STATE OF ILLINOIS HON. WILLIAM G. STRATTON, Governor

DEPARTMENT OF REGISTRATION AND EDUCATION

HON. VERA M. BINKS, Director

BOARD OF NATURAL RESOURCES AND CONSERVATION

HON. VERA M. BINKS, Chairman

W. H. NEWHOUSE, Ph.D., Geology

ROGER ADAMS, Ph.D., D.Sc, Lld., Chemistry

ROBERT H. ANDERSON, B.S., Engineering

A. E. EMERSON, Ph.D., Biology

LEWIS H. TIFFANY, Ph.D., Pd.D., Forestry

W. L. EVERITT, E.E., Ph.D.

Representing the President of the University of Illinois DELYTE W. MORRIS, Ph.D.

President of Southern Illinois University

GEOLOGICAL SURVEY DIVISION

JOHN C. FRYE, Ph.D., D.Sc, Chief

(46038—2500—10-56)

STATE GEOLOGICAL SURVEY DIVISION

Natural Resources Building, Urbana

JOHN C. FRYE, Ph.D., D.Sc, Chief

M. M. LEIGHTON, Ph.D., D.Sc, Chief, Emeritus

Enid Townley, M.S., Geologist and Assistant to the Chief

Velda A. Millard, Junior Assistant to the Chief

Helen E. McMorris, Secretary to the Chief

RESEARCH

(not including part-time personnel)

GEOLOGICAL RESOURCES SECTION

Arthur Bevan, Ph.D., D.Sc, Principal Geologist,

Emeritus Frances H. Alsterlund, A.B., Research Assistant

Coal Jack A. Simon, M.S., Geologist and Head G. H. Cady, Ph.D., Senior Geologist and Head, Emeritus Robert M. Kosanke, Ph.D., Geologist Raymond Siever, Ph.D., Geologist John A. Harrison, M.S., Associate Geologist Paul Edwin Potter, Ph.D., Associate Geologist William H. Smith, M.S., Associate Geologist Kenneth E. Clegg, M.S., Assistant Geologist Margaret A. Parker, M.S., Assistant Geologist David L. Reinertsen, A.M., Assistant Geologist Marcia R. Winslow, M.Sc, Assistant Geologist

Oil and Gas

A. H. Bell, Ph.D., Geologist and Head Virginia Kline, Ph.D., Associate Geologist Lester L. Whiting, B.A., Associate Geologist Wayne F. Meents, Associate Geological Engineer Margaret O. Oros, B.A., Assistant Geologist Jacob Van Den Berg, M.S., Assistant Geologist James H. Garrett, B.S., Research Assistant

Petroleum Engineering

Paul A. Witherspoon, M.S., Petroleum Engineer and Head

Frederick Squires, A.B., B.S., D.Sc, Petroleum Engi- neer, Emeritus

Industrial Minerals

J. E. Lamar, B.S., Geologist and Head Donald L. Graf, Ph.D., Geologist James C. Bradbury, A.M., Associate Geologist Meredith E. Ostrom, M.S., Assistant Geologist

Clay Resources and Clay Mineral Technology Ralph E. Grim, Ph.D., Consulting Clay Mineralogist W. Arthur White, Ph.D., Geologist Herbert D. Glass, Ph.D., Associate Geologist

Groundwater Geology and Geophysical Exploration

George B. Maxey, Ph.D., Geologist and Head Merlyn B. Buhle, M.S., Geologist Robert E. Bergstrom, Ph.D., Associate Geologist James E. Hackett, M.S., Associate Geologist John P. Kempton, M.A., Assistant Geologist Wayne A. Pryor, M.S., Assistant Geologist Lidia Selkregg, D.Nat.Sci., Assistant Geologist Margaret J. Castle, Assistant Geologic Draftsman

(on leave) Arthur J. Zeizel, B.A., Research Assistant Robert C. Parks, Technical Assistant

Engineering Geology and Topographic Mapping

George E. Ekblaw, Ph.D., Geologist and Head William C. Smith, M.A., Assistant Geologist

Stratigraphy and Areal Geology

H. B. Willman, Ph.D., Geologist and Head

Elwood Atherton, Ph.D., Geologist

David H. Swann, Ph.D., Geologist

Charles W. Collinson, Ph.D., Associate Geologist

Donald B. Saxby, M.S., Associate Geologist

T. C. Buschbach, M.S., Assistant Geologist

F. L. Doyle, M.S., Assistant Geologist

Edwin H. Franklin, B.S., Research Assistant

Charles C. Engel, Technical Assistant

Joseph F. Howard, Assistant

Carol L. Wood, Assistant

Physics R. J. Piersol, Ph.D.

Physicist, Emeritus

EDUCATIONAL EXTENSION George M. Wilson, M.S., Geologist and Head

August 16, 1956

GEOCHEMISTRY SECTION

Frank H. Reed, Ph.D., Chief Chemist Grace C. Johnson, B.S., Research Assistant

Coal Chemistry

G. R. Yohe, Ph.D., Chemist and Head

Thomas P. Maher, B.S., Special Assistant Chemist

Guey H. Lee, M.S., Research Assistant

Earle C. Smith, B.S., Research Assistant

Physical Chemistry

J. S. Machin, Ph.D., Chemist and Head Juanita Witters, M.S., Assistant Physicist Daniel L. Deadmore, M.S., Assistant Chemist Kozo Nagashima, Ph.D., Special Assistant Chemist Paul E. McMahon, M.S., Research Assistant

Fluorine Chemistry

G. C. Finger, Ph.D., Chemist and Head Carl W. Kruse, M.S., Special Research Assistant Richard H. Shiley, B.S., Special Research Assistant Raymond H. White, B.S., Special Research Assistant

Chemical Engineering

H. W. Jackman, M.S.E., Chemical Engineer and Head R. J. Helfinstine, M.S., Mechanical Engineer and

Supervisor of Physical Plant B. J. Greenwood, B.S., Mechanical Engineer Robert L. Eissler, M.S., Assistant Chemical Engineer James C. McCullough, Research Associate (on leave) Walter E. Cooper, Technical Assistant Cornel Marta, Technical Assistant Edward A. Schaede, Technical Assistant

X-Ray

W. F. Bradley, Ph.D.

Chemist and Head

Analytical Chemistry

O. W. Rees, Ph.D., Chemist and Head

L. D. McVicker, B.S., Chemist

Emile D. Pierron, M.S., Associate Chemist

William J. Armon, M.S., Assistant Chemist

Frances A. Coolican, B.S., Assistant Chemist

Donald R. Dickerson, B.S., Assistant Chemist

Charles T. Allbright, B.S., Research Assistant

(on leave) Joan M. Cederstrand, Research Assistant Sally K. Diller, B.A., Research Assistant Barbara Florini, A.B., Research Assistant Joseph M. Harris, B.A., Research Assistant JoAnne K. Wilken, B.A., Research Assistant George R. James, Technical Assistant

MINERAL ECONOMICS SECTION

W. H. Voskuil, Ph.D., Mineral Economist W. L. Busch, A.B., Assistant Mineral Economist Ethel M. King, Research Assistant JoAnn Munnis, Technical Assistant

RESEARCH AFFILIATES IN GEOLOGY

J Harlen Bretz, Ph.D., University of Chicago

John A. Brophy, M.S., Assistant Geologist, Stale Geol.

Survey Stanley E. Harris, Jr., Ph.D., Southern Illinois Uni- versity M. M. Leighton, Ph.D., D.Sc, Research Professional

Scientist, State Geol. Survey A. Byron Leonard, Ph.D., University of Kansas Paul R. Shaffer, Ph.D., University of Illinois Harold R. Wanless, Ph.D., University of Illinois

CONSULTANTS

Geology: George W. White, Ph.D., University of Illinois

Ralph E. Grim, Ph.D., University of Illinois Mechanical Engineering: Seichi Konzo, M.S., University of Illinois

GENERAL ADMINISTRATION

(not including part-time personnel)

PUBLICATIONS

Dorothy E. Rose, B.S., Technical Editor Meredith M. Calkins, Geologic Draftsman Donna R. Wilson, Assistant Geologic Draftsman

GENERAL SCIENTIFIC INFORMATION

Genevieve Van Heyningen, Technical Assistant Marian L. Wingard, Technical Assistant

LIBRARY

Olive B. Ruehe, B.S., Geological Librarian

MINERAL RESOURCE RECORDS

Vivian Gordon, Head

Sandra Mynlieff, B.A., Research Assistant Sue J. Cunningham, Technical Assistant Hannah Fisher, Technical Assistant Margery J. Miller, B.A., Technical Assistant Rosemary H. Reinarts, B.A., Technical Assistant Elizabeth Speer, Technical Assistant Joan R. Younker, Technical Assistant

TECHNICAL RECORDS

Berenice Reed, Supervisory Technical Assistant Miriam Hatch, Technical Assistant

Topographic Mapping in Cooperation with the United States Geological Survey

FINANCIAL RECORDS

Velda A. Millard, In Charge

Leona K. Erickson, Clerk IV (on leave)

Virginia C. Sanderson, B.S., Clerk-Typist III

Irma E. Samson, Clerk-Typist II

Patricia A. Northrup, Clerk-Typist I

CLERICAL SERVICES

Mary M. Sullivan, Clerk-Stenographer III Lyla Nofftz, Clerk-Stenographer II Lillian Weakley, Clerk-Stenographer II Marion L. Kenney, Clerk-Stenographer I Dorothy A. Ledbetter, Clerk-Stenographer I Virginia L. Minnie, Clerk-Stenographer I Marilyn Scott, Clerk-Stenographer I Laurel F. Griffin, Clerk-Typist I William L. Mathis, Messenger-Clerk II Lorene G. Wilson, Messenger-Clerk I

AUTOMOTIVE SERVICE

Glenn G. Poor, In Charge*

David B. Cooley, Automotive Mechanic

Everette Edwards, Automotive Mechanic (on leave)

Robert O. Ellis, Automotive Mechanic

OTHER TECHNICAL SERVICES

Wm. Dale Farris, Research Associate

Beulah M. Unfer, Technical Assistant

A. W. Gotstein, Research Associate

Glenn G. Poor, Research Associate*

Gilbert L. Tinberg, Technical Assistant

Wayne W. Nofftz, Supervisory Technical Assistant

Donovon M. Watkins, Technical Assistant

Mary Cecil, Supervisory Technical Assistant

Ruby D. Prison, Technical Assistant

August 16, 1956

*Divided time

CONTENTS

Introduction ....

Purpose and scope

Acknowledgements . Stratigraphic summary

Methods of study .

Collecting .... Processing. The conodont fauna .

Nature and distribution Correlations . Systematic descriptions . Genus Cavusgnathus .

C. characta Rexroad, n. sp.

C. convexa Rexroad, n. sp.

C. unicornis Youngquist and Miller Genus CIadognathusy n. gen. .

C. prima Rexroad, n. sp.

C. mehli Rexroad, n. sp.

C. sp. A . . .

C. sp. B . . .

Genus Gnathodus .

G. modocensis Rexroad, n. sp. Genus Hibbardella

#.sp

H. n. sp.? . . Genus Hindeodella

H. spp. . Genus Ligonodina

L. hamata Rexroad, n. sp.

L. obunca Rexroad, n. sp.

L. sp

Genus Neoprioniodus .

N. camurus Rexroad, n. sp.

N. epemoebus Rexroad, n. sp.

N. erectus Rexroad, n. sp.

N. loxus Rexroad, n. sp.

N. scitulus Branson and Mehl

TV. striatus Rexroad, n. sp.

N. tenuis Rexroad, n. sp. .

N. varians Branson and Mehl

N. sp. A . . .

N. sp. B . . . Genus Ozarkodina

0. compressa Rexroad, n. sp.

0. recta Rexroad, n. sp.

0. roundyi (Hass) .

O.P bella Rexroad, n. sp. Genus Spatho gnathodus

S. campbelli Rexroad, n. sp.

S. cf. S. commutatus Branson and Mehl

Page

7 7 7 8 8 8 9 9 9 11 15 15 15 17 17 28 28 29 29 30 30 30 31 31 31 31 32 32 32 32 33 33 33 34 34 34 35 35 35 35 36 36 36 36 36 37 37 37 37 38

Page

S. cristula Youngquist and Miller . . . 38

S. spiculus Youngquist and Miller 38

S. sp. A 38

S. sp. B 38

Genus Subbryantodus 39

S. stipans Rexroad, n. sp 39

S. sp 39

Genus Synprioniodina 40

S. sp 40

Genus Trichonodella 40

T.fragilis Rexroad, n. sp 40

T. imperfecta Rexroad, n. sp 41

Polygnathids 41

New genus? 41

Genus indeterminate 42

Indeterminate fragments 42

References 43

ILLUSTRATIONS Plates Page

1. Conodonts 19

2. Conodonts 20

3. Conodonts 25

4. Conodonts 26

Fig 1.

2.

3.

4.

5.

6.

7.

8.

9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

ity 1, Mitchell Island 10

ity 2, Dry Fork East ... 11

ity 3, St. Marys, Missouri 11

ity 4, Modoc South 12

ure Page

Index map of conodont collecting locality 8

Stratigraphic column of type Chester series . 9

Diagrammatic interpretation of Cladognathus Rexroad, n. gen. .... 10

Loca'

Loca

Loca

Loca

Loca

Loca

Loca

Loca

Loca

Loca

Loca

Loca

Loca

Loca

Loca

Loca

Loca

Loca

5, Floraville 12

6, Modoc East 13

7, Roots West 13

8, Marigold Northwest 14

9, Reily Lake North 14

ity 10, Coles Mill 15

ity 11, Marys River 15

ity 12, Chester East 16

ity 13, Marlin School 16

ity 14, Poland West 17

ity 15, Cora 17

ity 16, Ford W.P.A. quarry . . . . . . ..... , . . 28

ity 17, Clifton School East 28

ity 18, Type Kinkaid 29

Table

Table 1 — Stratigraphic distribution of the fauna and abundance of identifiable speci-

22-23

CONODONTS FROM THE CHESTER SERIES IN THE TYPE AREA OF SOUTHWESTERN ILLINOIS

BY

CARL B. REXROAD

ABSTRACT

The presence of conodonts in the Chester rocks of the type area has been known for some time. This study was undertaken to evaluate their use as Chester guide fossils in the expectation that they would prove valuable aids in correlating other strata in North America and Europe with the type section.

The shales and thin interbedded limestones of the entire stratigraphic sequence were care- fully sampled. Zones that contained conodonts were found in all the limestone-shale forma- tions— the Renault, Paint Creek, Golconda, Glen Dean, Vienna, Menard, Clore and Kinkaid.

The fauna consists of 27 identified species that represent nine genera; three additional genera are known from fragments. The genera present are Cavusgnathus, Cladognathus (a new genus), Gnathodus, Hibbardet/a, Hindeode/la, Ligonodina, Ozarkodinay Neoprioniodus, Spathogna- thodus, Subbryantodus, Synprioniodina, and Trichonodella. Single specimens or groups of fragments represent the polygnathids and two apparently new genera. The fauna is distinct from Kinder- hook, Valmeyer, and Pennsylvanian faunas. Species were found to be more useful than genera in subdividing the series.

Similar conodont faunas have been found in the Pella beds of Iowa, the Pitkin limestone of Arkansas and Oklahoma, the lower part of the Stanley shale of Arkansas and Oklahoma, the Barnett formation of Texas, and the portion of the Caney shale studied by Branson and Mehl.

INTRODUCTION

Purpose and Scope

Although conodonts have been proved valuable in stratigraphic correlation, only one paper (Cooper, 1947) describes them from the standard Chester sequence. Addi- tional work by Cooper (unpublished) showed conodonts to be present in Chester rocks of the type area, and it therefore seemed desira- ble to make a comprehensive study of these conodont faunas in order to evaluate them as guide fossils.

The southern Illinois Chester section is a standard of reference for rocks of upper Mississippian age of the North American continent as well as for comparison with the type sections of Great Britain and continental Europe. It was hoped that a broader base for correlation could be built through the recognition of a Chester conodont sequence. Such a faunal study is particularly important because European geologists have based their zonation of Mississippian rocks primarily upon goniatites, fossils that are rare in the southwestern Illinois area. Conodonts, how- ever, are present in both Europe and various regions of North America. Furthermore.

t

in the type area it is difficult to estimate the portion of Mississippian time represented by the unconformity between the Mississippian and Pennsylvanian strata, but comprehensive studies that include the study of conodonts are being made in Oklahoma on a sequence of strata apparently transitional from Mis- sissippian into Pennsylvanian.

The fact that this is the first study of Chester conodonts from the area surround- ing Chester, Illinois, imposes limitations on the problem. The complete stratigraphic se- quence was sampled. Therefore, the great thickness of strata analyzed for vertical dis- tribution of the fossils precluded collection at widely separated points to determine lat- eral variations of the conodont-bearing units. Thus, the collection adequately establishes the Chester fauna as a unit, but the basis for de- tailed subdivisions is less definite. The diver- sity of the present fauna indicates, however, that future work will establish valid distinc- tions between the formations.

Acknowledgments

Among the numerous people who gener- ously gave time and energy to this study, several deserve special mention. C. W. Col- 7]

8

ILLINOIS STATE GEOLOGICAL SURVEY

linson planned and coordinated the study, giving guidance throughout the project both in the laboratory and in the field. D. H. Swann provided the stratigraphic control for the project and not only made his field notes available but also spent time in the field, both with the author and separately to assure ac- curacy in the published stratigraphic sections. H. B. Willman gave valuable criticism of the manuscript. All are with the Illinois State Geological Survey. W. M. Furnish, of the State University of Iowa, directed the systematic paleontology and critically read the manuscript.

Nearly a week was spent in Columbia, Missouri, examining the collections of the University of Missouri through the courtesy of M. G. Mehl, whose advice and discus- sions of taxonomy were most helpful. Pres- ton E. Cloud and Wilbert H. Hass of the United States Geological Survey sent ma- terial from the Barnett formation of Texas for comparative study, and Carlyle B. Camp- bell of Knoxville, Iowa, gave residues from the Pella beds of Iowa. M. K. Elias of the Nebraska Geological Survey contributed pho- tographs of the plates from his unpublished manuscript.

Fig. 1. — Localities from which Chester conodonts 'were collected. See outcrop diagrams (figs. 4-12) . for detailed descriptions,

STRATIGRAPHIC SUMMARY

The stratigraphy of the Chester series (up- per Mississippian) as developed in the type region in Monroe, Randolph, and Jackson counties, Illinois, and Ste. Genevieve County, Missouri, is shown in figure 2. The forma- tions recognized in the lower and upper parts of the series — beneath the Cypress and above the Waltersburg — are named from lo- calities in this area. The figure shows the relation of three formations, the Ruma, Okaw, and Baldwin, to their correlatives from eastern Illinois and Kentucky. The above names were used originally for the type region but they have been replaced by the Cypress, Golconda, Hardinsburg, Glen Dean, Tar Springs, Vienna, and Walters- burg in the standard column.

The Hardinsburg formation in the area is a soft shale, in part red, with thin silt- stone lenses; the cherry limestone that has been mentioned in the literature as repre- senting the Hardinsburg is in the lower part of the Glen Dean limestone.

Nineteen outcrop sections were selected and shales in each outcrop were sampled. Conodonts occurred in eighteen of the sec- tions. The geographic position of the pro- ductive localities is shown in figure 1 and the stratigraphic position on figure 2. The sec- tions exposed and the positions of the pro- ductive and barren samples are detailed, for each outcrop in figures 4 to 21. The barren outcrop was in the middle of the Paint Creek formation and is equivalent to the lower barren part of the section at locality 6, Mo- doc East.

METHODS OF STUDY

Collecting

Only sections whose stratigraphic posi- tions are well established were chosen as collecting localities. The locations were se- lected also because they displayed a continu- ous, long, vertical section rwith well devel- oped shales. Where possible, sections with exposed formation boundaries were chosen.

Only the shales and thin interbedded limestones were sampled. In order not to miss any zones that might contain conodonts,

CONODONTS FROM THE CHESTER SERIES

sampling was done by continuous trenching, with each sample a representative composite of a 6-inch, 1-foot, or 2-foot section, depend- ing on the thickness of the lithologic unit be- ing sampled. The vertical interval sampled was modified, where necessary, in order not to include material from two lithologic zones in one sample.

The samples were then processed in the laboratory and the fossiliferous zones deter- mined. Later, bulk samples were taken from each zone that contained conodonts.

Processing

In the laboratory the limestones were dis- solved in 15 percent acetic acid to free the conodonts. The shales were dissociated either by washing the samples in the Campbell mi- cro-fossil washing machine or by boiling them with sal soda. The former method proved superior for the more highly indurated shales, the latter for the soft shales.

The residues were screened and the por- tion retained between the 16- and 115-mesh screens was examined. Many of the residues contained large quantities of calcitic material that was removed by acetic acid after a pre- liminary examination under the binocular microscope. The conodonts were further con- centrated by gravity separation in tetrabro- moethane whenever large quartzose residues remained.

THE CONODONT FAUNA

Nature and Distribution

Conodonts are present in moderate abun- dance in eight of the standard Chester for- mations, but none were found in the other formations. The eight formations that con- tain conodonts are the Renault, Paint Creek, Golconda, Glen Dean, Vienna, Menard, Clore, and Kinkaid — that is, the alternate formations in the sequence. As might be ex- pected, the above formations all contain ma- rine beds. The formations that do not have conodonts contain hepidodendron, coal, and

Fig. 2. — Generalized geologic column of the Chester series in the type area. Cross-hatched bars show stratigraphic intervals illustrated by outcrop diagrams (figs. 4 to 21). (Stratigraphic section by D. H. Swann.) R = red shale. C = coal.

10

ILLINOIS STATE GEOLOGICAL SURVEY

plant spores, all of which indicate an absence of typical marine conditions.

Twenty-seven species of conodonts belong- ing in nine genera are identified, and three additional genera are recognized from frag- ments. Single specimens or groups of frag- ments represent a number of additional spe- cies from these genera and from polygnathid types. In addition, there are almost certainly two new genera, unfortunately represented by specimens too fragmentary to allow de- tailed description. Broken material was used for description of new species only when a reasonable composite could be assembled. No new species are based on single speci- mens.

In samples from a location about 25 miles south and east of the type locality of the Kin- kaid formation, Cooper (1947) identified the genus Taphrognathus, which was not found in the present collection.

Stratigraphically, the new genus Cladog- nathus is the most significant. Its first ap- pearance is in the Glen Dean formation, and although both the Renault and Paint Creek formations, which are older, have an abun- dant and varied conodont fauna, no represent- atives of the genus were found, a fact that

LOCI-MITCHELL ISLAND	a> a. E o	E§ £o
Yonkeetown cherty sandstone float, probably covering a few feet of shole above outcrop.	=* 5 =r 4	_i < LiJ a:
i * j -iu CT l
Irregular I -8 'bands of LL j greenish-gray shale. 15' * i-L-!_i
l-.'rH-	■■ 5
V. ■•■'>•'
Claystone ( weathered shale ?) 2' i^0\O	■- 1
2l' of poorly exposed shale to Aux Vases sandstone.

Fig. 3. — Diagrammatic reconstruction of Cladognath- us Rexroad, n. gen., showing lateral and aboral

Fig. 4. — Mitchell Island, locality 1. Bluff of aban- doned (1881) Mississippi River channel opposite former Mitchell Island, midway between mouths of River Aux Vases and Saline Creek, and be- low a point on state highway 25, 0.8 mile south- east of River Aux Vases bridge, near center E3^ sec. 13 (extended), T. 37 N., R. 9 E., Chester quadrangle, Ste. Genevieve County, Missouri.

suggests that Cladognathus does not range below the Glen Dean. The upper limit of Cladognathus is the Kinkaid formation.

As far as I have been able to ascertain, fragments of the two indeterminable "new genera" of the type Chester have not been recorded in rocks of any other age. One of the two has been recorded in the Caney shales of Oklahoma by Branson and Mehl (1940) as Lonchodina sp. and in the Pella beds of Iowa by Youngquist and Miller (1949) as Lonchodina? sp. Both "new gen- era" are found in all eight Chester forma- tions that contain conodonts.

More than half the remaining genera have long stratigraphic ranges, from Ordovician or Silurian into the Permian or Triassic. These genera include: Spathognathodus, Ozarkodina, Trichonodella, Neoprioniodus, Ligonodina, and Hindeodella. All are abun- dant in the Chester collections. Hibbardella and Synprioniodina have ranges nearly as long.

There are several points of interest con- cerning the other genera. Subbryantodus is not common in the Chester and is limited to the Glen Dean and Menard formations, but it is usually considered a lower Mississippian form ; Subbryantodus roundyi Hass from the Barnett shale of Texas is referred to Ozarko- dina in this paper.

CONODONTS FROM THE CHESTER SERIES

11

L0C.2- DRY FORK EAST

Shale, red, purple, green, soft, with thin sandstone stringers

Limestone, gray, sandy. I

Limestone, gray, coarse, fossiliferous, upper part sandy, with shale partings. 13'

Limestone, greenish gray, interbedded with sandy greenish-gray shole. 81

Shale, green, calcareous, with limestone lenses. 3'

Limestone, gray, sandy.fossiliferous,^- and shale, green. 4'4" /3

rzzE

Sandstone, gray, In 6" beds, fine to medium, some shale pebbles, Scolithus borings numerous. 15'

J^.-

Sandstone, fine, cross-bedded. 2'

■^:.

Fig. 5. — Dry Fork East, locality 2. Banks of lowest tributary gulley to south of Dry Fork Creek, SEM SW34 sec. 23, T. 4 S., R. 9 W., Renault quadrangle, Monroe County, Illinois.

Gnathodus, whose range includes all the Mississippian and the lower half of the Pennsylvanian, was found only in the Paint Creek formation, but was present at two widely separated outcrops. Three polygna- thid fragments from two locations in the Renault formation are also of considerable interest because representatives of Polygna- thus found previously by other workers in rocks of Chester age or younger have been considered as reworked. There is no evi- dence, however, that such is the case here. The only other genus confined to a portion of the series is Synprioniodina, but it is rep- resented by only two fragments, both from the Renault formation.

Cavusgnathus is an important element of the Chester fauna. It probably appears first in rocks of Chester age but continues its de- velopment into the Permian.

In the type Chester strata, forms sug- gestive of the Pennsylvanian generally are lacking, so that the over-all aspect of the fauna is Mississippian. The Chester fauna also differs distinctively from faunas charac-

LOC. 3- ST. MARYS

Cherty sandstone rubble.

Shale, greenish and dark red, fissile, with thin limestone stringers. Top obscured. 7'

Limestone, light gray, massive to thin- bedded, in part crinoidal, with several T'green fissile shale partings in upper part. 23'

3' covered to Aux Vases

Fig. 6. — St. Marys, Missouri, locality 3. Roadcut on state highway 25, 0.7 mile northwest of bridge in St. Marys and 1.5 miles southeast of bridge over Saline Creek, NWM NW^ sec. 29 (ex- tended), T. 37 N., R. 10 E., Chester quadrangle, Ste. Genevieve County, Missouri.

teristic of Kinderhook and Valmeyer rocks. Genera characteristic of and forming an im- portant part of assemblages in those older rocks are absent in the Chester, nor were the long range genera, Prioniodina, Eurprionio- dina, Lonchodina, and Prioniodella, recog- nized among the Chester conodonts.

In terms of genera, the fauna described here is definitive of the type Chester series as a whole. In general, it appears that spe- cies will be more useful than genera in sub- dividing the series. Table 1 presents the stratigraphic distribution of the Chester con- odonts.

Correlations

As yet the literature on Chester conodonts is small. A number of reports mention con- odonts only briefly, and several additional papers describe groups of conodonts as nat- ural assemblages from single animals. In the latter case individual specimens are neither described nor illustrated in detail, so that their usefulness for stratigraphic correlation is limited. Fay's Catalogue of Conodonts (1952) is readily available and gives most references to Chester conodonts. Several of

12

ILLINOIS STATE GEOLOGICAL SURVEY

L0C.4-M0D0C SOUTH

Overlain by 34 feet of Cypress sand and shale and 30 feet of Golconda Is. and shale.

Limestone, gray, sandy, top of waterfall. l'7"

Limestone, fossiliferous.2'l"

Limestone, gray. 4'H"

Limestone, gray, sandy, ripple marked. 3'l0"

Limestone, gray, argil., fossil if erous, partly sandy, red and green in middle. 8' 3"

Limestone, gray, sandy, oolitic, cross-bedded. 8'?'

Limestone, gray, fossil. I'9" [J^\ ~\~W

Shale, green with gray limestone lenses. 5'3"

Fig. 7. — Modoc South, locality 4. Mouth of fourth ravine, about 2.6 miles southeast of Modoc, SWM SWJ4 sec. 4 (extended), T. 6 S., R. 8 W., Baldwin-Renault quadrangle line, Randolph County, Illinois.

the papers, however, merit mention here, and a few more deserve a fuller discussion.

Demanet in 1941 discussed several genera of conodonts from all three zones of the Lower Namurian in the type region of Bel- gium. In terms of cephalopods these would be, in ascending order, the zones of Eumor- phoceras pseudobilinque , E. bisculatum, and Homoceras beyrichianum. Three years ear- lier (1938) the same author described and figured several genera from the upper beds of passage between the Visean and Namurian. It thus is known that conodonts are present in most of the European standard section that corresponds to the Chester in age. In both articles Demanet used the concept of genetic assemblages, apparently following the ideas of Hermann Schmidt. In 1934 Schmidt, in discussing zoological affinities of cono- donts, described several genetic assemblages from the Eumorphoceras pseudobilingue, Cravenoceras edalense, and E. bisculatum zones developed in the Arnsberger gray- wacke of Germany. Genetic assemblages also were described by Scott (1942) from the Heath formation in Montana.

The most extensive papers on upper Mis- sissippian conodonts that use the form classi- fication describe faunas from the Barnett for-

L0C.5- FLORAVILLE

Limestone, gray, argil., fossil. 2

Limestone, gray, very argil., fossil. 3

Shale, greenish gray, weathering tan, fossi liferous with thin limestone beds. 12' 6"

Limestone, gray, crinoidal. 5' \ Stream level

Fig. 8. — Floraville, locality 5. Northeast bank of Prairie du Long Creek just above bridge 0.7 mile northeast of Vogel School, midpoint of section line between sees. 3 and 10.;, T. 2 S., R. 9 W., Waterloo quadrangle, St. Clair County, Illinois.

mation of Texas and the Mississippian por- tion of the Caney shale in Oklahoma. Cono- donts from the Pella beds of Iowa have been described by Youngquist and Miller (1949), and Hass (1950) studied the lower part of the Stanley shale in Arkansas and adjacent Oklahoma. He found the Stanley conodonts to be conspecific with those of the Barnett formation's upper faunal zone and with the Caney shale fauna of Branson and Mehl. Accordingly he correlated parts of the lower Stanley with the Barnett and Caney forma- tions. More recently Hass (1954) listed a conodont fauna from the subsurface of north- eastern Mississippi that contained species much the same as those in the Barnett.

Branson and Mehl (1941) described con- odonts from a single zone in the Caney shales of Oklahoma "as a start to building up a zonal distribution of the conodonts" in these shales (p. 167). The authors state: "The inference, then, is that the fauna described in this paper belongs in the Upper Mississip- pian (Chester Group). . . . We anticipate that additional conodont collections from the Mississippian Caney and the Upper Missis- sippian of other regions will establish this correlation" (p. 168, 169). The evidence of the present paper seems to confirm their evaluation.

Of the eleven genera from the Caney zone and the fourteen type-Chester genera, nine are common to both. Gnathodus, present in both, is found only in the Paint Creek for- mation of the type Chester area. The re- maining common genera range from Renault

CONODONTS FROM THE CHESTER SERIES

13

L0C.6-M0D0C EAST

Limestone, very fossiliferous. 20

J—L

Shale, buffish to blulsr^gray lower 3' red, upper 10' deeply weathered. I9'6"

Sandstone, olive-gray, fine, calcareous l'6"

Shale, gray with red streaks. 8' / — ~ It

9 covered

Limestone, gray, in part argillaceous, algal, oolitic, cross-bedded, with very thin interbedded shale. 3l'6'

Shale, bluish gray, calcareous, fossiliferous, with thin limestone stringers, especially near top. 9l3"

Siltstone, gray, calcareous, and shale. I1 3"

42

Shole, gray, with cole. nodules. 5' /§2-2_f

Sandstone, gray, calcareous. I'

Shale, green and gray, poorly laminated with a few calcareous nodules. 41

Clay, red, and poorly lam- inated shale; partly covered. 28'

IT^MTz:

5'covered

Fig, 9.— Modoc East, locality 6. Outcrops 1000 to 2500 feet above mouth of second ravine about 1.4 miles southeast of Modoc, NW34 sec. 5 (ex- tended), T. 6 S., R. 8 W., Renault quadrangle, Randolph County, Illinois.

to Kinkaid, inclusive, in the type Chester. Two of the genera found only in the Illinois area are limited to a portion of the series.

L0C.7- ROOTS WEST	a. E o	il o — u_ o
,	E 9	< a o 3 o
rossiliterous. <L ^^Jy=±=. \ J_j
Shale, gray, weathers buff, ) — — —
very fossiliferous, contains /— — — — thin limestones. II' / ~ — ~	I: 7 E 5 ML 3

Fig. 10. — Roots West, locality 7. Roadcut and ditch about two-thirds of the way up the hill, 0.6 mile west-northwest of Roots on blacktop road to Ruma, SWM $E% sec. 10 (extended), T. 6 S., R. 8 W., Baldwin quadrangle, Randolph County, Illinois.

These are Cladognathus, found only in the Glen Dean and younger formations, and Subbryantodus, found in the Glen Dean and Menard formations. The Chester polygna- thid fragments are all from the Renault for- mation. The absence of Metalonchodina in the type Chester presents a puzzle because it has been recognized in numerous upper Mississippian collections, including the Caney. Conspecific and closely related forms also indicate a correlation of the Caney with the type Chester series. It should be noted that Cavusgnathus cristata, a Caney form, was present in the Kinkaid microfauna de- scribed by Cooper (1947), but it was not found in the present collection. Future stud- ies to establish possible lateral variations of conodonts in the area of the standard Chester sequence should make possible detailed corre- lation of the Caney zone with the standard formations.

Roundy in 1926 described and illustrated a few conodonts from the Barnett shale. His work was revised and greatly enlarged by Hass (1953). The upper faunal zone of the Barnett shale has been variously treated as Meramec, Chester, and Lower Pennsylvan- ian. Hass summarized this history and refers to Weller et al. (1948) for a summary of current opinion, that indicated doubt still ex- isted as to the age of the Barnett formation. Subsequently Hass (1954, p. 32) stated, "This zone [upper conodont faunal zone of the Barnett formation] is considered to be of Meramec and possibly also partly of Chester age." The results of the present study tend to substantiate his correlation.

14

ILLINOIS STATE GEOLOGICAL SURVEY

L0C.8- MARIGOLD NORTHWEST

Shale, groy,calc, very fossil. 2'

2 covered

Shale, gray, calcareous, fossil. 2*6" Shale, red, gray and purple. 6'6"

Silfstone, buff, massive. I1

Shale, variegated, fissile. 6

Shale, dark gray, fissile. 4 / -

Limestone, reddish gray with shale partings. 2'

Shale, dark gray, fissile, nonfossiliferous. 8'

Fig. 11. — Marigold Northwest, locality 8. Bank on southeast side of stream, about 800 feet north- east of farmhouse, % mile northwest of Mari- gold, NE34 NWM NW34 sec. 20, T. 5 S., R. 8 W., Renault quadrangle, Randolph County, Illinois.

The generic composition of the Barnett shale fauna is closely similar to the Caney shale fauna of Branson and Mehl, but when each of these faunas is compared to the fauna of the Chester series, the number of genera common to the Barnett and the Chester is found to be less than the number of genera common to the Caney and Chester. The Bar- nett shale contains four genera not found in the Chester; the Chester has six genera, plus the two "new genera," not present in the Bar- nett; and six genera are common to both collections. Of these six genera Cavusgnathus and Gnathodus have the most limited strati- graphic range.

The described conodont fauna that corre- sponds most closely to that of southwestern Illinois is the one from the type area of the Pella beds of Iowa. In the paper describing this fauna, Youngquist and Miller (1949, p. 618) state, "It can be said that the conodonts we are studying are indicative of either a Meramec or a Chester age for the Pella beds — present lack of published information on conodont faunas of this general age pre- cludes a more nearly precise determination."

All the genera recognized by Youngquist

L0C.9-REILY LAKE NORTH

NORTH QUARRY

Limestone, gray, medium to coarse, shaly; very J i j i

shalyand fossiliferous toward base. 18'

Shale.gray, soft, fossiliferous. 5'6"

Limestone, coarse, fossiliferous. 2'

Limestone, gray,weathers\ buff, nodular, shaly. 2'6"

Limestone, light gray, coarse, fragmental, with f to 4 ' gray fossiliferous shale bed. 12' to 17'

Shale, gray, fossil. 6' dark limestone lentil near top. 3'6"

Limestone, gray, fossiliferous. 3

8'6" covered

Fig. 12. — Reily Lake North, locality 9. Small quar- ries in Mississippi Valley bluff about 1.1 miles northwest of Reily Lake, SE^ SE^ sec. 24 (extended), T. 6 S., R. 8 W., Chester quadrangle, Randolph County, Illinois.

and Miller in the Pella beds are present in the type Chester series. Of the seven species described from the Pella beds three are abundant in the Chester rocks. The remain- ing identified species and figured specimens from the Pella beds are closely similar to Chester forms. Additional specimens from the Pella further confirm the correlation. Within the Chester, the common species have a long range, but there is a suggestion of cor- relation with the lower part of the series.

It has been noted above that studies of Chester conodonts have been few and scat- tered. As future research fills in more de- tails of the stratigraphic sequence and widens the geographic scope, it seems certain that conodonts will provide a basis for sound cor- relations of widely separated upper Mississip- pian strata.

CONODONTS FROM THE CHESTER SERIES

15

Fig. 13,.— Coles Mill, locality 10. Waterfall just above mouth of ravine, east of flour mill at south edge of Chester, W. line NWM sec. 30, T. 7 S., R. 6 W., Chester quadrangle, Randolph County, Illinois.

SYSTEMATIC DESCRIPTIONS

The type and figured specimens described and illustrated in this paper have been re- posited at the Illinois State Geological Sur- vey. Comparative specimens have been re- posited at the State University of Iowa and the University of Missouri. Under the head- ing Distribution, only the formations in which that species occurs are listed. For de- tailed information about the stratigraphic and geographic distribution of each species see table 1.

Genus Cavusgnathus Harris and Hollingsworth, 1933

Type species: Cavusgnathus alta Harris and Hollingsworth

Harris and Hollingsworth's original de- scription (1933, p. 200-201) is as follows:

This genus is erected to include those lance- olate-plated conodonts with no semblance of a median crest in the median oral channel. Out- line of plate lanceolate to claviform ; oral face of plate with complete, deep, median longi- tudinal channel without crest and bordered by marginal rims ornamented with denticles, nodes, corrugation, or combinations of the same; posterior bar denticulate.

A revised description by Ellison (1941, p.

125, 126) follows:

Elongate platform-like teeth with high sides ex- tending parapet-like above a median longitudinal trench ; one parapet continued into a free longi-

LOC.II- MARYS RIVER

Limestone, dark buff. 4'

Shale, gray.5'

Limestone, dark, shaly near middle. 6'6"

Shale, greenish gray, silty, 3" to 6' limestone near base. 2 '6"

Limestone, buff, fine, argillaceous nodular ol top. 3'6"

Shale, gray, fossiliferous. I'

Shale, dark gray, weak. 32'

Limestone, buff, cherty toward base, with 3" bed of calcareous shale. 10'

Fig. 14. — Marys River, locality 11. Cut for rail- road and road north of mouth of Marys River, NWi^ NEK sec. 32, T. 7 S., R. 6 W., Chester quadrangle, Randolph County, Illinois.

tudinal blade and connected at the posterior end to opposite parapet whose length is limited by the length of the platform ; aboral surface of plat- form smooth, deeply excavated as a longitudinally elongate laterally asymmetrical, spathodid-like cup, pointed at each end, traversed by a median longitudinal groove which extends to the ends of the platform and along the aboral edge of blade; sides of platform somewhat constricted laterally above the aboral margin to produce a lip-like lat- eral margin of variable width; oral surface of platform more or less grooved transversely; oral edge of blade denticulate and crenulate.

For purposes of description the blade is di- rected anteriorly. It is continued posteriorly as the outer edge of platform, the blade parapet. The elevated inner edge of the platform is the inner parapet.

Remarks. — This genus differs from Idiognatho- dus in that the blade of the latter is median. It differs from Polygnathodella Harlton in that the latter has no oral trough.

Cavusgnathus characta Rexroad, n. sp. Plate 1, figures 1 and 2

Oral View. — Outer parapet convex out- ward, anterior end offset outward from blade ; inner parapet nearly straight except convex at tip ; trough straight, deep, with one

16

ILLINOIS STATE GEOLOGICAL SURVEY

L0C.I2-CHESTER EAST

Shale, gray to ton, calcareous, fossiliferous. 6'

Limestone, gray, partly cherty. 6

Shale, gray to ton. 2

6 covered

Limestone, gray. 6

Shale and limestone, bluish gray, dense. 8'

12 covered Ouarry bench r

Limestone, buff with 3 1-inch shale beds. 5'

Limestone, buff, massive to thin-bedded with shale partings. 15'

Limestone, buff, argi I laceous.2

Limestone, buff, fossiliferous. 36

Shale, gray, irregular , limestone stringers. 3

Limestone, buff, with inter- bedded dark gray shale. 5'

Limestone, buff. 8

Shale, calc. with argillaceous limestone. 3' 6"

Sandstone, very sholy, fossil. 2*6" £^-~^— 1 -M

Shale, gray. 2' /

10' covered

Shole, dark gray, fissile. 14'

CE

Limestone, buff to gray, argillaceous, fossiliferous. 5' / ' I ' I ,' I

I I

9' covered to road level.

Fig. 15. — Chester East, locality 12. Abandoned high level quarry in Mississippi River bluff opposite sand and gravel docks, about 1.4 miles above mouth of Marys River, SWM SEM sec. 30, T. 7 S., R. 6 W., Chester quadrangle, Randolph County, Illinois.

L0C.I3-MARLIN SCHOOL	a> a. E o	Eo
Shale, ton, fissile, fossiliferous. I'		Q a: < ■z. LU 2
Limestone.buff, argil., fossil.
	w 2
Shale, gray, fossiliferous. l'6" ^V ! ~ ' ~~L
colc.zon'es. 4' /— ^r"-"=="	t.8 covered	)f
Si[fstone,argil.5/^rv!r^£=v	J— -:— — r ■_ t— : ^_ t	i (/) LUCE
North side < tributary gulley.
Siltst.,buff .sandy, argil. 2'6 " 25 yards above gulley, on Gravel Creek.

Fig. 16. — Marlin School, locality 13. Outcrops at and near mouth of a tributary gulley entering Gravel Creek from the west, 1500 feet below the bridge on Marlin School road, W. line, SW^ SE34 sec. 2, T. 7 S., R. 7 W., Chester quadrangle, Randolph County, Illinois.

to several median nodes commonly present posteriorly; both parapets ornamented with regularly spaced, parallel, transverse ridges obsolescent into trough; blade straight, par- allels trough, denticles much compressed lat- erally.

Lateral view. — Platform high; oral mar- gin of both parapets gently convex, outer one the higher; postero-aboral angle strongly obtuse; distinct notch between outer parapet and blade ; blade composed of six to eight denticles, subequal, but generally smaller at anterior, thus presenting low, crenulate, slightly convex oral margin ; blade slightly over one-third length of specimen, as much as one-third free; platform constricted above navel; attachment scar present immediately anterior to navel.

Aboral view. — Navel shallow, asymmetric, lanceolate outline, pointed posteriorly, not quite reaching posterior tip, greater flare by inner lateral lip, which extends farther an- teriorly than outer lip ; navel divided by a groove which extends to both anterior and posterior lips of specimen on otherwise sharp aboral edge.

Distribution. — Renault, Paint Creek for- mations.

Repository. — Illinois State Geological Sur- vey, 2P1 (holotype) and 2P2, 2P3 (para- types).

CONODONTS FROM THE CHESTER SERIES

17

L0C.I4-P0LAND WEST

Limestone, light gray, medium crystalline. 3'

e

Shale, gray, poorly exposed. 10'

Limestone, gray, shaly, fossil. 3

e

Estimated 10'

covered

Shale, gray, estimated 7.'

Limestone, gray, dense, thin-bedded.2

Shale, blue to buff, fossil. 4

Shale, black, alternating with sandy gray siltstone. 2'6"

Limestone, dark gray, fine, ( argil., base more resistant. 3 6/

Shale, tan and gray, fissile. 3'

50 of partially exposed Palestine sandstone and shale.

Fig. 17. — Poland West, locality 14. Outcrops in first south-draining gulley west of secondary road, about 0.2 mile north of County Farm — Poland road, near east edge of NW^ SW34 sec. 15, T. 7 S., R. 6 W., Chester quadrangle, Randolph County, Illinois.

Cavusgnathus convexa Rexroad, n. sp. Plate 1, figures 3-6

Oral view. — Platform long, narrow; deep trough straight, one or two nodes may be present at posterior end; parapets nearly straight, ornamented with regularly spaced, parallel, transverse ridges becoming obso- lescent into the trough; denticles of blade laterally compressed.

Lateral view. — Oral margin of both para- pets convex, more convex posteriorly; pos- terior end rounded ; blade composed of four to six denticles fused nearly to apices, blade with regularly convex oral outline, highest at mid-length, length of blade less than one- third length of specimen, a small part free.

Aboral view. — Navel of moderate depth, asymmetric, lanceolate-shaped outline, point reaching posterior tip, inner lip with greater flare; central groove extends anteriorly from navel along otherwise sharp aboral margin.

Distribution. — Renault, Golconda, Glen Dean, Menard, Clore, and Kinkaid forma- tions.

L0C.I5-C0RA

40' bluffs of Degonia sandstone above a 35' covered interval.

Limestone, lower part medium to dark gray, upper part light; medium to very fine crystalline, chert near base. 15'

Limestone, dark gray, with shale beds. 3'

Shale, calcareous, with limestone stringers. 5'

22' covered

Shale, light gray. I'

4'8" covered

Shale, dark gray, weathers buff, j=xz^EZ= with thin.sandy, fossiliferous limestone lentils. 7'

Cool, 4

Shale, gray, grading upward to underclay. 8'6"

Sandstone, buff, with 6"shale near base. I0'6"

Sandstone, buff, with inter- bedded dark fissile shale. 8'

Shale, sandy, with thin- bedded fucoidal sandstone. 9'

o "*-

u_ o

Fig. 18. — Cora, locality 15. Bluff" of Mississippi valley just east of valley mouth of Degonia Creek near Cora, SE^SW^ sec. 16, T. 8 S., R. 5 W., Campbell Hill quadrangle, Jackson County, Illinois.

Repository. — Illinois State Geological Sur- vey, 2P4 (holotype) 2P5, 2P6 (paratypes) and 2P7 (figured specimen).

Cavusgnathus unicornis Youngquist and Miller

Plate 1, figure 7

Cavusgnathus unicornis Youngquist and Miller, 1949, Jour. Paleontology, v. 23, no. 6, p. 619, pi. 101, figs. 18-23.

Cavusgnathus cristata Cooper (part), 1947, Jour. Paleontology, v. 21, no. 2, p. 91, figs. 7-10.

The Chester species is similar in all re- spects to that from the Pella beds, namely in shape of platform and trough, ornamentation of parapets, configuration of blade with

18 ILLINOIS STATE GEOLOGICAL SURVEY

EXPLANATION OF PLATE 1

All figures X 40

Numbers in parentheses after explanations refer to locality and sample numbers, for example (2-12) refers to locality 2, sample 12.

Figure

I, 2. Cavusgnathus char acta Rexroad, n. sp.; 1. outer lateral view of a paratype (2-8); 2. inner lateral

and aboral views of holotype (2-12).

3-6. Cavusgnathus convexa Rexroad, n. sp.; 3. outer lateral view of a freak (18-4); 4. outer lateral and

aboral views of holotype (9-15); 5. inner lateral view of a paratype (10-14); 6. oral view of a paratype (10^-10).

7. Cavusgnathus unicornis Youngquist and Miller; outer lateral view (10-6).

8-10. Cladognathus prima Rexroad, n. sp.; 8. outer lateral view of a paratype (10-4); 9. inner lateral

view of holotype (10-7); 10. inner lateral and aboral views of a paratype (18-5).

II, 12. Cladognathus mehli Rexroad, n. sp.; 11. inner lateral view of a paratype (10-11); 12. outer lateral

view of holotype (10-11).

Cladognathus sp. A; inner lateral view (10-8).

Cladognathus sp. B; outer lateral view (lft-10).

Gnathodus modocensis Rexroad, n. sp; 15. Outer lateral view of a paratype (5-8); 16. inner lateral view of a paratype (5-1); 17. oral and aboral views of holotype (6-41).

Hibbardella sp.; posterior view (10-7).

Hibbardella n. sp.?; lateral view (6-41).

Ligonodina sp.; 20. inner lateral view (6-41); 21. outer lateral view (2-10).

Ligonodina obunca Rexroad, n. sp.; 22. inner lateral view of holotype (6-40); 23. outer and inner lateral views of a paratype (10-8).

24, 25. Ligonodina hamata Rexroad, n. sp.; 24. outer lateral view of a paratype (17-4); 25. inner lateral

view of holotype (10-14).

14.
15-	■17.
18.
19.
20,	21.
22,	23.

Illinois State Geological Survey

R. I. 199, Plate 1

Rexroad, Chester Conodonts

Illinois State Geological Survey

R. I. 199, Plate 2

Rexroad, Chester Conodonts

CONODONTS FROM THE CHESTER SERIES 21

EXPLANATION OF PLATE 2

All figures X 40

Numbers in parentheses after explanations refer to locality and sample numbers, for example, (10-11) refers to locality 10, sample 11.

Figure

I, 2. Ozarkodina compressa Rexroad, n. sp.; 1. outer lateral view of a paratype (10-11); 2. inner lateral

and aboral views of holotype (10-6).

3, 4. Ozarkodina? bella Rexroad, n. sp.; outer and inner lateral views of cotypes (6-40).

5, 6. Ozarkodina recta Rexroad, n. sp.; 5. inner lateral view of holotype (2-9); 6. lateral view of para-

type (6-40).

7. Ozarkodina roundyi (Hass); inner lateral view (10-10).

8, 9, 14. Neoprioniodus loxus Rexroad, n. sp.; 8. inner lateral view (10-6); 9. inner lateral view of holo-

type (10-11); 14. outer lateral view of a paratype (8-17).

10. Neoprioniodus varians Branson and Mehl; inner lateral view (10-4).

II, 12. Neoprioniodus striatus Rexroad, n. sp.; 11. inner lateral view of holotype (17-4); 12. outer lateral

view of paratype (2-5).

13, 16. Neoprioniodus tennuis Rexroad, n. sp.; 13. outer lateral view of a paratype (16-30); 16. inner

lateral view of holotype (10-11).

15,21. Neoprioniodus epemoebus Rexroad, n. sp.; 15. outer lateral view of paratype (6-40); 21. inner

lateral view of holotype (12— 13b).

17. Neoprioniodus sp. A, inner lateral view (4-4).

18-20. Neoprioniodus camurus Rexroad, n. sp.; 18. inner lateral view of holotype (10-10); 19. inner

lateral view of a paratype (10—11) ; 20. outer lateral view of a paratype (18-2).

22, 26. Neoprioniodus scitulus Branson and Mehl; 22. inner lateral view (11-2); 26. outer lateral view

(8-16).

23, 25. Neoprioniodus erectus Rexroad, n. sp.; inner and outer lateral views of cotypes (2-7).

24, Neoprioniodus sp. B; inner lateral view (6-39).

22

1TE GEOLOGICAL SURVEY TABLE	1. - STRATIGRAPHIC OCQS Collecting lo 1
Number of identifiable specimens	Formation	-p d CD	-P M d CD •H CD CO P, ex, o	CO o o 1— 1 o o
Locality	1 2 3	4 5 6	7 8
Sample
i i i	Cavusgnathus characta convexa unicornis	- x - - x - - X -	- - X XXX	X X X X
Cladognathus prima mehli sp. A sp. B
Gnathodus modocensis	_ » _	- X X	- -
Hibbardella sp. n.sp.
- X - '	- - X	X -
Hindeodella sp.	XXX	XXX	X X
Ligonodina hamata obunca sp.	- X - - X X - X -	XXX - X X XXX	X - - X X -i;
Ozarkodina compressa recta roundyi ?bella			X X
- X -	- - X
- X -	- - X	- — !
Neoprioniodus camurus epemoebus erectus loxus scitulus striatus tenuis varians sp. A sp. B	- x -	- - -	1 1 | X X X X 1 X X 1 1 1 1 1 X 1 1 1 1
1 1 1 1 1 X 1 1 1 1 1 X X X X X 1 1 1 1 1 X 1 1	1 X 1 X | X 1 1 1 1 X 1 | 1 | 1 X 1 X X X X X 1 >
Spathognathodus campbelli cf. commutatus cristula spiculus sp. A sp. B	1 1 1 1 X X X X 1 \ 1 1	1 X 1 X 1 1 1 X X 1 X X	XXIX XIII
Subbryantodus stipans sp.
Synprioniodina sp.	- X -
Trichonodella fragilis imperfecta	- X - - X -	- - X	x -
Polygnathids	XX-
New genus?	- x -	X - X	X x
Genus indeterminate	- X -	XXX	X X
o o o mom — i —i	Number of 200 specimens collected 40°

Sample numbers such as - refer to samples 1 through 7. Prec samples are shown on the outcrop diagrams (figs. 4-21).

CONODONTS FROM THE CHESTER SERIES

23

NCE OF CONODONTS IN THE CHESTER SERIES ties shown in figure 1

c 03 Q C i— 1 O	ft) c c •H >	T3 u CO c 0)	o 1—1 o	73 fO c •H
9	10	11	11	12	13	14 15	16	17 18
i 16 21 15 20 26	1 6 4 16		7 14 13 18	9 17 25 16 19 26			1 24 5 31
XX- X X	X X X X	-	X X X	XX- XXX	X X	- -	X	X X X X
	X X X X X		X	X - X			X -	X X
- X	X X X	_	X -	XX-	_	X -	X X	- X
X X -	X X	X	X X	X - X	X	X X	X X	X X
- - X	X X X - X		X X X -	X - - X - —	X	X	X X	X X
- X —	X X X		X -	x - -				X
1 1 1 1 I 1 1 1 1 1 1 1 1 1 1 X 1 1 1 1 1 1 1 X 1 1 X 1 1 t	X X X X X X X X X X	-	X X X X X X	X - - X XXX X	X	- -	X X X X	- X X X - X
XXX	X X X	-	X X	- X - X - -			X X	- X
— — —	- X	~	X	X - -	~"	~ "~	— ~	_ _
	X							- X
X X	X X	-	X X	X - X	X	_	X	X X
X X	X X	-	X	X - X	-		X —	X X

stratigraphic positions of

24 ILLINOIS STATE GEOLOGICAL SURVEY

EXPLANATION OF PLATE 3

4 All figures X 40

Numbers in parentheses after explanations refer to locality and sample numbers, for example (11-16) refers to locality 11, sample 16.

Figure

1-9. Hindeodella spp.; lateral views (11-13, 18-2, 11-8, 10-11, 11-13, 6-39, 10-8, 10-6, 10-7, respec-

tively).

10-12. Polygnathus; 10. oral view (2-12); 11. oral view (8-12); 12. aboral and oral views (2-14).

13-15. Spathognathodus campbelli Rexroad, n. sp.; 13. inner lateral view of a paratype (2-1 8u); 14. aboral

view (10-14); 15. outer lateral view of holotype (5-8).

16, 17. Spathognathodus cristula Youngquist and Miller; 16. inner lateral view (10-6); 17. aboral view

(10-6).

18-21. Spathognathodus spiculus Youngquist and Miller; 18. lateral and aboral views (6-40); 19-21.

lateral views (8-17, 6-40, respectively).

22. Spathognathodus sp. B; inner lateral view (12-9b).

23, 24. Spathognathodus cf. S. commutatus Branson and Mehl; 23. inner lateral view (2-11); 24. oral view

(2-2).

25. Spathognathodus sp. A; lateral view (12-14).

Illinois State Geological Survey

R. I. 199, Plate 3

Rexroad, Chester Conodonts

Illinois State Geological Survey

R. I. 199, Plate 4

Rexroad, Chester Conodonts

CONODONTS FROM THE CHESTER SERIES 27

EXPLANATION OF PLATE 4

All figures X 40

Numbers in parentheses after explanations refer to locality and sample number, for example (10-6) refers to locality 10, sample 6.

Figure

1. Subbryantodus stipens Rexroad, n. sp.; inner lateral and aboral views of holotype (10-6).

2. Subbryantodus sp.; inner lateral view (10-4).

3. Synprioniodina sp.; inner lateral view (2-12).

4. 5. Triohonodella imperfecta Rexroad, n, sp.; posterior and anterior views of cotypes (18-4).

6, 7. Trichonodella fragilis Rexroad, n. sp.; 6. anterior and lateral views of holotype (6-39); 7. lateral

view (18-7).

8-13. New genus? 8-10. posterior? views (2-14, 6-40, 10-6, respectively); 11-13. aboral views (10-6,

6-41, respectively).

14-18. Indeterminate fragments; (10-6, 1-17, 6-41, 6-40, 2-10, respectively).

19-22. Genus indeterminate; 19. postero-lateral view (6-41); 20. anterior view (4-4); 21. posterior view

(6-40); 22. postero-lateral view (6-40).

28

ILLINOIS STATE GEOLOGICAL SURVEY

L0C.I6-F0RD W.P.A QUARRY

Sandstone, buff, I to 4 foot beds 18

Shale, dark gray to bluish gray. 3'

Limestone, medium crystalline, fossil. 6"- 2'

Shale, gray to greenish gray sparingly fossiliferous. 8'

Limestone, light gray. 0 - I 6

Shale, gray to greenish gray, sparingly fossiliferous. 5' 6

Limestone, brownish gray, medium to coarsely, crystalline, nodular. 3'6

Limestone, dork gray, shaly. 6

Limestone, dark gray, fine to medium crystalline. 8'

Shale, dark gray, calc. and fossil. 6"

Limestone, gray, crinoida

Shale, dark gray, fossil.

Limestone, buff to gray, org

Shale, dk. gray, sparingly fossil. 7 Quarry Floor

Fig. 19.— Ford W.P.A. quarry, locality 16. Small abandoned quarry in Mississippi River bluff above state highway 3, about 1.3 miles southeast of Marys River bridge, NW^ SElA sec. 33, T. 7 S., R. 6 W., Chester quadrangle, Randolph County, Illinois.

larger denticle posterior, and shape and pro- portions of navel. The blade is commonly more than one-third total length of speci- men with only a small part free.

Distribution. — Renault, Paint Creek, Gol- conda, Glen Dean, Menard, Clore, and Kin- kaid formations.

Repository. — Illinois State Geological Sur- vey, 2P8 (figured specimen) and 2P9, 2P10 (unfigured specimens).

Genus Cladognathus, n. gen. Type species: Cladognathus prima Rexroad, n.sp. Complex dental unit. Posterior bar usu- ally moderately long, thin, denticulate, and slightly arched ; denticles of bar commonly discrete, large and small denticles alternat- ing; posterior bar terminated anteriorly by recurved fang. Anterior to the fang are two denticulate processes. One is directed later- ally and somewhat downward and backward, an inner lateral process. Usually the prox- imal denticle of this process is the denticle

L0C.I7-CLIFT0N SCHOOL EAST

Limestone, dark gray, silty, fossiliferous. 7'

■Shale, fossiliferous, with thin limestone layers. 3" .

Shale, gray, soft. 10'

Sandstone, buff, fine. 41

£

Shale, gray, red, and green. 4' \ — — —

Shale, gray, soft, sandy layers, few siderite concretions. 10'

Sandstone, light gray, shaly. 2 /-^-^J-^-^.

Sandstone, buff. 2

c

Sandstone, buff, shaly. 1*6'

40 feet of buff medium to fine Degonia sandstone.

u_ o

^

Fig. 20. — Clifton School East, locality 17. Outcrops on east branch of gulley about 1500 feet above fork at Clifton School, two miles northeast of Rockwood, N3^ SWM sec. 1, T. 8 S., R. 6 W., Campbell Hill quadrangle, Randolph County, Illinois.

immediately anterior to the fang. The other process, the anterior process, is directed an- teriorly and may continue in the direction of the posterior bar or may incline somewhat outward. Aborally the posterior bar, inner lateral process, and generally the anterior process are medially grooved, the groove en- larging at the juncture of the posterior bar and inner lateral process.

Cladognathus is closely related in form to Ligonodina and Hindeodella, two genera be- tween which there are transitional forms. Af- finities of Cladognathus to Ligonodina, or perhaps to a ligonodinid transitional with Hindeodella, seem most probable. The inner lateral process of Cladognathus seems to cor- respond to the inner lateral process or anti- cusp of Ligonodina, and the anterior process of Cladognathus apparently arises from the inner lateral process. It is the development of the anterior process that sets the genus apart from Ligonodina.

Cladognathus prima Rexroad, n. sp. Plate 1, figures 8-10

Posterior bar moderately long, thin, some- what arched and bowed, bearing discrete, rounded denticles with several small ones al-

CONODONTS FROM THE CHESTER SERIES

29

L0C.I8-TYPE KINKAID

Sandstone, conglomerate. 0'- 8' / Limestone, light, fine to medium, W , I *? I

light che i i nodule; \J \ , I *? I ,

Shale, very dark, carbonaceous. 6''^-Lc^--Lp=l

Limestone, gray, fine to medium.no chert. I4'6"

O

Shale, gray, fossiliferous, thin limestone lenses. 2*6'

Limestone, irregularly bedded, dark gray, fine to medium, dark chert nodules and bed. I4'6"

Limestone, light, main quarry floor. 31

Limestone, gray, lithographic to medium crystalline. 8'6"

This point 5'above Degonia

k%

>i

z<

uJ>

Q-

Fig. 21.— Type Kinkaid, locality 18. MacRow, J. R. Giffin or Cromwell quarry on north bank of Kinkaid Creek, SEK NWM NWM sec. 6, T. 8 S., R. 4 W., Campbell Hill quadrangle, Jack- son County, Illinois.

ternating with each larger denticle; germ denticles may be visible; attachment scar on anterior portion of inner-lateral face, and in some cases also on outer-lateral face, in which case it is continued anteriorly on the outer- lateral face of anterior process; aboral edge medially grooved, slightly broadened ante- riorly, and here may be twisted slightly in- ward. Fang long, slender, laterally com- pressed, but rounded fore and aft, recurved. Inner lateral process arises anterior to fang, is directed inward, somewhat backward, and downward; aboral margin medially grooved; proximal denticle the largest, rounded except for faint sharpening in plane of process, on some specimens minute denticle between it and fang; remaining denticles discrete, rounded, slightly recurved, each arising from single germ denticle. Anterior process deep, essentially continues the direction of the pos- terior bar, and aboral margin continues arch of bar; bears two, three, or four rounded dis- crete denticles, anterior-most varying in de- gree of development, posterior denticles erect

or recurved. Commonly continuous attach- ment scar present on inner lateral face of anterior process and anterior face of inner lateral process. Aborally, minute pit at pos- terior side of juncture of bar and lateral process.

Distribution. — Glen Dean, Menard, Clore, and Kinkaid formations.

Repository. — Illinois State Geological Sur- vey, 2P11 (holotype) and 2P12, 2P13, 2P14 (paratypes).

Cladognathus mehli Rexroad, n. sp. Plate 1, figures 11 and 12

Posterior bar of moderate length, arched, bearing discrete denticles, marked attachment scar on anterior part of inner lateral face with aboral margin visible here showing me- dial groove. Fang recurved, laterally com- pressed. Inner lateral process projects in- ward, backward, and downward ; denticles discrete, rounded, recurved, proximal den- ticle anterior to fang but inward. Proximal denticle of anterior process anterior to and outward from first denticle of inner lateral process; anterior process carries arch of pos- terior bar sharply downward and is inclined outward about 15° to 20° ; process bears two to four discrete, rounded denticles. In- ner face of anterior process and anterior face of inner lateral process form gently convex surface. Both processes, as well as bar, me- dially grooved aborally.

Distribution. — Glen Dean formation.

Repository. — Illinois State Geological Sur- vey, 2P15 (holotype), and 2P16, 2P17 (par- atypes).

Cladognathus sp. A

Plate 1, figure 13 This single specimen with a broken pos- terior bar and inner lateral process appears to be a transition from Ligonodina. The an- terior process is very short, bears a single, node-like denticle, and makes an angle of about 40° outward from the direction of the posterior bar. The anterior process is ap- parently an outpushing from the inner lateral process of a specimen that in all other re- spects is like a typical Ligonodina.

30

ILLINOIS STATE GEOLOGICAL SURVEY

Distribution. — Glen Dean formation. Repository. — Illinois State Geological Sur- vey, 2P18 (figured specimen).

Cladognathus sp. B

Plate 1, figure 14

The general form of this single, badly broken fragment is similar to that of Cladog- nathus prima. It differs principally in that the six denticles of the anterior process and those of the posterior bar are fused nearly to their apices, resulting in a deep process and bar.

Distribution. — Glen Dean formation.

Repository. — Illinois State Geological Sur- vey, 2P19 (figured specimen).

Genus Gnathodus Pander, 1856

Type species: Gnathodus mosquensis Pander, 1856

Pander's original description (1856, p.

33-34) :

In den Mergeln, der untersten Schichten des Bergkalks im Tulaschen und der hoheren des Mos kauschen Gouvernements kommen wohlerhaltene kieferartige Ueberreste vor, die sich durch ihre Gestalt und die Beschaffenheit ihrer Basis von den bis jetzt beschriebenen unterscheiden, durch die mikroscopische Structur aber sich eng an sie anschliessen. Auf einer hohen, aus doppelten Wanden bestehenden, schmalen Platte, erheben sich, in einer Reihe, kleine Zahnchen und geben dieser das Ansehen, als wenn sie von einem gezahnten Rande begrenzt werde. Nach unten gehen diese Platten auf der einen Seite stark auseinander und bilden eine Hohle, wahrend sie auf der entgegengesetzten noch aneinander blelben. Diese Hohle, welche die Pulphole darstellt, ver- langert sich seitwarts hinein und giebt, wie zu vermuthen ist, fur jedes Zahnchen einen hinaufstei- genden Fortsatz ab.

A revised description by Branson and Mehl (1938, p. 144):

Jaw pieces consisting of a thin straight or slightly curved, spathodus-like blade which at the posterior end is expanded into a more or less hemispherical, thin-walled cup, opening aborally ; the blade extending across the oral surface of the cup as a low nodose or denticulate carina that terminates on the cup or a short distance behind it; oral edge of blade sharply crenulate through the growth of laterally compressed, partly fused denticles; oral surface of cup ornamented by nodes that tend to align themselves into ridges which typically radiate from the center of the cup.

Orientation. — For purposes of description the cup is called posterior. In forms with curved axes the concavity is toward the inner side. This seems to correspond to a less expanded cup on

the inner side in markedly asymmetrical forms. The greater lateral extension of the cup marks the outer side and should take precedence over curved axes orientations that do not agree with the above.

Remarks. — Although the tendency toward radial ornamentation is not evident in all the gnatho- dids this character and the nearly equal cross diameters of the cup seem to be the most trust- worthy means of separating the group from the less typical streptognathodids which they resem- ble, and some of the highly modified spathodids which have posteriorly placed, expanded navels and accessory denticles on the expansion at one side of the blade.

Gnathodus

ODOCENSIS

Rexroad, n. sp.

Plate 1, figures 15-17

Oral view. — Axis essentially straight ; nar- row, parapet-like inner side of platform par- allels carina, except that both curve slightly to unite in a point at the posterior end of specimen, both range in length up to, but generally less than, one-half length of speci- men ; inner margin bears single row of nodes and is set off from carina by straight, narrow trough ; outer side of platform sub-rectangu- lar in outline, but expanded anteriorly ; nodes on upper surface irregularly disposed to longi- tudinally linearly arranged.

Lateral view. — Carina strongly down- curved posteriorly, denticles broad, low, no- dose ; blade highest near anterior end, de- creases regularly in height posteriorly; den- ticles about nine to twelve, laterally com- pressed, fused nearly to apices; anterior end of blade convex, aboral edge straight.

Inner lateral view. — Inner margin of platform about same height as carina ; an- teriorly it terminates sharply along a line in- clined about 80° posteriorly (using line of aboral edge of blade as reference) ; face rounded, laterally flaring lip along aboral margin ; aboral profile concave.

Outer lateral view. — Shallow outer lateral platform unites with carina at about mid- height of blade, aboral profile concave.

Aboral view. — Outline of cup asymmetric and in shape the same as oral view, apex of cup near anterior end, marked groove ex- tends along otherwise sharp edge of blade to its anterior end.

This species closely resembles Gnathodus bilineatus (Roundy). It differs chiefly in that

CONODONTS FROM THE CHESTER SERIES

31

the outer margin of the platform is straight, parapet-like, and is separated from the carina, which it very nearly parallels, by a marked trough.

Distribution. — Paint Creek formation.

Repository. — Illinois State Geological Sur- vey, 2P20 (holotype) and 2P21, 2P22, 2P23 (paratypes). '

Genus Hibbardella Bassler, 1925 Type species: Hibbardella angulata Hinde Bassler's original description (1925, p. 219):

Anterior and posterior ends equally developed, the tooth being bilaterally symmetrical and the main cusp erect and enormously developed.

Branson and Mehl (1940, p. 175, 176) state :

The generic description of Hibbardella by Ul- rich and Bassler was based on the natural as- sumption that it is a simple bilaterally symmet- rical arch with discrete limb denticles and an ex- ceptionally large denticle at the apex. [The speci- mens originally studied were found on the bed- ding planes of hard, fissile shales, so that any pro- jection normal to the plane of the arch would be either broken off by splitting or concealed beneath the specimen.]

Revised description of Hibbardella:

Highly arched bar-like teeth, bilaterally sym- metrical, with limbs of equal length that bear dis- crete erect or recurved denticles, an erect or re- curved denticle of large size at the apex of the arch; a bar bearing discrete denticles extending back from the base of the apical denticle normal to the plane of the arch; without conspicuous excavation beneath the apex of the arch at the union of the arch limbs and the posterior bar.

Remarks. — This genus resembles closely Tricho- gnathus, differing chiefly in that the latter is deeply excavated beneath the apex of the arch at the union of the arch limbs and the posterior bar. In its later development Hibbardella may have the posterior bar very much shortened and in some species there is only a vestige of the arch limbs.

Hibbardella sp. Plate 1, figure 18

A single fragment referred to this genus is figured because it can be easily recognized as distinct from associated forms in spite of the fact that it is broken.

Distribution. — Glen Dean formation.

Repository. — Illinois State Geological Sur- vey, 2P24 (figured specimen).

Hibbardella n. sp.? Plate 1, figure 19

Lateral bars moderately deep, all incom- plete, but probably with four or five discrete denticles each and with spatulate distal ends ; denticles long, larger toward distal end of bars; aboral edges of lateral bars thin, grooved, meeting at base of cusp in an acute angle, bars incline 5° to 10° posteriorly; an- terior faces convex and inclined posteriorly downward. Cusp large, recurved, elliptical in cross section, sharp edged fore and aft, but increasingly rounded toward tip. Posterior bar stout anteriorly; none complete, but per- haps somewhat extended as thin bar, few denticles or nodes on oral surface, bar thin- ner in young specimens; marked attachment scars anteriorly in lateral view; aboral mar- gin wedge-shaped with longitudinal groove.

Distribution. — Renault, Paint Creek, Gol- conda, Glen Dean, Menard, Clore, and Kin- kaid formations.

Repository. — Illinois State Geological Sur- vey, 2P25 (figured specimen).

Genus Hindeodella Bassler, 1925

Type species: Hindeodella subtitis Bassler

Bassler's original description (1925, p.

219):

Bar long and straight, bearing 6 to 8 small denticles in front of the strong, long, main den- ticle and a long series of small denticles, often alternating behind it.

Branson and Mehl (1933, p. 194) add:

At this time we may add to the generic de- scription by Ulrich and Bassler as follows: Long bar — or somewhat blade-like piece — straight or slightly curved laterally, or arched, or both. Some species with the upper edge laterally sinuous. An- terior end broadly flexed or sharply curved inward in the horizontal plane or slightly bent downward. Posterior end tapered, spatulate, slightly down- curved or recurved beneath the bar. Denticula- tion consisting of a fang of large size at or some- what behind the anterior curvature, and closely spaced to articulating, more or less sheathed denticles of appreciably smaller size in front and back of the fang. The smaller denticles usually alternate in size regularly or irregularly with one to several minute denticles between the larger. The aboral side of the bar is sharp, usually with- out evidence of a longitudinal groove except near a small pit which marks the position of the sub- terminal fang.

Orientation. — For convenience of description, all units are oriented as though edging the lower

32

ILLINOIS STATE GEOLOGICAL SURVEY

jaw with the anterior curvature directed toward the median line. In species where the anterior end is not curved inward, there is more or less lateral flexure of the unit as a whole and the concave side is designated inner side.

The genus is closely related to Ligonodina Ulrich and Bassler, differing chiefly in that the anterior end of Ligonondina is much more con- spicuously downturned and the smaller denticles seldom suggest an arrangement of alternating sizes and are not sheathed.

HlNDEODELLA Spp. Plate 3, figures 1-9

The hindeodellid element in the Chester fauna shows a wide variety of forms in the fragmentary specimens present. Specific ref- erences are not justified on the basis of the single complete specimen and the termini of bars, much less on the mid-section of bars. However, representative forms are figured to indicate the nature of the material.

One fragment of a rod-like bar (fig. 9) is similar to the bar of typical hindeodellids except that the denticles, which alternate in size and diminish in size toward the tapered tip of the bar, are inclined in the direction opposite to that expected.

Distribution. — Renault, Paint Creek, Gol- conda, Glen Dean, Vienna, Menard, Clore, and Kinkaid formations.

Repository. — Illinois State Geological Sur- vey, 2P26-2P34 (figured specimens).

Genus Ligonodina Bassler, 1925

Type species: Ligonodina pectinata Bassler

Bassler's original description (1925, p.

218):

[Like Prioniodus but] distinguished by the de- velopment of a series of sucker-like impressions on the downward extension of the main cusp.

Branson and Mehl's description (1933, p.

48):

Complex dental units consisting of a moder- ately long straight to down-curved basal bar with aboral side more or less excavated lengthwise, oral surface set with discrete denticles of nearly circular cross section; bar terminated anteriorly by an erect or recurved long stout denticle, typ- ically with circular cross section and with base (aboral surface) more or less excavated; inner side produced strongly downward, in some cases extended to a conspicuous point. Lower inner side bearing a few stout discrete denticles which project inward and downward.

The sucker-like depressions on the down- ward extension of the main cusp by which Bassler distinguished the genus are the scars left where discrete denticles have been broken away.

Ligonodina hamata Rexroad, n. sp.

Plate 1, figures 24 and 25

Posterior bar long, very thin, nearly straight; aboral margin truncated, medially grooved ; groove expands and deepens slightly beneath terminal (sub-terminal) fang where aboral edge is wedge-like ; faint outer-lateral lip, attachment scar marks inner face of bar anteriorly; denticles alternate in size, several small denticles between each pair of larger denticles, germ denticles usually visible. An- terior fang long, inclined backward by bend near base, laterally compressed with sharp fore and aft edges. Antero-lateral process short, directed outward, downward, and backward ; arises from anterior margin of fang; proximal of three (rarely four) den- ticles immediately anterior to fang; adjacent denticle may not be completely offset from fang; process deepens distally.

Distribution. — Renault, Paint Creek, Gol- conda, Glen Dean, Menard, Clore, Kinkaid formations.

Repository. — Illinois State Geological Sur- vey, 2P35 (holotype), 2P36, 2P37 (para- types).

Ligonodina obunca Rexroad, n. sp.

Plate 1, figures 22 and 23

Posterior bar long, thin, nearly straight, but may be slightly arched ; aboral margin of bar truncated, medially grooved, expanded at anterior end; outer lateral lip present; at- tachment scar may be present toward ante- rior end of inner face ; denticles of bar small, discrete, widely spaced, in some cases smaller ones present between larger. Terminal fang long, slender, recurved with greatest curva- ture near base, somewhat compressed later- ally. In some specimens a very small denticle is present on anterior margin of terminal fang near its base but entirely distinct from denticles of infero-lateral process. Infero-lat- eral process short, directed inward, backward,

CONODONTS FROM THE CHESTER SERIES

33

and sharply downward ; aboral edge medially grooved; process bears three (or rarely four) discrete denticles, the proximal one nearly round in cross section, the distal one com- pressed in plane of process, distal end of proc- ess spatulate.

Distribution. — Renault, Paint Creek, and Glen Dean formations.

Repository. — Illinois State Geological Sur- vey, 2P38 (holotype), 2P39, 2P40, 2P117 (paratypes).

LlGONODINA sp. Plate 1, figures 20 and 21

Posterior bar thin, aborally truncated and medially grooved, inner lateral attachment scar near anterior end. Terminal (sub-ter- minal) fang long, thin, laterally compressed, recurved, inclined somewhat inward. An erect, discrete denticle present anterior to terminal fang; it is the first denticle of four or five on the antero-lateral process, which is directed inward, downward, and backward.

Distribution. — Renault, Paint Creek, Gol- conda, Glen Dean, and Menard formations.

Repository. — Illinois State Geological Sur- vey, 2P41, 2P42 (figured specimens).

Genus Neoprioniodus Rhodes and Miiller, 1956 Type species: Prioniodus conjunctus Gunnell Rhodes and Muller's original description

(1956, p. 698):

Diagnosis. — Compound conodonts consisting of a denticulated posterior bar, at the anterior end of which a large fang (main cusp) is developed. The base of this fang may or may not extend downward below the level of the bar to form an "anticusp," the anterior edge of which may or may not be denticulated. There is usually a basal cavity below the fang, which may be extended as a shallow groove on the aboral surface of the posterior bar.

Remarks. — Rhodes and Miiller have pro- posed the genus Neoprioniodus to include material that by long accepted usage has been referred to Prioniodus Pander, but which Lindstrom (1954, p. 589) excludes from Prioniodus by a redefinition of that genus.

Pander's original specimens were frag- mental and the description brief, and the re- definition of Prioniodus Pander by Branson

and Mehl (1933, p. 129) has been com- monly accepted. In a subsequent discussion of the genus (1944, p. 241), Branson and Mehl indicate that topotypes of Pander's ma- terial show considerable gradational varia- tion and include specimens that fit Lind- strom's redefinition of Prioniodus as well as those Lindstrom would exclude. However, Branson and Mehl state: "The acceptance of an atypical species as genotype seems less confusing than drastic change in taxonomy." Although it is not stated, Lindstrom ap- parently redefines Prioniodus Pander, not be- cause the original types were fragmental, but because he feels the type species and closely similar forms are sufficiently atypical that they belong in a separate genus. Rhodes and Miiller (1956, p. 697) accept Lindstrom's redefinition stating:

If the redefinition is accepted as valid (and the present writers believe that it should be), it will have the effect of excluding from the genus Prioniodus the majority of species previously as- signed to it. In any case, the genus as redefined by Lindstrom cannot be regarded as congeneric with the following proposed new genus [Neo- prioniodus]. The differences between them are considerable and are easily recognized in complete specimens. Since the stratigraphic range of the two genera is different, the division is also of practical value.

And further:

The only method of dealing with the many species of Prioniodus which are now excluded from the genus by Lindstrom's redefinition, ap- pears to be to assign them to a new genus [Neo- prioniodus]. In spite of Branson and Mehl's (1944) suggestion of a gradation between such forms and those with a lateral process (Prionio- dus s.s.) in topotype specimens of P. elegans, the two broad groups appear to be well differentiated in younger faunas.

Neoprioniodus camurus Rexroad, n. sp.

Plate 2, figures 18-20

Posterior bar long, very thin, straight from lateral view, bowed inward with sharp flex- ure immediately posterior to fang, and bear- ing about ten to thirteen laterally compressed, sharp-pointed denticles ; aboral margin of bar grooved, groove visible from inner lateral but not outer lateral view. Terminal fang laterally compressed, in cross section inner side more convex than outer; from lateral view anterior edge of fang and aboral pro- jection straight with angle between fang and

34

ILLINOIS STATE GEOLOGICAL SURVEY

posterior bar about 140° ; from anterior view fang and aboral projection together concave inward ; oral termination of fang not known. Aboral projection very long, anterior and posterior margins nearly parallel, termination square; some specimens show slight evidence of suppressed denticles on anterior margin. Seen aborally, pit is minute with asymmetric elliptical outline, inner lateral lip with greater flare; from lateral view in transmit- ted light, shape of pit is isosceles triangle with short base, one side a direct continuation of aboral margin of bar, the other essentially a continuation of posterior margin of aboral projection.

Four specimens placed in this species vary gradationally in that the posterior bar is somewhat thicker in proportion to the den- ticles than in the remaining specimens. The four specimens are from the Renault and Paint Creek formations, and the others are from the Golconda, Glen Dean, and Kinkaid formations.

Distribution. — Renault, Paint Creek, Glen Dean, Golconda, and Kinkaid formations.

Repository. — Illinois State Geological Sur- vey, 2P53 (holotype), 2P54, 2P55 (para- types).

Neoprioniodus epemoebus Rexroad, n. sp. Plate 2, figures 15, 21

Bar long, thin, bowed, with sharp inward flexure at juncture with fang, slightly arched, lateral faces flat or nearly so; bar bearing more than twenty laterally com- pressed denticles, appressed in adult forms, small denticles (commonly two) alternate with large, each tapering sharply to point; aboral margin medially grooved, some speci- mens twisted to show groove from inner lat- eral view. Terminal fang incomplete, appar- ently of moderate length and straight; fang laterally compressed, biconvex, sharp edges fore and aft; base truncated nearly at right angle. Moderately deep pit present, pit sub- round but asymmetric in outline, inner lat- eral lip with greater flare; medial groove ex- tends to anterior tip of base, and posteriorly along bar.

Distribution. — Paint Creek and Menard formations.

Repository. — Illinois State Geological Sur- vey, P256 (holotype) and 2P57 (paratype).

Neoprioniodus erectus Rexroad, n. sp. Plate 2, figures 23, 25

Posterior bar short, thin, arched, bowed in- ward ; denticles probably seven or eight in number, slightly compressed laterally, free. Terminal fang long, narrow, strongly com- pressed laterally with sharp edges fore and aft ; outer side more convex in cross section ; from lateral view anterior margin slightly convex, posterior margin straight ; viewed an- teriorly fang is concave inward; tip slightly twisted. Aboral projection long, pointed, pos- tero-aboral margin convex, meeting aboral margin of bar at low obtuse angle. Lateral tips of pit not flared, extending from tip of aboral projection onto aboral margin of pos- terior bar, making the pit exceptionally long and narrow ; pit shallow except for small con- ical inner pit pointed sharply anteriorly and located at juncture of aboral margin of pos- terior bar with the fang.

P. erectus has an outline almost identical with that of P. ligo Hass. However, P. erec- tus lacks the beveled and finely lined charac- teristics of the aboral portion of the bar and aboral projection of cusp, and it has a long, narrow excavation rather than a small pit with associated aboral grooves.

Distribution. — Renault formation.

Repository. — Illinois State Geological Sur- vey, 2P58 (cotypes, two specimens).

Neoprioniodus loxus Rexroad, n. sp.

Plate 2, figures 8, 9, 14

Posterior bar long, slightly arched and bowed, lateral faces rounded, aboral margin truncated, bar bearing short denticles; den- ticles sub-round in cross section, unequal in size with an irregular alternation of sizes. Terminal fang narrow, moderately long; in cross section greatly convex on inner side, slightly so on outer side, sharp-edged fore and aft; anterior margin in lateral view straight or somewhat concave, in anterior view con- cave inward. Aboral projection short, sharp ; angle of postero-aboral margin with bar ob- tuse to near 90°. Subapical pit shallow ex- cept minute, deep, conical inner pit ; pit

CONODONTS FROM THE CHESTER SERIES

35

asymmetric in outline reflecting asymmetry of fang and emphasized by laterally flaring in- ner lip and flat outer lip. Medial groove present along aboral margin of bar and ex- tending to tip of aboral projection of fang.

Distribution. — Renault, Paint Creek, Gol- conda, Glen Dean, Menard, and Clore for- mations.

Repository. — Illinois State Geological Sur- vey, 2P59 (holotype), 2P60, 2P61 (para- types), and 2P62 (figured specimen).

Neoprioniodus scitulus (Branson and Mehl)

Plate 2, figures 22, 26

Prioniodus scitulus Branson and Mehl, 1940, Deni- son University Bull. Jour. Sci. Labs., v. XXXV, p. 173, pi. V, figs. 5, 6; Cooper, 1947, Jour. Paleontology, v. 21, no. 2, p. 92, pi. 20, figs. 1-3.

This is the most common species of Neo- prioniodus in the Chester series. It is some- what variable, and some specimens are nearly identical with representatives of the same species from the Caney shale. The anterior margin of the fang viewed laterally may be straight or convex, and the depth and thick- ness of the posterior bar vary. Denticles are slightly to moderately compressed laterally. The young show no attachment scar, but this feature becomes well developed in old speci- mens.

Distribution. — Renault, Paint Creek, Gol- conda, Glen Dean, Menard, Clore, and Kin- kaid formations.

Repository. — Illinois State Geological Sur- vey, 2P64, 2P63 (figured specimens).

Neoprioniodus striatus Rexroad, n. sp.

Plate 2, figures 11 and 12

Posterior bar thin, shallow, nearly straight, bears four to six laterally compressed den- ticles, each wider than the one anterior to it ; denticles free, of sub-equal length. Terminal fang strongly compressed laterally, sharp- edged, recurved ; viewed from anterior, con- cave inward. Aboral projection large with convex postero-aboral margin ; broadly flared lateral lips extend from tip of projection onto aboral margin of bar forming long, narrow excavation with medial groove ; small conical,

inner pit present at juncture of posterior bar and fang.

Distribution. — Renault, Paint Creek, Gol- conda, Glen Dean, Menard, Clore, and Kin- kaid formations.

Repository. — Illinois State Geological Sur- vey, 2P65 (holotype), 2P66, 2P67 (para- types ) .

Neoprioniodus tenuis Rexroad, n. sp. Plate 2, figures 13, 16

Posterior bar long, thin, moderately deep, somewhat arched and bowed ; in cross section outer face nearly straight, inner face convex ; appressed, laterally compressed denticles un- equal in size, with irregular alternation of small with large. Terminal fang greatly com- pressed laterally, sharp-edged fore and aft; viewed laterally, posterior margin convex, anterior margin slightly concave except at base and aboral projection; viewed anterior- ly, anterior margin of fang and aboral pro- jection is slightly sigmoidal with fang con- cave inward and aboral projection convex in- ward. Aboral projection short, sharp, its pos- tero-aboral margin forms an angle with pos- terior bar ranging from broadly obtuse to near 90°. Apical pit asymmetric in outline, outer side flat, inner side with laterally flar ing lip ; pointed anterior end of pit extends to tip of aboral projection. Median groove extends posteriorly along narrow aboral mar- gin of bar.

Distribution. — Renault, Paint Creek, Gol- conda, Glen Dean, Menard, Clore, and Kin- kaid formations.

Repository. — Illinois State Geological Sur- vey, 2P68 (holotype) 2P69 (paratype) and 2P70 (paratypes, two specimens).

neoprioniodus

— — IfjWBH varians (Branson and Mehl)

Plate 2, figure 10

Prioniodus varians Branson and Mehl, 1940, Denison Univ. Bull., Jour. Sci. Labs., v. XXXV, p. 174, pi. V, figs. 7, 8

The Chester specimens, although variable, conform well to the Caney shale forms. Bran- son and Mehl's thorough description needs no elaboration.

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ILLINOIS STATE GEOLOGICAL SURVEY

Distribution. — Paint Creek, Golconda, Glen Dean, and Clore formations.

Repository. — Illinois State Geological Sur- vey, 2P71 (figured specimen).

Neoprioniodus sp. A.

Plate 2, figure 17

Posterior bar long, slightly bowed, lateral faces and oral margin rounded ; aboral edge medially grooved, shallowly excavated with very narrow, flared, lateral lips; bar bearing seven or more discrete denticles that vary slightly in size and are round in cross sec- tion. Terminal fang incomplete; anterior edge sharp, mid-portion concave in lateral view. Aboral projection probably short, sharp, with indications of denticulation on anterior margin. Postero-aboral margin shal- lowly excavated with pit under base of fang ; inner lateral lip greatly flared, outer margin nearly straight.

Only a single specimen was found.

Distribution. — Paint Creek formation.

Repository. — Illinois State Geological Sur- vey, 2P73 (figured specimen).

Neoprioniodus sp. B

Plate 2, figure 24

Posterior bar short, straight, bearing four node-like discrete denticles; bar thick and deep at anterior, tapers sharply to point pos- teriorly ; viewed aborally, bar not set off from remainder of aboral margin of specimen. En- tire base viewed aborally, doubly pointed, widest centrally where conical pit is present in otherwise shallowly excavated base, lateral lips not flared. Terminal fang long, recurved ; near base almost triangular in cross section with sharp anterior and lateral edges, poste- rior face slightly convex, antero-lateral faces nearly straight ; toward tip cross section mod- ified with sharp edges fore and aft and some- what convex lateral faces. Aboral projection short, broad, with sharp tip.

Distribution. — Paint Creek formation.

Repository. — Illinois State Geological Sur- vey, 2P74 (figured specimen).

Genus Ozarkodina Branson and Mehl, 1933

Type species: Ozarkodina typica Branson and Mehl

Branson and Mehl's original description

(1933, p. 51):

Compound dental units consisting of a thin, blade-like, denticulate arched bar with a denticle of superior size near mid-length and approxi- mately an equal number of parallel subequal smaller denticles on either side of it. Denticles laterally compressed, sharp-edged, more or less confluent or actually sheathed. Base excavated beneath large denticle.

Ozarkodina compressa Rexroad, n sp. Plate 2, figures 1 and 2

Arched and bowed, thin, blade-like unit with posterior limb commonly the more bowed ; anterior limb with nine to eleven fused denticles, slightly compressed laterally; denticles of posterior limb two or three fewer in number and more compressed, inclined strongly posteriorly; denticles vary in size; most arise from single germ denticle. Apical denticle twice width of others, longer, tapers to point, inclined posteriorly. Moderately deep navel, asymmetric elliptical in outline, inner lateral lip only slightly flared, outer lateral lip flared more, but is shorter; longi- tudinal groove of navel extended to ends of specimen.

Distribution. — Golconda, Glen Dean, Me- nard, and Kinkaid formations.

Repository. — Illinois State Geological Sur- vey, 2P44 (holotype), 2P45 (paratype).

Ozarkodina recta Rexroad, n. sp. Plate 2, figures 5 and 6 Blade-like unit, thin, bowing negligible, aboral margin nearly straight. Denticles of anterior limb about ten in number, erect, with short, sharp, free apices; most arise from single germ denticles, few suppressed ; denticles of posterior limb about eight in number, strongly compressed laterally, wider and shorter than denticles of anterior limb, inclined strongly posteriorly, increasingly so to the rear. Apical denticle two or three times wider than anterior denticles, tapers to point, inclined somewhat posteriorly, narrows

CONODONTS FROM THE CHESTER SERIES

37

downward because of adjacent suppressed denticles. Sharp aboral edge marked by groove extending from sub-apical pit to an- terior end and part way to posterior end of specimen; pit with heavy asymmetric lips only slightly flared. Some specimens show attachment scars in lateral view.

Distribution. — Renault and Paint Creek formations.

Repository. — Illinois State Geological Sur- vey, 2P47 (holotype), 2P48, 2P49, 2P50 ( paratypes ) .

OZARKODINA ROUNDYI (Hass) Plate 2, figure 7

Subbryantodus roundyi Hass, 1953, U. S. Geol. Survey Prof. Paper 243-F, p. 89, pi. 14, figs. 3-6.

The several fragments of this form pres- ent in the Chester series are undoubtedly con- specific with Subbryantodus roundyi Hass, which is referred to the genus Ozarkodina be- cause of the small sub-apical pit that it pos- sesses in contrast to an elongate excavation.

Distribution.— Glen Dean formation.

Repository. — Illinois State Geological Sur- vey, 2P51 (figured specimen).

Ozarkodina? bella Rexroad, n. sp.

Plate 2, figures 3 and 4

Thin blade-like unit arched and bowed with nearly straight limbs. Anterior limb bears about six to eight laterally compressed denticles, increasing in size posteriorly, fused nearly to apices, and inclined posteriorly. Posterior limb shorter with several fewer laterally compressed denticles that incline posteriorly nearly parallel to apical denticle. Apical denticle twice as wide as other den- ticles, longer, inclined strongly posteriorly, laterally compressed, and sharp edged. Asym- metrical navel, elliptical in outline, extends almost to posterior tip, outer lateral tip of navel the larger; navel deep near its anterior end with small conical extension upward un- der apical denticle, remainder shallow; me- dial groove extends anteriorly along aboral margin of anterior limb.

Distribution. — Renault and Paint Creek formations.

Repository. — Illinois State Geological Sur- vey, 2P52 (cotypes, two specimens).

Genus Spathognathodus Branson and Mehl, 1941

(Spathodus Branson and Mehl, 1933) Type species: Spathodus primus Branson and Mehl

Branson and Mehl's original description (1933, p. 46):

Compound, straight, blade-like dental units with nearly straight aboral margin, and, oral margin curved or straight but highest at or near anterior end. A short lateral expansion near mid-length produces on the otherwise comparatively sharp aboral edge a cup-like excavation or navel, which ranges in shape from slightly elongate antero-pos- teriorly, through circular, to laterally elongate ; either bilaterally symmetrical or asymmetrical in relation to the blade. Oral edge or crest consist- ing of a single row of "germ denticles," evident in transmitted light, completely sheathed to form a continuous crenulate oral edge. Oral surface of mid-length basal expansion or navel typically smooth but in some species bearing one or a few separate denticles.

Species of this genus with accessory denticles on the oral side of the navel expansion constitute connecting links between typical Spathodus and another development in which more or less fused navel denticles produce a denticulated platform on either side, comparable in appearance to Poly- gnathus.

Spathognathodus campbelli Rexroad, n. sp.

Plate 3, figures 13-15

Blade delicate, bowed in posterior two- thirds, composed of about 20 laterally com- pressed denticles in mature form ; denticles subequal in size, each from distinct germ denticle, nearly vertical in anterior half, but tend to incline posteriorly in posterior half.

Lateral view. — Oral margin crenulate, convex, convexity increasing posteriorly; blade distinctly thinner aboral to horizontal line that runs the length of the blade imme- diately oral to navel ; navel deepest near an- terior end.

Aboral view. — Length of navel about one- half length of specimen ; lateral lips of navel thin ; navel curved and asymmetric, posterior- ly pointed, extending to rear of specimen, anteriorly less pointed, extended as groove on oral edge of blade ; outer lip flared uniformly, inner lip with greatest flare anteriorly.

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ILLINOIS STATE GEOLOGICAL SURVEY

Specimens very similar in gross features but too poorly represented for differentiation are present in the Chester. They appear to differ from S. campbelli in having a shorter blade and more uniformly convex oral mar- gin.

Distribution. — Renault, Paint Creek, Gol- conda, Glen Dean, Menard, Clore, and Kin- kaid formations.

Repository. — Illinois State Geological Sur- vey, 2P75 (holotype), 2P76, 2P77 (para- types), and 2P78 (figured specimen).

SPATHOGNATHODUS cf. S. COMMUTATUS

Branson and Mehl Plate 3, figures 23 and 24

Spathognathodus commutatus, Branson and Mehl, 1941, Jour. Paleontology, v. 15, no. 2, p. 98, pi. 19, figs. 1-4.

The Chester specimens appear to have a thinner lipped, proportionately longer navel, and fewer denticles than do the syntypes from the Pitkin limestone. Otherwise they agree very closely. Variation was noted in the Pitkin specimens by Branson and Mehl, and it is felt that the differences of the Ches- ter specimens do not justify erection of a new species.

Distribution. — Renault and Paint Creek formations.

Repository. — Illinois State Geological Sur- vey, 2P79, 2P80 (figured specimen).

Spathognathodus cristula Youngquist and Miller

Plate 3, figures 16 and 17

Spathognathodus cristula Youngquist and Miller, 1949, Jour. Paleontology, v. 23, no. 6, p. 621, pi. 101, figs. 1-3.

Blade short, very slightly bowed, com- posed of eight to twelve denticles fused nearly to apices; denticles elliptical in cross section with sharp edges fore and aft, nearly equal in size except posterior two or three which are smaller and anterior-most denticle which is about two times wider and consid- erably longer than remainder ; in lateral view crenulate oral edge slopes posteriorly, sharply so near posterior tip ; anterior edge is straight or slightly convex; aboral edge anterior to

navel is straight. Navel deepest near an- terior and with conical extension pointed strongly anteriorly evident in transmitted light ; navel two-thirds to three-fourths length of specimen. Viewed aborally navel has nearly symmetrical, oblong-lanceolate out- line; about two to two and one-half times longer than wide with point extending to pos- terior end of blade; lateral lips thin; navel divided by medial groove that extends to an- terior end of blade.

Distribution. — Renault, Paint Creek, Gol- conda, Glen Dean, Menard, Clore, and Kin- kaid formations.

Repository. — Illinois State Geological Sur- vey, 2P81, 2P82 (figured specimens).

Spathognathodus spiculus Youngquist and Miller

Plate 3, figures 18-21

Spathognathodus spiculus Youngquist and Miller, 1949, Jour. Paleontology, v. 23, no. 6, p. 622, pi. 101, fig. 4.

The Chester representatives of this spe- cies show a great amount of variation. Some are identical in all respects with the holotype from the Pella beds, but most show varia- tion, particularly in the number and shape of the major anterior denticles. Future work may show that several Chester species are separable.

Distribution. — Renault, Paint Creek, Gol- conda, Glen Dean, Menard, Clore, and Kin- kaid formations.

Repository. — Illinois State Geological Sur- vey, 2P84-2P87 (figured specimens).

Spathognathodus sp. A

Plate 3, figure 25

Blade composed of twelve denticles strong- ly compressed laterally ; denticles have short, blunt, free apices inclined somewhat irregu- larly posteriorly ; anterior denticle larger and posterior three smaller than remainder. In lateral view crenulate oral margin slopes posteriorly, increasingly so near rear; an- terior end convex; aboral margin is straight anterior to and posterior to very shallow navel. In aboral view navel has symmetrical, oblong-lanceolate outline; navel divided by medial groove that extends nearly to pos-

CONODONTS FROM THE CHESTER SERIES

39

terior and anterior tips of specimen; navel not quite half length of specimen with its ends equidistant from ends of specimen.

Because only a single specimen was found, a specific designation was not given.

Distribution. — Menard formation.

Repository. — Illinois State Geological Sur- vey, 2P88 (figured specimen).

Spathognathodus sp. B Plate 3, figure 22

Blade short, thick, bowed, composed of about ten denticles, one of which (located just anterior to middle and resulting from fusion of two germ denticles) is wider and longer than remainder; suppressed germ den- ticles evident; denticles sharply pointed, free in approximately upper half.

Aboral view. — Navel slightly asymmetric, outer lip with wider flare; navel doubly pointed with longer, narrower point reach- ing posterior tip of specimen ; navel widest near anterior; groove extending from navel to anterior end of specimen; navel deepest near anterior end.

The single specimen represented does not justify specific designation.

Distribution. — Menard formation.

Repository. — Illinois State Geological Sur- vey, 2P89 (figured specimen).

Genus Subbryantodus Branson and Mehl. 1933

Type species: Subbryantodus arcuatus Branson and Mehl

Branson and Mehl's original description (1933, p. 285):

Conspicuously arched denticulate bars with the anterior limb commonly the longer, and one or both limbs laterally flexed so as to produce a fairly regular concave inward curve of the unit as a whole ; denticles confined to a single row on the oral edge, all somewhat laterally compressed and closely crowded or in contact, all inclined somewhat backward, one denticle of exceptional size, the apical denticle at the apex of the arch ; germ denticles not conspicuously developed but when present corresponding to oral terminations ; the aboral edge of the bar excavated beneath the arch apex by a }ong pit that tends to extend as a distinct groove along the edge of each limb.

Orientation. — The denticles are inclined pos- teriorly and the laterally concave side of the arch is the inner side. In most specimens the pos- terior limb is the shorter.

This genus is probably most closely related to Bryantodus Ulrich and Bassler. It differs most in that ordinarily there is no tendency toward lateral thickening of the oral edge of the bar and no development of apical lip on the aboral edge as in Bryantodus, and its trend is toward a split or grooved aboral edge through the development of the elongate pit rather than the sharp edge and limited pit of Bryantodus. Subbryantodus ap- proaches some forms of Ozarkodina Branson and Mehl in the curvature of the bar and its blade- like proportions but lacks the germ denticle de- velopment and the suppression of germ denticles which is characteristic of Ozarkodina. Further- more, all the ozarkodinids have thin sharp aboral edges. The closely crowded to fused, laterally compressed denticles and tendency toward split aboral edge serve to distinguish Subbryantodus from Prioniodina Ulrich and Bassler, in which the denticles are discrete and nearly circular in cross section.

Subbryantodus stipans Rexroad, n. sp.

Plate 4, figure 1

Arched and bowed blade-like unit ; anterior limb composed of about ten denticles, gen- erally three fewer on posterior limb ; sharp- pointed denticles partially fused, laterally compressed, increasingly so posteriorly; den- ticles of anterior limb somewhat recurved and inclined posteriorly, those of posterior limb strongly inclined posteriorly; denticles tend to increase slightly in size posteriorly. Apical dentical about twice as wide as other denticles and much longer. Subapical pit greatly elongate, extending essentially the entire length of specimen; minute, conical, inner pit present below apical denticle.

Distribution. — Glen Dean and Menard formations.

Repository. — Illinois State Geological Sur- vey, 2P90 (holotype).

Subbryantodus sp.

Plate 4, figure 2 Bar strongly and uniformly arched, bowed. Anterior limb deeper than posterior, each with six denticles, in contact, moderately compressed laterally; a small and a large denticle alternate regularly behind the small anterior-most denticle. Apical denticle about as wide as a pair (one large, one small) of other denticles, gently inclined posteriorly. Apical pit elongate, narrow with small, in- ner cone extending well up into bar, grooves continue pit to anterior and posterior ends of specimen.

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ILLINOIS STATE GEOLOGICAL SURVEY

The collection contained only one essen- tially complete specimen and one fragment that was doubtfully referred to this genus.

Distribution. — Glen Dean formation.

Repository. — Illinois State Geological Sur- vey, 2P91 (figured specimen).

Genus Synprioniodina Bassler, 1925 Type species: Synprioniodina alternata Bassler

Bassler's original description (1925, p. 219) was:

Like Palmatodella, except that the down-turned front is much smaller, bar thick, denticles not turning forward so sharply, and the main cusp proportionately very large.

Huddle (1934, p. 53-54) adds:

Tooth consisting of cusp, denticulated bar and anticusp. The denticles on the anticusps are in the vertical plane of the bar and cusp. Synprionio- dina differs from Euprioniodina in having the denticles closely appressed and joined by bar material; and the cusp is inclined upward rather than forward as in Palmatodella. The anticusp in Palmatodella is longer than the anticusp in Synprioniodina.

Synprioniodina sp.

Plate 4, figure 3 Posterior limb long, thin, somewhat arched, bowed inward, bearing appressed and laterally compressed denticles probably num- bering about twelve. Apical denticle strongly compressed laterally, fore and aft edges sharp, inner face the more convex in cross section; probably straight in lateral view. Longitud- inal axes of apical denticle and anterior limb nearly coincident ; axes of the two limbs form angle of approximately forty degrees. An- terior limb bearing small, appressed, and lat- erally compressed denticles subparallel to api- cal denticle, but inclined more anteriorly. Minute pit at juncture of limbs, in outline has very slightly flared lateral lips; pit deep with sharp point extending into base of apical denticle.

Only a few fragmental specimens were found. The general form is similar to Neo- prioniodus camurus and a relationship be- tween the two is. likely..

Distribution. — Renault formation.

Repository. — Illinois State Geological Sur- vey, 2P92 (figured specimen).

Genus Trichonodella Branson and Mehl, 1948

Type species: Trichognathus prima Branson and Mehl

Branson and Mehl's original description (1933, p. 36):

Dental units consisting of an arched denticulate bar symmetrical in reference to the axis of an apical denticle. Apical denticle curved posteriorly, the base deeply excavated, the posterior aboral margin produced laterally into a horizontally ex- tending more or less bar-like process.

The orientation of these dental units is assumed as transverse to the jaw for convenience of de- scription.

Subsequently Hass (1953, p. 88-89) pro- posed the new genus Roundya for species for- merly assigned to Trichonodella but which possess a denticulated posterior bar. In 1954 Lindstrom (1954, p. 599) indicated he, also, questioned the placing of forms with the den- ticulated posterior bar with Trichonodella but he hesitated to split the genus. I, too, at this time hesitate to accept the splitting of Roundya from Trichonodella.

Trichonodella fragilis Rexroad, n. sp.

Plate 4, figures 6 and 7

Posterior bar straight, long, slender, bear- ing widely spaced denticles or nodes; aboral surface broadly and shallowly excavated an- teriorly, with medial groove extending pos- teriorly. Fang large, recurved, laterally com- pressed, elliptical near base and more rounded toward tip in cross section. Lateral bars shal- low, bearing about three discrete, rounded denticles, the distal ones the larger; distal ends of bars spatulate, aboral edges sharp, but in some specimens faintly grooved medially; bars inclined about ten or fifteen degrees pos- teriorly; viewed from anterior, aboral mar- gin of bars meet in obtuse angle at base of fang.

Distribution.— -Renault, Paint Creek, Gol- conda, Glen Dean, Menard, and Kinkaid formations.

Repository .- — Illinois State Geological Sur- vey, 2P93 (holotype) and 2P94 (figured specimens).

CONODONTS FROM THE CHESTER SERIES

41

Trichonodella imperfecta Rexroad, n. sp.

Plate 4, figures 4 and 5

Lateral bars in one plane, thin, blade-like, each with about eight to twelve appressed denticles that increase in length distally ex- cept for one or two much reduced at distal ends ; denticles subround in cross section ; aboral edges of lateral bars sharp, straight or slightly concave downward, the two meet- ing at approximately a right angle below ap- ical denticle; anterior faces somewhat con- vex, posterior faces somewhat concave. Ap- ical denticle gently recurved, triangular with rounded edges in cross section with base of isosceles triangle anterior and the longest face, posterior edge, tends to flatten toward base ; base of apical denticle deeply excavated by a minute pit. There is a slight posterior expansion at the base of apical denticle, but it is not developed into a posterior bar.

Distribution. — Renault, Glen Dean, and Kinkaid formations.

Repository. — Illinois State Geological Sur- vey, 2P95 ( co types) and 2P96 (paratype variant).

POLYGNATHIDS Plate 3, figures 10-12

Three fragments found in the Renault for- mation at two locations apparently are re- ferable to Polygnathus , although in the two that show a pit, the pit is somewhat larger than would commonly be expected in the genus. Because each fragment differs from the other and because Polygnathus has not been recorded from this part of the column, each is figured and briefly described.

One fragment (fig. 12) is sharply arched with a well defined, nearly round pit imme- diately anterior to point of sharpest arch; aboral keel present. Oral outline nearly sym- metrical, inner side slightly convex, outer somewhat more so. Carina nearly straight, distorted anteriorly. Nodes on margins of platform are the only ornamentation.

Another form (fig. 10) is strongly bowed with inner side concave, outer convex; plat-

form ornamented with regular parallel trans- verse ridges, the posterior three or four merging with carina to form continuous transverse ridges across the specimen. Slight- ly arched; pit narrow, not sharply defined, keel present aborally.

The third specimen (fig. 11) is strongly bowed, asymmetric, the outer side the wider. Carina formed by completely fused denticles so its oral margin is smooth. Outer margins of plate nearly smooth, slightly lobate. Keel poorly developed.

Distribution. — Renault formation.

Repository. — Illinois State Geological Sur- vey, 2P97, 2P98, 2P99 (figured specimens).

New Genus?

Plate 4, figures 8-13

More than two dozen fragmentary cono- donts were found which vary considerably among themselves, but that are united in es- sential characteristics. Unfortunately the specimens are too fragmentary to provide an adequate picture of the individuals in the group. However, they apparently represent a single, undescribed genus. They seem to consist of three unequal, curving, denticulate limbs at whose union is an apical (?) den- ticle of moderate-to-small size that is sub- triangular in cross section. At the base of the denticle (at the union of the limbs) is a deep pit, triangular in outline. One limb may be designated a posterior bar because of the recurvature, and in some cases slight compression, of the apical denticle. In rela- tion to it one limb curves in an antero-lateral direction, the other in a postero-lateral di- rection. All three limbs may be arched. Dif- ferences among the specimens occur espe- cially in the angular relations of the three limbs and the depth, curvature, and denticu- lation of the limbs.

Distribution. — Renault, Paint Creek, Gol- conda, Glen Dean, Menard, Clore, and Kin- kaid formations.

Repository. — Illinois State Geological Sur- vey, 2P100-2P105 (figured specimens).

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ILLINOIS STATE GEOLOGICAL SURVEY

Genus Indeterminate Plate 4, figures 19-22

Lonchodina sp. Branson and Mehl, 1940, Denison

Univ. Bull, Jour. Sci. Labs., v. XXXV, p. 171,

pi. V, figs. 10, 12. Lonchodina? spp., Youngquist and Miller, 1949,

Jour. Paleontology, v. 23, no. 6, p. 620, pi. 101,

figs. 7, (8?).

Many related specimens represented in the collection are too fragmentary for reference to a genus or for description because only one limb or process is complete. The other limb or bar is represented by only a fracture or very short portion because of its fragile nature and the large angle between the two limbs. I would interpret the poorly represented por- tion as a bar with a small main cusp, posterior to which is a series of denticles. Base of cusp has a deep pit. From the lateral face of the cusp arises an antero-lateral process, bowed convexly posteriorly, and bearing sev- eral stout discrete denticles, the whole larger than the main bar.

This interpretation does not fit known genera, although the specimens seem most closely related to Ligonodina. Differences among specimens occur in number of den-

ticles of lateral process, in its length, depth, termination, and character of attachment scar; and in the denticulation and form of main bar.

Distribution. — Renault, Paint Creek, Gol- conda, Glen Dean, Menard, Clore, and Kin- kaid formations.

Repository. — Illinois State Geological Sur- vey, 2P106, 2P107, 2P108 (figured speci- mens).

Indeterminate Fragments

Plate 4, figures 14-18

Many denticulate fragments, either bar- like or blade-like, in the collection could be- long to any of a number of genera such as Neoprioniodus, Ligonodina, Hibbardella, Trichonodella, Hindeodella, Lonchodina, Gladognathus, or Prioniodina. Although these specimens are too fragmentary to be classified, the more distinctive forms are fig- ured.

Repository. — Illinois State Geological Sur- vey, 2P112, 2P113, 2P114, 2P115, 2P116 (figured specimens).

CONODONTS FROM THE CHESTER SERIES

43

REFERENCES

Bassler, Ray S., 1925, Classification and strati- graphic use of conodonts (abstract): Geol. Soc. Am. Bull. 36, no. 1, p. 218-220.

Branson, E. B., and Mehl, M. G., 1933, Conodont studies: Missouri Univ. Studies, v. VIII, 349 p., 28 pis.

, 1938, Conodonts from the Lower Mississip-

pian of Missouri, in Stratigraphy and paleontol- ogy of the Lower Mississippian of Missouri, pt. 2: Missouri Univ. Studies, v. XIII, no. 4, p. 128— 148, pis. 33, 34.

, 1940, Caney conodonts of Upper Mississip- pian age: Denison U.niv. Bull., Jour. Sci. Labs., v. XXXV, p. 167-178, pi. V.

, 1941, New and little known Carboniferous

conodont genera: Jour. Paleontology, v. 15, no. 2, p. 97-106, pi. 19.

1948, Conodont homonyms and names to

replace them: Jour. Paleontology, v. 22, no. 4,

p. 527-528.

Cooper, Chalmer L., 1947, Upper Kjnkaid (Mis- sissippian) microfauna from Johnson County, Illinois: Jour. Paleontology, v. 21, no. 2, p. 81- 94, pis. 19-23; reprinted as Illinois Geol. Survey Rept. Inv. 122.

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