The Lower Ordovician Gastropod 

Ceratopea

By ELLIS L. YOCHELSON and JOSIAH BRIDGE

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 294-H

Ceratopea Ulrich is redes crib edfrom both 

operculum and shell. Ranges and variations 

of the several species are discussed

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1957
UNITED STATES DEPARTMENT OF THE INTERIOR 

FRED A. SEATON, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

For sale by the Superintendent of Documents5 U. S. Government Printing Office 

Washington 25, D. C. - Price 75 cents (paper cover)
CONTENTS

	Page 

Abstract_______________________________________ 281

Introduction,______________________________________ 281

Acknowledgments- __________________________________ 281

Previous work_______________,______________________ 282

Terminology.____________________________________ 282

Preservation and local occurrence.____________________ 284

Orientation in life___________________________________ 286

The associated shell and the nomenclatural problem____ 287

Paee

Other Ordovician opercula.__________________________ 290

Geographic distribution____________________________ 291

Stratigraphic occurrence.____________________________ 291

Phylogeny_._____________________________ 294

Systematic paleontology_________-____-__-____._____- 296

References cited________--___-__--__----__.-___----- 301

Index_ ______________.______________ 303

ILLUSTRATIONS

[ Plates follow index J

PLATE 35. Ceratopea opercula and Pondia figured by Oder, 1932.

36. Ceratopea opercula from Texas, Colorado, Oklahoma, Missouri, and Tennessee.

37. Ceratopea opercula and shells from Arkansas, Texas, Oklahoma, and Pennsylvania.

38. Ceratopea shell and opercula, and opercula of C.I pygmaea Stauffer and its allies. 

FIGUBE 102. Orientation and terminology for operculum of Ceratopea. _________ ____________

103. Stratigraphic occurrence of Ceratopea species____-___________________________

104. Suggested phylogeny of Ceratopea species__-_-_-________-_-_-_-_-___---.___.

Pace

283

293

295

TABLES

TABLE 1. Linear measurements of Ceratopea opercula illustrated by various authors .

2. Linear measurements of Ceratopea opercula illustrated in this paper______

3. Geographic distribution of species of Cerafopea_---_-___-___-__-____-__

285

285

292

in

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

THE LOWER ORDOVICIAN GASTROPOD CERATOPEA

By ELLIS L. YOCHELSON and JOSIAH BRIDGE

ABSTRACT

Ceratopea Ulrich is interpreted as a gastropod whose description has been based heretofore only on its thickened operculum. 

Terminology is introduced, predicated on the assumption that 

the operculum is that of a dextral, low-spired shell. The operculum of Ceratopea is distinguished from that of Maclurites and 

other opercula occurring in Ordovician strata, by its muscle pit or 

pits and its peculiar tusklike shape. The orientation in life of the 

operculum is inferred from its morphology, witti the carina of 

the operculum being a reflection of the shell periphery. Other 

generalizations can be made about the shell. Most occurrences 

of opercula suggest sorting, but six collections of shells and 

opercula are known. Three of these contain well-preserved 

pleurotomarian shells fitting the general form inferred from 

the operculum.

A new family, Ceratopeidae, is proposed for pleurotomarian 

gastropods with thickened opercula. The opercula alone do not 

furnish clear evidence as to whether the group is monophyletic 

or polyphyletic. Study of three associations of opercula and 

shells suggests that these shells are congeneric. From this, it is 

inferred that Ceratopea is monophyletic, though additional associations of shell and operculum are needed to prove this conclusively. Five species groups are recognized, based on the 

opercula, but they do not warrant formal taxonomic treatment 

or rank.

Several Ceratopea species are widely distributed geographically and occur within well-defined stratigraphic units; thus, 

they are valuable guides to interregional correlation. All available geographic and detailed stratigraphic data on all species 

are summarized. All known species of Ceratopea are figured 

and described. Of 14 species recognized, 7 are new; 9 formerly 

named species are placed in synonymy. Ceratopea? pygmaea 

Stauffer is rejected from the genus but is redescribed.

INTRODUCTION

Ceratopea is a distinctive fossil in Lower Ordovician 

strata. Most specimens are elongate and twisted, and 

like a tusk or a simple horn in shape. They are considered to be the opercula of gastropods. The relatively great thickness of the opercula is conchologically 

uncommon. Nonassociation of opercula and shells has 

presented nomenclatural problems and problems of 

morphologic interpretation. While it is impossible 

to solve all these problems at the present time, this 

paper attempts to clarify some of the issues involved.

Six occurrences of shells and opercula have been found 

during many years of collecting. Three of these contain shells that are considered congeneric and thus 

provide much new information pertinent to the taxonomy of this group.

Geratopea is widespread in the Lower Ordovician of 

North America; it is considered a guide to middle and 

upper strata of the Lower Ordovician series (Twenhofel and others, 1954). The geologic occurrence of 

Geratopea species independently confirms presently accepted interregional correlations based on other f aunal 

elements. Restudy of formerly named species of Geratopea and delimitation of new species have been undertaken to provide the basis for more detailed and closer 

correlation.

ACKNOWLEDGMENTS

Study of Geratopea was begun by the late E. O. 

Ulrich during the first decade of this century, based 

primarily on specimens from the southern Appalachians and the Ozark Plateaus. Ulrich's original work 

was never published. Subsequently he and Josiah 

Bridge collaborated on a manuscript which was not 

brought to completion. After Ulrich's death the study 

was continued by Bridge, but it was interrupted by 

more pressing studies during World War II. Since 

then, Bridge and P. E. Cloud, Jr., collaborated on the 

study of Geratopea^ based primarily on specimens from 

the Llano uplift. The continued press of other duties 

and Bridge's untimely death again prevented completion of the project. The study has since been turned 

over to Yochelson. He is responsible for all conclusions 

reached, but needless to say, he has been influenced by 

these earlier manuscripts and is indebted to them and to 

discussions with Messrs. Bridge and Cloud for many 

of the ideas expressed.

William Ham of the Oklahoma Geological Survey 

has given invaluable assistance. He generously allowed 

study of his excellent collection of Geratopea and provided detailed information on stratigraphic occurrence 

of the species in the Arbuckle Mountains. In 1956 he

281
282 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

spent 5 days in the Arbuckle Mountains with Yochelson, 

guiding him to the best collecting localities and showing him the regional stratigraphy.

William J. Sando, U. S. Geological Survey, lent 

specimens from western Maryland and provided unpublished information about their stratigraphic occurrence. Ralph L. Langenheim, Jr., University of 

California, lent specimens from Colorado. Type specimens were generously loaned by Carl O. Dunbar, Yale 

Peabody Museum, A. C. Spreng, Missouri School of 

Mines and Metallurgy, and Robert E. Sloan, University 

of Minnesota.

J. Brookes Knight, U. S. National Museum, and 

W. P. Woodring, U. S. Geological Survey, have discussed the difficult problem of nomenclature with the 

authors on several occasions. Other colleagues, particularly Robert B. Neuman, have contributed ideas and 

suggestions.

PREVIOUS WORK

The genus Ceratopea was named by Ulrich (1911, p. 

665-666) in his monumental "Revision of the Paleozoic 

systems." He named G. keithi as the type, basing this 

species on a specimen from Virginia which Bassler 

(1909, pi. 20, fig. 3) had illustrated as the "Operculum 

of an undetermined gastropod, probably a species of 

Maclurea." Previously, Billings (1865) described three 

opercula from Lower Ordovician strata at Cape Norman, Newfoundland, and a fourth from Pistolet Bay. 

Billings, referred to these as opercula of Macbwrites but 

at least two of the opercula belong to Geratopea.

The first paper dealing almost exclusively with Ceratopea was published by Oder in 1932. He proposed 

terminology, discussed orientation, and redescribed the 

genus, suggesting that the specimens were the opercula 

of a genus allied to Maclurites. Oder recognized 10 

species in eastern Tennessee, 9 of which were considered 

as new. Unfortunately, many of his illustrations are 

poorly reproduced, and consequently some uncertainly 

surrounded several of his species. His illustrated material has been rephotographed and is reproduced on 

plate 35. His paper contains little detailed information 

on ranges of the species.

Another important paper is that of Cullison (1944). 

As part of the study of the fauna of certain Lower 

Ordovician formations in the Ozark area, he recognized 9 species, 7 of which were considered new. Cullison (1944, p. 60) suggested that ceratopean opercula 

were not the opercula of Maolurites, but rather should 

be considered opercula of orthostrophic dextral shells, 

crediting the suggestion to Knight and to Bridge.

Specimens from Virginia were illustrated by Bassler 

(1919) and Butts (1941), from Alabama, by Butts 

(1926), and from Georgia, by Alien and Lester (1954).

Knight (1941, p. 73-74) redescribed the type species, 

and figured it and two other species with short descriptions (Knight, 1944, p. 447). Cloud and Barnes 

(1946) noted the distribution and range of Ceratopea 

species in the Llano uplift of central Texas. They 

figured six forms, three of which they considered new, 

but did not describe or name them. Stauffer (1937) 

described a species from Minnesota, but doubtfully referred to the genus.

TERMINOLOGY OF THE OPERCULUM

The terminology proposed for the operculum of Ceratopea differs somewhat from that given by Oder (1932). 

He assumed that Ceratopea represented the operculum 

of a hyperstrophic coiled shell, whereas the shell is 

here, following Cullison, considered to be dextral orthostrophic. Conventional orientation and illustrations 

of some of the morphologic features are presented in 

figure 102. Taki (1950) classified opercula into three 

main groups: spiral, concentric, and lamellate. The 

ceratopean operculum is placed in the spiral group 

and may be considered as paucispiral in general pattern 

although some forms show little spiral growth and 

differ from the typical Recent paucispiral operculum in 

being greatly thickened.

The tusk or horn shape of the ceratopean operculum 

is caused by growth on the logarithmic pattern following a large radius of curvature, simultaneously with 

coiling about an imaginary axis, whereby the carina is 

twisted out of horizontal plane. It is possible to distinguish this logarithmic curvature of the operculum 

from axial coiling, as the first is several times larger 

than the second. For descriptive purposes, form produced by growth following the logarithmic spiral will 

be referred to as curvature, and coiling about the axis 

will be called torsion. In few species does torsion complete as much as one-eighth revolution. Ceratopea 

torta Cullison shows the most torsion of all species 

known.

For only one or two species are there enough 

specimens from any one locality to provide significantly large statistical populations. These specimens 

probably have been sorted and do not represent an 

unbiased sample of a natural population. Further, 

many specimens are worn or broken and are not 

suited for precise measurement. It is doubtful that 

detailed mathematical description of the spiral of the 

operculum and statistical study of variation would aid 

materially in differentiation of the several species.

By holding a specimen apex toward the observer, 

one can see that it is sinistrally torted; that is, in a 

counterclockwise direction. With the exception of the. 

pelagic heteropod Atlanta Le Sueur, it is axiomatic
THE LOWER ORDOVIGIAN GASTROPOD CERATOPEA. 283

Carinal surface 

Apex

Dorsal ridge

Parietal 

surface

Dorsal angle

Apex

Growth lines

£— Umbilical ridge—f£^_^~ 

Ventral surface

Notch

DORSAL VIEW UMBILICAL VIEW VENTRAL VIEW

Width

Carinal surface 

Carina Carinal 

margin

Parietal 

margin

Height

Attachment 

surface

margin 

INTERIOR VIEW

FIGURE 102.—Orientation and terminology for operculum of Geratopea, as illustrated by that of (7. tennesseensis Oder.

CARINAL VIEW

that the coiling of the operculum in Recent gastropods 

is opposite to that of the associated shell. For this 

reason, the shell of Ceratopea is presumed to have been 

dextral.

The only apparent exception to the rule of opposite 

coiling of shell and operculum is to be found in hyperstrophic shells. In these shells, the spire is so strongly 

depressed that it actually projects downward. Oriented 

with this false umbilicus downward, the specimen appears as a sinistral shell with a sinistral operculum. 

Hyperstrophic coiling, with particular reference to 

Maclurites, is discussed by Salter (1859a, p. 9) and by 

Knight (1952, p. 38-39) and will not be elaborated on 

here. It is this unusual coiling, and the supposed homologies of Ceratopea and Maclurites opercula, that 

confused earlier writers about the shape of the shell of 

Ceratopea.

Growth of this form of operculum begins at the apess 

(nuclear apex of Oder), which is also approximately 

the origin of the logarithmic curve. On many specimens, the apex is abraded, obscured by silicification, or' 

broken by weathering after exposure. Dorsal, ventral 

and umbilical views are obtained respectively by holding the specimen with the apex up and to the right, 

up and to the left, and up and facing the observer. 

A carmal view is obtained by holding a specimen with 

the carina horizontal, apex to the left. An interior

is obtained by holding the apex to the right. As 

in other groups of fossils, the orientations are chosen 

for convenience and do not necessarily reflect the position in life. Dorsal and ventral, of course, have no 

real meaning in gastropod morphology, but they are 

convenient for describing the isolated operculum.

One edge of the ceratopean operculum is characterized by a sharp carina (dorso-ventral carina of 

Oder). This carina follows the convex, outer curvature 

from the apex. When the carina is held almost horizontally it separates an upper and lower surface of the 

operculum. Deviation of the carina from the horizontal is caused by the torsion of the operculum. A less 

distinct umbilical ridge (anterior opercula margin of 

Oder) runs from the apex on the inner concave 

curvature.

A dorsal ridge may be present on the dorsal surface 

of some species. The two ridges are unequally developed, and one or both may be missing. On a few 

species, even the carina is poorly developed or wanting.

The dorsal ridge divides the dorsal surface into two 

sections, which are commonly distinct even though the 

ridge be poorly developed. The parietal surface is 

limited by the umbilical and dorsal ridges; the carinal 

surface is limited by the dorsal ridge and the carina. 

Commonly the parietal surface is flat to concave when 

viewed in section, and in many specimens it is the wider
284 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

of the two. The carinal surface may be flattened, but 

normally is convex. The ventral surface is not divided 

by a ridge.

From the apex to the proximal end, numerous growth 

lines can be observed. The growth lines commonly are 

closely and fairly uniformly spaced and are incised. 

Most prominent growth lines occur at nearly regular 

intervals on some specimens. As in a gastropod shell, 

they mark successive growth increments. The portion 

of the operculum actually sealing the aperture is the 

opercular rim. It may be conveniently delimited into 

three segments. The parietal margin (inner opercular 

margin of Oder) is the opercular rim of the parietal 

surface; the carinal margin (posterior opercular margin of Oder) is that of the carinal surface; and the ventral margin (outer opercular margin of Oder), that of 

the ventral surface.

The opercular rim as a whole is inclined forward from 

the umbilical ridge to the carina, but its edges are interrupted by several irregularities. In some species, 

for example, Geratopea buttsi, n sp., a distinct prong 

extends forward at or just ventral from the carina and 

forms the extreme forward projection of the opercular 

rim. When the prong is present, a narrow sharp sinus 

is commonly developed in the dorsal margin near the 

carina. A wider, very shallow sinus may occupy most 

of the parietal margin. The dorsal angle at the juncture of the carinal and parietal margins is also generally distinct. The approximate angle of this suture 

can be estimated readily. The ventral margin is incised by a notch, the lowest point of which is just to the 

right of the umbilical ridge in ventral orientation. The 

part of the ventral margin to the right of and above the 

notch and the parietal margin join with a only slight 

angulation.

The opercular rim surrounds a depressed area, the 

attachment surface (opercular muscle cavity of Oder). 

This surface is commonly smooth except for a muscle pit 

incised above and to the right of the notch, when the 

surface is viewed with the proximal end of the carina 

to the observer's left. Some species develop a second 

pit near the carina and have a narrow groove connecting the two pits. In some specimens, the single pit may 

be elongated as a groove. When two muscle pits are 

present, the one nearest the notch is invariably the 

deeper.

Opercula of Recent gastropods consist of a disk of 

tough, horny material (conchiolin). This disk may be 

calcified throughout, or may be calcified and thickened 

on the inner or outer surface only, or may not be calcified at all. In Ceratopea, calcification and thickening 

presumably were limited to the inner surface, as specimens grew from a point (apex) by accretion on one

margin. In keeping with the terminology of Recent 

opercula, thickness is defined as growth normal to the 

aperture. It is measured in a straight line from the 

apex to the proximal end of the carina. Width is measured across the opercular rim from the proximal end of 

the carina to the proximal end of the umbilical ridge, 

and is the longest linear measurement obtainable across 

the opercular rim. Height is taken as the largest measurement approximately at right angles to the width 

from the crest of the opercular rim on the dorsal and 

ventral margins. Measurements of previously illustrated Ceratopea opercula and those figured herein 

were made by Yochelson with a vernier caliper and are 

given in tables 1 and 2.

PRESERVATION AND LOCAL OCCURRENCE

Field evidence suggests that recovery of opercula of 

Ceratopea is governed by the chemical history of the 

enclosing strata, and that the specimens collected are 

probably not a true reflection of the original distribution or abundance of the several species. The ideas 

presented below are derived from study of outcrops of 

Lower Ordovician carbonate rocks in the ArbucMe 

Mountains but may be applicable to other areas. In the 

collections studied, Ceratopea appears to be rare in the 

Ozark Plateaus, and in the northwestern outcrop belts 

of eastern Tennessee. The collections indicate that 

Ceratopea is much more common in the southeastern 

outcrop belts of Tennessee. In both Tennessee and 

Oklahoma where beds are limestone rather than dolomite, specimens are more abundant.

Ham (1955, p. 29) has pointed out that the rocks of 

the Arbuckle Mountain area are divisible into two distinct provinces. The Lower Ordovician of the southern area is nearly twice as thick as that of the northern 

area. Along with this difference in thickness, there is 

a marked difference in lithologic character, the northern area being mostly dolomite, and the southern area 

being mostly limestone.

The preponderant number of Ceratopea specimens 

were obtained from the southern limestone area where 

they are restricted to relatively narrow stratigraphic intervals, with the beds between lacking them. No obvious differences in lithologic character are known between those beds bearing specimens and those from 

which they are absent (Ham, oral communication). 

Within these fossiliferous beds, Ceratopea is common 

near algal masses in pellet limestones, but exceptions 

are known.

Specimens are commonly sparse, only one occurring 

in several square feet or more of outcrop area. Locally, 

lanes are crowded with Ceratopea^ but this is
THE LOWER OEDOVICIAN GASTROPOD CE RAT OPE A 285

TABLE 1. — Linear measurements of Ceratopea opercula 

illustrated by various authors

[ >, measurement on broken specimen, the true distance being signiflcantly larger; 

» , indicates approximate measurement] 

ThickHeight Width ness 

Name Source (mm) (mm) (mm)

fBassler 1909 pi 20 fig 3 } Ceratopea keithi Which .... Ijjnjojit' 1941* nl 66* fie 4a I 10' 3 17' 3 31 '°

Do.....————— — ——— 1919, pi. 36, fig. 15 (c)—— 10.4 14.7 29.5

Do———.—————— ——— 1919, pi. 36, fig. 15 (d)—— — _ ...... 27.8

——— 1919, pi. 36, fig. 15 (a)—— | 

Butts, 1926, pi. 18, fig. 5, 6—.- [ 100 14. 7 31. 4 

Knight, 1941, pi. 66, fig. 4b-4e._ J

Do.————————— Oder, 1932, pi. 13, fig. 13, 14—. 8 12 31 

Do... _ — —— —— ——— 1932, pi. 13, figs. 15, 16... 8.4 15.5 26.1

tennesseensis Oder __ ——— 1932, pi. 13, figs. 4, 8, 12.. 10.9 11.3 23.3

cttreeotaOder.—— — ——— 1932, pi. 13, flgs. 1, 3—— 10.4 15.6 21.1 

Do.. — ——— —— —— ———— 1932, pi. 14, fig. 14....— . ... ... ...... «27.5

capuliformis Oder.. — ——— 1932, pi. 14, figs. 1, 6, 6 _ 11.9 15.0 16.5

robusta Oder————— - ——— 1932, pi. 13, figs. 9, 11.... 11.8 16.5 23.3

awtaKaOder..—— _ ——— 1932, pi. 14, figs 10, 12... 8.4 14.5 23.3 

Do.—.————— _ ——— 1932, pi. 14, flgs. 9, 13-... 10.0 15.5 »26

corniformis Oder.--... ——— 1932, pi. 14, figs. 2, 4. __ 4. 5 6. 1 13. 4 

sp— . _ ---..—— __ Butts, 1941, pi. 72, figs. 1, 2. __ 13.0 18.7 40.0

Do..———————— ——— 1941, pi. 72, flgs. 3, 4——— 14.2 18.8 34.7 

keithi Ulrich————.. ——— 1941, pi. 72, figs. 5, 6..... 12 >16 >35

tennesseensis Oder. _ ——— 1941, pi. 72, fig. 7—.. __ 11.9 >20 >30

jenkinensis Cullison... Cullison, 1944, pi. 31, figs. 1-3— - 12.3 18.0 26.8 

Do——————.. _ ——— 1944, pi. 31, figs. 4-6—.- »14 23.8 35.0

Do—..—————— ——— 1944, pi. 31, figs. 10-12.... 8.4 10.2 14.0

ankylosa Cullison.- _ ——— 1944, pi. 31, figs. 13-15.... 13. 0 14. 0 24. 0 

Do.....——.———— ——— 1944, pi. 31, flgs. 16-18— . 7.3 13.0 22.1

torta Cullison— ___ ——— 1944, pi. 31, figs. 19-21.... 9. 0 »12 31

Doi— ———— _ . _ ——— 1944, pi. 31, figs. 28-30.... — — ———

Do——.——————— ——— 1944, pi. 31, fig. 38—— — «14 s»18 »22

inftata Cullison—— ... ——— 1944, pi. 31, fig. 39-41— .. *»9 »13 25.8

sp. 1..—— —— ... —— Cloud and Barnes, 1946, pi. 43, 4.1 5.7 7.2

figs. 1-3. 

Do. —————————. ——— 1946, pi. 43, fig. 4.....—— 4.6 5.8 6.4

formis Oder.

Tin ... 1 0dfi nl ^11 fi crc ft Q 1ft 1 ft ft 141 171

Do.. ———————— ——— 1946, pi. 43, flgs. 7, 8.—— «7 10.5 12.1

capuliformis robusta ——— 1946, pi. 43, figs. 11, 12. . . 13. 7 16. 5 23. 5 

Oder. 

Do. —— ——————— ——— 1946, pi. 43, fig. 13—— ... 12.8 15.3 f»24

on A — - — 1 Olfi nl A3. fi cr 11 £M 7 SK 1 1 StJ 91

Do..———————— ——— 1946, pi. 43, fig. 15-.—.. «8 «9 «27

Do—..——————— ——— 1946, pi. 43, flgs. 16, 17.. . 7.5 10.4 27.1

sp. 5———— .... —— — ——— 1946, pi. 43, fig. 18—— ... 11.1 16.2 21.0

Do—..———————— ——— 1946, pi. 43, figs. 19, 21... 12.5 16.9 21.6

Do——.———————. ——— 1946, pi. 43, fig. 20— ..... 11.4 16.5 19.3

keithi subconiea Oder.. ——— 1946, pi. 43, figs. 22, 23... 9.1 14.4 33.0 

Do.——-—————— ——— 1946, pi. 43, fig. 24— ..... 11.9 18.2 34.3

awfcofaOder.. ____ Alien and Lester, 1954, pi. 3, 9.5 14.0 >25

flgs. 15, 19. 

ct. C. calceoliformis ——— 1954, pi. 3, fig. 14...... ... 10.4 16.1 26.1

Oder. 

capuliformis Oder. __ Sando, 1957, pi. 11, figs. 27, 28, 12.4 14.0 17.0 

32,33.

n

c-n ......... 1O17 nl 11 firr? 94 9A 7 4 SWO SWtfi

Do.....————— _ ——— 1957, pi. 11, fig. 26-— ... 5.7 7.6 13

i Missing and presumed lost.

TABLE 2. — Linear measurements of Ceratopea opercula illustrated 

in this paper

[>, measurement on broken specimens, the true distance being signiflcantly larger]

ThickHeight Width ness 

Name Illustrated on— (mm) (mm) (mm)

Ceratopea ankylosa Cullison-... „ pi. 37, figs. 1-4... ...... . 11.3 17.4 24.8 

Do——————————— pi. 37, figs. 5, 6..———— 12.8 22.8 29.5

n. sp. 

buttsi Yochelson and Bridge, pi. 36, figs. 25, 26....— 12.0 17.7 >46

n. sp.

Do-.————————— pi. 36, flgs. 27-30..— — 10.2 15.1 35.6 

capuliformis Oder——— —— - pi. 36, figs. 5, 8-10....- 9.7 12.9 14.8 

corniformis Oder— ..... — — pi. 36, figs. 14-17— —— 8.2 11.6 30.3

germana Yochelson and Bridge, pi. 36, figs. 6, 7, 11, 12— 7. 9 11. 7 17. 8 

n. sp. 

Do——————— —— — pi. 36, fig. 13— .———. 10.3 13.3 22.8

hami Yochelson and Bridge, pi. 37, figs. 15-18— —— 9.2 13.9 29.8 

n. sp. 

incurvata Yochelson and pi. 36, figs. 42-46—. —— 10.9 14.9 17.6

Bridge, n. sp.

keithi Ulrich..—— ... —— — pi. 36, figs. 31, 32, 41, 42. 11.7 17.1 33.7 

knighti Yochelson and Bridge, pi. 37, figs. 7-10— .—— 8.6 13.2 21.5

n. sp. 

subconiea Oder— .... —— —— pi. 36, figs. 35, 36, 39, 40. 9.6 13.2 26.6

tennesseensis Oder. ... —— ... pi. 36, figs. 33, 34, 37, 38. 11.1 17. 9 25. 4 

torta Cullison.— ... —— —— . pi. 36, figs. 21-24.——— >8 5.5 >13

unguis Yochelson and Bridge, pi. 38, figs. 8, 9. . ———— 11.6 >18 >29 

n. sp. 

Do...-————-——— pi. 37, figs. 11-14....—— 14.2 18.5 30.4

Do . —————————. pi. 37, figs. 19-22.———— 13.6 19.9 43.9 

Do-..——————-— pi. 37, figs. 23, 24, 28.— 11.8 >18 >22

the exception. The crowded bedding planes are almost 

certainly accumulations after death. 

In the beds where Ceratopea is sparse, far less than 

half of the specimens have been silicified. These stand 

in partial relief above the enclosing matrix. This silicification is most erratic in distribution, with one specimen being silicified and one next to it not. No explanation for this can be given. Except at a very few 

localities, silicified molluscan remains, other than 

cephalopods, are exceedingly rare. Sponges and 

brachiopods, where present, are commonly silicified. 

After a ledge containing Ceratopea has been found, 

the customary procedure is to trace it laterally until one 

finds well-preserved specimens that can be removed 

from the rock by a chisel. At some localities where 

Ceratopea is relatively common, as much as a mile of 

outcrop must be examined to obtain a dozen silicified 

specimens. 

In the northern dolomitic area, few Ceratopea localities are known. All specimens recovered have been 

silicified. These few localities were found only after 

considerable searching and only after Ham. had spent 

several years working out the general sequence of beds 

in the limestone area to the south. 

The available evidence suggests that, in some beds at 

least, silicification preceded dolomitization. Had the 

processes been reversed, virtually all the Ceratopea
286 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

specimens would have been destroyed during dolomitization. As it is, not only are there few silicified 

specimens left to collect, but the calcareous specimens, 

which are generally a clue leading to 'better preserved 

material, have been destroyed, making silicified specimens even more difficult to discover.

Deep weathering of the Lower Ordovician rocks of 

the Ozark Plateaus and the southern Appalachians 

has freed enclosed silicified specimens of Ceratopea. 

In these areas, most specimens have been recovered from 

residual soils. Other specimens have been obtained, as 

have those from the Arbuclde Mountains, by dissolving the calcareous matrix in hydrochloric acid. Commonly, the specimens prepared by use of acid are better 

preserved than those collected from soil and show details, particularly of the attachment surface, that are 

lost on the others.

Although silicification has resulted in the recovery 

of many individuals, it has also produced certain peculiarities. Some specimens are so coarsely silicified, with 

development of beekite rings, that growth lines are not 

preserved, and the surface appears to be smoothed by 

a secondary deposit. On a few specimens the outer layers may be lost, and the inner surface thus exposed 

shows fine striae radiating from the apex.

Differential silicification may result in loss of part of 

the specimen. Silicification may be confined to a thin 

outer layer, so that a specimen which appears to be 

siliceous may still be filled with calcite. Silicification of 

the outer walls but not of the attachment surface would 

allow for solution of the calcitic filling between this 

surface and the apex. At least two species have been 

named for specimens with supposedly deep muscle pits 

(Ceratopea calceoliformis Oder, C. jenkenensis Cullison.) The attachment surface of both holotypes is 

missing, and it is believed that may be due to incomplete 

silicification.

Winsnes (1955, p. 21), however, dealing with specimens from which the attachment surface appears to be 

missing, interprets this missing surface as the aperture, 

and the remaining walls as the shell of a simple gastropod related to Tryblidium. He suggests that if the 

cavity were filled with calcite, the weight of such an 

operculum would be almost too great for a gastropod to 

carry.

At many localities where specimens have been dissolved from limestone, ceratopean opercula are abundant and other fossils are exceedingly rare. Because of 

weight, size, and shape differential between these opercula and gastropod shells, it is postulated that a winnowing action left the opercula behind, like a lag gravel. 

Worn specimens suggest that this may be the correct 

interpretation.

A comparable situation is found in strata of Pliocene age in California, where calcareous opercula are 

concentrated in a relatively thin layer, with shells being exceedingly rare (Woodring, Eoundy, and Farnsworth, 1932, p. 33-36). Similar concentrations of the 

cephaJopod opercula (aptychi) are well known; at 

most localities, these accumulations are devoid of 

cephalopod shells.

Cullisoii (1944, p. 61) has suggested sorting, because 

of weight and shape differential, as one of the reasons 

for lack of association of ceratopean opercula and 

gastropod shells. He has further suggested that in 

areas where deep residuum has developed, Ceratopea, 

being compact would be little affected by weathering 

action, but more fragile shells would probably disintegrate. Both suggestions, especially the idea of sorting, 

are endorsed by the writers.

ORIENTATION IN LIFE

A platelike or dishlike operculum characterizes many 

living gastropods. Commonly, the operculum is borne 

on the posterior dorsal portion of the foot when the 

soft parts are extended from the shell. In this position, 

the operculum functions as a pad upon which the shell 

is rested. The relation of operculum and shell may be 

readily observed in the living Vimparus common to 

many aquaria.

The ceratopean operculum differs most from opercula of Recent gastropods in being so greatly thickened 

that it is tusklike. However, in spite of this difference 

in shape, it seems reasonable to presume that the operculum was borne on the foot in a similar position. 

Trials with clay models suggest that the best fit of 

opercular rim to foot would have been obtained with 

the notch posterior, and the apex inclined to the left 

side of the foot. In this orientation, the parietal surface is forward. On most specimens of the operculum 

of Ceratopea this surface is flattened or concave, and 

it could have acted as a shelf upon which the shell was 

rested.

The most important use of the operculum in living 

gastropods is to seal the aperture against enemies or 

adverse environmental conditions. With the exception 

of certain opisthobranchs which have an incomplete 

operculum, the operculum is a relatively effective seal. 

Commonly, it is withdrawn into the shell one-fourth a 

volution or more, with the lower part retracted slightly 

further inward than the upper part.

Assuming that this Lower Ordovician operculum 

functioned in a similar manner, its edges are an approximation of the aperture it sealed. The carina 

marks the sharp juncture of the upper and outer whorl 

surfaces of the aperture; the flattened or concave parie-
THE LOWER ORDOVICIAN GASTROPOD CERATOPEA 287

tal surface follows the shape of the parietal lip. In 

this orientation, the notch is ventral. Probably much 

of the mass of the retractor muscle or muscles may have 

passed through this notch, and it was the last part of 

the operculum to be withdrawn.

It is not known how far the operculum of Ceratopea 

could be withdrawn into the aperture. The logarithmic 

spiral angle (vector angle), which is a measure of the 

rate of expansion, of this operculum is quite different 

from that of a gastropod shell. In gastropod shells 

this angle is near 80°. In opercula of Ceratopea, it 

ranges from near 5° to near 20°. When the operculum 

was withdrawn, the curvatures would approximate one 

another for a short distance but would soon become 

strongly discordant and prevent further movement inward. Further, if the ceratopean operculum were 

withdrawn nonunif ormly, its thickness would have prevented much movement into the body whorl.

Considering these two factors, it seems doubtful that 

this form of operculum could have been withdrawn as 

much as one-fourth whorl into the shell. Tests with a 

clay model of the soft parts, using simulated withdrawal motions of the operculum, suggest that with the 

operculum protruding outward from the aperture, the 

shell would settle to the bottom, umbilicus downward in 

most, if not all, instances.

These opercula show one other feature reflecting the 

soft anatomy of the gastropod, namely the muscle pit 

or pits in the attachment surface. The individual species show considerable differences, with some showing 

one pit, a pit and groove, a groove, a pit groove and 

faint second pit, and two distinct pits. Further, there 

is some individual variation. In large specimens of 

species which normally only show a single pit, for example, Ceratopea buttsi, n. sp., a second faint pit is developed. This variation is taken to indicate two 

opercular muscles, with only one leaving a distinct muscle scar.

When the ceratopean operculum is oriented in the 

aperture, the muscle pit closest to the columella is the 

deeper. In Maclurites the muscle prong nearest the 

columella is again the most prominent. Even though 

some opercula of Ceratopea consistently show only a 

single pit or at most a pit and groove, they too are believed to have had two muscles.

Hedley (1917) has discussed the evolution of gastropod opercula briefly. He suggests that as the living 

pleurotomariids and trochids have a multispiral operculum, the course of operculum evolution has been from 

multispiral, through paucispiral, to lamellate forms. 

Ceratopea differs from the living pleurotomariids, however, in having a paucispiral rather than a multispiral 

operculum, and in having two muscles rather than one,

if the interpretation of muscle pits given above is correct. Evolution of the operculum thus may have gone 

to multispiral and lamellate forms as independent developments from a primitive paucispiral form.

THE ASSOCIATED SHELL AND THE NQMENCLATURAL 

PROBLEM

On many opercula the outer edge of the operculum is 

a reasonably close counterpart of the interior of the 

gastropod aperture that it closes. From the shape of 

the ceratopean operculum, it is possible to infer that the 

associated shell was a low-spired pleurotomarian gastropod. This conclusion is confirmed by three occurrences of opercula and well-preserved shells of this type.

In the ceratopean operculum, the carina is of prime 

importance. Presumably, it marks the trace of the interior angle formed by the juncture of the upper and 

outer lips, which was almost certainly on the periphery 

of the shell. The angle formed by the dorsal and ventral surfaces near the carina gives an approximation 

of the inclination of these two shell surfaces. Though 

it cannot be measured accurately, this angle is less than 

90°. In none of the known specimens does height exceed width. These two facts suggest a moderately lowspired to exceedingly low-spired shell.

The curvature of the carinal surface indicates a flattened to slightly convex upper whorl surface. Similarly, the curvature of the parietal surface suggests a 

parietal lip convex inward in relation to the axis of the 

shell. In turn, this almost necessitates a phaneromphalous shell, in some species widely so. The umbilical 

ridge of the operculum and the curvature of its ventral 

surface supply additional information about the shape 

of the Tower part of the shell aperture, but in many 

gastropods this part of the aperture is so thickened that 

curvature of the interior, as derived from study of the 

operculum, may not be accurate for reconstruction of 

the shell exterior.

Examination of the growth lines on the operculum 

suggests that the upper lip of the shell swept back 

smoothly from the suture, with curvature becoming 

more nearly tangential as the periphery is approached, 

and formed a V-shaped sinus with the outer lip at the 

periphery. It cannot be determined from the opercuhun whether this sinus culminated in a slit.

The description given above, derived from study of 

the opercula, suggests a typical low-spired pleurotomarian gastropod such as are common in the Ordovician. Unfortunately, it is not detailed enough to suggest any one genus, or even necessarily a single family.

Opercula of Ceratopea are alike in the following respects : all have a carina, though in some it is more distinct than in others; all are paucispiral to nearly
288 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

uncoiled; almost all grow to a large size. This operctilar form is unique in the Paleozoic, and indeed in the 

geologic record. For this reason a new family is proposed below to include gastropods which have this form 

of operculum.

From the opercula, species can be discriminated on 

differences of shape and on the character of the attachment surface. As discussed in the section on phylogeny, 

these species can be placed in five groups. The critical 

problem is the rank to be given to these five groups. 

The two extreme alternatives in interpretation are that 

either each group is independent and that Ceratopea is 

polyphyletic or that the groups are closely related and 

form a natural genus.

In the first interpretation, emphasis may be placed 

on the differences between the several species discussed 

under "Systematic paleontology." Available literature 

indicates that workers consider the apertural shape of 

Lower Ordovician gastropods to be an important generic character, which varies considerably among genera, 

but only in slight detail among species of the same 

genus. The opercular rim of the recognized species of 

Ceratopea appears to show such variation as would 

characterize several distinct genera. Accordingly, Ceratopea as used in the literature would be polyphyletic 

and would be a dumping ground for any Lower Ordovician operculum fitting the general size and shape defined. Ceratopea thus defined would have little or no 

biologic significance.

On the other hand, one may be impressed with the 

similarities shown by the several species. Except for 

Ceratopea? pygmaea Stauffer discussed in another part 

of this paper, the opercula are remarkably similar. It 

seems unreasonable to assume that this unusual opercular form developed independently in more than one 

genus of Lower Ordovician gastropods. Logically, 

then the genus with its several species must be natural 

and monophyletic.

Analogies with living gastropods provide little help 

with this problem. Turbo and its allies were examined, 

because they are characterized by a paucispiral calcified operculum. Within the family, a generalized opercular form characterizes many distinct genera. However, other closely allied genera or subgenera are each 

characterized by a distinctive operculum. If one had 

opercula alone, in some cases natural genera could be 

distinguished, in others they could not.

Study of the ceratopean operculum thus leads to an 

unsolvable taxonomic problem. Fortunately, it is possible to discuss the shell with which this operculum 

form is to be associated in more than the general terms 

given above.

For many years Bridge exhibited to his colleagues a

pleurotomarian shell fitting the general description 

given above, into the aperture of which he had glued 

an operculum of Ceratopea unguis, n. sp. According to 

Bridge's incomplete manuscript, silicified fragments of 

the gastropod are common at the long-abandoned Iowa 

mine on the west side of the Smithville-Imboden road, 

about 2 miles north of Smithville, Ark. Opercula of 

C. unguis, n. sp., are rare here but are abundant on the 

dumps of several abandoned prospect pits about half 

a mile further south. The strata are nearly horizontal, 

and it is presumed that the same zone is found at each 

locality. All collections were made from weathered 

material on the dumps, however, and as the shafts are 

now caved, there is no way of determining the depth 

from which the specimens were derived or whether 

more than one horizon is represented. The specimens 

are figured on plate 38, figures 8 and 9, and are instructive in showing the presumed orientation of the operculum in position of closure.

In west Texas Knight collected opercula of Ceratopea 

hami, n. sp., mixed with shells of a low-spired gastropod, from the upper part of the El Paso limestone. A 

partially etched block showing this assemblage is 

figured (no. 29) on plate 37. The gastropod again fits 

the general description given above. Yochelson revisited the area in 1956 but was unable to find additional 

specimens.

In 1956, Ham discovered an outcrop of the West 

Spring Creek limestone in the Criner Hills, Okla., 

which contained many silicified gastropods. All the 

shells are well preserved and all are referable to one 

species. Speciments are shown on plate 37. Opercula 

identified as Ceratopea buttsi, n. sp., also occur at this 

outcrop but are relatively rare.

Ham and Yochelson found another locality in Oklahoma containing numerous opercula of Ceratopea hami, 

n. sp. During acid solution, the same blocks yielded 

many incomplete shells. Most shells have only the 

umbilical region preserved, but a few show part of the 

basal surface. No specimens showing the upper surface were recovered. Some of the fragments hjavje 

sharp breaks, but others have the edges rounded from 

abrasion during transportation. One specimen is illustrated on plate 37, figure 26.

A single fragment of an umbilicus was also found in 

the West Spring Creek limestone at a locality which 

has yielded many opercula of Ceratopea ungids, n. sp. 

This is illustrated on plate 38, figure 6. Finally, scraps 

of gastropods were obtained in Maryland from the 

upper part of the Rockdale Run formation from the 

same blocks which also yielded opercula.

These six occurrences, only three of which contain 

well-preserved material, constitute the only known oc-
THE LOWER ORDOVICIAN GASTROPOD CERATOPEA 289

currences of gastropod shells and ceratopean opercula 

that have been found in nearly 50 years of collecting 

by American workers.

Though many occurrences of certopean opercula show 

sorting of the shells, the available geologic evidence 

suggests to the authors that the opercula and shells discussed above, though they may be sorted to a certain 

extent, are in each instance to be considered as a life 

association. Conclusive proof of biologic association 

of course can be obtained only by finding an operculum 

in place within the aperture of the shell. The probabilities of finding such a natural association are exceedingly small, although opercula have been found 

within the apertures of a few Paleozoic gastropods.

Comparisons between the shells in the three best preserved associations are complicated by the preservation 

of different growth stages in the Arkansas and west 

Texas shells. A summary of the differences is tabulated below.

Additional information about the shell of Ceratopea 

can be derived from study of the umbilical and basal 

shell fragments found by Ham and Yochelson. In 

the earliest stages they show steep umbilical walls and 

a strong circumumbilical cord. With increasing maturity, the walls become more strongly arched simultaneously with impression of the suture. At maturity 

the cord becomes less distinct and marks the juncture of 

the base and the curvature into the umbilicus. The immature stage of the umbilical area of the shell in this 

association and that in the west Texas association thus 

appear to be identical. It had previously been determined that the opercula from these two associations 

were conspecific. In this one case at least, the same 

opercular form occurs in the same type shell from two 

widely separated regions.

The other two assemblages provide little detailed information about the shell. The umbilical fragment 

from the Ceratopea unguis beds in Oklahoma shows 

some differences from the others described. In this 

specimen, the umbilical walls are gently arched, with

smooth sutures in the early stages. The mature stage 

has the walls more strongly arched and the sutures impressed. The Maryland specimens are so fragmentary 

that they cannot be compared with any of the other 

shells. They show a rounded juncture of base and umbilicus in a mature shell.

One must next evaluate the similarities and differences among these shells. As noted above, some workers make specific distinctions of Lower Ordovician gastropods based on slight variation, in extreme cases describing half a dozen species of a genus from a thin 

stratigraphic unit of limited extent. It is the opinion 

of Yochelson and of Bridge, shortly before his death, 

that so little attention had been paid to the population 

concept and individual variation that more specific 

names were proposed than are warranted. Some genera 

proposed may only be of specific rank, because of overrefinement of the systematics.

Yochelson concludes, that though the shells show 

some differences, these differences are considered to be 

slight and within the limits of one genus; other workers 

may consider these shells to represent distinct genera. 

In this regard, the locality found by Ham in Oklahoma 

is particularly significant, as it has yielded numerous 

well-preserved specimens, which for the first time allow 

one to gain an adequate idea of the range of individual 

variation within this shell form. This variation in the 

shell is reflected by individual variation among the 

opercula assigned to any one species.

Though associated shells and opercula of other species 

may not be collected for many years, Yochelson takes 

the position that the similarities among all the 

opercula and the shells that are known are more important than the differences. What evidence there is 

indicates a monophyletic origin for the ceratopean 

type of operculum. Accordingly, Ceratopea is here considered to be a natural genus. As a practical consideration, this is the simplest solution to a difficult taxonomic 

problem. In those three species for which the operculum and shell are believed known, the operculum has

Comparison of three shells

Oklahoma West Texas

Upper whorl surface___ Flattened in mature stage. ____ Gently arched, turning up slightly

in immature stage, less so in

mature stage. 

Selenizone_____________ Across periphery; broad_______ On upper surface at periphery;

very narrow. 

Outer whorl surface_____ Inclined near 60° at maturity__ Inclined near 50° at maturity.-__

Juncture of umbilicus and Weakly angulated in immature Sharply angular in immature 

base. stage, rounded at maturity. stage; slightly rounded at maturity. 

Umbilicus__________ Steplike; walls nearly vertical.- Sutures smooth, walls inclined.— Walls inclined; sutures unknown.

Moderately arched in immature 

stage.

On upper surface at periphery;

moderately broad. 

Inclined near 30° in immature

Sharply angular; a prominentcircumumbilical cord.
290 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

been chosen as type. This has the advantage of making 

the bulk of the material, the numerous opercula, readily 

identifiable by other workers, even though they may 

doubt the validity of the associations.

It is of course fundamental that an association of 

operculum and shell be found for Ceratopea keitM 

Ulrich, the type species. Until such an association is 

collected and studied, the classification of the several 

species as monophyletic remains clouded. Should the 

shell associated with the operculum of C. keithi not be 

congeneric with the shells described above, an idea 

considered but rejected in this paper, the ceratopean 

opercula will obviously be polyphyletic. It is hoped 

that no new genera or subgenera will be proposed within 

this group until additional occurrences of shell and 

opercula have been found and carefully evaluated.

On a lower taxonomic level, Ceratopea presents still 

another problem. Cloud and Barnes (1946, pi. 15) 

recognize C. capuliformis Oder in beds lower than C. 

robusta Oder, with some overlap of range. They suggest that the two forms be considered subspecies. The 

two forms do have essentially the same proportions 

but differ in size, G. robusta being the larger. Subspecific rank may be justified by the collections and 

stratigraphic information available for the Llano region of central Texas, but this information is lacking 

for other areas. Though subspecies may exist, it seems 

best to recognize none at this time. Overemphasis of 

one species would suggest that subspecies are not present 

in other species, and this can be determined only by 

examination of many additional specimens accurately 

located stratigraphically.

OTHER ORDOVICIAN OPERCULA

111 the past, Ceratopea has been confused with other 

calcified and secondarily silicified opercula occurring 

in Ordovician strata. Pondia Oder and Maclurites 

opercula are here differentiated from Ceratopea in an 

attempt to eliminate this confusion. Brevicone cephalopods also bear a resemblance to specimens of this 

genus, but they are only superficially similar, and are 

readily distinguished by the presence of a siphuncle, 

and by their bilateral symmetry.

Pondiia Oder is based on two opercula from the Jonesboro limestone in eastern Tennessee. Both specimens 

are of medium size, subcircular, and fairly flat, being 

thickest near the apex. The apex overhangs the margin of the operculum. Details of the inner surface cannot be observed. Pondia differs from opercula of Ceratopea in being much thinner, considerably wider and 

broader. After a restudy of the types, Knight (1941, 

p. 267) has suggested that Pondia might be the operculum of a species of Maclurites. Knight, Batten, and

Yochelson (in preparation) place Pondia in Archaeogastropoda incertae sedis. The holotype of Pondia is 

reillustrated on plate 35, figures 29 and 30,

Until the work of Cullison (1944), Ceratopea was 

considered to be the operculum of Maclurites or an allied genus. The operculum is known for nearly a 

dozen species of Maclurites. For the most part, these 

opercula are similiar to the operculum of M. logani 

(Salter), well illustrated and described by Salter 

(1859a, p. 8, pi. 1, figs. 2-6). In this form the apex is 

in the lower left quadrant, when viewed from the exterior, and is the locus of a short, thick eccentric cone 

encircled by several growth lines. The operculum is 

roughly shield-shaped, with the left margin excavated 

to fit the parietal lip. Although the apex is thickened, 

like Pondia, the operculum is considerably thinner than 

that of Ceratopea. Rarely are the proportions of the 

Maclurites operculum such as to be confused with that 

of the typical ceratopean operculum.

Aside from general shape, Maclurites opercula are 

readily differentiated from those of Ceratopea by the 

characteristic pronglike muscle process on the interior, immediately posterior to the apex and near the 

parietal margin. These opercula have another muscle 

attachment as a roughened area or short prong above 

the major prong and also near the parietal margin, but 

the ceratopean operculum has the muscle attachment 

in a pit or pits, rather than on a prong.

Billings (1865) figured and described three opercula 

from the Lower Ordovician rocks of Cape Norman, 

Newfoundland. Both he (Billings, 1865, p. 244) and 

Ulrich and Scofield (1897, p. 1041) commented on the 

absence of a muscle process from each of the Cape Norman specimens, but they did not realize its significance. 

Study of photographs and plaster casts of the original 

specimens of Billings' figures 228 and 230, obtained by 

Bridge, indicates that they are referable to Ceratopea. 

The third specimen (figure 229) appears to be a Maclurites operculum from which the muscle process has 

been broken.

Winsnes (1955, p. 20) suggested that the operculum 

of Maclurites peachii (Salter) from the Durness region 

of Scotland is referable to Ceratopea. The operculum 

is greatly thickened, and there is some superficial similarity, but the illustrations (Salter, 1859b, pi. 12, figs. 

1-5) clearly show the muscle process characteristic of 

Maclurites. So far as it is known no other European 

specimens have been considered members of this genus.

What appears to be a natural group of opercula includes the operculum of Maclurites profundus (Butts, 

1926, pi. 21, figs. 4-6), the operculum probably belonging to M. oceanus (Billings, 1865, p. 238), M. odenvillensis (Butts, 1926, pi. 18, fig. 26) a species known only
THE LOWER ORDOVICIAN GASTROPOD CERATOPEA 291

from its operculum, and another unnamed operculum 

(Billings, 1865, p. 243, figs. 229). In this group, the 

operculum is thicker, but narrower than that of the M. 

logani type. It is correspondingly more openly coiled 

and has a smaller vector angle. The apex is not encircled by growth lines, and the outer face is relatively 

smooth. Except for this last feature, this opercular 

form is superficially similar to the ceratopean operculum, but it is readily distinguished by its characteristic muscle prong. Further study may show that this 

group of opercula differ enough from the M. logani 

type to suggest that the species bearing them might 

form a subgenus or genus distinct from Madurites. 

The shells of these species should be compared closely 

with those of typical Maclurites.

Stauffer (1937, p. 56) described a diminutive operculum from the Shakopee dolomite of Minnesota, as 

Ceratopea? pygmaea. His types are not well preserved, 

but the general characters of this species can be observed. This form of operculum is also known from 

western Maryland (Sando 1957, p. 128). Similar opercula have been collected from Lower Ordovician strata 

near Spavinaw, Okla. A large chert slab collected from 

the Cotter dolomite, Christian County, Mo., bears numerous opercula similar to C.f pygmaea and many 

specimens of Orospira ftigranosa Butts in juxtaposition. 

One of these opercula is shown in the upper right corner 

of a reillustration of Orospira (Knight, 1941, pi. 75, fig. 

Ib). Parts of the slab mentioned above are illustrated 

on plate 38. The occurrence of Orospira with numerous 

small opercula in what appears to be an unsorted assemblage suggests that the shell and operculum might 

be associated in life.

Ceratopea? pygmaea and the other opercula mentioned above differ markedly from the genotype of 

Ceratopea, C. keitJii Ulrich, in being much smaller and 

slightly more compressed dorso-ventrally. Most important, they have a distinct sinus, or notch, developed 

at the proximal end of the carina, whereas in typical 

specimens of ceratopean opercula the ventral notch is 

wanting or only weakly developed.

In the writers' opinion these differences are of such 

magnitude as to suggest that Ceratopea? pyganaea and 

its allies are distinct from all Ceratopea, even those species based on opercula of the C.f pygmaea type should 

be excluded from Ceratopea and further, no new species based on opercula or the C.f pygmaea type should 

be named. Because of its small size and relative simplicity, it is not unlikely that several different species 

could bear this type of operculum without any differences being reflected in the operculum.

In his original description, Stauffer (1937) suggested 

that Ceratopeaf pygmaea might be questionably referred to a form identified as Raphistoma by him. 

Examination of Stauffer's types indicates the feasibility 

of this suggestion. Stauffer's specimens may not be 

correctly referred to Raphistoma, but better material is 

needed to clarify the identification. To preclude further nomenclatural difficulties, however, this species 

will be referred to as Ceratopea? pygmaea Stauffer, 

until additional evidence of its biologic placement is 

forthcoming. The species will be described here in 

order to illustrate how it differs from opercula of 

Ceratopea. The fauna of the Shakopee dolomite is 

currently being restudied (Kobert L. Heller, oral 

communication).

GEOGRAPHIC DISTRIBUTION

In the Appalachian area, specimens of Ceratopea 

have been illustrated from Lower Ordovician rocks in 

Tennessee, Georgia, Alabama, and Virginia. They are 

known from West Virginia (Woodward, 1951, p. 102- 

103). A few specimens have been collected in Maryland and Pennsylvania, but none has been found in New 

York State (Donald W. Fisher, oral communication). 

Further north, Ceratopea is known from western Newfoundland (Billings, 1865, p. 243) and Spitzbergen 

(Winsnes, 1955, p. 20).

In the midcontinent of the United States Ceratopea 

occurs in the Ozark region of Missouri, northern Arkansas, and northeastern Oklahoma. Ceratopea tennesseensis Oder has been identified in a core from a well 

drilled in Stafford County, Kans. Farther south, Ceratopea occurs in the Arbuckle and Wichita Mountains 

of Oklahoma (Chase, Frederickson, and Ham, 1956, p. 

52). It is also common in the Llano uplift of Texas.

Ceratopea has been found at Beach Mountain and in 

the Baylor Mountains near Van Horn, Tex., and in the 

Franklin Mountains north of El Paso, Tex. Kecently, 

K. L. Langenheim, Jr., (written communication) 

collected Ceratopea capuliformis Oder from Gunnison County, Colo., where it occurs near the top of one 

of the thickest known sections of the Manitou dolomite. 

He indicates that most of the portion of the formation 

which may have borne Ceratopea has been eroded in 

this area. This is the most westerly occurrence of 

Ceratopea so far known in North America.

The known geographic occurrence of the several species of Ceratopea is summarized in table 3.

STRATIGRAPHIC OCCURRENCE

The published record and the present study suggest 

that several distinct stratigraphic zones of Ceratopea 

may be recognized. These zones independently confirm interregional correlations based on stratigraphic 

succession and on other groups of fossils. Besides
292 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

TABLE 3.—Geographic distribution of species of Ceratopea as determined from published illustrations and collections studied

tennesseensis Oder_ _________

torta Cullison_ _____________

Ga.

X

X

X

Ala.

X

X

X 

X

Tenn.

X 

X

X

X 

X

Va.

X

X 

X

X

X

X

Md.

X

Pa.

X

X

X

X 

X

X

Mo.

X

X

X

X

X 

X

Ark.

X 

X

X

X

X

Oklahoma

Arbuckle

Mtns.

X

X 

X 

X 

X 

X 

X 

X 

X

X 

X

Wlehita

Mtns.

X 

X

X 

X

X 

X

Texas

Llano

X

X 

X

X 

X

X 

0)

West 

Texas

X

X 

X 

X

X

1 Cloud and Barnes (1946, p. 356) report Ceratopea tennesseensis Oder from highest ledges of the Honeycut formation but do not figure it.

several widespread species, others more restricted geographically appear to have local usefulness in mapping. 

The available stratigraphic information is summarized 

below and illustrated schematically in figure 103.

The stratigraphic sequence of Ceratopea zones in the 

Llano region of central Texas has been summarized by 

Cloud and Barnes (1946, pi. 14). A similar summary 

for the southern Missouri and northern Arkansas 

Lower Ordovician sequence was presented by Cullison 

(1944, pi. 2). These summaries are reproduced here as 

columns 2 and 4 respectively of figure 103. Certain 

changes in nomenclature of the species and identification of specimens, and correspondingly, in some of the 

ranges, have been introduced. These changes are discussed in this paper under the systematic^ or are listed 

in the proper synonymy.

A general section for west Texas has been prepared 

partly from the Beach Mountain section of Cloud and 

Barnes (1946, p. 352-361). This has been supplemented 

by an unpublished section of Beach Mountain measured 

by Knight, and by collections made by Knight and 

Bridge. Specimens of Ceratopea from the El Paso 

section of Cloud and Barnes have also been included 

in this regional summary. Ranges of Ceratopea species 

in this area are summarized in column 1 of figure 103.

Several collections from Arbuckle Mountains have 

been studied. All specimens are from sections measured 

by Ham. The ranges of species are given in the generalized section presented as column 3 of figure 103. The 

same general sequence of species is known from the 

Wichita Mountains, but the collections were made several decades ago and are not well documented stratigraphically.

The western Maryland section of Lower Ordovician 

contains few specimens of Ceratopea (Sando, 1957, p. 

127-128) ; all the available information is plotted in

column 6, figure 103. Rocks of similar age in West 

Virginia and Pennsylvania bear Ceratopea, but detailed information on the stratigraphic occurrence of 

the species is not available.

Bridge accumulated much information on the stratigraphic occurrence of Ceratopea in Tennessee. His 

death prevented completion and summarization of this 

work. All that is now available is the mention of a few 

species in one measured section near Kingsport, Term. 

(Bridge 1956, p. 51-53). Yochelson infers from this 

paper (p. 59) and another posthumous paper (Bridge, 

1955, p. 727) that another species of Ceratopea can be 

placed in the general sequence. Incomplete as it is, 

this is virtually the only published information available for the southern Appalachian region; it is presented as column 5 of figure 103. Oder (1934) described a section containing several species of Ceratopea in Tennessee. His specimens could not be found 

for study and, accordingly, are omitted. Ceratopea 

is known from Alabama and Georgia, but little detailed stratigraphic information is available and ranges 

of the species cannot be presented at this time.

In Tennessee, Rodgers and Kent (1948, p. 1 and 26), 

aided by Bridge, and Bridge himself (1956, p. 54) reported the occurrence of Ceratopes capuliformis Oder 

in the Kingsport formation, but its position in the 

formation was not given. They (Rodgers and Kent, 

p. 28, Bridge p. 58) also record that the Mascot dolomite 

includes three zones of Ceratopea, C. keitM Ulrich, C. 

tennesseensis Oder, and an unnamed species, later identified (Bridge 1956, p. 59) as C. ankylosa Cullison.

Sando (oral communication) collected Ceratopea 

from an incomplete section of the Mascot dolomite exposed on the north bank of the East Fork of the Little 

Pigeon River, 0.5 mile due east of the covered bridge 

at Harrisburg, Tenn. Ceratopea JeeitJii Ulrich occurs
THE LOWER ORDOVICIAN GASTROPOD CERATOPEA 293

1. WEST TEXAS

Cloud and Barnes, 1946; 

Knight, unpublished

|

1

0)

c

o

<u

o

I

LLJ

r ———————————— 

U -g

• §

O

•a

1

i

| 1 |

3 O » •S • •

u

\

2. LLANO UPLIFT

Cloud and Barnes, 1946, 

modified

—— ——————— jj- 1 18 —

o s

< Ij

I 11 I

1 fill in=380 i 0 € , ,ii I I

I .g • §

u

1

2. ARBUCKLE MOUNTAINS

Ham, unpublished

c

o

4=

ro

E

o>

o>

O

00

.«

Q. in

i

c

'+->o

as

E

a

Kind blade

o

,1

5, '

|

«o

o

I 1 • o

I •

IO

1Q

.13

c |

aj ^

II

o

1

!|!t ••ii

o

•a .a 05

a E ""-S if

4. OZARK UPLIFT

Cullison, 1944, 

modified

«c

i= O

>*= 11

= o |'f

•S

0

IS

E

V

0

o

If1*E 1"1

£c 

o

"0°

§

o

1-

1

O

1

Eg

Ipl £"S

Bliss(?) Gorman Cool Creek

sandstone formation formation

•a

E

5

s

I

S

0

7

5 

a 'S §* 

§ 0

s • o. I

1' 

1

!

u

1 a

1

5. EASTERN TENNESSEE

Oder, 1932; Bridge, 1955, 

1956; Sando, unpublished

1

o

1

.•tH

o 

o

13

•a

O a ^ 

| .a 1 | |

:| o U „

s" "

0

•«- •.»

•c i

| |

QO |

i2 o

6. WESTERN MARYLAND

Sando, 1957

o

to

E

.0

c:

cn

0) "ro

T3

O

0 

CC

Iv5i

§

0

•a

^

|

o

1

Roubidoux Longview Stonehenge

formation limestone limestone

-2400'

2000'

FIGURE 103.—Stratigraphic occurrence of Ceratopea species in Lower Ordovician rocks of the United States. Datum is base of 

lowest formation containing Ceratopea. All formations to the same scale. Queries indicate placement, not identification.

428755—57———8
294 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

in the lowest exposures and G. keithi and O. subconica 

Oder occur 10 feet above stratigraphically. About 30 

feet above these fossils a specimen of O. tennesseensis 

Oder was collected. By presuming that the occurrence 

of G. keithi noted by Bridge (1956, p. 51), is at the same 

stratigraphic level, in both this and Bridge's section, 

Yochelson added these two other species to column 5 

of figure 103. Ceratopea tennesseensis Oder is known 

to range through part of the section, but its limits cannot now be determined, as all other collections studied 

are from residual soils rather than bedrock.

Shortly before his death, Bridge examined many of 

the collections from the Arbuckle Mountains used in 

this study. At the time, he prepared a six-page typescript with remarks on correlation with other regions. 

This typescript and the additional information noted 

above form the basis for a general summary. The best 

documented and most nearly complete sequence of Ceratopea specimens available for this study is from the 

Arbuckle Mountains.

The lowest zone generally recognized is that of Geratopea capuliformis Oder. This species is common in the 

basal 300 feet of the Kindblade formation of Oklahoma. 

It is characteristic of the Kingsport formation in Tennessee and is represented in the Rich Fountain formation of Cullison (1944) in Missouri. It is common in 

the lower part of the Honeycut formation of central 

Texas.

Geratopea incurvata, n. sp., occurs above G. capuliformis Oder, with the ranges of the two species overlapping. Nevertheless, G. incurvata is so common that 

it may be considered as marking another distinct zone; 

it occurs in the Kindblade and Honeycut formations 

and El Paso limestone. Geratopea germana, n. sp., is 

also present but rare in this zone, occurring in the 

Kindblade formation and the Theodosia formation of 

Cullison (1944). G. corniformis Oder ranges through 

both overlapping zones; locally it is a common fossil.

Geratopea tennesseensis Oder occurs in the upper 

part of the Kindblade formation. This species is characteristic of the lower part of the Mascot dolomite in 

Tennessee and the lower part of the Cotter dolomite in 

Missouri. It also occurs below the middle of the El 

Paso limestone. In the Kindblade formation, G. tennesseensis Oder occurs in two separate levels; a single 

lower occurrence is known. Too little detailed information from other areas is available to show whether 

the specimens have similar stratigraphic distribution 

elsewhere. In one collection from the Newala limestone of Alabama G. keithi, G. tennesseensis, and G. subconica have been identified.

Bridge has noted (unpublished manuscript) that G. 

keithi Ulrich is associated with G. tennesseensis Oder

in Tennessee but occurs at a slightly different horizon 

(Rodgers and Kent, 1948, p. 28). In the Arbuckle and 

Wichita Mountains G. keithi Ulrich occurs near the 

lowest occurrences of G. tennesseensis Oder. The 

available information is not sufficient for discrimination of a zone of G. keithi at this time.

In the West Spring Creek formation and its correlatives, the lowest zone is that of Geratopea ankylosa 

Cullison. In Oklahoma most specimens come from two 

levels, one about 175 feet above the base, and the second 

about 400 feet above the base, but scattered specimens 

occur between. G. ankylosa occurs near the middle of 

the Cotter dolomite in Missouri. It also occurs in 

Tennessee, but because of erosion of the upper part of 

the Mascot dolomite and the discontinuity of exposures, it is difficult to determine the precise stratigraphic interval between it and the occurrence of the 

next older species.

Geratopea buttsi, n. sp., occurs above G. ankylosa in 

the West Spring Creek formation and is a distinctive, 

locally useful fossil. It has been found in Virginia, 

but its stratigraphic position there is not well known. 

Geratopea knighti, n. sp., is known from one locality 

within this zone.

Geratopea hami, n. sp., is known from west Texas and 

the Arbuckle Mountains. In this latter area, the species occurs in the northern f acies only and has not been 

found in the southern f acies. Some evidence indicates 

that the species occurs a considerable distance stratigraphically above G. buttsi, n. sp., though more information is needed before its stratigraphic position can 

be fixed.

The highest zone is that of Geratopea wiguis, n. sp. 

In the Arbuckle section this form has a relatively long 

range. In west Texas, the species occurs about 50 feet 

below the top of the El Paso limestone on Beach Mountain. G. unguis occurs in Maryland in the upper part 

of the Rockdale Run formation. It occurs in Arkansas, Virginia, and Pennsylvania, but like other species, 

its stratigraphic position in these States is not well 

known.

PHYLOGENY

Examination of the several species based on opercula 

referred to Geratopea suggests that they can be divided into five more or less distinct groups. Differentiation among the groups of opercula is commonly easier 

than distinction among the species of any one group. 

The groups are not formally named but simply referred 

to by the name of the best known species included. 

Grouping aids in identification of the species by emphasizing similarities. A tentative phylogeny of Gera-
THE LOWER ORDOVIOIAN GASTROPOD CERATOPEA 295

C. unguis

C. hami

C. buttsi

C. tennesseensis

^C. subconica

C. keithi

7

\ ^. C. germana 

C. incurvata

\

C. knighti c ankylosa

C. torta

C. comiformis

C. capuliformis

C. arietina

FIGURE 104.—Suggested phylogeny of Ceratopea species based on stratigraphic occurrence and morphologic similarity.

topea, based on morphology and stratigraphic sucession 

is outlined in figure 104. In the present state of our 

knowledge, it is difficult to join these groups, as one 

does not know which features of morphology are most 

significant. For example, the G. keithi and C. capuliformis groups show less torsion than the others, but the 

C. keithi group shows the least curvature and the G. 

capuliformis group, the most. Again the G. comiformis and G. keithi groups each have a distinct carina 

but differ markedly in curvature. Assumptions have 

been made that torsion and sharpness of carina are 

most important, but as in any other phylogeny they are 

only assumptions and may not be correct.

The group first appearing in the geologic record is 

that of Geratopea capuliformis Oder. This includes 

G. arietina, G. incurwata, and G. germana, all new 

species. Opercula of all species are strongly incurved, 

commonly completing nearly one full volution. They 

are measurably wider than high; so the opercular rim is 

oval. The attachment surface appears to be smooth or

with a single indistinct pit near the notch. Morphologically the group is the most closely knit of the five 

recognized. The species show a progressive reduction 

in torsion through time. For this reason the group is 

assumed to have given rise to the relatively untorted 

G. keithi group.

Geratopea keithi and its allies, G. subconica Oder and 

G. tennesseensis Oder, appear in rocks younger than 

those containing G. capuliformis and its associates. 

Specimens of this group are very little curved and only 

slightly torted. They expand rapidly, the width being 

greater than the height. This shape and the sharp 

carina together produce a distinctly lenticular opercular rim. The attachment surface has either a shallow muscle pit or a groove deepening near the notch.

The group of Geratopea comiformis Oder appears 

first within the stratigraphic range of G. capuliformis 

and its members constitute the longest ranging of the 

groups. They include G. torta Cullison and G. ~buttsi, 

n. sp. Opercula are markedly torted and show a sharp 

carina, at least in the earlier growth stages. The specimens show little curvature. The attachment surface is 

oval in outline and commonly shows a single deep pit. 

Differences between them and the G. capuliformis group 

are large enough to suggest that the two may be independently derived from a common ancestor rather than 

being more closely related.

The fourth group is that of Geratopea unguis, n. sp., 

and includes G. hami and G. knighti, both new. Though 

these opercula are also thickened, they lack the sharp 

carina of the G. comiformis group and are somewhat 

less curved than members of that group. The opercular 

rim is oval, but height approaches width in a few of the 

narrow specimens. Some individuals show a second pit. 

The species of this and the G. comiformis group are 

similar enough in being thickened and little torted to 

suggest that they may be closely allied.

Finally, the fifth group recognized is that of Geratopea ankylosa Cullison. This species is distinguished 

from the others in that the attachment surface clearly 

shows two deep muscle pits separated by a ridge. The 

operculum is curved but does not complete more than 

one-fourth of a volution; torsion is distinct. Width expands with age, giving the operculum a hook-shape, but 

the height remains relatively very low. The carina is 

so poorly developed that the opercular rim has the general shape of a greatly elongated irregular ellipse. 

Derivation of C. ankylosa from the C. unguis group 

through a form similar to C. knighti, n. sp., is tentatively suggested. The unique attachment surface of G. 

ankylosa may indicate, however, that this species is 

another branch from a common ancestor.
296 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

SYSTEMATIC PALEONTOLOGY

Glass GASTROPODA

Subclass PROSOBRANCHIA

Superfamily PLETTROTOMARIACEA

Family CERATOPEIDAE Yochelson and Bridge, new family

Diagnosis.—Low-spired to lenticular pleurotomarians, with a calcined, thickened, operculum; shell low 

spired, and distinctly phaneromphalous; a slit located 

at the periphery; operculum paucispiral, in most species not completing one whorl, exceedingly thickened, 

and with a cuplike depression at lower end, containing 

one or two muscle pits; operculum sinistrally torted, 

the torsion most conspicuous on carina; ornament of 

shell and operculum, prominent growth lines alone.

Discussion.—The features of the shell suggest that 

this family be placed close to the Kaphistomatidae 

which are also characterized in part by a well-developed 

anal emargination. The family is particularly close to 

the Liospiridae, whose members have a lenticular shell, 

but differs from it in being more widely phaneromphalous, and in possessing a thickened, calcified operculum.

Genus GERATOPEA Ulrich, 1911

Type species.—Ceratopea keithi Ulrich, 1911. 

Ceratopea Ulrich, 1911, p. 665; Oder, 1932, p. 139; Wenz, 1938, 

p. 211; Gullison, 1944, p. 60-61; Knight, 1944, p. 447.

Diagnosis.—With the characters of the family.

Discussion.—As a matter of convenience, the notation 

that the species is known only from the operculum has 

been omitted from most species descriptions. For convenience in comparison, species have been described in 

stratigraphic order within the groups discussed in the 

section on phylogeny, and the groups themselves are 

arranged as discussed in that section.

Length, width, and height of all formerly illustrated 

specimens, and those illustrated herein are tabulated on 

page 285, following the specific descriptions. Measurements were taken with a vernier caliper.

Geratopea arietina Yochelson and Bridge, n. sp.

Plate 36, figures 1-4 

Ceratopea sp. 1, Cloud and Barnes, 1946, pi. 43, figs. 1-4.

Description.—Small, strongly incurved opercula; 

carina distinct but not sharp, relatively more ventral 

than in other species; other ridges wanting; carinal 

and parietal surfaces strongly inflated, the parietal surface not clearly set off; ventral surface very gently 

convex to concave; completing more than one whorl; 

strongly incurved so that apex almost touches parietal 

surface; distinctly torted; opercular rim not known 

in detail, but with a shallow ventral notch and little,

if any, development of prong; attachment surface relatively deep and probably smooth.

Discussion.—Opercula of Ceratopea arietina differs 

from those of O. mcurvata n. sp. and G. germcma n. sp., 

in being more strongly torted. These opercula bear 

some similarity to those of G. capuliformis Oder but 

are differentiated by the ventral surface being flattened 

to concave, and by the carina being much lower on the 

side. All known species of G. arietina are less than 

half the size of average specimens of G. capuliformis 

(see p. 285).

Geratopea capuliformis Oder 

Plate 35, figures 1-5, 9; plate 36, figures 5-8, 10

Ceratopea capuliformis Oder, 1932, p. 143-144, pi. 14, figs.

1, 5, 6.

Ceratopea robusta Oder, 1932, p. 142-143, pi. 13, figs. 9-11. 

Ceratopea capuliformis Oder. Oullison, 1944, p. 63, pi. 31,

figs. 7-12. 

Ceratopea capuliformis Oder. Knight, 1944, p. 447, pi. 181,

figs. 11-13. 

Ceratopea capuliformis capuliformis Oder. Cloud and Barnes,

1946, pi. 43, figs. 5-10. 

Ceratopea capuliformis robmta Oder. Cloud and Barnes, 1946,

pi. 43, figs. 11-13.

Description.—Strongly curved, distinctly torted, relatively thick opercula; apex torted upward, not touching parietal surface; commonly completing nearly threefourths of a whorl; carina distinct and sharp, becoming 

slightly less sharp with maturity, other ridges lacking ; 

dorsal and ventral surfaces distinctly inflated; opercular rim thickened only at parietal margin; parietal 

margin sinuate; dorsal angle near 130°; distinct prong 

developed on ventral margin just ibelow carina; muscle 

pit just above wide, shallow notch.

Discussion.—The strong curvature readily separates 

this operculum from that of all others except Ceratopea 

incurvata, n. sp. The operculum of Ceratopea capuliformis Oder is distinguished from that of C. incurvata 

by its greater torsion, particularly near the apex. Incomplete specimens of the two species, preserving only 

the mature portion, cannot be distinguished with certainty.

Ceratopea robusta Oder appears to be identical with 

C. capuliformis Oder, except that it is somewhat larger. 

Cloud and Barnes, (1948, pi. 14) note that the larger 

form characterizes younger beds than does the smaller 

form. The two overlap slightly in rang© in the Llano 

area, and for this reason they are not recognized here 

as distinct. If a clear stratigraphic separation, or only 

a consistent slight overlap, can be recognized in other 

areas, G. robusta might eventually be recognized as a 

larger subspecies of C. capuliformis.
THE LOWER ORDOVICIAN GASTROPOD CERATOfEA 297

Ceratopea iiicurvata Yoehelson and Bridge, tt. sp.

Plate 36, figures 42-46 

Ceratopea sp. 5, Cloud and Barnes, 1946, pi. 43, figs, 18-21.

Description.—Strongly incurved, slightly torted, 

thickened opercula; carina relatively sharp; carina] 

and parietal surfaces flattened but without a dorsal 

ridge; strongly incurved so that apex nearly touches 

parietal wall; only slightly torted; parietal margin 

very gently sinuate; dorsal angle near 140°; carinal 

margin straight except bending sharply downward near 

carina; ventral margin having a short prong starting 

at carina; notch exceedingly wide and shallow; attachment surface smooth, with only a shallow obscure 

muscle pit near the notch.

Discussion.—Ceratopea incurvata opercula are similar to those of G. capuliformis Oder but differ in being 

so much less strongly torted that the apex nearly touches 

the parietal surface rather than projects above it. Geratopea incurvata has nearly the same torsion as G. germana, n sp. but differs from that species in being more 

strongly incurved. Typically, opercula of both these 

species are relatively wider than those of G. capuliformis Oder, but there is much individual variation 

in this feature.

Ceratopea germana Yochelson and Bridge, n. sp. 

Plate 36, figures 6, 7, 11-13

Ceratopea, subconica Oder. Cullison, 1944, p. 63, pi. 31, figs. 

34-36.

Description.—Thickened, distinctly curved, relatively narrow opercula; carina distinct, but not sharp; 

dorsal and umbilical ridges lacking, so that all surfaces 

are gently inflated; strongly curved, completing nearly 

one-half whorl, but with the apex distinctly separated 

from the parietal surface; relatively narrow, maintaining nearly the same width for most of its thickness; 

parietal and carinal margins nearly straight, dorsal 

angle more than 150°, probably near 160°; prong poorly 

developed; attachment surface with a single pit just 

dorsal and inward from the narrow notch.

Discussion.—Geratopea germana differs from G. incurvata, n. sp., the only closely similar species, in being 

much less strongly curved, so that the apex does not 

approach the parietal wall. The species is rare, being 

known only from a few well-preserved specimens and 

several poor specimens from the Arbuckle Mountains, 

and a single specimen from Missouri.

Ceratopea keithi TTlrich 

Plate 35, figures 28, 31-33; plate 36, figures 31, 32,41, 42

Operculum of undetermined gastropod, Bassler, 1909, pi. 20,

fig. 3. 

Ceratopea keithi Ulrieh, 1911, p. 665.

Ceratopea keithi Ulrich. Bassler, 1919, p, 299-300, pi. 26, fig. 15. 

Ceratopea Jceithi Ulrich. Butts, 1926, pi. 18, figs. 5, 6. 

Ceratopea Jceithi Ulrich. Oder, 1932, p. 139-140, pL 13, figs.

13-16.

Ceratopea keithi Ulrich. Butts, 1941, pi. 72, figs. 5, 6. 

Ceratopea jonesi Cullison 1944, p. 63-64, pi. 31, figs. 31-33, 

Ceratopea supraplana Cullison 1944, p. 64, pi. 21, figs 25-30. 

Ceratopea keithi Ulrich. Knight, 1944, p. 447, pi. 181, figs. 5-10,

Description.—Thick, little curved and gently torted 

opercula; carina sharp; umbilical ridge indistinct, dorsal ridge wanting; dorsal surface gently inflated, parietal surface flattened; opercula thick and relatively 

wide, gently pointed and little curved at apical end; 

opercular rim thickened on ventral margin above notch, 

and thickened and excavated on parietal margin; parietal margin gently sinuate; dorsal angle near 150°; 

carinal margin nearly straight, with only slight development of prong; notch relatively wide and shallow; attachment surface having a single pit.

Discussion.—The operculum of Geratopea keithi is 

thicker and narrower than that of G. tennesseensis Oder. 

Oeratopea keithi is closely similar to G. subconica Oder 

but is differentiated from that species by being less 

strongly curved, particularly in the early portion, and 

by being relatively wider. Most specimens appear to 

be triangular in dorsal view, with nearly straight sides, 

whereas G. subconica Oder always shows a distinct if 

slight, curvature of the carina. G. keithi is slightly 

variable in curvature and relative width, but the species 

appears to be distinct. Cloud and Barnes (1946, p. 458) 

suggested that G. keithi and G. subconica be reduced to 

subspecific rank. The two forms can be distinguished 

at one locality in Tennessee, without any intergrades 

being noted. It has been the practice in this paper to 

recognize no taxa smaller than species, pending the 

availability of more specimens better documented 

stratigraphically.

Geratopea supraplana Cullison is based on specimens 

approximately half the size and slightly less curved 

than typical specimens of G. keithi. All specimens of 

G. supraplana are worn, and some appear to be crushed. 

When the preservation of the specimens is taken into 

account, G. supraplana appears to be a junior synonym 

of G. keithi.

Ceratopea subconica Oder 

Plate 35, figures 17-22, 26, 27; plate 36, figures 35, 36, 39, 40

Ceratopea keithi Ulrich. Butts, 1926, pi. 18, figs. 7, 8. 

Ceratopea subconica Oder, 1932, p. 147-148, pi. 14, figs. 15-17. 

Ceratopea sulcata Oder, 1932, p. 146-147, pL 14, figs. 9-13. 

Ceratopea jonesi Cullison, 1944, p. 63-64, pi. 31, figs. 31-33. 

Ceratopea inflata Cullison, 1944, p. 64, pi. 31, figs. 39-41. 

Ceratopea keithi subconica Oder. Cloud and Barnes, 1946, pi.

43, figs. 22-24. 

Ceratopea sulcata Oder. Alien and Lester, 1954, pi. 3, figs.

15, 19.
298 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

Not Ceratopea subconica Oder of Cullison, 1944, p. 63, pi. 31, 

figs. 34-36, or Butts, 1942, pi. 72, fig. 8.

Description.—Thickened, distinctly curved, and gently distorted opercula; carina sharp; umbilical ridge 

distinct, dorsal ridge wanting; parietal and carinal surfaces very gently inflated, almost flat; parietal margin 

straight; dorsal angle near 150° in early stages, increasing with maturity; carinal margin straight except for 

a small sinus near carina; notch shallow; attachment 

surface smooth, with a single pit.

Discussion.—Ceratopea subconwa opercula differ 

from those of C. tennesseensis Oder in being much 

thicker and less curved. They differ from those of 0. 

keithi Ulrich in being more strongly curved, particularly in the apical portion. Typically, C. subconica has 

relatively the narrowest opercula of these three species, 

but specimens are known that are wider than the narrowest specimens of the other two species. G. subconica 

and G. keitM are probably the most difficult species to 

distinguish from worn specimens. The specimen 

figured approaches that species closely in curvature; 

Oder's type diverges markedly from it.

The type specimens of Ceratopea subconica and C. sulcata Oder are badly worn. There are some slight differences between the specimens, but they have in common a relatively strongly curved early portion. The 

name C. subconica is preferred because the type specimen is better preserved. On the basis of this curvature 

the two species are considered to be synonymous. The 

type of G. mflata Cullison is also badly worn but again 

appears to be conspecific with C. subconica. The holotype of C jonesi Cullison, although it is slightly less 

curved, is without question, conspecific with the type of 

C. subconica Oder.

Ceratopea tennesseensis Oder 

Plate 35, figures 6-8, 10-16; plate 36, figures 33, 34, 37, 38

Ceratopea, tennesseensis Oder, 1932, p. 142, pi. 13, figs. 4, 8, 12. 

Ceratopea calceoliformis Oder, 1932, p. 141, pi. 13, figs. 5-7. 

Ceratopea cuneata Oder, 1932, p. 144-145, pi. 13, figs. 1-3. 

Ceratopea oompressa Oder, 1932, p. 145-146, pi. 14, fig. 14. 

Ceratopea tennesseenis Oder. Butts, 1942, pi. 72, fig. 7. 

Ceratopea jenkinensis Cullison, 1944, p. 61-62, pi. 31, figs. 1-6. 

Ceratopea tennesseensis Oder. Cullison, 1944, p. 62-63, pi. 31,

figs. 37-38. 

Ceratopea tennesseensis Oder. Knight, 1944, p. 447, pi. 181, figs.

14-16. 

Ceratopea cf. C. calceoliformis Oder. Alien and Lester, 1954, pi.

3, fig. 14.

Description.—Eelatively thin, rapidly expanding, 

slightly curved to well-curved opercula; carina sharp, 

very slightly torted; umbilical ridge poorly developed 

or absent; dorsal ridge distinct; carinal and parietal 

surfaces gently inflated; opercular rim thickened, being 

thickest at the parietal margin and within the notch of

the ventral margin; parietal margin sinuate; dorsal 

angle near 125°; carinal margin nearly straight except 

for an exceedingly shallow narrow sinus near carina; 

notch relatively wide; attachment surface with a single 

elongated pit.

Discussion.—Opercula of Geratopea tennesseensis 

Oder are most similar to those of G. subconica Oder, 

but differ in being thinner and somewhat more curved. 

They are much thinner and are more strongly curved 

than are those of G. Jceithi Ulrich. Opercula of G. tennesseensis show more variation in shape than many of 

the other species: some specimens are relatively narrow 

and others widely cuneate. In spite of this individual 

variation, it is probably the most easily identified 

species of Geratopea.

Examination of the holotypes of both Geratopea calceoliformis Oder and G. jenkenensis Cullison suggest 

that these species are based on specimens from which 

the floor of the attachment surface was removed before 

silicification. Cullison (1944, p. 61) considered this 

possibility before naming G. jenkenensis, but rejected 

it. Geratopea compressa Oder has as its type a large 

specimen which appears to be badly crushed. Geratopea 

cuneata Oder is based on specimens which have the 

apex worn. All the specimens noted above appear to 

fall well within the limits of variation of G. tennesseensis as recognized here, and accordingly, their specific names have been placed in synonymy.

Ceratopea corniformis Oder 

Plate 35, figures 23-25; late 36, figures 14-17

Ceratopea corniformis Oder, 1932, p. 146, pi. 14, figs. 2-4. 

Ceratopea sp. 4, Cloud and Barnes, 1946, pi. 43, figs. 14-17.

Description.—Thick, well-curved opercula, with inflated parietal surface; carina poorly developed to wanting, other ridges wanting; dorsal, parietal, and ventral 

surfaces distinctly inflated; well curved, especially in 

the juvenile portion; gently torted; width expanding 

rapidly from apex for short distance, then expanding 

gradually less rapidly; dorsal angle 180°; prong wanting; notch exceedingly shallow and relatively wide; 

attachment surface having a single deep narrow pit.

Discussion.—Opercula of Geratopea corniformis 

Oder are less torted and more rounded in outline than 

those of G. torta Cullison. The species is more strongly 

curved than G. buttsi, n. sp. It is similar in curvature 

and relative width to G. unguis, n. sp., but differs from 

that species in having the parietal surface convex rather 

than concave and by being relatively narrower. The 

holotype is much smaller and less well preserved than 

specimens from Oklahoma and Texas. No major differences were observed, however, and the concept of the 

species has been expanded to receive them. The Okla-
THE LOWER OEDOVICIAN GASTROPOD OERATOPEA 299

homa specimens indicate that there is some slight variability in curvature at maturity,

Ceratopea torta Cullison 

Plate 36, figures 18-24 

Ceratopea torta Cullison, 1944, p. 63, pi. 31, figs. 19-24.

Description.—Greatly thickened, strongly torted 

opercula; carina sharp; umbilical ridge Weak, dorsal 

ridge wanting so that dorsal surface is gently inflated j 

strongly torted, but only gently curved, widening very 

gradually; parietal margin having a broad shallow 

sinus; carinal margin straight; ventral margin straight 

except for a very short prong; attachment surface having a single pit above a relatively shallow notch.

Discussion.—The strong torsion of the operculum of 

this species, together with the sharp carina, readily 

distinguishes it from all others. In addition, Ceratopea 

torta, Cullison is relatively narrower than G. buttsi, n. 

sp., C. unguis, n. sp., and C. comiformis Oder and it is 

less strongly curved than the last two named species.

Ceratopea buttsi Yochelson and Bridge, n. sp. 

Plate 36, figures 25-30; plate 37, figures 27, 30, 31, 33, 34 

Ceratopea subconica Oder. Butts, 1941, pi. 72, fig. 8.

Description.—Lenticular gastropods with a narrow selenizone and, thick, gently curved, gradually 

widening opercula; carina of operculum a poorly developed ridge, umbilical and dorsal ridges weak to 

wanting; parietal surface of operculum concave, carinal surface convex; slightly torted, gently curved, and 

widening very gradually; parietal margin straight; 

opercular carinal margin having a slight sinus and a 

wide shallow prong, ventral notch so shallow as to be 

almost wanting; attachment surface having a single 

narrow exceedingly deep pit.

Shell lenticular, the upper whorl surface gently 

arched except near periphery where, in immature stage, 

it bends upward, this bending gradually decreasing 

with maturity; growth lines curving back strongly from 

suture to an exceedingly narrow selenizone on upper 

surface at the periphery below the selenizone, the growth 

lines curving forward and then proceeding straight 

downward so that they enter the umbilicus normal to 

the circumumbilical ridge; umbilical sutures smooth, 

the umbilical wall straight and steeply inclined; base 

with a sharp circumumbilical angulation becoming 

somewhat rounded in maturity; ornamented by strongly 

impressed growth lines on basal surface and fainter 

growth lines on upper surface.

Discussion.—The opercula of Ceratopea buttsi differs from that of C. unguis, n. sp. and C. comiformis 

Oder by being less strongly curved and by being relatively slightly narrower. It differs from that of C. 

torta Cullison by being less torted, relatively wider, and 

lacking a sharp carina. Specimens of C. ~buttsi opercula are some of the thickest known, but unlike thick 

mature opercula of C. unguis they do not show much 

wear of the juvenile portion. The shell is compared 

with others on page 289.

Ceratopea ankylosa Cullison

Plate 37, figures 1-6 

Oeratopea ankylosa Oullison, 1944, p. 62, pi. 31, figs. 13-18.

Description.—Low to moderately low, wide, rapidly 

expanding, distictly torted opercula; carina poorly developed ; dorsal and umbilical ridges, wanting; parietal 

surface distinctly concave, carinal surface convex; 

strongly curved, distinctly torted, the width increasing 

markedly in relation to thickness; parietal margin 

straight; dorsal angle wide and indistinct, probably 

near 160°; carinal margin with a sinus at carina; ventral margin straight for most of its length, with weak 

development of a notch near parietal surface; attachment surface with a deep pit near the notch, and a 

second shallower pit near the sinus, the two pits being 

connected by a distinct groove crossing a shelf like area 

between the pits, the attachment surface as a whole 

being shallow and bending abruptly out of one plane 

at this shelf area.

Discussion.—This species shows some variation in 

shape, the same population including both relatively 

narrow and extremely wide specimens. Though the 

type is narrow, the abundance of specimens indicates 

that the wide form is more typical. The narrower 

specimens can be separated from opercula of C. hami, 

n. sp., by being more strongly curved in the earliest 

portions and expanding in width more rapidly. A 

few specimens superficially resemble C. tennesseensis 

Oder, but opercula of that species have a sharp carina, 

are less torted, and have a single muscle pit.

Considerable difficulty arose at one time during this 

investigation in differentiating specimens of this species 

from wide opercula of C. unguis, n. sp. Indeed, incomplete specimens or those exposed only partially 

from the rock cannot be differentiated with certainty. 

They can be distinguished by three features: C. ankylosa is more torted, has a more strongly curved apex, 

and has two muscle pits with a shelflike area between. 

The character of the attachment surface seems to be 

most important. Though some specimens of C. unguis 

have two pits, they are commonly in a relatively deep 

attachment surface. In 0. ankylosa this surface is 

shallow, except in the vicinity of the pits, and shows a 

fairly abrupt bend at the shelf area between the pits.
300 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

Ceratopea knighti Yochelson and. Bridge, n. sp. 

Plate 37, figures 7-10

Description.—Well-curved, slightly torted opercula; 

carina indistinct; umbilical and dorsal ridges weakly 

developed to wanting; parietal surface wide, flattened, 

carinal and ventral surfaces gently inflated; ventral 

margin having a wide notch; parietal margin straight, 

joining carinal margin at an angle near 150°; carina 

ending in a distinct prong; attachment surface shallow, 

with a small pit near notch and a long shallow groove.

Discussion.—Opercula of this species bear some similarity to those of Ceratopea tennesseensis Oder in general cuniform shape, but they differ in having a more 

strongly curved apical area and in lacking a sharp 

carina. Ceratopea knighti opercula also bear resemblances to those of C. ankylosa Cullison, but differ by 

being less torted and by being less curved and narrower. 

The species is rare, being known only from a single 

locality where it is represented by three specimens.

Ceratopea hami Yochelson and Bridge, n. sp. 

Plate 37, figures 15-18, 25, 26, 29, 32

Description.—Lenticular gastropods with a sharp 

circumumbilical cord and strongly curved, relatively 

low operculum with two muscle pits; carina of operculum wide but distinct; dorsal and umbilical ridges 

wanting; parietal surface of operculum flattened to 

gently concave, dorsal surface gently convex; operculum strongly curved, distinctly torted with width increasing gradually, approximately twice the height; 

parietal margin of operculum straight, dorsal angle 

near 150°, carinal margin straight except for a shallow 

sinus formed by sharp bending of opercular rim near 

carina, so that a distinct prong is formed; operculum 

ventral margin with an exceedingly shallow notch; attachment surface having a deep pit near the notch, and 

a wider shallow pit near dorsal sinus, the two pits 

being connected by a shallow, faint groove.

Shell moderately low spired, the upper sutures smooth 

only in mature stage; growth lines curving back from 

upper sutures to a relatively narrow selenizone on the 

upper whorl surface at the periphery; base with a sharp 

circumumbilical angulation, surmounted by a circumumbilical cord in the immature stage, the juncture of 

base and umbilicus being rounded in mature stage but 

still bearing a moderately distinct cord.

Discussion.—The relatively greater thickness and 

lesser width, combined with the lesser curvature, distinguish the operculum of Ceratopea hami from that of 

C. ankylosa Cullison. It is superficially similar to that 

of C. buttsi and C. unguis but differs from opercula of 

these species in showing two distinct pits in the attachment surface of many specimens rather than one. It is

much narrower and more strongly curved than either of 

these two species. The specimen illustrated is somewhat worn in the apical area, but because of its unusually large size, shows the development of two pits more 

strongly than in many of the other specimens known. 

It is to be noted that the attachment surface is typically 

deeply depressed, not shallow as in C. cmkylmd Cullison. There is some slight variation in width, particularly in the early growth stages before development of 

the concavity of the parietal surface.

Ceratopea unguis Yochelson and Bridge, n. sp. 

Plate 37, figures 11-14, 19-24, 28; plate 38, figures 8, 9

Ceratopea sp., Butts, 1941, pi. 72, figs. 1-4.

Ceratopea sp., Butts and Gildersleeve, 1948, pi. 1, figs. 6-9

(reillustration of Butts 1941). 

Ceratopea, n. sp. Sando, 1957, p. 127-128, pi. 11, figs. 24-26.

Description.—Lenticular gastropods, with a broad 

selenizone and greatly thickened well-curved, wide 

opercula; operculum carina distinct, but commonly 

worn; umbilical and dorsal ridges of operculum wide 

and ill defined parietal surface distinctly concave, carinal surface convex; operculum moderately well curved, 

gently torted, relatively wide; parietal margin of operculum straight, dorsal angle near 160°; carinal margin 

then bending downward to carina so that it forms a 

wide sinus; operculum ventral margin straight and inclined posteriorly for about two-thirds of its length, 

then bending gently, so that notch formed is exceedingly shallow; attachment surface having a single pit.

Shell lenticular, the upper surface gently arched; 

growth lines on upper surface sweeping back strongly 

to broad selenizone on periphery, most of the width of 

selenizone being on the upper whorl surface; below the 

periphery the growth lines curving more strongly 

downward and forward, so that lower half of outer 

whorl face has almost orthocline growth lines; umbilicus with arched walls, the whorls set back in steplike 

arrangement.

Discussion.—The operculum of this species is readily 

separated from those of Ceratopea buttsi and C. torta 

Cullison by being more strongly curved, by lacking a 

sharp carina, and by 'being relatively wider. Some 

specimens appear to be superficially similar to C. corniformis Oder but have the parietal surface concave 

rather than convex; specimens of this species commonly 

are thicker and significantly wider than those of C. 

corniformis.

Wide specimens of C. unguis opercula may develop 

two muscle pits and may have the same general shape 

as opercula of C. ankylosa Cullison, but there are significant differences between the two. C. unguis is less 

curved in the apical area and expands less rapidly.
THE LOWEE ORDOVICIAN GASTROPOD CERATOPEA 301

The attachment surface is cup shaped and sunken, with 

the pits being still lower, whereas in G. ankylosa the 

area between the pits approaches the level of the surrounding rim.

This is one of the most common species, being represented by large collections from the Arbuckle Mountains and from near Smithville, Ark. Specimens from 

these areas show considerable variation in both width 

and thickness, with some specimens being one-third 

again as wide as narrower examples. Generally the 

narrower form, which is the more common of the two 

in the Arbuckle Mountains collections, is slightly more 

curved. There is such complete intergradation in 

shape, however, that there is no other course but to 

treat this as a single species. Certainly there is more 

variation in this species than in the others described in 

this paper.

There is again considerable variation in the attachment surface. On some specimens this is smooth, on 

others there is a single pit. On still others, two distinct 

pits are developed. Most commonly the wider specimens have two pits, but there are exceptions. In spite 

of this considerable individual variation in shape and 

attachment surface, G. unguis is still one of the easiest 

species to identify.

Ceratopea? pygmaea Stauffer

Plate 38, figures 2-5, 7 

Ceratopea pygmaea Stauffer, 1937, p. 56, pi. 9, figs. 3, 9,10.

Description.—Strongly curved, distinctly torted, 

small opercula with an elongate groove in attachment 

surface; opercula so strongly curved that in outline they 

are hook shaped; rapidly expanding, with width greater 

than twice the height; carina sharp, dorsal and umbilical ridges poorly developed; parietal surface concave; 

parietal margin straight; dorsal angle near 140° but 

varying widely among specimens; carinal margin bending up near carina; ventral margin joining parietal 

margin smoothly, with faint or no development of notch, 

but bending up near carina so that a distinct sinus is 

formed at juncture with carinal margin; attachment 

surface with an elongate faint groove, or smooth.

Discussion.—If the great difference in size is ignored, 

this species appears closest to the operculum of G. tennesseenis Oder. It differs from that species by being 

lower, having a concave parietal surface, and being more 

strongly torted. Study of the types and topotypes suggests that there is considerable individual variation in 

shape, not all of which is to be attributed to the poor 

preservation that is characteristic of the specimens.

The opercula from Spavinaw, Okla., mentioned previously show a slightly deeper ventral notch and a more 

pronounced groove. They also have a sinus at the

proximal end of the carina. If the interpretation given 

to the function of the ventral notch in Ceratopea is correct, then the carinal notch of these opercula suggests 

a fundamental difference in musculature between these 

opercula and those of Geratopea.

REFERENCES CITED

Alien, A. T. and Lester, J. G., 1954, Contributions to the paleontology of northwest Georgia: Ga. Geol. Survey Bull. 63, 

166 p.

Bassler, R. S., 1909, The cement resources of Virginia west of the 

Blue Ridge: Va. Geol. Survey Bull. 2a, 309 p.

——— 1919, Cambrian and Ordovician: Md. Geol. Survey Bull.,

424 p. 

Billings, Elkanah, 1865, Paleozoic fossils containing descriptions

and figures of new or little known species of organic remains

from the Silurian rocks 1861-1865: Canada Geol. Survey,

426 p. 

Bridge, Josiah, 1955, Disconformity between Lower and Middle

Ordovician series at Douglas Lake, Tenn.: Geol. Soc.

America Bull., v. 66, p. 725-730.

——— 1956, Stratigraphy of the Mascot-Jefferson City zinc district, Tennessee: U. S. Geol. Survey Prof. Paper 277.

Butts, Charles, 1926, Geology of Alabama: The Paleozoic rocks: 

Ala. Geol. Survey, Special Rept. no. 14, p. 41-230.

——— 1941, Geology of the Appalachian Valley in Virginia—

part 2, Fossil plates and descriptions: Va. Geol. Survey Bull.

52, iii 271 p. [1942]. 

Butts, Charles, and Gildersleeve, Benjamin, 1948, Geology and

mineral resources of the Paleozoic area in northwest

Georgia: Ga. State Div. of Conserv., Dept. Mines, Mining

and Geology, Bull. 54,176 p. 

Chase, G. W., Frederickson, E. A. and Ham, W. E., 1956, Re'sume'

of the geology of the Wichita Mountains, Okla.: Am. Assoc.

Petroleum Geologists Bull., v. 40, p. 36-55. 

Cloud, P. E., Jr., and Barnes, V. E., 1946, The Ellenberger group

of central Texas: Texas Univ. Bur. Econ. Geol. pub. 4621,

473 p. [1948]. 

Cullison, J. S., 1944, The stratigraphy of some Lower Ordovician

formations of the Ozark uplift: Mo. School Mines Metallurgy, Bull. Tech. ser., v. 15,112 p. 

Ham, W. E., 1955, Field conference on geology of the Arbuckle

Mountain region: Okla. Geol. Survey, Guidebook III, 61 p.,

Norman, Okla. 

Hedley, Charles, 1917, Notes on opercular evolution: Nautilus,

v. 30, p. 97-99. 

Knight, J. B., 1941, Paleozoic gastropod genotypes: Geol. Soc.

America Special Paper 32, 510 p., 96 pis.

——— 1944, Paleozoic gastropods, revised by J. Brookes Knight, 

with the cooperation of Josiah Bridge, in Shimer, H. W., and 

Shrock, R. R., Index fossils of North America: New York, 

John Wiley and Sons, p. 437-479.

——— 1952, Primitive fossil gastropods and their bearing on

gastropod classification: Smithsonian misc. coll., v. 117, 56 p.

Knight, J. B., Batten, R. L., and Yochelson, E. L., in preparation, 

Paleozoic Gastropoda, in Moore, R. C. (ed.) treatise on invertebrate paleontology: New York, Geol. Soc. America.

Major, Harald, and Winsnes, T. S., 1955, Cambrian and Ordovician fossils from S0rkappland, Spitsbergen—part 1, A preliminary description of the Hecla Hock rocks and its Cambrian and Ordovician faunas, by Thore S. Winsnes: Norsk 

Polarinstitutt Skrifter Nr. 106, p. 6-31, pis. 1-3.
302 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

Oder, C. R. L., 1932, Fossil opercula from the Knox dolomite: 

Am. Midland Naturalist, v. 13, p. 133-153, pis. 13, 14.

——— 1934, Preliminary subdivision of the Knox dolomite in

east Tennessee: Jour, Geology, v. 43, p. 469-497. 

Rodgers, John, and Kent, D. F., 1948, Stratigraphic section at Lee

Valley, Hawkins County, Tenn.: Tenn. Div. Geol. Bull. 55,

57 p. 

Salter, J. W., 1859a, Fossils from the base of the Trenton Group:

Figures and Descriptions of Canadian organic remains,

decade I, Geol. Survey of Canada, 47 p.

——— 1859b, Descriptions of the organic remains from the Durness limestone in Murchison, R. I., On the succession of the 

older rocks in the northernmost counties of Scotland; with 

some observations on the Orkney and Shetland Islands: 

Geol. Soc. London Quart. Jour., v. 15, p. 374-381.

Sando, William J., 1957, Beekmantown group (Lower Ordovician) of Maryland: Geol. Soc. America Mem. 68,161 p., 15 pis.

Stauffer, 0. R., 1937, A diminutive fauna from the Shakopee 

dolomite (Ordovician) at Cannon Falls, Minn.: Jour. Paleontology, v. 11, p. 55-60, pis. 9-11.

Taki, Iwao, 1950, Morphological observations on the gastropod 

operculum: Venus, v. 16, p. 32-48. (Japanese with English 

summary.)

Twenhofel, W. H., and others, 1954, Correlation of the Ordovician formations of North America: Geol. Soc. America Bull., 

v. 65, p. 247-298.

Ulrich, E. O., 1911, Revision of the Paleozoic systems: Geol. Soc. 

America Bull., v. 22, p. 281-680.

Ulrich, E. O., and Scofield, W. H., 1897, The Lower Silurian Gastropoda of Minnesota, in Geology of Minnesota: Final Report, v. 3, pt. 2, p. 813-1081, pis. 61-82.

Wenz, Wilhelm, 1933, Handbuch der palaozoologie (Herausgegeben v. Schindewelf) : Band 6, Gastropoda, Teil. 1 and 2, 

Allgemeiner Teil und Prosobranchia (pars). Berlin.

Winsnes, T. S., 1955, see Major, Harald, and Winsnes, T. S.

Woodring, W. P., Roundy, P. V., and Farnworth, H. R., 1932, 

Geology and oil resources of the Elk Hills, Calif., including 

Naval Petroleum Reserve No. 1: U. S. Geol. Survey Bull. 835.

Woodward, H. P., 1951, Ordovician system of West Virginia: 

W. Va. Geol. Survey, v. 21, 627 p.
INDEX

[Italic numbers indicate descriptions]

Page

Abstract____.__—_-___— ___.______...__.________ 281 

Acknowledgments____,___._..._...._.______...__. 281

ankylosa, Ceratopea———.-.. —..,.. —.......... 285,292,294,295, $99, 300, pi. 37

Apex of operculum, defined____....__...._____..__..._.___ 283

arietina, Ceratopea.... ..........——.____..._.__.___.___.. 285,292,295, 296, pi. 36

Atlanta. _______.__..___...._____.__..____________ 282

Attachment surface of operculum, defined.________.______ 284

Bibliography..._..___...._....__.....__....._....___..... 301

bigranosa, Orospira.-...... .___..........._..___.___..___. 291,pi. 38

Bridge, Josiah, studies of Ceratopea by_.......___.___...._._____ 281

buttsi, Ceratopea..----.----.._._.. 284, 285, 287,288,292,294,295,298, $99, pis. 36,37

ealceoliformis, Ceratopea....-..................................... 285,286,298,pi. 35

capuliformis, Ceratopea.................... 285,290,291,292,294,295, $96, 297,pis. 35,36

capuliformis capuliformis, Ceratopea....__._...________.__.. 285,296

capuliformis robusta, Ceratopea..... _____--..-____....______ 285,296

Carina, denned_._..__._______________________.__ 283 

margin of, defined..________.______...._________ 284

surface of, defined_______________________ ______ 283

views of, defined_____________________________.___ 283

Ceratopea..................................................................... 296

ankylosa..—..................................... 285,292,294,295, m, 300,pi. 37

arietina........... ....... ................................. 285,292,295, 896, pi. 36

buttsi.......................... 284,285,287,288,292,294,295,298, $99, 300, pi. 36,37

ealceoliformis................................................. 285,286,298, pi. 35

capuliformis.......................... 285,290,291,292,294,295, 896, 297,pis. 35,36

capuliformis... ______________________________ 285,296 

robusta.............................................................. 285,296

compressa............................................................. 298, pi. 35

corniformis.—.............................. 285, 292, 295, 298, 299, 300, pi. 35, 36

cuneata——————————. ________.___________ 285, 297, pi. 35

germana........................................ 285, 292, 294, 295, 296, W, pi. 36

hami.—................................... 285, 288, 292, 294, 295, 299, 300, pi. 37

incurvata...-.................................. 285, 292, 294, 295, 296, 297, pi. 36

inflata........................_________________________ 285

jenkinensit......................................................... 285, 286, 298

jonesi...-.............................................................. 285,297

keithi..—-................... 282, 285, 290, 291, 292, 294, 295, 296, $97, pis. 35, 36

subconica....___._______________.._________ 285

knighti—..——.-.-..-._... ..................... 285, 292, 294, 295,500, pi. 37

opercula, linear measurements of___ __________ ________ 285 

pygmaea.........._——___..___.____________ 288, 291, SOI, pi. 38

robusta...................................................... 285, 290, 296, pi. 35

subconica...--.............................. 285, 292, 294, 295, 297, 299, pis. 35, 36

sulcata...—-...-.............................................__ 285, 297, pi. 35

supraplana..................... ._______________________ 285, 297

tennesseensis.............. 285, 291, 292, 294, 295, 297, 298, 299, 300, 301, pis. 35, 36

torta............................................ 285, 292, 295, 298, 899, 300, pi. 36

unguis........................ 285, 288, 289, 292, 294, 295, 298, 299, 300, pis. 37, 38

n. sp____.___________________________________ 285, 300 

sp._________________________________________ 300 

sp. I.......—.......................................................... 285, 296

sp. 4.....——._——._._--.-. ——..——._-._--.._-_-....—... 285, 298

sp. 5........-...................-........—............................ 285, 297

Ceratopeidae________.__________________________ $96 

Collection localities:

Alabama......—.................................._............ 291, 292, 294

Appalachians-..___.___._..--.-..__..___...___... 281, 286, 292 

Arbuckle Mountains____.___....________ 281, 284, 286, 291, 292, 294

Arkansas_ _ ________________ ______________ 288,291,292

Baylor Mountains, Tex_____________________________ 291 

Beach Mountain, Tex_____________________________ 291,292 

Colorado.....—-..—-......-......-.................................- 291

Cotter dolomite, Missouri___________________________ 291,294

Page 

Collection localities—Continued

El Paso limestone__-----_..-.--.—.„.—-————-——-.— 288,294

Franklin Mountains, Tex.-....„...—..——--—.————.....— 291

Georgia.— — .——————————— ———————— 291,292

Honeycutformation...-----------.--------------------———...—. 292,294

Jonesboro limestone in Tennessee—— ——————. — -------- ——.——— 290

Kansas_-_______------- —— -_ —— — —— — - —— ———————— 291

Kindblade formation of Oklahoma.__——.. ——— ——— — ———— —— -- 294

Kingsport formation, Tennessee.___._-_.-.--_ —— —— — __- —— —— 292,294 

Llanouplift-..—————————--———- ———— 281,282,290,291,292

Manitou dolomite, Colorado.— - — —— —— ———— —— —— - ——— —— - 291

Maryland---------------------—--------._-----_———__ 289,291,292

Mascot dolomite, Tennessee--------_-----————.————...-.. 292,294

Minnesota___________...--——-————— —— — —— ——— 291

Missouri....———.————-— ——————_---—---. 291,292,294

New York.—————————— ——————————————. 291

Newala limestone of Alabama......————— — ——— - —— —— — —— 294

Newfoundland-.—.———. ———————————————— 290,291

Oklahoma-------------------------_... — —— ———. 284,291,294

Oklahoma, Criner Hills.....—————————————————— 288

Ozark Plateaus———————————————————— 281,282,286,291

Pennsylvania.—————— — — - — ————— — ————-——— 291,294

Rich Fountain formation in Missouri..--------- —— —————— —— —— 294

Eockdale Run formation...—————————————————— 288,294

Shakopee dolomite of Minnesota———————————————————————— 291 

Spitzbergen_..._-___..————— ————....—————.——— 291

Tennessee___—— —— ——————————___-_-_-- 284,291,292,294

Texas....————————————————————— 288,291,292,294

Theodosia formation_______---_—--——————.-———————— 294 

Virginia-.----.----.----____-_-_------------__-__-- 291,292,294

West Spring Creek limestone.—-———————————————- 288,294

West Virginia___________________________________ 291,292 

Wichita Mountains———.—— —— ———————————— 291,292,294

compressa, Ceratopea——..—-——————————————————————— 298, pi. 35

corniformis, Ceratopea.—————-———.- 285,292,295,298, 299,300, pis. 35,36

Cotter dolomite, Missouri, specimens from...._——————————————— 291,294

cuneata, Ceratopea-———--——---—...........——-----——— 285,297,pi. 35

Dorsal angle of operculum, defined——-— — ——— ———— ——— — — — 284

Dorsal ridge of operculum, defined.——-——— —— ——— ———— —— —— —— 283

Dorsal surface of operculum, defined———————————————————————— 283

Dorsal view of operculum, defined———————————-————————————— 283

Distribution, geographic__—.—————————————————————————— 291

El Paso limestone, specimens from.—— ————————— —— ———————— 288,294

germana, Ceratopea-—.-.—————————— 285,292,294,295,296, 297, pi. 36

Groove of operculum, defined...-...- ———— —————— ———————————— 284 

Growth lines of operculum, defined.- ——— —— —————————————————— 284

hami, Ceratopea.................................. 285,288,292,294,295,299,500,pi. 37

Height of operculum, defined.-.—————————————————————————— 284 

Honeycutformation—__——...———————————————————————— 292,294

incurffata, Ceratopea...-...--...--..——.._____— 285,292,294,295,296,297,pi.36 

inflata, Ceratopea.————————————————————————— 285

Interior view of operculum, defined..-..———————— ————— ———————— 283 

Intloduction..—-—--—-—...———.———————————————— 281

ns, Ceratopea...... ... ———————— — —— ———— —— —— —— 285,

Jonesboro limestone in Tennessee— —— — — — ——— ————————— —— 290

jonesi, Ceratopea............................—...—......——————— 285,297

i, Ceratopea...................... 282, 285,290,291,292,294, 295,296, 297, pis.35,36

keithi subconica, Ceratopea.— — —— — —————— ——— ———————————— 285

Kindblade formation of Oklahoma———————- —— ——————————————— 294

303
304 INDEX

Page

Kingsport formation, Tennessee.._.__-__-___-__________ 292,294 

knighti,[Ceratopea--...-— ............................... 285,292,294,295, 300, pi.37

Llano uplift, study of Ceratopea m.............................. 281,282,290,291,292

logani, MadurUet.................-.—....——..————...———... 290,291

Madurea......................................................________ 282

Madurites.......................................................... 282,283,287,290

logani..............-__——__....—-..——————.—..—.... 290,291

oceanus....................___.__.__..______-__-___. 290

odenvillensis..........................._____-__-__-_____ 290

peachii-...... ___-________________________.______ 290

profundus________________-...._.-________...... 290

Manitou dolomite, Colorado, specimens from....-_.________.____ 291

Margin, ventral, of operculum, denned_ ___. ____________.___ 284 

Mascot dolomite, Tennessee__________________________ 292,294

Newala limestone of Alabama.._________________________ 294 

Notch of operculum, defined—_..._________._____..___ 284

Occurrence, local..._.-__________....___..___-----_____ 284-286

stratigraphic-___.______.__....____.__._____.___ 291-294

oceanus, Maclurites......._...___._.__.__________.____ 290

odenvillensis, Maelurttes..... ______.__.__________________ 290

Oder, classification of operculum by........._................._,._-_. 282

Operculum, classification of by Taki__....._-__..._-----__-__ 282

measurements of in various species__..._...__.....__-----_..... 285

terminology of defined.....__._____________..._...__.._ 282-284

apex___.__.....__.__.___....__.___.........____... 283

attachment surface...--....-._........._..._.....__...._ 284

carina...-———. —........._......__._____...._.___.. 283

carinal margin..-- — — -. — — — _--_-__--_-_...._............ 284

carinal surface-....__..-_....._........_......_.-_.....___ 283

carinal view..____.___.___.___.___..._____..__ 283

dorsal angle...-____.___...__________________ 284

dorsal ridge_.._______.__.._....___......______. 283

dorsal surface..—._________._____________.____ 283

dorsal view__-___________._________._________ 283

groove..—————...._________________.________ 284

growth lines_—______________________________ 284

height.....-—.————___—___—_—_.____........._____„ 284

interior view..._______________________...___ 283

notch_____________._______.________._____ 284

parietal margin——_.___________________. ____ 284

parietal surface. __ ________ _____ ________ _ __ ___ 283

prong..—————.—.——————_----—————.._—_._..... 284

rim__.________________________________ 284

thickness._____.._________________________ 284

umbilical view. _____________________________ 283

umbilical ridge. _______________________________ 283

ventral margin-._______________________________ 284

ventral surface______________ _____________ ___ 284

ventral view_________________________. ______ 283

width..——————....__........__._.___.___..___._ 284

Opisthobranchs._____________________.__________ 286

Page 

Orientation in life.-————— ——— —————————————— 286-287

Orospirabigranosa........ ... ——— -----—. ————.... — ..——..———- 291,pi.38

Other Ordovician opercula__.__- — -————. —. —— -———————— 290-291

Parietal margin of operculum, defined... — —— —. —.... — —— —— —— 284

Parietal surface of operculum, defined--————————————————..—— 283 

peachii, Maclurites_____.______...__..._——.———.———— — 290 

Phytogeny.....———————————————————————————— 294-295

Pondia.......................................—...—————————— 291

powetti- _——- ———————————— ———————————————————.. pi. 35 

powelli, Pondia............................................................... pi. 35

Preservation....___.___....._________._—._...———— 284-286

Previous work________________.__——_————————————— 282 

profundus, Maelurttes...........................———————————————— 290

Prong of operculum, defined...._————————————————————————— 284

pygmaea, Ceratopea.............................................. 288,291, SOI, pi.38

Eaphistoma....——.—....——.———————————————————————— 291

Rich Fountain formation in Missouri, specimens from.————————————— 294 

Ridge of operculum, umbilical, defined....__..__—__————————— 283

Rim of operculum, defined.,.__.___—_———.———————————— 284 

robusta, Ceratopea................................................ 285,290,296, pi. 35

Ceratopea capuliformis............__—_——_——.———————— 285,296

Rockdale Run formation, specimens from..__......... — ————————. 288,294

Shakopee dolomite of Minnesota, specimens from..__———.——.————— 291 

Shell, associated, and the nomenclatural problem___——..—.... ——— 287-260

subconica, Ceraiopea............................ 285, 292, 294, 295, 897, 299, pis. 35, 36

Ceratopea keithi._______. ________________________— 285 

sulcata, Ceratopea.................................................... 285,297, pi 35

supraplana, Ceratopea-..................................................... 285,297

Surface, ventral, of operculum defined._..____...——„..——————— 284 

Systematic paleontology ____________________.___.„.... 296-301

tennesseensis, Ceratopea ....__ 285,2W, 292,294,295,297, 298, 299,300,301, pis. 35,35

Terminology of the operculum (see also Operculum)...——_——_——... 282-284 

Theodosia formation, specimens from-__——..——_——...————————— 294 

Thickness of operculum, defined_..__...._..__—_____——_.. 284

torta, Ceratopea........................................ 285,292,295,298,289,300, pi. 36

TryMidium.................................................................... 286

Turbo........................................................................ 288

Ulrich, E. 0., studies of Ceratopea by-____.________.........__ 281,282

Umibilical ridge of operculum, defined. ____________.___.__.. 283 

Umbical view of operculum, defined——..——_—__——..———.——_— 283 

unguis, Ceratopea .................... 285,288,289,292,294,295,298,299,300, pis. 37,38

Ventral margin of operculum, denned—.——_—__—_..__—__— 284

Ventral surface of operculum, defined._.___________________ 284

Ventral view of operculum, defined——_—._—__..__—__..__.. 283

Views of operculum defined, ventral..__.._________...__...__ 283

Views of specimen defined__._______ ______ _________.. 283

Vtpipams-.................................................................... 286

West Spring Greek limestone, specimens from. __________. ____ 288,294 

Width of operculum, denned_________________________-- 284

o
PLATES 35-38
PLATE 35

[All figures \}$ times natural size except 23-25, 3 times natura size

FIGURES 1-5, 9. Ceratopea capuliformis Oder (p. 296).

1-3. Reillustration of Oder, 1932, pi. 14, figs. 1, 5, 6. From the athletic field of Carson-Newman College, Jefferson City, Tenn. Holotype, USNM 128169.

4, 5, 9. Reillustration of Ceratopea robusta Oder, 1932, pi. 13, figs. 9-11. From Old Mossy Creek Mine, Jefferson City, Tenn. Cotype, USNM 128164a. 

6-8, 10-16. Ceratopea tennesseensis Oder (p. 298).

6. Reillustration of Ceratopea compressa Oder, 1932, pi. 14, fig. 14. From Lee Valley, 8.5 miles northwest of 

Rogersville, Tenn. Holotype, USNM 128171.

7. 8, 11. Reillustration of Ceratopea calceoliformis Oder, 1932, pi. 13, figs. 5-7. From Mossy Creek, 1.5 miles

southeast of Jefferson City, Tenn. Holotype, USNM 128161. 

10, 15, 16. Reillustration of Ceratopea tennesseensis Oder, 1932, pi. 13, figs. 4, 8, 12. From 1 mile southwest

of Alpha, Tenn. Holotype, USNM 128165.

12, 13, 14. Reillustration of Ceratopea cuneata Oder, 1932, pi. 13, figs. 1-3. From 0.4 mile northeast of intersection of Lee Highway and Bloomingdale road, Kingsport, Tenu. Cotype, USNM 128172a. 

17-22, 26, 27. Ceratopea subconica Oder (p. 297).

17, 18, 21. Reillustration of Ceratopea subconica Oder, 1932, pi. 14, figs. 15-17. From 2 miles west of Marble

Hall, about 8 miles southwest of Rogersville, Tenn. Holotype, USNM 128177. 

19, 20. Reillustration of Cerotopea sulcata Oder, 1932, pi. 14, figs. 9, 13. From exposure on Lee Highway, 1

mile west of Church Hill, Tenn. Cotype, here designated lectoparatype, USNM 128173b. 

22, 26, 27. Reillustration of Ceratopea sulcata Oder, 1932, p.l 14, figs. 10-12. From exposure on Lee Highway

1 mile west of Church Hill, Tenn. Cotype, here designated lectotype, USNM 128173a. 

23-25. Ceratopea corniformis Oder (p. 298).

Reillustration of Ceratopea corniformis Oder, 1932, p. 14, figs. 2-4. From Old Mossy Creek Mine, Jefferson

City, Tenn. Holotype, USNM 128167. 

28, 31-33. Ceratopea keithi Ulrich (p. 297).

28, 33. Reillustration of Ceratopea keithi Ulrich as figured by Oder, 1932, pi. 13, figs. 13, 14. From Springvale,

Tenn. Hypotype, USNM 128178b.

31, 32. Reillustration of Ceratopea keithi Ulrich as figured by Oder, 1932, pi. 13, figs. 15, 16. From Springvale, Tenn. Hypotype, USNM 128178a. 

29, 30. Pondia powelli Oder (p. 290).

Reillustration of Pondia powelli Oder, 1932, pi. 14, figs. 7, 8. From Bristol, Tenn. Holotype, USNM 128174.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 294 PLATE 35

REILLUSTRATION OF ODER'S SPECIMENS OF CERATOPEA AND POND IA OPERCULA FROM TENNESSEE
GEOLOGICAL SURVEY PROFESSIONAL PAPER 294 PLATE 36

CERATOPEA OPERCULA FROM TEXAS, OKLAHOMA, MISSOURI, TENNESSEE, AND COLORADO
PLATE 36

[All figures natural size, except 5-12, 21-24, and 45-36, 2 times natural size, and 1-4, 4 times natural size]

FIGURES 1-4. Ceratopea arietina Yochelson and Bridge, n. sp, (p. 296).

From Honeycut formation 30 to 50 feet above baseT Cloud loc. TF-265, from valley of Slickrock Creek, 1.83 

miles airline south from a point about 7 miles"by odometer': west-south west of Marble Falls, southeastern corner 

of Llano County, Tex. Holotype, IISNM 128191. 

5, 8-10. Ceratopea capuliformis Oder (p. 296).

From Manitou dolomite in stratigraphically highest beds exposed on the mountain about 330 feet above base 

of the formation. University of California loc. B-1827, from top of Bald Mountain, at north end; in the NE% 

sec. 23, T. 50 N., R. 4 E., Garfield quadrangle, Gunnison County, Colo. Hypotype, University of California, 

no. B1827/36494. 

6, 7, 11-13. Ceratopea germana Yochelson"andJBridge, n. sp. (p. 297).

6, 7, 11, 12. From Kindblade formation, 328 feet above base. Ham loc. Ok 119, from 1,650 feet west and 250 feet

north of SE corner sec. 17, T. 2 S., R. 4 E., Murray County, Okla. Holotype, USMN 128179. 

13. From same locality as figure 6. Paratype, USNM 128180. 

14—17. Ceratopea corniformis Oder (p. 298).

From Kindblade formation, 100 feet above base. Ham loc. Ok 108, from 2,400 feet east, and 2,150 feet north of the

SW corner sec. 6, T. 2 S., R. 1 E., Murray County, Okla. Hypotype, USNM 128181. 

18-24. Ceratopea torta Cullison (p. 299).

18-20. From lower part of Theodosia formation of Cullison (1944). University of Missouri, School of Mines, 

loc. 103.2, from center of W/2 sec. 2, T. 21" N., R. 25 W., elevation 1,000 feet, south of road junction, 

Barry County, Mo. Reillustration of holotype, Yale Peabody Museum no. 17160. 

21-24. From Cotter formation (of Ulrich). USGS loc. 474e (old series), from head of drain in SWM sec. 23, T. 37

N., R. 8 W., Rolla quadrangle, Phelps County, Mo. Hypotype, USNM 128192. 

25-30. Ceratopea buttsi Yochelson and Bridge, n. sp. (p. 299).

25, 26. From West Spring Creek, formation 595 feet above base and about 960 feet below top. Ham loc. Owsc 

112, from 1,500 feet east, 1,000 feet north of SW corner, sec. 10, T. 2 S., R. 1 E., Murray County, Okla. 

Paratype USNM 128184.

27-30. From West Spring Creek formation about 550 feet above base, and about 700 feet below top. Ham loc. 

Owsc 108, from 1,400 feet east and 1,700 feet north of SW corner sec. 6, T. 3 S., R. 4 E., Carter County, 

Okla. Holotype, USNM 128185. 

31, 32, 41, 42. Ceratopea keithi Ulrich (p. 297).

From about 300 feet below top of exposure, and about 50 feet above Ceratopea incurvata zone (of Ulrich). USGS 

loc. 461al (old seiies), from inlier, 3 miles southwest of Alden, Okla., and 10 miles south of Carnegie, Okla.; north 

side of Wichita Mountains, in sec. 25, T. 6 N., R. 14 W., Kiowa County, Okla. Hypotype, USNM 128193. 

33, 34, 37, 38.-. Ceratopea tennesseensis Odei (p. 298).

From Kindblade formation, 30 feet below top. Ham loc. Ok 113, from SE% sec. 10, T. 2 S., R. 1 W., Murray

County, Okla. Hypotype, USNM 128188. 

35, 36, 39, 40. Ceratopea subconica Oder (p. 297).

From Knox group ("in upper 100 feet of Canadian" of Ulrich). USGS loc. 473z (old series), from Trundles Cross

Roads, 12 miles southeast of Knoxville, Knox County, Tenn. Hypotype, USNM 128189. 

42-46. Ceratopea incurvata Yochelson and Bridge, n. sp. (p. 297).

From Kindblade formation 279 feet above base. Ham loc. Ok 104, 220 feet east and 1,400 feet south of N W corner 

sec. 3, T. 2 S., R, 1 W., Murray County, Okla. Holotype, USNM 128186.
PLATE 37

[All figures natural size, except 7-10, 2 times natural size]

FIGURES 1-6. Ceratopea ankylosa Cullison (p. 299).

I-4. From West Spring Creek formation, 400 feet above base. USGS loc. 2091 (new series), 750 feet east, 

1,200 feet south of NW corner sec. 19, T. 2 S., R. 4 E., Murray County, Okla. Hypotype, IJSNM 

128195.

5, 6. From Geodiferous beds of upper part of Beekmantown group. USGS loc. 289a (old series) from quarry 

opposite ribbon factory at Carlisle, Cumberland County, Pa (May, 1908). Hypotype, USNM 128194. 

7-10. Ceratopea knighti Yochelson and Bridge, n. sp. (p. 300).

From West Spring Creek formation, 610 feet above base. Ham loc. Owsc 113, from center of the NEJ4 sec.

5, T. 2 S., R. 1 W., Murray County, Okla. Holotype, USNM 128187. 

11-14, 19-24, 28. Ceratopea unguis Yochelson and Bridge, n. sp. (p. 300).

II-14. From Smithville formation, USGS loc. 104L (old series) from Iowa mine, 2 miles north of Smithville,

Lawrence County, Ark. (1905 and later collections). Paratype, USNM 128198. 

19-22. From West Spring Creek formation, 238 feet below top. Ham loc. Owsc 102, from 1,100 feet south of

the E % corner sec. 9, T. 2 S., R. 1 W., Murray County, Okla. Holotype, USNM 128183. 

23, 24, 28. From El Paso limestone, 50 feet below top. From USGS loc. K 2759 (old series), north end of

Beach Mountain, Van Horn quadrangle, Texas. Paratype, USNM 128196. 

15-18. Ceratopea harni Yochelson and Bridge, n. sp. (p. 300).

From West Spring Creek formation, about 600 feet above base. Ham loc. Owsc 114, from 300 feet west, and

950 feet north of SE corner sec. 14, T. 2 S., R. 2 W., Carter County, Okla. Holotype, USNM 128182. 

25, 26, 29, and 32. Association of Ceratopea hami, n. sp. (p. 288).

25. Top view of shell. From upper half of the El Paso limestone (probably 200-400 feet from top of section). 

Knight loc. X-15, from northeastern part of Baylor Mountains, 14.6 miles west and 17.3 miles north 

of southeast corner of Van Horn quadrangle, Culbertson County, Tex. Paratype, USNM 128197.

26. Basal view of shell. From West Spring Creek formation (probably in upper half). USGS loc. 2095 (new 

series), near center SW^sec. 16, T. 1 S., R. 5 E., in an open pasture, a few hundred feet west of main 

road to Douglass ranch headquarters, Johnson County, Okla. Paratype, USNM 128199. 

29. Top view of a partially etched block showing shell and opercula. From same locality as figure 25. Paratype, USNM 128201. 

32. Side view of same block. 

27, 30, 31, 33, 34. Shell of Ceratopea buttsi, n. sp. (p. 288).

27, 31, 33. Side, top, and basal views of shell. From West Spring Creek formation, near middle. USGS loc. 

2097 (new. series), in small, abandoned building-stone quarry, 400 feet west and 200 feet north 

of E}£ corner sec. 17, T. 5 S., R. 1 E., Carter County, Okla. Paratype, USNM 128200b. 

30. Basal view of another specimen from same locality. Paratype, USNM 128200a. 

34. Top view of a small specimen from same locality. Paratype, USNM 128200c.
GEOLOGICAL, SURVEY PROFESSIONAL PAPER 294 PLATE 37

CERATOPEA OPERCULA AND SHELLS FROM OKLAHOMA, PENNSYLVANIA, ARKANSAS, AND TEXAS
GEOLOGICAL SURVEY PROFESSIONAL PAPER 294 PLATE 38

-H'

CERATOPEA AND CERATOPEA? OPERCULA AND SHELLS FROM MISSOURI, MINNESOTA, AND OKLAHOMA
PLATE 38

[Figures 6, 8-10, natural size; 1, 4 times natural size, 2-5, 8 times natural size; 7,12 times natural size]

FIGUBES 1, 10. View of a chert slab showing occurrence of opercula of Ceratopeal pygmaea type near numerous specimens of Orospira bigranosa Butts (p. 291). Cotter dolomite. From Armstrong mines, Christian County, Mo. USNM 

collection. 

1. Detail of upper part of block shown in figure 10, inverted. Note opercula in side view to left of high-spired

gastropod, and specimen showing attachment surface just to right of gastropod. 

10. Top view of most of the slab. The well-preserved specimen just to the left of center in the lower part of the

photograph is the lectotype of Orospira bigranosa Butts. 

2-5, 7. Ceratopea? pygmaea Stauffer (p. 301).

All specimens from the oolitic chert of the Shakopoe dolomite at Cannon Falls, Minn. 

2, 3, 5. ReiUustratiou of Stauffer, 1937, pi. 9,

Geology Museum, no. 4854. 

4. Reillustration of Stauffer, 1937, pi. 9, fig. J

Geology Museum, no. 4848. 

7. Slightly tilted ventral view of largest specimen known, showing deep notch near carina.

designated, University of Minnesota, Geol

6. Fragment of gastropod umbilicus obtained from b

West Spring Creek formation, 260 feet below top.

T. 2 S., R. 2 E., Carter County, Okla. Figured

, 9. Lectotype, here designated, University of Minnesota, 

Lectoparatype, here designated. University of Minnesota,

Lectoparatype, here 

igy Museum,no. 4848a.

ids carrying the operculum of Ceratopea unguis n. sp. (p. 288). 

USGS loc. 2096 (n. se.), 1,400 feet north of SW corner sec. 19, 

specimen, USNM 128190.

8, 9. Association of Ceratopea unguis, n. sp. (p. 288).

8. Top view of shell of Ceratopea unguis Yoche.son and Bridge, n. sp., with operculum glued into presumed life 

position. From Smithville formation. Operculum from USGS loc. 104m (old ser.), 1.5 miles northeast of 

Smithville, on road to Imboden, Lawrenc^ County, Ark. In red debris from four or five closely related 

localities (several different collections were Combined by E. O. Ulrich). Paratype, USNM 128202. Locality 

of gastropod shell not certainly known, but probably nearby. Paratype, USNM 128203.

9. Umbilical view of specimens figured above. See also page 288 for discussion of this synthetic association.