Succession and Speciation 

of the Pelecypod Amelia

GEOLOGICAL SURVEY PROFESSIONAL PAPER 314-G

Succession and Speciation 

of the Pelecypod Amelia

By RALPH W. IMLAY

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 314-G

A study of the utility of the pelecypod 

Aucella for mapping rock units in the 

Pacific coast region and in Alaska

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1959
UNITED STATES DEPARTMENT OF THE INTERIOR 

FRED A. SEATON, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

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

Washington 25, D. C.
CONTENTS

Page

Abstract_ _ _______________________________________ 155

Introduction. ______________________________________ 155

Definition of the genus -4uceMa_______________________ 156

Origin and ecology of Aucella_________________________ 156

Speciation in -4itceMo________________________________ 156

Range of variation within Aucellan species.________ 156

Aucella concenlrica (Sowerby)____________________ 157

Aucella spitiensis Holdhaus______________________ 157

Aucella rugosa (Fischer) and A. mosquensis (von

Buch)_______________________________ 157

Aucella piochii (Gabb)_________________________ 157

Aucella fischeriana (d'Orbigny)___________________ 159

Speciation in Aucella Continued

Aucella okensis Pavlow______ _ ________

Aucella subokensis Pavlow_ ____________

Aucella volgensis Lahusen_____________-

Aucella sublaevis Keyserling. ___________

Aucella crassicollis Keyserling_ _________

Aucellan species of questionable validity_

Stratigraphic distribution of Aucella.-. ______

Descriptions of mentioned U. S. Geological Survey Mesozoic localities _ ________________________---_-----_

Literature cited ____________________-_____------_--_

Page 

160 

160

160

161

161

162

164

166

166

167

169

ILLUSTRATIONS

[Plates 16-19 follow index] 

PLATES 16, 17. Jurassic Aucellas.

18, 19. Cretaceous Aucellas. 

FIGURE 36. Stratigraphic distribution of Aucella in the Western States and Alaska.

Page 

165

TABLE

TABLE 1. Characteristic North American species of Aucella.

Page 

158

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

SUCCESSION AND SPECIATION OF THE PELECYPOD AUCELLA

BY EALPH W. IMLAT

ABSTRACT

The pelecypod Aucella, of latest Jurassic and earliest Cretaceous age, has been subdivided into more than a hundred species 

on the basis of minor differences without allowing for biological variation, or for variation due to crowding that is normal 

for an attached gregarious pelecypod. As a result, in any 

large collection from a single locality, specimens can be selected 

that fit the definitions of a number of species and yet these 

so-called species are connected by many specimens showing 

transitional characteristics. Such an association appears, therefore, to represent a single variable population. If the species of 

Aucella are defined making allowance for variation, the number of species is greatly reduced, but the specific concepts can 

be grasped readily by geologists and used for mapping purposes. 

Seven zones based on species of Aucella, can now be recognized 

easily in the field in North America, as has been demonstrated 

by geologists of the TL S. Geological Survey.

INTRODUCTION

Until a few years ago the pelecypod Aucella was considered by paleontologists of the U. S. Geological Survey to be of very little stratigraphic value in the study 

of the Mesozoic. Its presence denoted mainly that 

the beds in which it occurred were not older than the 

late Oxfordian stage of the Jurassic or younger than 

the Hauterivian stage of the Cretaceous. Aucellas from 

the west coast or Alaska that were small and elongate 

and had slender, highly incurved beaks were generally compared to, or referred to, A. piochii (Gabb) 

and were assigned questionably to the latest Jurassic 

Portlandian stage. Aucellas that were medium to fairly 

large, rounded in outline, and very robust were generally identified as, or compared with, A. crassa Pavlow 

or A. Jceyserlingi Lahusen and assigned a probable 

Early Cretaceous age. Aucellas that were medium to 

large, elongate, highly convex, and had a constriction 

ventral to a swollen umbonal part of the shell were 

generally identified as A. crassicollis Keyserling and 

assigned an Early Cretaceous age.

One reason for doubting the stratigraphic usefulness 

of the species of Aucella was that in any large collection from a single locality a number of species of 

Aucella could generally be recognized by selecting specimens that fitted the definitions of various species and 

by disregarding other specimens that had slightly different characteristics. Such diversity of species seemed

unreasonable. As a result not only the validity of the 

species of Aucella as defined was questioned, but, also, 

the age assignments made for those species.

Such uncertainties concerning the stratigraphic 

value of Aucellas might have continued indefinitely 

except for persistent requests for aid from many geologists of the Geological Survey who have been mapping Aucella-bQ&Ymg beds in Alaska and in the west 

coast States. In both areas the need arose to trace the 

boundary between the Jurassic and Cretaceous systems, 

to help identify certain formations by means of fossils 

in areas of complex structures, to help subdivide sequences involving thousands of feet of strata, to correlate those subdivisions over considerable distances, 

and to interpret the stratigraphic succession in terms 

of geologic history as revealed by f aunal changes. In 

both areas Aucellas were the only fossils sufficiently 

abundant and widespread for purposes of tracing systematic and formational boundaries. Evidently a 

stratigraphic evaluation of Aucella was necessary in 

order to solve certain geological problems.

Before undertaking such an evaluation, the writer 

first read many papers dealing with Aucella. Two of 

them were found to be of particular importance. One 

was a fairly short but well documented and illustrated 

discussion by Pompeckj (1901) on the characteristics, 

origin, distribution, and biological relationships of 

Aucella. The other was a comprehensive discussion by 

Pavlow (1907) in which he summarized everything 

that had been published previously concerning Aucellas, 

redescribed and reillustrated all known species, and 

described many new species. Many of the older species 

were divided into a number of new species. Eeassignments of species were made with great positiveness 

on the basis of illustrations only. His descriptions 

were detailed and clearly written; characteristics that 

might be used to differentiate similar appearing species 

were discussed fully; and the stratigraphic ranges of 

the various species were presented adequately. Pavlow's treatment of his subject was masterly and 

thorough.

Most publications on Aucella published since 1907 

have dealt with the Aucellas of particular areas. In

155
156 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

general, European paleontologists dealing with Eurasian Aucellas have coined few new species and have 

tended to reduce the number of recognized species. In 

contrast American paleontologists since 1907 have accepted as valid all the species described by Pavlow and 

have added many more.

The name Aucella was ruled invalid in favor of 

Buchia in 1957 by the International Commission on 

Zoological Nomenclature (Opinion 492). This decision 

was received too late to make modifications herein.

DEFINITION OF THE GENUS AUCELLA

The genus Aucella, as discussed by Pompeckj (1901, 

p. 325-332) and Pavlow (1907, p. 8-11), has an obliquely elongated, inequivalved shell. Its beaks are 

inclined forward and are more or less twisted forward. 

The beak of the left valve is more prominent than 

the beak of the right valve and rises above and generally over the right valve. On the right valve, the 

anterior ear is short and triangular in shape. The 

posterior ear is a little longer and either merges evenly 

into the body of the shell or is separated from the main 

body of the shell by a hollow groove. The byssal notch 

is long and narrow. The surface of the shell is covered 

with concentric ribs, or radial striae, or both. The 

cardinal plate is short, straight, or nearly straight, 

and mostly posterior to the beak. Its posterior part is 

occupied by a long, triangular ligamental groove and 

its anterior part by a notch. Teeth are absent.

ORIGIN AND ECOLOGY OF AUCELLA

Concerning the origin of Aucella, Pompeckj (1901, 

p. 333-351) pointed out that the earliest species, in 

beds of Oxfordian age, were very similar to associated 

pelecypods that he referred to the genus Pseudomonotis, but which are now called Meleagrinella (equals 

Echwotis Marwick as discussed by Cox, 1940, p. 90,91). 

He considered that Aucella developed from Pseudomonotis by shortening of the ears and cardinal area, 

by the beaks becoming inclined forward, by the beak 

of the left valve becoming more prominent, by the 

development of a distinct articulating groove on the 

hinge of the left valve, and by concentric ribbing becoming more prominent than radial ribbing.

The origin of Aucella from Meleagrinella (equals 

Jurassic species of Pseudomonotis) as suggested by 

Pompeckj is in harmony with the inference that both 

genera preferred the same kind of hard substratum on 

which to attach themselves. Meleagrinella before the 

appearance of Aucella, lived in abundance on the surfaces of sediments that gave rise to thin beds of limestone, sandy limestone, sandstone, and conglomeratic 

sandstone. In the western interior region it is commonly associated with Ostrea in sandy beds and with 

Oamptonectes, or rarely with Gryphaea, in limestone 

beds. In southwestern and south-central Alaska in the 

Middle Jurassic (Bajocian) beds it is associated with 

such pelecypods as Trigonia, Inoceramus, G-ervillia, 

Modiolus, Pleuromya, Ostrea, Astarte, and various 

genera of pectens (Martin, 1926, p. 146-148). In overlying sandy beds of late Oxfordian and Kimmeridgian 

ages it is associated with Aucella, Pleuromya, As~ 

tarte, Trigonia, and various pectens (Martin, 1926, p. 

177,178, 214r-2l7), but Aucella occurs in much greater 

numbers than all the other genera. The resemblance 

of Meleagrinella to Aucella, its occurrence in similar 

kinds of rocks, its scarcity after the appearance of 

Aucella, and its disappearance early in the Early 

Cretaceous suggests that both genera lived under 

similar environmental conditions and that Meleagrinella was crowded out by Aucella.

Aucella thrived apparently on hard bottoms in shallow, much agitated waters. Pompeckj (1901, p. 332) 

attributed to agitation the smooth surface on the anterior side of the umbone of many left valves. Such 

an environment is indicated by the abundance of 

Aucella on hard surfaces of attachment as discussed 

above, and its scarcity in thick units of siltstone except 

for widely separated, thin, coquinoid layers. It is indicated, according to the writer's observations, by the 

failure of Aucella and Inoceramus to occur together 

in the same bed. In fact in Alaska they have never 

been found associated in the same formation. Considering that species of Inoceramus are noted for being 

facies breakers and are found in most kinds of sediments except those that are conglomeratic, it appears 

that Aucella either lived in shallower waters than 

Inoceramus or that wherever it lived Inoceramus could 

not obtain a foothold. These possibilities are not mutually exclusive.

It has, also, been observed that Aucellas may become 

uncommon or disappear along the strike of certain 

beds even though lithologic characteristics have not 

changed. Such a relationship may be explained by an 

increase in depth of the sea bottom, by an increase in 

rate of sedimentation, or by lack of a hard substratum. 

Of course, the presence of only a few specimens of 

Aucella in a thick unit might be explained by submarine slumping and does not prove that the unit was 

deposited in shallow water.

SPECIATION IN AUCELLA 

RANGE OF VARIATION WITHIN ATJCELLAN SPECIES

With the various publications by Pompeckj, Pavlow 

and other paleontologists as background information, 

the writer attempted to identify the species of Aucella
SUCCESSION AND SPECIATION OF THE PELECYPOD AUCELLA 157

present in the Geological Survey collections from 

Alaska, California, and Oregon. At first many names 

were used. Then it was realized that most specimens 

could be placed easily in a few distinctive species, and 

that most of the remaining specimens were either deformed, immature, or poorly preserved or were connected with one of the species by specimens having 

transitional characteristics.

Fortunately it was possible to test these ideas concerning species of Aucella in the field where hundreds 

of specimens could be examined at many localities and 

at many stratigraphic levels. As a result the writer 

became convinced that Stanton's (1895, p. 42-47 

[1896]) idea that only a few species of Aucellas were 

present in the west-coast Mesozoic rocks was more 

nearly correct than Pavlow's idea that many species 

were present. It became apparent that neither Pavlow 

(1907) nor Anderson (1938, 1945) took into account 

the variations in shape, size, and ornamentation that occurred in a single Aucella population under different 

degrees of crowding. When allowance was made for 

such variations, it was found that the species were 

greatly reduced in number, but that they could be defined in such a manner as to be easily recognized by 

field geologists and used for mapping purposes. Such 

has been demonstrated in both Alaska and Oregon.

Most of the specimens of Aucella from North 

America that have been described can be accommodated 

in the few species listed on table 1.

AUCELLA CONCENTKICA (SOWEKBY)

Aucella concentrica (Sowerby) (see pi. 16, figs. 1-7) 

includes the specimens referred to A. bronni (Roullier), 

A. erringtoni (Gabb) in Meek (1865, p. 479-480, pi. 1, 

fig. 2), A. elongata Hyatt, and A. aviculaeformis Hyatt 

(Martin, 1926, p. 177, 216; Hyatt, 1894, p. 430-434; 

Pavlow, 1907, p. 14, 82; Crickmay, 1933, p. 53-56; Imlay, 1955, p. 83). A subspecies, A. concentrica leguminosa Stoliczka (Holdhaus, 1913, p. 405-408, pi. 97, figs. 

5a-d), has been recorded from the west side of Vancouver Island in the lower part of the range of A. concentrica (Sowerby) (Jeletsky, 1950, p. 27-29). It has 

also been found on the west side of Katmai Bay (pi. 16, 

figs. 8-10) on the Alaskan Peninsula (USGS Mes. Iocs. 

3124 and 3127) associated with A. concentrica. This 

subspecies differs from the typical species by being much 

more elongated posteriorly and by the umbones on 

both valves being considerably inflated. Its stratigraphic position on Vancouver Island suggests that its 

range is late Oxf ordian.

AUCELLA SPITIENSIS HOLBHAUS

Aucella spitiensis Holdhaus (pi. 16, figs. 11-17) has 

been recorded from northern Alaska in association with 

A. concentrica and the ammonite Amoeboceras (Imlay, 

1955, p. 84, pi. 9, figs. 1-10). This association shows 

that A. spitiensis existed in late Oxfordian or early 

Kimmeridgian time. It has been obtained in talus collections (USGS Mes. Iocs. 3124 and 3127) from the 

Alaskan Peninsula. Another record of A. spitiensis, 

or of a closely similar species, is from the west side of 

Vancouver Island in the upper part of the range of A. 

concentrica (Sowerby) (Jeletsky, 1950, p. 28,29), above 

beds containing A. concentrica leguminosa Stoliczka. 

Jeletsky (1950, p. 31, 32) suggests that the beds containing A. spitiensis are of early Kimmeridgian age.

AUCELLA KUGOSA (FISCHEK) AND A. MOSQUENSIS 

(VON BUCH)

Aucella rugosa (Fischer) (pi. 16, figs. 18, 19, 22-25) 

and A. mosquensis (von Buch) (pi. 16, figs. 20, 21) 

are widespread in Alaska in beds that the writer considers to be of middle Kimmeridgian to early Portlandian age (Imlay, 1955, p. 74, 75, 85). A. mosquensis 

may range a little higher than A. rugosa, however, into 

beds of middle Portlandian age. In Mexico it has been 

reported with the ammonites Kossmatia and Durangites (Burckhardt, 1912, p. 206, 221, 236). In California 

a few specimens similar to A. mosquensis have been 

found in the lower and middle parts of the Knoxville 

formation (Anderson, 1945, p. 940, 966). These specimens are possibly an aberrant variety of A. piochii 

(Gabb), but they have stouter umbones and shorter, 

less incurved beaks than is typical of that species. 

Their possible identity with A. mosquensis needs to be 

confirmed, however, by further collecting in the lower 

part of the Knoxville formation.

One consideration suggesting caution in identifying 

Aucella mosquensis in the Knoxville formation is its 

constant association with Aucella rugosa (Fischer) in 

Alaska. Of the two species, A. rugosa is much more 

abundant. In contrast not a single specimen of A. 

rugosa has been recorded from the west coast of the 

United States. Its absence, however, is in harmony 

with the absence of ammonites of middle Kimmeridgian 

to early Portlandian age in that area and is part of the 

evidence for dating the duration of the Nevadan 

orogeny of southwestern Oregon and northern California.

AUCELLA PIOCHII (GABB)

Aucella piochii (Gabb) (1864, p. 187, pi. 25, fig. 173) 

(see pi. 17? figs. 7-10? 12-29) was redescribed by
158 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

TABLE 1. Characteristic

Species

Aucetta rugosa (Fischer).. . .. .

AuceUa mosquensis (von Buch)- . .....

Aucella piochii (Gabb) __ . 

AuceUa flscheriana (d'Orbigny). . . . _ _ .

Aucetta okensls Pavlow. ------------

Aucetta volgensis Lahusen.... . _ ...

Aucella sublaevis Keyserling - - -.-.-.

Relative

size for 

genus

large.

 - .do ....

 - .do. ...

Small...- 

 ..do ....

Small. ......

large.

Cross section

pressed.

moderately convex.

convex. 

 -do 

Slightly inequivalved, 

plump.

very stout.

Shape of valve

Left valve

bones, flattened posteririorly, elongated obliquely.

elongated obliquely.

gated posteriorly.

gated posteriorly. 

 .do,. 

gated posteriorly.

siderably elongated, trigonal in outline.

ately elongated, ovate 

in outline.

gated posteriorly.

Strongly convex, ventral 

margin truncated.

gated in adult.

Eight valve

left valve.

vex.

flat.

 ..do. 

 ..do 

 .do ..... 

 - .do ... - . .- 

Strongly convex, ventral 

margin truncated.

gated in adult.

Beak of left valve

slightly over beak of 

right valve.

curved over beak of 

right valve.

curved.

slightly twisted forward. 

Long, slender, much incurved, slightly twisted 

forward. 

Narrow, not very prominent, gently incurved.

beak of right valve. 

Stout, curved over beak

of right valve. 

Stout, moderately incurved, slightly twisted 

forward.

Small, pointed, projecting.

curved.

Stanton (1895, p. 42-44 [1896]) and restricted to 

Aucellas whose left valves have a slender, obliquely 

ovate shape, a prominent, narrow umbo, a strongly incurved beak, and fairly regular weak concentric ribs 

and undulations. He noted that a few specimens have 

faint radiating striae. The species as defined by Stanton was subdivided into the following species by 

Pavlow (1907, p. 82, 83) on the basis of Stanton's publication and of fossils that Stanton sent to the University of Moscow:

Aucella, gabU Pavlow (1907, p. 54; Gabb, 1864, p. 187, pi.

25, fig. 173; Stanton, 1895, pi. 4, figs. 2, 3, 5 [1896]). 

russiensis Pavlow (1907, p. 50, 83; White, 1888, pi. 3,

figs. 10,11 [1889]). 

stantoni Pavlow (1907, p. 48; Stanton, 1895, pi. 4, figs.

6, 7[1896]). 

uncitoides Pavlow (1907, p. 61, 83; Stanton, 1895, pi. 4,

fig. 14 [1896]). 

andersoni Pavlow (1907, p. 57, pi. 4, fig. 7; Stanton, 1895,

pi. 4, fig. 8 [1896]).

suUnflata Pavlow (1907, p. 67, pi. 6, fig. 4a-c). 

tenuicollis Pavlow (1907, p. 49, pi. 3, fig. 6). 

hyatti Pavlow (1907, p. 49, pi. 3, figs. lOa, b).

In addition, one specimen figured by Stanton 

(1895, pi. 4, fig. 14 [1896]) as AuceUa piochii var. 

ovata was placed by Pavlow (1907, p. 61, 83) in a new 

species, A. uncitoides Pavlow. The writer considers 

the specimen in question to be merely an usually large 

specimen of A. piochii (see pi. 17, figs. 12,29) that lived 

under conditions favoring its growth.

All these species were accepted by Anderson (1945, 

p. 964^973), and the following were added.

Aucella gracilis Pavlow of Anderson (1945, p. 967, pi. 3,

fig.22a-c).

attenuata Anderson (1945, p. 970, pi. 12, fig. 4a-c). 

elderensis Anderson (1945, p. 967, pi. 4, figs. 1-4). 

Tmo&villensis Anderson (1945, p. 966, pi. 3, figs. 12-14, pi.

4, fig. 6). 

aff. A. bononiensis Pavlow (Anderson, 1945, p. 967, pi.

4,fig.lla-d). 

cf. A. bonowiensia Pavlow (Anderson, 1945, p. 968, pi.

6, fig. 5). 

terebratuloides Lahusen in Anderson (1945, pi. 13, figs.

7a,b). 

russienais Pavlow in Anderson (1945, p. 968, pi. 3, fig. 21).

Thus an assemblage of Aucellas from the Knoxville 

formation of Jurassic age that Stanton considered a 

single species was subsequently subdivided into 15 species. Apparently Stanton had an entirely different 

concept of a species than either Pavlow or Anderson. 

This difference in the writer's opinion reflects differences in training, in amount of fieldwork, and in stratigraphic application. Stanton was a practical geologist concerned with the stratigraphic usefulness of 

fossils. He spent several months in the field each year 

during most of his active life. He made superb fossil 

collections. His field notes dealing with stratigraphy 

are thorough and are still very useful. He recognized 

differences among the specimens of Aucella that are 

common in the Jurassic Knoxville formation, but as-
SUCCESSION AND SPECIATION OF THE PELECYPOD AUCELLA

North American species of Aucella

159

Concentric markings

Ribs

Sharp, regular, fairly low..

Irregular in strength and 

spacing.

High, narrow, widely and 

regularly spaced. 

Low, variable in strength, 

irregularly spaced.

- _do...._ - 

Sharp, low, widely spaced, 

some shells nearly 

smooth. 

Sharp, fairly high, moderately spaced.

Sharp, high, very widely 

spaced, becoming coarse 

in adult. 

Fine to coarse, fairly 

regular.

Commonly weak, become 

faint near ventral margin.

Highly variable, weak to 

strong, regular to irregular in spacing.

Undulations and 

constrictions

Weak undulations on 

some large specimens.

Common, irregularly 

spaced, conspicuous.

Fairly common, irregular, 

weak.

.. ...Ao....... ............ ..

-....do... -- -- .

Fairly common, irregular, 

generally weak.

A constriction occurs on 

several of the largest 

specimens. 

Irregular, weak to strong, 

present on medium to 

large specimens.

Radial markings

Ribs

. do..... .

 . _do- 

 .do.... .... -

Uncommon, 

weak, scattered.

 do . -

--.do .---

..-.do... ..... .

Striae

Fine, dense, continuous across 

concentric ribs.

Weak, scattered, 

mostly on umbones. 

Very fine, dense ...

Fairly fine, scattered, not evident on some 

specimens.

---..do --------

.---.do ... -------

-...do .... .. -

 ..do ... ....

Very fine, closely 

spaced.

Ranges

Northern Eurasia

Late Oxfordian to middle 

Kimmeridgian.

Late Oxfordian to Kimmerdigian.

Late Kimmeridgian to 

early Portlandian.

Portlandian (mainly 

middle and late).

Middle to late Portlandian (most common m 

late Portlandian). 

Latest Jurassic? (Riasanites Rjasanensis zone) 

and early Berriasian.

Late Portlandian, Berriasian, and early Valanginian. 

Middle to late Valanginian 

Hauterivian?

Valanginian (also, possibly late Berriasian).

Alaska

Late Oxfordian to 

middle Kimmeridgian.

Late Oxfordian to 

early Kimmeridgian. 

Middle Kimmeridgian 

to early Portlandian. 

Middle Kimmeridgian 

to early(?) Portlandian.

. .do .............

Probably early 

Valanginian.

Oregon and 

California

Late Oxfordian? to 

early Kimmeridgian.

Not identified.

Do.

Not definitely identified.

Middle to late Portlandian.

Middle? to late 

Portlandian.

Not identified.

Do. 

Do. 

Do.

Middle to late 

Valanginian.

cribed the differences to normal variation within a 

species, to environmental factors, or to accidents of 

preservation. In contrast, Pavlow and Anderson considered the differences worthy of specific distinctions 

and described them in great detail. As with many other 

paleontologists of their time, they made no allowance 

for biological or ecological factors in their definitions 

of species.

Concerning Aucella piochii (Gabb), the writer considers that Stanton's concept (1895, p. 42-43 [1896]) of 

the species is correct. In any large collection from a 

single locality (see pi. 17, figs. 12-29) in the Knoxville 

formation specimens can be selected that will fit the 

concepts of many of the species of Aucella described by 

Pavlow and Anderson, but many other specimens will 

not quite fit and yet they appear to be part of the same 

population as the described species. Whenever minute 

fragmentation of species results in the listing of many 

species of a single genus from a single locality the 

validity of the species may be suspect.

An extreme example of such fragmentation is afforded by Anderson (1945, p. 942, 971), who lists 11 

species of Aucella from 1 locality (California Acad. 

Sci. loc. 28037) near the top of the Knoxville formation. These species are reported to have been obtained 

from a thickness of 400 feet. Such a thickness in some 

parts of the world might represent considerable time, 

but within the 12,000 to 16,000 feet of the Knoxville

484259 50 2

formation, dated as middle to late Portlandian on the 

basis of ammonites, the 400 feet represents a minute 

part of Jurassic time. All the aucellan specimens except one from the locality in question may easily be assigned in the writer's opinion to two species, namely 

Aucella piochii (Gabb) and A. fischeriana (d'Orbigny). 

The exception is A. occidentalis Anderson (1945, p. 971, 

pi. 12, fig. 2a-c), which resembles A. volgensis Lahusen 

and will be discussed later.

AUCELLA FISCHERIANA (d'ORBIGNY)

Aucella fiscTieriana (d'Orbigny) (pi. 17, figs. 1-6,11) 

is employed herein for Aucellas from California and 

Oregon that have been described under the following 

names:

Aucella piochii var. ovata Stanton (1895, p. 43, 44, pi. 4,

figs. 11-13 [1896]). 

terebratuloicles Lahusen in Pavlow (1907, p. 60, 83;

Stanton, 1895, pi. 4, figs. 11-13 [1896]). 

sollasi Pavlow (1907, p. 39; Stanton, 1895, pi. 4, figs. 4

[1896]). 

fischeriana (d'Orbigny) in Anderson (1945, p. 970, pi.

12, figs. 1,5). 

trigonoides Lahusen in Anderson (1945, p. 971, pi. 13,

figs. 4a-e). 

sollasi Pavlow in Anderson (1945, p. 965, pi. 3, figs. 8-11;

pi. 2, figs. 9,10).

The Aucellas from the west coast listed under the 

above names were considered by Stanton (1895, p. 43
160 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

[1896]) to be merely a variety (subspecies of modern 

usage) of Auoella piochii and to differ from the typical 

variety "by its larger size, more broadly triangular 

form, greater convexity, and coarser more remote concentric undulations. The posterior ear is scarcely at all 

developed in either valve, and the beak of the right 

valve is much more prominent and pointed so that the 

hinge line is short and angular."

Most of the specimens in the Geological Survey collections that are labeled by Stanton as Aucella piochii 

var. ovata greatly resemble A. trigonoides Lahusen 

(1888, p. 36, 37, pi. 2, figs. 21-24; Pavlow, 1907, p. 55, 

pi. 4, figs. 23-25), as noted by Stanton (1895, p. 43 

[1896]), but likewise resemble A. fischeriana 

(d'Orbigny) (1845, p. 472, pi. 46, figs. 8-10; Lahusen, 

1888, p. 37, pi. 2, figs. 14-20; Pavlow, 1907, p. 58, pi. 

4, figs. 15-19). Lahusen (1888, p. 37) distinguishes A. 

fischeriana (d'Orbigny) from A. trigonoides Lahusen 

by its finer ribbing, more swollen right valve, and more 

elongate, less trigonal-shaped shell. The writer, after 

examining the various illustrations of these species and 

several specimens of each species from Russia identified 

by A. P. Pavlow in 1892, doubts very much whether 

A. trigonoides is more than a variant of A. fischeriana. 

Regardless of possible synonomy, most of the specimens 

in question from California show characteristics that 

are typical of A. fischeriana. Furthermore, the name 

A. fischeriana (d'Orbigny) has the advantage over A. 

trigonoides Lahusen of being one of the oldest used 

for an Aucetta; both Pavlow and Anderson have published excellent illustrations of the species, and both 

authors mention that the species is very common near 

the top of the Jurassic.

Interestingly, Pavlow (1907, p. 55, 58) notes that 

some specimens of Aucella trigonoides Lahusen greatly 

resemble A. gdbbi Pavlow (1907, p. 54), but that other 

specimens are more triangular, more elongate, and 

have shorter beaks. As A. gabbi is a synonym of A. 

piochii (Gabb), Stanton's (1895, p. 43 [1896]) comparison of his A. piochii var. ovata with A. trigonoides 

is quite apt. Similarly the writer has noted that in 

beds containing both A. piochii (Gabb) and A. fischeriana (d'Orbigny), there are many small specimens that 

could belong to A. piochii or could be immature specimens of A. fischeriana. Such an association suggests 

that A. fiscfieriana is closely related to A. piochii.

Aucella fischeriana (d'Orbigny) is probably represented in the lower and middle parts of the Knoxville 

formation by the specimens that Pavlow (1907, p. 39; 

Stanton, 1895, pi. 4, fig. 4 [1896]) and Anderson (1945, 

p. 965, pi. 2, figs. 9, 10, pi. 3, figs. 8-11) referred to A. 

sottasi Pavlow. It is common, however, only in the 

upper part of the formation. It is associated with A.

piochii (Gabb) throughout its range and becomes more 

common than that species at the top of its range.

AUCELLA OKENSIS PAVLOW

Aucella okensis Pavlow (1907, p. 40, pi. 1, figs. lOa-c, 

lla-c) (see pi. 18, figs. 15-19) is one of the most easily 

recognized species of Aucella because of its large size 

and very coarse, widely spaced ribbing. In some respects it resembles certain species of Inoceramus. It has 

considerable stratigraphic value, too, because it occurs 

at the very base of the Cretaceous. In North America 

it has been identified in northern Alaska, in the Upper 

Yukon region in east-central Alaska, in the Harrison 

Lake area of British Columbia (Crickmay, 1930, p. 

40-42), and in the west side of Vancouver Island 

(Jeletsky, 1950, p. 42, 43). One specimen illustrated 

by Pavlow (1907, pi. 1, figs. lOa-c) is reported to be 

from California. This report may be an error because 

the collections of the U. S. Geological Survey do not 

contain any representative of the species from the 

west-coast States. Anderson (1945, p. 940, 942) mentioned the species as occurring in the uppermost part 

of the Knoxville formation but did not publish any 

illustration. It is probable that he had in mind some 

variant of A. fischeriana (d'Orbigny).

AUCELLA SUBOKENSIS PAVLOW

Aucella subokensis Pavlow (1907, p. 41, 42, pi. 1, 

figs. I7a-c) (see pi. 18, figs. 9,10) is associated with A. 

oJeensis in the basal Cretaceous beds in Alaska and 

northern Eurasia. It resembles A. oJeensis Pavlow considerably, but is distinguished by its smaller size, more 

elongate, trigonal outline, smaller beaks, and finer, 

more closely spaced ribs. Its characteristics are somewhat intermediate between A. okensis and A. fischeriana (d'Orbigny). From the latter it is distinguished 

by being larger, stouter, and less elongate, and by having coarser, sparser ribbing. Somewhat less comparable is A. volgensis Lahusen (1888, p. 38, pi. 3, figs. 

1-16), which is more elongate posteriorly, has more 

elongate umbones, and bears weaker, less regular, closer 

spaced ribs.

AUCELLA VOLGENSIS LAHUSEN

Aucella volgensis Lahusen (pi. 18, figs. 7, 8, 12-14) 

has features intermediate between those of A. subohensis Pavlow and A. crassicollis Keyserling. Comparisons with A. suboJcensis have been made under the 

discussion of that species. It differs from A. crassicollis by being larger, higher, more obliquely elongated, 

and less inflated, by the beak on the left valve being 

much less incurved, and by the right valve being much 

less convex. When specimens showing both valves are
SUCCESSION AND SPECIATION OF THE PELECYPOD AUCELLA 161

compared in lateral view the differences are striking. 

A. crassicollis is much more inflated and more nearly 

equivalved.

The range of Aucella volgensis according to Lahusen (1888, p. 26, 38, 39) in his original description 

is from the Late Jurassic zone of Craspedites nodiger 

Eichwald into the earliest Cretaceous zone of Subcraspedites spasskensis. Its range according to Pavlow (1907, p. 27, chart opposite p. 84) is through the 

lowest three zones of the Cretaceous as high as the 

base of the zone of Polyptychites keyserlingi, and it is 

most abundant in the lowest zone of Subcraspedites 

spasskensis. In spite of the different ranges assigned 

by these authors, their published illustrations show 

that they were discussing the same species. Confirmation of this is afforded by three specimens identified 

by Pavlow and sent by him to the U. S. National 

Museum in 1892.

Aucella volgensis Lahusen has not been definitely 

identified in North America. This seems rather strange 

considering that it is well characterized, has a long 

range, and is fairly common in northern Eurasia. The 

specimens from northern Alaska that the writer assigns to A. subokensis and A, crassicollis were examined carefully to see if any of them might more 

properly be assigned to A. volgensis. Jeletsky (1950, 

p. 41) mentions the presence of some Aucellas similar 

to A. volgensis Lahusen in beds of Early Cretaceous 

age on the west side of Vancouver Island. In California, an AuceUa found in the basal sandy beds of 

the Cretaceous was identified by Anderson (1945, p. 

972, pi. 10, fig. 1) as Aucella aff. A. volgensis Lahusen, 

but he notes that his specimen does not conform to the 

published, figures of the species.

Possibly Aucella volgensis is represented in the 

highest Jurassic beds in California by the specimens 

that were named A. occidentalis Anderson (1945, p. 

971, 972, pi. 12, figs. 2a-c). This species is represented 

by 3 specimens found only at 1 locality that furnished 

many specimens of A. fischeriana (d'Orbigny) and A. 

piochii (Gabb). It differs from the associated A. 

 fischeriana (d'Orbigny) by being considerably more 

convex, by its left valve having a much stouter umbo 

and a less strongly incurved beak, by its right valve 

being more inflated, and by its ribbing being more irregular in strength and spacing. It differs from A. crassicollis Keyserling in the overlying Cretaceous beds by 

having a much less convex right valve. Its chances of 

being derived from the Cretaceous beds because of 

some accident of stream erosion, or mishandling, seems 

unlikely because three specimens were found. It is 

possibly a representative of A. volgensis Lahusen, but

its identification with that species or any other species 

cannot be made until a sufficient number of specimens 

are found to show its range in variation.

AUCELLA STTBLAEVIS KEYSERLING

Aucella sublaevis Keyserling (pi. 18, figs. 1-6, 11) 

is characterized by being small and plump, by the 

right valve being only slightly smaller and less convex than the left, by the ventral margins of the two 

valves bending abruptly toward each other, and 

by the shell bearing numerous fine radial striae. 

In Alaska it occupies a stratigraphic position directly 

above A. okensis Pavlow and A. subokensis Pavlow and 

directly below A. crassicollis Keyserling. It has not 

been found in Cretaceous beds 'in the west-coast States. 

In northern Kussiia and Spitzbergen A. sublaevis is 

reported in beds of middle to late Valanginian age 

(Pavlow, 1907, p. 64; Sokolov and Bodylevsky, 1931, 

p. 118) and is associated at the top of its range with 

A. crassicollis Keyserling. Some specimens from 

Hauterivian beds 'in northern Germany have been 

assigned to A. sublaevis Keyserling (Sokolov and 

Bodylevsky, 1931, p. 45, 118; Wollemann, 1900, pi. 2, 

figs. 8, 9; Pavlow, 1907, p. 63, 79), but they have a 

much less convex right valve.

AUCELLA CRASSICOLLIS KEYSERLING

Aucella crassicollis Keyserling (pi. 19, figs. 1-24) is 

employed herein for Aucellas from Alaska and the 

United States that have been described under the 

following names:

Amelia piochii (Gabb) in part (1869, pi. 32, figs. 92, 92a, b). 

ooncentrica Fischer in White (1884, p. 13, 14, pi. 6, figs.

2-12; 1888, p. 231, pi. 4, figs. 3-5, 11-17, 21 [1889]). 

crassicottis Keyserling (Stanton, 1895, p. 45-47, pi. 5,

figs. 1-4, 7-13, pi. 6, figs. 1-5[1896]). 

crassicollis Keyserling (Pavlow, 1907, pi. 5, figs. 8, 10, 11,

pi. 6, figs. 3-5). 

crassa Pavlow (1907, p. 69; White, 1888, pi. 4, figs. 16,

17 [1889]; White, 1884, pi. 6, figs. 9, 10; Stanton, 1895,

pi. 5, figs. 1-6, 9, pi. 6, figs. 1, 2 [1896] ; Stewart, 1930,

p. 112, pi. 2, fig. 4). 

keyserUngi Lahusen in Pavlow (1907, p. 62; Stanton,

1895, pi. 5, figs. 12,13 [1896]). 

terebratuloides var. regularis Pavlow (1907, p. 60, 83, pi.

5, fig. 7). 

terebratvloides Lahusen in Pavlow (1907, p. 60, 81; White,

1884, pi. 6, figs. 2-5). 

piriformis Lahusen in Pavlow (1907. p. 63, 81; White,

1884, pi. 6, figs. 6, 7; Anderson, 1938, pi. 8, figs. 3, 4). 

solida Lahusen in Pavlow (1907, p. 64, 81; White, 1884,

pi. 6, fig. 8; 1888, pi. 4, fig. 21 [1889]; Anderson, 1938,

p. 105, pi. 10, figs. 3,4). 

inflata Toula in Pavlow (1907, p. 68, 81; White, 1884,

pi. 6, fig. 11; Anderson, 1938, p. 104, pi. 8, figs. 5, 6). 

undtoides Pavlow (1907, p. 83; Stanton, 1895, pi. 6, fig.

5[1896]).
162 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

The Aucellas described by C. A. White in 1884 were 

obtained from a single locality in the Port Moller area 

near the southwest end of the Alaskan Peninsula. 

White (1884, p. 14) considered that the fossils showed 

such perfect gradation of form that all belonged without doubt to one variable species. He published many 

figures simply to show the amount of variation possible 

within a single species. To the writer his conclusions 

are sound. Yet Pavlow (1907, p. 81) assigned the 

specimens figured by White to five species.

Among the specimens from California described by 

T. W. Stanton as Aucella crassicoUis Keyserling, Pavlow (1907, p. 62, 69) recognized four species. In a 

California collection of Aucellas at the University of 

Moscow, Pavlow (1907, p. 83) recognized a variety of 

still another species. However, he referred most of 

the specimens to A. crassa Pavlow and A. crassicoUis 

Keyserling. Most of the Aucellas from the Cretaceous 

of California discussed by Pavlow were considered by 

Stewart (1930, p. 112, 113) to belong to one species 

which he called A. crassa Pavlow rather than A. crassicoUis Keyserling because he did not know the relationships of the American Aucellas with the Eurasian 

Aucellas and preferred, therefore, to use a local name.

The writer agrees with Stanton (1895, p. 46 [1896]) 

and Stewart (1930, p. 108, 112, 113) that the robust 

Aucellas in the Early Cretaceous Paskenta formation 

(equals upper part of Knoxville formation of Stanton, 

1895, p. 11-13 [1896]) belong to a single highly variable 

species and that the variants to which Pavlow has attached so many names are connected by many specimens showing transitional characteristics. The variation in coarseness of ribbing is probably mostly biologic, 

but is no greater than in other species of Aucella as 

defined by Pavlow. The variations in shape, in curvature of the beak, or in the strength of constrictions are 

probably related to crowding on the sea bottom, to 

changes in the environment during growth, or to deformation after burial. The shape of any particular 

species of Aucella, is not apt to be any more stable than 

that of other gregarious pelecypods, such as Ostrea or 

Gryphea, and considerable allowance must be made, 

therefore, in the definition of species of such pelecypods. 

If any of the named variants had stratigraphic significance, the name might properly be retained as a subspecies, but such has not yet been proven.

Among the variants of Aucella crassicoUis Keyserling to which Pavlow gave specific names, the most common has been called A. crassa Pavlow (pi. 19, figs. 10, 

11,13,16,18-20, 23, 24). This variant is highly convex 

in cross section; its left valve is fairly round in outline 

and has a strongly incurved beak; its shell bears pronounced, widely spaced concentric ribs and generally

weak constrictions, but may be weakly ribbed. The 

next common variant represented is the one to which the 

name A. crassicoUis was originally applied (pi. 19, figs. 

3-6, 9, 17, 22). This variant differs from A. crassa by 

being more elongate, by having at least one pronounced 

constriction that separates a swollen umbonal area from 

the rest of the shell, and by its ribbing varying from 

fine to coarse on different specimens. However, the 

umbonal part of the shell is identical in appearance 

with small specimens of A. crassa, and the greater 

elongation of A. crassicoUis than of A. crassa appears 

to be related to the development of one or more constrictions that modified the normal growth of the shell.

The other variants of Aucella crassicoUis are not 

common in the basal Cretaceous beds in California and 

Oregon but can be selected in large collections of Aucellas. The variant called A. solida Lahusen (pi. 19, fig. 

12, 21) differs from the typical variant A. crassicoUis 

by being less elongate, by lacking a constricted umbo, 

and by its surface being nearly smooth, or marked by 

a few wide concentric constrictions. The variant A. 

inftata Toula is as convex as A. crassa, but differs in 

being less regularly rounded, a little more elongate posteriorly, and generally has slightly finer ribbing. The 

variant that Pavlow (1907, p. 83; Stanton, 1895, pi. 

6, fig. 5 [1896]) referred to A. undtoides Pavlow is 

slightly more elongate than the associated variant called 

A. crassa. A comparable specimen is shown on plate 19, 

fig. 14.

Another possible variant is Aitoella Tceyserlingi Lahusen (1888, p. 40, 41; Pavlow, 1907, p. 62, 63) (see pi. 

19, figs. 1, 2, 7, 8, 15), which differs from A. crassa by 

being much less convex and slightly more elongate, 

by having rather closely and regularly spaced thin 

concentric ribs, and by the presence rarely of radial ribs. 

A. keyserlingi appears to be a distinct, well-characterized species in Eurasia. In collections from California 

and Oregon, however, specimens that fit the descriptions of A. keyserlingi fairly well are associated with 

others that are transitional to A. crassa and A. 

crassicoUis.

Evidently in California and Oregon the robust Aucellas of middle to late Valanginian age all represent one 

variable species. This conclusion does not mean that 

all the robust Aucellas of the same age in Eurasia belong 

to one species. There may be local species in Eurasia 

that never existed in North America and the names 

of some Eurasian species may have been misapplied in 

North America.

ATJCELLAN SPECIES OF QUESTIONABLE VALIDITY

In addition to the 10 aucellan species from North 

America whose validity seenis well established, there
SUCCESSION AND SPECIATION OF THE PELECYPOD AUCELLA 163

may be several others whose validity can be determined 

only by additional fieldwork. These include the species 

identified by Anderson (1938, p. 106, pi. 8, figs. 8, 9) 

with Aucella lahuseni Pavlow (1907, p. 51, pi. 3, figs. 

16-23), which species occurs in Russia in the latest 

Jurassic and the earliest zone of the Cretaceous. Anderson's specimens have more elongate umbones and 

more strongly incurved beaks than A. lahuseni, but 

otherwise his comparison is quite apt. He notes, however, that his specimens are from the basal beds of the 

California Cretaceous and are younger than A. lahuseni. 

Interestingly the specimen shown by Anderson on his 

plate 8, figure 8, is remarkably similar to one of the 

specimens figured by Stanton (1895, pi. 4, fig. 14 

[1896]) that Pavlow (1907, p. 61, 83) placed in a new 

species, A. uncitoides. Also, Andersen's specimen on 

his plate 8, figure 9, is nearly identical with a specimen 

figured by Stanton (1895, pi. 4, figs. 11-13 [1896]) that 

Pavlow (1907, p. 60, 83) placed in A. terebratuloides 

Lahusen. The writer, as discussed previously, considers the last mentioned specimen as an immature 

representative of A. fischeriana d'Orbigny and the 

other specimen illustrated by Stanton on his plate 4, 

figure 14, as an adult of A. piochii Gabb. The discovery 

of these species in the basal beds of the Paskenta formation, overlying beds where they normally occur, 

suggests that they may have been derived by erosion of 

the Jurassic Knoxville formation. 

Another Aucella was referred by Anderson (1945, p.

968. pi. 6, figs. 7a-c) to A. Jcrotovi Pavlow (1907, p. 32, 

pi. 2, figs. 31,32) on the basis of specimens from Quinto 

Creek, Stanislaus County, Calif. The species occurs 

in Russia in the latest Jurassic. Anderson's specimen 

of Aucella was considered by him to be of Late Jurassic 

age because of its association with certain ammonites 

and with Aucella stantoni Pavlow (Anderson, 1945, p.

969. 983, 984). The ammonites probably belong to the 

genera Lytoceras and Phylloceras and, as such, have 

little age value. However, A. stantoni is a synonym 

of A. piochii (Gabb) in the writer's opinion and is 

indicative of a middle to late Portlandian age. This 

identification is confirmed by the presence of A. piochii 

(Gabb) from Quinto Creek in the collections at Stanford University.

Aucella krotovi Pavlow of Anderson differs from any 

other known species in the Jurassic Knoxville formation by the beak on its left valve being only weakly incurved and by the umbonal part of the right valve 

being nearly as prominent as the corresponding part 

of the left valve. In most characteristics it resembles 

A. Jcrotovi Pavlow from Russia, but differs by having 

a relatively larger, more convex right valve.

484259 59 3

A small, elongate Aucella from the Cretaceous Paskenta formation was recorded by Anderson (1938, p. 

106, pi. 29, figs. 7-9) under the name A. nuciformis 

Pavlow (1907, p. 52, pi. 3, figs. 27a-c, 28a-c), which 

species occurs in Russia in the Berriasian. The specimen illustrated by Anderson on his plate 29, figures 8,9, 

is a left valve that resembles the left valve of A. nuciformis as figured by Pavlow, but could be an immature 

specimen of A. crassicollis (Keyserling). The other 

specimen illustrated by Anderson on his plate 29, figure 7, is characterized by its right valve being nearly 

as convex as the left valve and by having swollen umbones that are marked ventrally by a constriction. 

This specimen appears to be a variant of A. crassicollis that is slightly more elongate than average for the 

species. The identification of such Aucellas can be 

made more easily in the field than in the laboratory 

because many more specimens are available to show 

the possible variations within aucellan populations.

Still other aucellan species may be present in Cretaceous beds near McCarthy Creek in Tehama County, 

Calif., above the 1,200 to 1,500 feet, or more, of sandy 

beds that contain an abundance of A. crassicollis Keyserling. According to Anderson (1932, p. 322; 1938, 

p. 46), these sandy beds are overlain by a sequence 

consisting mostly of shale that has furnished a few 

specimens of Aucella. In particular he records Aucella 

as much as 1,200 feet above the highest occurrence of 

Valanginian ammonites near the base of the shale sequence. This record is interesting because these shale 

beds were considered by Stanton (1895, p. 17, 18 

[1896]) to belong in the lower part of the Horsetown 

formation. The question arises whether the Aucella 

recorded by Anderson actually belongs to that genus, 

or to the similar appearing genus Aucellina of late 

Aptian to Cenomanian age, or even to an immature 

Inoceramus.

Stratigraphically the presence of Aucella on McCarthy Creek as much as 1,200 feet above the top of the 

sandy beds containing Aucella crassicollis Keyserling 

seems improbable, considering that Stanton (1895, p. 

18 [1896]) found the late Hauterivian ammonite 

"Neocraspedites" aguila Anderson (USGS Mes. Iocs. 

1092, 2267) nearby in Tehama County only 400 to 500 

feet above the beds containing Aucella crassicollis 

Keyserling. The age of this ammonite is determined 

in the Ono area, Shasta County, by its position only a 

few hundred feet above beds containing the middle 

Hauterivian ammonite Simbirskites (Anderson, 1938, 

p. 47, 111, 122, 147, 154, 208) and many hundreds of 

feet below beds containing the early Barremian ammonite Pulchellia (Anderson, 1938, p. 65, 197). The 

age of 'W aguila Anderson is younger, therefore, than
164 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

the reported occurrence of Aucella in beds of early 

Hauterivian age in England (Woods, 1905, p. 71) and 

of middle Hauterivian age in northern Germany (Wollemann, 1900, p. 56-59; Pavlow, 1907, p. 79) and central 

Russia (Sokolov and Bodylevsky, 1931, p. 118; Chetyrkina and Shugin, 1937, p. 25).

These occurrences of Aucella in beds of Hauterivian 

age have not been well substantiated. Aucellas are 

easily reworked into younger beds, in a manner similar 

to Gryphaeas and Belemnites. The occurrence in the 

early Hauterivian Claxby Ironstone in England is particularly suspect because Spath (1924, p. 81, 82) reports that some of the ammonites are derived from the 

underlying formations of Valanginian and Berriasian 

age. Except for these possible occurrences, Aucella 

disappeared abruptly at the end of Valanginian time 

and, therefore, the higher occurrences of Aucella on 

McCarthy Creek reported by Anderson are probably 

misidentifications.

It is possible that the specimens in question from 

McCarthy Creek belong to the genus Aucellina, which 

is closely similar to Aucella in shape and ornamentation. It differs from Aucella mainly by lacking an articulating groove in the hinge area of the left valve, 

by the right valve having a long, low, flat anterior ear, 

instead of a short triangular ear, and by the presence 

of a comblike row of small teeth on both edges of the 

byssal notch (Pompeckj, 1901, p. 365, 366; Pavlow, 

1907, p. 85). These features that distinguish the two 

genera are commonly not preserved or exposed and 

generally have to be exposed by laborious picking and 

grinding methods. The genus Aucellina has been recognized in Albian beds in the western interior of Canada (McLearn, 1945, pi. 5, fig. 3,1948), in Alaska (Imlay and Reeside, 1954, p. 229, 240), and in the Mitchell 

area of central Oregon. It is probably represented in 

California in beds of Late Aptian and Albian age by 

specimens that Anderson (1938, p. 65, 107) refers to 

Aucella, but the hinge characters of those specimens 

should be examined to decide their generic assignment.

It is possible, also, that the specimens recorded as 

Aucella by Anderson from 1,200 feet above sandy beds 

containing Valanginian ammonites are actually immature specimens of Inoceramus ovatoides Anderson 

(1938, p. 100, pi. 6, fig. 2). The immature specimens of 

this species, which were named /. colonicus Anderson 

(1938, p. 100, pi. 4, figs. 10-12, pi. 5, fig. 1), are similar 

in shape to Aucella piochii (Gabb). Their identification with Inoceramus rather than Aucella ordinarily 

should be easily made because their shell has an inner 

nacreous layer and an outer prismatic layer. Very 

small specimens lacking the prismatic layer might

easily be mistaken for Aucella, however, as even T. W. 

Stanton was confused. In his notebook, dated September 3, 1900, he mentions finding a "Crioceras and a 

small Aucellafn (USGS Ales. loc. 2269), about threequarters of a mile southeast of the building at the Wilcox Ranch and from 400 to 500 feet above the sandy 

beds containing Aucella crassicollis Keyserling. The 

specimen of "Criocerftx" herein identified with IIoplocrioceras remondi (Gabb), appeared to Stanton to be 

at about the same level as USGS Mes. Iocs. 1092 and 

2267, from which he obtained an ammonite now identified as "A7eocraspedites" aguila Anderson. Stanton had 

collected the same ammonites near Ono, Shasta County, 

and had not found Aucella with them. lie was much 

puzzled, therefore, to find an Aucetta-YikQ pelecypod 

associated with these ammonites elsewhere. The pelecypod that puzzled Stanton is about 11 millimeters in 

length, has a thin nacreous layer, and is indeed similar 

in shape to immature Aucellas. Its nacreous layer and 

its shape can be matched, however, with immature 

specimens of Inoceramus ovatoides Anderson in the 

Geological Survey collections.

STRATIGRAPHIC DISTRIBUTION OF AUCELLA

The stratigraphic distribution of the common species 

of Aucella in the Western States and Alaska is shown 

on figure 36. Seven zones based on species of Aucella 

are clearly defined. In addition the zone of Aucella 

concentrica may be devisible locally into two subzones 

by the presence of A. concentrica leguminosa Stoliczka 

in the lower part of the zone and A. spitiensis Holdhaus 

in the upper part. Such a division still has to be 

proved finally by fieldwork. Also, the overlap of the 

range of A. concentrica with that of A. rugosa (Fischer) 

and the associated A. mosquensis (von Buch) has 

proved useful stratigraphically in Alaska. In the 

Lower Cretaceous rocks there may be another zone 

between the zones of A. okensis Pavlow and A. sublaevis 

Keyserling that should be represented by A. volgensis 

Lahusen. This seems probable considering the ranges 

reported for those species in Eurasia, the fact that A. 

volgensis appears to be well characterized, and the 

reported occurrence of an Aucella similar to A. volgensis from the west side of Vancouver Island (Jeletsky, 

1950, p.41).

The usefulness of these seven zones for mapping purposes is evident, but it could be greatly increased by 

careful studies of the population variation and stratigraphic succession of Aucella. Most of such work must 

be done in the field rather than the laboratory because 

of the greater ease in examining great numbers of 

Aucellas at many places and many levels.
SUCCESSION AND SPECIATION OF THE PELECYPOD AUCELLA 165

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166 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

CONCLUSIONS

In summation, Aucella has been divided into so 

many species on the basis of minute differences of 

shape, size, and ornamentation that in many large 

collections the so-called species appear to grade into 

each other and to represent a single population. Most 

authors dealing with Aucella have not considered that 

an attached gregarious pelecypod is apt to exhibit 

considerable variation owing to crowding or to slightly 

different ecological conditions from place to place. 

Some of the species that have been described have 

been based on immature or deformed specimens. If 

species of Aucella are denned, making allowance for 

both biological and environmental factors, their 

numbers are greatly reduced, but the specific concepts 

can be grasped and applied readily by field geologists 

for mapping purposes as has been done in recent years 

in Alaska and in the west-coast States.

DESCRIPTIONS OF MENTIONED U. S. GEOLOGICAL 

SURVEY MESOZOIC LOCALITIES

997. Half a mile northwest of Snellings Ranch, near 

Paskenta, Tehama County, Calif. J. S. Diller 

and James Storrs, 1893.

1010. One-fourth mile northwest of Shelton Ranch buildings, in upper part of sandy beds containing abundant Aucellas, Tehama County, Calif. J. S. Diller 

and James Storrs, 1893.

1091. Half a mile east of Wilcox Ranch buildings, in upper 

part of sandy beds containing abundant Aucellas, 

Tehama County, Calif. J. S. Diller, T. W. Stanton, 

and James Storrs, 1893.

1092. One-half to three-fourths of a mile northeast of Wilcox Ranch buildings, in lower 200 feet of shale beds 

directly overlying the sandy beds containing Aucella, 

crassicollis Keyserling, Tehama County, Calif. J. 

S. Diller, T. W. Stanton, and James Storrs, 1893.

1225. Knoxville formation at Buck Hill near Cache Greek, 

5 miles northeast of Palmer Ranch, Lake County, 

Calif. T. W. Stanton, 1894.

2267. One-half to three-fourths of a mile northeast of Wilcox Ranch buildings, about 400 to 500 feet above 

the top of the sandy beds containing Aucella crassicollis Keyserling, Tehama County, Calif. T. W. 

Stanton, 1900.

2269. About three-fourths of a mile southeast of Wilcox 

Ranch buildings, from 400 to 500 feet above the 

top of the sandy beds containing Aucella crassicollis Keyserling, Tehama County, Calif. T. W. Stanton, 1900.

2275. Knoxville formation, 5 miles west of Lowry's Ranch 

in gulch south of North Fork of Elder Creek, Tehama County, Calif. T. W. Stanton, 1900.

2285. Knoxville formation, Stony Creek at Stulls Hole, 

about 5 miles west of Fruto, Glenn County, Calif. 

T. W. Stanton, 1900.

2287. Conglomeratic sandstone, 450 feet thick, overlying 

shale beds containing Aucella piochii (Gabb), in 

Stony Creek about 5 miles west of Fruto, Glenn 

County Calif. T. W. Stanton, 1900.

3124. Naknek formation, west side of Katmai Bay, 2% miles 

southwest of village of Katmai, Alaskan Peninsula, 

Alaska. G. C. Martin, 1904.

3127. Naknek formation, from talus half a mile north of 

TJSGS Mes. loc. 3124 and at about same stratigraphic position. G. C. Martin, 1904.

10248. Naknek formation, about 500 feet above sea level on 

Bear Mountain, Katmai Bay, Alaskan Peninsula, 

Alaska. C. N. Fenner, 1919.

11360. Naknek formation, Fossil Creek, north of Lake 

Becharof, southwest Alaska. Dr. Laymore, 1922.

20343. Swift formation, sandy shale above thick sandstone 

ledge in upper part of lower member, on north side 

of Great Northern Railway about one-quarter of 

a mile east of Autumn Creek at south side of Glacier Park, Mont. Wm. Cobban and R. W. Im-lay, 

1946.

21028. Kingak shale, Canning River, 2V2 miles south of Black 

Island, lat 69°30'45" N., long 146°18'45" W., northern Alaska. George Gryc, 1947.

22127. Tiglukpuk formation, large cutbank on southwest side 

of Kukpowruk River, lat 68°42'30" N, long 163°14' 

W., northern Alaska. E. G. Sable, 1949.

22472. Okpikruak formation, north bank of Seagull Creek, 

Nimiuktuk Valley, DeLong Mountains, lat 68°19'50" 

N., long 159°59' W., northern Alaska. M. C. and 

A. N. Lachenbruch, 1950.

22514. Okpikruak formation, northeast of Ekakevik Mountain, 

lat 68°36' N., long 156°57' W., northern Alaska. B. 

H. Kent, 1950.

22724. Okpikruak formation, ridge one-fourth of a mile west 

of lakes at base of Thunder Mountain, lat 68°40'30" 

N, long 160°20'50" W., northern Alaska. R. H. 

Morris, 1951.

22736. Okpikruak formation, east bank of Nuka River, lat 

68°40'30" N, long 160°03' W., northern Alaska. R. 

H. Morris, 1951.

22757. Okpikruak formation, Kemik Creek, lat 69°26' N, long 

147° 10' W., northern Alaska. Samuel Keller, 1951.

22762. Okpikruak formation, Kashivi Creek, lat 69°12' N, 

long 147°44' W., northern Alaska. Samuel Keller, 

1951.

22768. Kingak shale, from 500 to 800 feet above local base 

at Lupine River, lat 68°52' N., long 148°22' W., 

northern Alaska. Samuel Keller, 1951.

22769. Kingak shale, about 300 feet above local base at Lupine

River, Iat68°52' N., long 148°22' W., northern Alaska.

Samuel Keller, 1951. 

22780. Okpikruak formation, hills three-fourths of a mile east

of east-central fork of Driftwood Creek, lat 68°38'05"

N, long 160°29'20" W., northern Alaska. E. G.

Sable, 1951. 

22790. Okpikruak formation, north bank of Nuka River, lat

68°42'10" N., long 159°56'50" W., northern Alaska.

E. G. Sable, 1951. 

23554. Okpikruak formation, north bank of Nuka River, lat

68°40'45" N., long 160°02'45" W., northern Alaska.

E. G. Sable, 1951. 

23560. Okpikruak formation, north bank of Nuka River, lat

68°41'30" N., long 159°59' W., northern Alaska.

E. G. Sable, 1951.
SUCCESSION AND SPECIATION OF THE PELECYPOD AUCELLA 167

LITERATURE CITED

Anderson, F. M., 1932, Jurassic and Cretaceous divisions in the 

Knoxville-Shasta succession of California: Mining in California, v. 28, nos. 3, 4, p. 311-328, 5 figs., 2 pis., correlation 

table.

 1938, Lower Cretaceous deposits in California and Oregon: Geol. Soc. America Spec. Paper 16, 339 p., 84 pis., 

3 figs.

 1945, Knoxville series in the California Mesozoic: Geol.

Soc. America Bull., v. 56, no. 10, p. 909-1014, 15 pis.

Burckhardt, Carlos, 1912, Faunes jurasiques et cretaciques de 

San Pedro del Gallo (Etat de Durango, Mexico) : Bol. Inst. 

Geol. Mexico, no. 29, 264 p., 46 pis.

Chetyrkina, A. A., and Shugin, A. A., 1937, Geological description of the Vjatka-Kama phosphorite-bearing area, in Geological investigations of agricultural ores USSR: Sci. Inst. 

Fertilizers, Trans. 142, p. 22-31,1 fig.

Cox, L. R., 1940, The Jurassic Lamellibranch fauna of Kuchh 

(Cutch) : Paleontologia Indica, ser. 9, v. 3, pt. 3, p. 1-157, 

pis. 1-10.

Crickmay, C. H., 1930, Fossils from Harrison Lake area, British 

Columbia: Canada Nat. Mus. Bull. 63, p. 33-66, 82-113, pis. 

8-23.

 1933, Some of Alpheus Hyatt's unfigured types from the 

Jurassic of California: U. S. Geol. Survey Prof. Paper 

175-B, p. 51-58, pis. 14-18.

Gabb, W. M., 1864, Description of the Cretaceous fossils: Geol. 

Survey Calif. Paleontology, v. 1, p. 55-236, pis. 9-31.

 1869, Cretaceous and Tertiary fossils: Geol. Survey 

Calif. Paleontology, 299 p., 36 pis.

Holdhaus, Karl, 1913, The fauna of the Spiti shales Part 4, 

Lamellibranchiata and Gastropoda: Paleontologia Indica, 

Mem., ser. 15, v. 4, pt. 2, p. 397-456, pis. 94-100.

Hyatt, Alpheus, 1894, Trias and Jura in the Western States: 

Geol. Soc. America Bull., v. 5, p. 395-434.

Imlay, R. W., 1955, Characteristic Jurassic mollusks from 

northern Alaska: U. S. Geol. Survey Prof. Paper 274-D, 

p. 69-96, pis. 8-13.

Imlay, R. W., and Reeside, J. B., Jr., 1954, Correlation of the 

Cretaceous formations of Greenland and Alaska: Geol. Soc. 

Am. Bull., v. 65, p. 223-246,2 figs., 1 pi.

Jeletsky, J. A., 1950, Stratigraphy of the west coast of Vancouver Island between Kyuquot Sound and Esperanza Inlet, British Columbia: Geol. Survey Canada Paper 50-37, 

52 p., map and correlation table.

Lahusen, J., 1888, Uber die russischen Aucellen: Com. g6ol. St.

Petersbourg Mem., v. 8, no. 1, p. 1-46, 5 pis. 

Martin, G. C., 1926, The Mesozoic stratigraphy of Alaska: U. S.

Geol. Survey Bull. 776, 493 p., 13 figs. 

McLearn, F. H., 1945, Revision of the Lower Cretaceous of the

western interior of Canada: Geol. Survey Canada Paper

44-17 (2d ed.), 14 p., 2 tables, 12 pis. 

Meek, F. B., 1865, Descriptions of fossils from the auriferous

slates of California : California Geol. Survey, v. 1, App. B.,

p. 477-482, 1 pi. 

Orbigny, Alcide d', in Murchison, Verneuil, and Keyserling,

1845, Ge"ologie de la Russie d' Europe , v. 2, Terrains

Second., Syst. Jurass., Mollusques, p. 419-488, pis. 28-42. 

Pavlow, A. P., 1907, Enchainement des aucelles et aucellines

du Cr6tac6 Russe: Nouv. M6m. Soc. Imp. Nat. de Moscou,

v. 17, Livr. 1, p. 1-93, pis. 1-6. 

Pompeckj, J. F., 1901, Uber Aucellen und Aucellen-ahnliche

Formen: Neues Jahrb., Beilage-Band 14, p. 319-368, pis.

15-17, 2 text figs. 

Sokolov, D., and Bodylevsky, W., 1931, Jura- und Kreidefaunen

von Spitzenbergen: Skrifter om Svalbard og Ishavet, Nr.

35,151 p., 14 pis. 

Spath, L. F., 1924, On the ammonites of the Speeton clay and

the subdivisions of the Neocomian: Geol. Mag., v. 61, p.

73-89.

Stanton, T. W., 1895, Contributions to the Cretaceous Paleontology of the Pacific Coast The fauna of the Knoxville

beds: U. S. Geol. Survey Bull. 133, 132 p., 20 pis. [Issued

Feb. 3,1896, according to T. W. Stanton]

Stewart, R. B., 1930, Gabb's California Cretaceous and Tertiary Type Lamellibranchs: Acad. Nat. Sci. Philadelphia

Spec. Pub. 3, 314 p. 

White, C. A., 1884, On Mesozoic fossils: U. S. Geol. Survey

Bull. 4, 36 p., 9 pis.

 1888, Remarks on the genus Aucella, with special reference to its occurrence in California: U. S. Geol. Survey

Mon. 13, p. 226-233, pis. 3, 4. [Published in March, 1889] 

Wollemann, A., 1900, Die Bivalven und Gastropoden des deutschen und hollandischen Neocoms: Abh. preuss. geol.

Landesanst, N. F., Heft. 31. 

Woods, Henry, 1899-1913, A monograph of the Cretaceous

Lamellibranchia of England: Paleontogr. Soc., v. 53-66

(also 2 v., illus.).

INDEX

[Italic numbers indicate descriptions]

Page 

aguOa, Ncocraspcdites......................................................... 163

Amoeboceras.................................................................. 157

andersoni, Aucella............................................................ 158

Astorte....................................................................... 156

attenuata, Aucetta............................................................. 158

Aucella andersoni............................................................. 158

attenuate ....-. ......... ................................. 158

aviculaeformis............................................................. 157

bononiensto-.............................................................. 168

broma.................................................................... 157

eoneen^iea................................................ 157, 158,161,164, pi. 16

leguminosa.................................................... 157,164, pi. 16

traaa............................................................... 165,161,162

crasiicoUis.................................... 155,168,160, 161, 162,163,166, pi. 19

elderentis................................................................. 168

elongate................................................................... 167

erringtoni.............................................................__ 157

fitcheriana ......................................... 168, 159, 160,161,163, pi. 17

gabbi.

kyata.

.............................................................. 168

........ ...................................................... 168

.............................................................. 168

toflata............... ................................................... 161,162

keyserlingi ...... .................................................... 155, 161, 162

knoxvMensis .... ...................... ..... ....... .... . ... ......... ....... 168

krotoci ..... . ....... ............ ... . .... ... ......... .. ... ............. .... . 163

lahuseni... .............. ... ... ... ................. ... ............. .... ... 163

mosquentis....... ............................................. 157, 168, 164, pi. 16

nudformis ......... . .... . ................................................. 163

occidentalit... ... ...... __ ... ___ .. _ .............................. 159,161

okemlt.. ............................................... 168, 180, 161, 164, pi. 18

j*xM.- ..--. - .-. ........... 156, 167, 168, 159, 160, 161, 163, 166, pi. 17

oeata......... ....................................................... 159,160

piriformis....... ........................................ ...... ............ 161

rugota.......... .............................................. 157, 168, 164, pi. 16

russiemte... .............................................................. 158

tolida........ ........................................................... 161,162

toOasi .... ................................................................ 169

tpWmsii........ ...... ........................................167,158,m,pl. 16

itantonl... .......................................... ................ 158,163

subinflata.. .... . ... ... ... ................................................. 168

tuOaevls.. ........ .................... ..................... 168, 181, 164, pi. 18

tubokemis ... .................................... ... .......... 168, 160, 161, pi. 18

tenuicoUis ... ................ ........ ........ ... ................ .... ....... 158

terebratuloldes ............. .......... ......... .............. 168, 159, 161, 163

regularis ....... .... ........ ............ ..... ...... ... . ... . .... ........ 161

trigonoides .......... ........ ... ... ... . ... ..... .... ...... ......... ....... 159,160

uncitoides ... . ...... ....................... ... .............. ..... .... 168, 161, 163

eolgeruis........ ................................ ...... 168, 159, 180, 161, 164, pi. 18

Aucettina. ...... ............................................................ 163,164

aviculaeformis, Aucella......... ............. ....... ... ... ..................... 157

bononiemis, Aucella..-.. ..................... ... ................. .... ......... 168

bronni, AueeUa. .... ................ .... .......................... ... .......... 157

Buchia (tee alto Aucetta) ...................................................... 156

Camptonectes ...... ... .. ............. . ................................ ... . .... 156

concentrica, Aucella.-... ...................... .... ............ 157, 168, 161, 164, Pi. 16

concentric* leguminosa, Aucetta .... ................. ..... .............. 157, 164, pi. 16

Conclusions . . .. .. _. .... ............... 164

Craapedita nodiger... ..... . ......................... . ......................... 161

ipastkeruis ........ ... ... ... ... . ........................................... 161

crawo, Aucetta..... ...... ................ ............................... 155, 161, 162

cratticottls, Aucetta.....-. ..................... 155, 168, 160, 161, 162, 163, 166, pi. 19

Crioceras .............. ....... ... .............. ... . ........ ..... ... ......... ... 164

Definition of /htcdta -----..---- ....................... .................... 156

Descriptions of mentioned U. 8. Geological Surrey Mesozoic localities _ - - 166

Durangites ........... ..... .... ................. ..... ............... ... ... ... .. 157

Echinotb ..... .. ... ........................................................... 158

Ecology of Aucetta ......... . ...... ........................... .... ....... ... ... 156

elderentit, Aucetta ... ........ ___ ................................... 168

elongata, Aucella.. .... ... ... ..... . ...................................... . ..... 157

erringtoni, Aucetta ............................................................ 157

fitcheriana, Aucetta. ................................. 158,159,160,161,163, pi. 17

gabbi, Aucella...............................i................................. 158

Qereittia............................................... . ... 156

gracilis, Aucella............................................ ................ 158

Gryphaea................................................................... 156,162

Hoplocrioceras remondi......................................... 164

hyatti, Aucetta............. ............................. .. 158

Index ... . ................... . - ... . 169

inflata, Aucella............................................................. 161,162

Inoceramus............................................................. 156,160,163

keyserlingi, Aucetta...................................................... 155161,162

PolyptvcMtes............................................. ......... 161, pi. 16

Knoxville formation....__ _ - 159

knoxeittensis, Aucetta........-..... ........-..... .......-.. .- ..- 168

Kottmatia.................................................................... 157

krotovi, Aucetta................................ .. ........... 163

lahuseni, Aucetta.............................................................. 163

leguminosa, Aucetta concentrica................................................ 157

Literature cited . 167

Lytocerat......................................... . . 163

Meleagrinella......... .......................... . .-... . .. 156

Modtolus... ................... . .............................. 156

mosquemis, Aucella................---....-.. . -.-. ... 157,158,164, pi. 16

Neocraipeditesaguila..-....................................................... 163

nodiger, Craspedites................................................ .-. 161

nudformis, Aucetta. ............ --- - 163

occidentalis, Aucrtta.. .. ... ........ ... . . 159,161

okautt.AuceOa....-.. ... 158,160,161,164, pi. 18

Origin of Aucella........................ ..................... .......... 156

Ottrea.................................., ........ 156,162

ovata, Aucetta piocMi........................ ... . . 159

piochii, Aucetta....... ... 155,157,158,159,160,161,163,166, pi. 17

ptochilooata, Aucetta...- 159,160

pir if ormis, Aucella............................................ . -- 161

Pleuromya......... - 166

PolyptvcMtes keyterlingi...............................-.-.-... . . 161

Port Moller area.... . ... .. ............. - ... .... . 162

Pseudomonotis.............................................. - --.... 158

Pulchettia.................. . - .... 163

Range of variation within Aucellan species 156 

regularis, Aucella terebratuloidet.............-................................. 161

remondi, Hoplocrioceraa.............................. ... .. . 164

rugo9a,Aucetta... . . 157,168,164, pi. 16

russiensis, Aucetta..........- - 158

Simbirskites... -..........^................-..-. .- ..- - - 163

tolida, Aucella......... ... ..... 161,162

sollasi, Aucetta..... ..................... -.... - ------ 159

spasskensis, Craspedites._. .. - 181

Subcraspedites............................................................ 161

Speciation in Aucella......................... .. . - --. -. 156

tpitlensit, Aucetta.. ............... - 157,158,164, pi. 16

stantoni, Aucetta........................- - - - --- 158,163

Stratigraphic distribution of Aucella................... - --------- - 164

Subcraspedites spasskemtis. . -- 161

subinflata, Aucena..................................................... 158

sublaevis, Aucetta... 158,161,164, pi. 18

tubokensis, Aucetta. .. .. ------ 158,160,161, pi. 18

tenuicottii, Aucetta ................................ ......... 158

terebratuloldes, Aucetta............ ....... ... ... 158,159,161,163

terebratuloidei regularis, Aucetta........- - Wl

Trigonia .....................--. -- I*8

trigonoides, Aucetta........ . 159,160

uncitoides, Aucetta.........-.-.-..--- 158,161,163

volgensit, Aucetta.. 158,159.160.161.164.01.13

169

o

PLATES 16-19
PLATE 16

[Figures natural size unless otherwise indicated]

FIGURES 1-7. Aucella concentrica (J. de C. Sowerby) (p. 157).

I-3. Two left valves and one right valve of plesiotypes, USNM 129046, from USGS Mes. loc. 20343, at south

edge of Glacier Park, Mont. 

4, 5. Left and right valves of plesiotype, USNM 108749, from USGS Mes. loc. 10248 near Katmai Bay, southwest

Alaska. 

6, 7. Right and left valves of plesiotype, USNM 129047, from USGS Mes. loc. 10248, near Katmai Bay, southwest

Alaska. 

8-10. Aucella concentrica leguminosa Stoliczka (p. 157). Dorsal and lateral views of plesiotype, USNM 129048, from

USGS Mes. loc. 3124, near Katmai Bay, southwest Alaska. 

11-17. Aucella spitiensis Holdhaus (p. 157).

II-13. Left valve, dorsal view, and right valve of plesiotype, USNM 129050, from USGS Mes. loc. 3127, near

Katmai Bay, southwest Alaska.

14, 15. Left and right valves of plesiotype, USNM 129049, from USGS Mes. loc. 3124, near Katmai Bay, southwest Alaska.

16, 17. Right valves of plesiotypes, USNM 108746 c, d, from USGS Mes. loc. 21028, northern Alaska. 

18, 19, 22-25. Aucella rugosa (Fischer) (p. 157).

18, 19, 23-24. Left valves of plesiotypes, USNM 108741, from USGS Mes. loc. 22768, northern Alaska.

Fig. 24 is a ventrodorsal view showing greater convexity of the left valve. 

22. Left valve of plesiotype, USNM 129051, from USGS Mes. loc. 11360, southwest Alaska. 

25. Small right valve and larger left valve of plesiotype, USNM 108740, from USGS Mes. loc. 22127,

northern Alaska. Specimens are enlarged two times to show radial markings. 

20, 21. Aucella mosquensis (von Buch) (p. 157).

Left valves of plesiotypes, USNM 108748, from USGS Mes. loc. 22769, northern Alaska.
PROFESSIONAL PAPER 314 PLATE 16

JURASSIC AUCELLAS
GEOLOGICAL SURVEY PROFESSIONAL PAPER 314 PLATE 17

23 24 25 26

JURASSIQ AUCELLAS

27 28 29
PLATE 17

[All figures natural size]

FIGUKES 1-6, 11. Aucella fischeriana (d'Orbigny) (p. 159).

1, 5. Left valves of plesiotypes, Calif. Acad. Sci. 8679 and 8677, from GAS loc. 28037 on Watson Creek, 6 miles

north of Winslow bridge, Glenn County, Calif. 

2-4. Left valve, posterior dorsal view, and right valve of plesiotype, USNM 22221, from Khorochowo, near

Moscow, Russia. 

6, 11. Lateral and dorsal views of left valve of plesiotype, USNM 129054, from USGS Mes. loc. 2285, Glenn

County, Calif. 

7-10, 12-29. Aucella piochii (Gabb) (p. 157).

7-9. Dorsal view, left and right valves of plesiotype, USNM 23032, from USGS Mes. loc. 1084, Tehama

County, Calif. This specimen was illustrated by Stanton (1896, pi. 4, figs. 6, 7) and was assigned by Pavlow

(1907, p. 48) to a new species, A. stantoni Pavlow. 

10. Left valve of plaster replica of holotype in University of California type collections, from Colusa County,

Calif. 

12-20. Left valves from a single locality showing variations in shape, size, and ornamentation. Plesiotypes,

USNM 129052, from USGS Mes. loc. 1225, Lake County, Calif. 

21-29. Left valves from a single locality showing variations in shape, size, and ornamentation. Plesiotypes,

USNM 129053, from USGS Mes. loc. 2275, Tehama County, Calif.
PLATE 18

[Figures natural size unless otherwise indicated]

FIGURES 1-6, 11. Aucella sublaevis Keyserling (p. 161).

1-3. Right valve, anterior view, and left valve of an average specimen. Plesiotype 128680, USGS Mes. loc. 

22736, northern Alaska.

4. 11. Left valve (XI and X2) of a specimen in which radial striation is conspicuous. Plesiotype, USNM 

128681, from USGS Mes. loc. 23554, northern Alaska.

5. 6. Left valve and anterior view of a large specimen. Plesiotype, USNM 128680, from USGS Mes. loc. 22736,

northern Alaska. 

7, 8, 12-14. Aucella volgensis Lahusen (p. 160).

7, 8. Left valve and anterior view of plesiotype, USNM 22223, from Kachpour, Russia. 

12-14. Anterior view, right valve and left valve of plesiotype, USNM 22223b from Kachpour, Russia. 

9, 10. Aucella subokensis Pavlow (p. 160).

Anterior view and left valve of plesiotype, USNM 128677, from USGS Mes. loc. 22762, northern Alaska. 

15-19. Aucella okensis Pavlow (p. 160).

15. Right valve of plesiotype, USNM 128675, from USGS Mes. loc. 22790, northern Alaska.

16. 17. Left valve and anterior view of plesiotype, USNM 128672, from USGS Mes. loc. 22472, northern Alaska.

18. Rubber cast of external mold of left valve. Plesiotype, USNM 128673, from USGS Mes. loc. 22724, northern 

Alaska.

19. Left valve of plesiotype, USNM 128674, from USGS Mes. loc. 22757, northern Alaska.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 314 PLATE 18

19

CRETACEOUS AUCELLAS
GEOLOGICAL SURVEY PROFESSIONAL PAPER 314 PLATE 19

19

CRETACEOUS AUCELLAS
PLATE 19

[All figures natural size] 

FIGTJBES 1-24. Aucella crassicollis Keyserling (p. 161).

1, 2, 8. Anterior view, left valve, and right valve of plesiotype, USNM 23038, from USGS Mes. loc. 1091, Tehama 

County, Calif. This specimen was figured by Stanton (1896, pi. 5, figs. 12, 13) and assigned by Pavlow (1907, 

p. 62) to A. keyserlingi Lahusen. 

3-6. Left valve, anterior view, posterior view, and right valve of a single individual. Plesiotype, USNM 23252,

from USGS Mes. loc. 1010, Tehama County, Calif.

7. Left valve showing fine, concentric ribbing similar to specimen shown in figs. 1, 2, 8. Plesiotype, USNM 

129057, from USGS Mes. loc. 1091, Tehama County, Calif.

9. Left valve showing constricted umbone. Plesiotype, USNM 128686, from USGS Mes. loc. 22780, northern 

Alaska.

10. 11. Left valve and anterior view of plesiotype, USNM 128683, from USGS Mes. loc. 22514. Similar plump

specimens are commonly referred to A. crassa Pavlow. 

12. Left valve marked by broad undulations. Plesiotype, USNM 128687, from USGS Mes. loc. 23560, northern

Alaska. Similar plump, smooth specimens are commonly referred to A. solida Lahusen. 

13-18. Left valves from a single locality to show variation in shape and ornamentation. Plesiotypes, USNM

129055. from USGS Mes. loc. 997, Tehama County, Calif. 

19-24. Left valves from a single locality to show variation in shape and ornamentation. Plesiotypes, USNM

129056. from USGS Mes. loc. 2287, Glenn County, Calif.