Late Jurassic Ammonites 

From the Western Sierra 

Nevada, California

GEOLOGICAL SURVEY PROFESSIONAL PAPER 374-D
Late Jurassic Ammonites 

From the Western Sierra 

Nevada, California

By RALPH W. IMLAY

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 374-D

Ammonites furnish correlations with Jurassic rocks 

elsewhere on the Pacific coast and with the standard 

European stages

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1961
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, 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,__________________________________________ D-l

Introduction. ______________________________________ D-l

Biologic analysis--_--_-__-_----____--__-__-__--_____ D-2

Stratigraphic summary______________________________ D-2

Ages and correlations______________________________ D-3

Cosumnes formation. ___________________________ D-3

Logtown Ridge formation______________________ D-6

Colfax formation of Smith, 1910_._______.____-_-. D-6

Mariposa formation._----______-_-_______--_--__ D-7

Monte de Oro formation_____-___________--__-__- D-8

Comparisons with other faunas_______________________ D-9

Page 

Comparisons with other faunas Continued

Taylorsville area, California______________________ D-9

Central Oregon_______________________-_________ D-10

Southwestern Oregon__________________________ D-10

Western British Columbia _______________________ D-10

Alaska Peninsula and Cook Inlet regions, Alaska. __ D-ll 

Mexico-...-._______._--__-________-__-______ D-12

Geographic distribution___________________________-__ D-13

Summary of results___________________-_____________ D-13

Systematic descriptions_-____-__-_-__-_-_-_____-_-_ D-19

Literature cited.__________________________________ D-27

Index.__________________-___-__.______-___-__--_ D-29

ILLUSTRATIONS

[Plates 1-6 follow index]

PLATE 1. Kepplerites, Gowericeras, and Taramelliceras.

2. Pseudocadoceras, Amoeboceras (Amoebites), and Grossouvria.

3. Perisphinctes (Discosphinctes) and Grossouvria.

4. Perisphinctes (Dichotomosphinctes).

5. Subdichotomocerasf', Perisphinctest, Dichotomosphinctesf, Idoceras, and Buchia.

6. Peltoceras (Metapeltocerast).

FIGURE 1. Correlation of the Late Jurassic formations in the Pacific coast region. ______

2. Correlation of the Late Jurassic faunas in the Pacific coast region.__________

3. Index map of Jurassic localities in the western Sierra Nevada, Calif. ________

Page

D-4

D-5

D-l 5

TABLES

TABLE 1. Ammonite genera and subgenera from late Jurassic beds in the western Sierra Nevada, Calif.

2. Geographic distribution of the Late Jurassic megafossils in the western Sierra Nevada, Calif_

3. Descriptions of the Late Jurassic fossil localities in the western Sierra Nevada, Calif________

Page

D-2

D-l 4

D-16

m

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

LATE JURASSIC AMMONITES FROM THE WESTERN SIERRA NEVADA, CALIFORNIA

By RALPH W. IMLAY

ABSTRACT

The ammonites from the Jurassic strata in the western part of 

the Sierra Nevada represent the Callovian, Oxfordian, and the 

lower part of the Kimmeridgian stages of the Upper Jurassic. 

There is no faunal evidence for the presence of any older Jurassic 

rocks, although the lower and middle parts of the Cosumnes 

formation have not furnished any fossils and could be in part 

older than the Callovian. The upper part of the Cosumnes 

formation has furnished one fragmentary ammonite indicative 

of a Callovian age. The lower part of the overlying Logtown 

Ridge formation has furnished many ammonites of early to 

middle Callovian age not older than the European zone of 

Sigaloceras calloviense. Because the formations grade into each 

other, the part of the Cosumnes formation that contains the 

Callovian ammonite must be of early Callovian age older than 

that zone.

The early Callovian is definitely represented by the ammonites 

Kepplerites (Seymourites) and K. (Gowericeras) obtained near 

Colfax, Calif. These indicate an age slightly older than the 

ammonites in the lower part of the Logtown Ridge formation 

on the Cosumnes River. The late Callovian is represented by 

a large specimen of Peltoceras obtained near Indian Creek in 

Amador County, presumably from the Logtown Ridge formation.

There is no faunal record of the early Oxfordian in California. 

The late Oxfordian to early Kimmeridgian is represented by the 

ammonite Idoceras obtained near the top of the Logtown Ridge 

formation on the Cosumnes River. The late Oxfordian is 

represented in the Mariposa formation by species of Perisphinctes 

(Dichotomosphinctes) and P. (Discosphinctes) that are virtually 

identical with species in Mexico and Cuba. These ammonites 

show that the lower part of the Mariposa formation and similar 

slatey units are locally of the same approximate age as the 

upper part of the Logtown Ridge formation on the Cosumnes 

River.

The early Kimmeridgian is represented in the Mariposa 

formation by Amoeboceras (Amoebites) and probably by Subdichotomoceras in association with the pelecypod Buchia concentrica (Sowerby).

The late Oxfordian to early Kimmeridgian is represented 

in the Monte de Oro formation by an ammonite, Perisphinctes 

(Dichotomosphinctes) cf. P. elisabethaeformis Burckhardt, and 

by two crushed specimens of Buchia cf. B. concentrica (Sowerby).

The Mariposa and Monte de Oro formations have not furnished any fossils that are younger than the early Kimmeridgian. The same is true of the Galice formation of southwestern 

Oregon and northwestern California which is lithologically 

similar to the Mariposa and likewise is characterized by the 

presence of Perisphinctes (Dichotomosphinctes} and Buchia 

concentrica (Sowerby). As the Galice formation is overlain

with pronounced angular unconformity by beds of middle to 

late Portlandian age (Riddle formation), the middle Kimmeridgian to early Portlandian time appears to be represented, at 

least in part, by the unconformity.

The affinities of the Callovian ammonites in the Sierra Nevada 

are mainly boreal as indicated by the presence of such ammonites as Cadoceras, Paracadoceras, Pseudocadoceras, Kepplerites, 

and Gowericeras. The affinities of the late Oxfordian ammonites are mostly with ammonites in Mexico and Cuba but partly 

with those in Alaska. The early Kimmeridgian ammonite 

Amoeboceras indicates boreal affinities as the genus is rare in the 

Tethyan region. These affinities indicate that the seas in California were connected freely northward with Alaska and southward with southern Mexico.

INTRODUCTION

This study of the Late Jurassic ammonites from the 

western part of the Sierra Nevada, Calif., is based 

mainly on collections made by field parties of the U.S. 

Geological Survey since 1884. It includes, also, 4 

specimens from Leland Stanford Junior University 

furnished by Siemon Win. Muller, 1 specimen from 

the University of California furnished by Wyatt 

Durham and Joseph H. Peck, Jr., and 1 specimen from 

the Museum of Comparative Zoology at Harvard 

furnished by Bernhard Kummel. It does not include 

any fossils from the Taylorsville, Downieville, or 

Sailors Canyon area in the eastern part of the western 

Sierra Nevada metamorphic belt.

The description of the ammonites is a byproduct of 

paleontological assistance to Lorin D. Clark, of the 

Geological Survey, in his comprehensive analytical 

studies of the geology of the western Sierra Nevada. 

The assistance mainly involved determining the age 

limits of the rock units that Clark had mapped. This 

appeared at first to be a difficult task because of the 

wretched preservation of most of the fossils. After a 

little study, however, it was found that some of the 

fossils belonged to well-known genera and species 

from Alaska, Mexico, and Cuba and that rather 

precise dating of the rock units was locally possible 

by comparisons with the faunal successions in those 

areas. Such faunal dating is useful in making correD-l
D-2 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

lations with Jurassic rocks elsewhere on the Pacific 

coast, in unraveling complex stratigraphic and structural problems, and in interpreting the history of 

Jurassic sedimentation in California.

BIOLOGIC ANALYSIS

The Late Jurassic ammonite specimens from the 

western part of the Sierra Nevada that are available 

for study number about 200. Of these, 150 belong to 

the Cardioceratidae, 29 to the Perisphinctidae, and 13 

to the Kosmoceratidae. Most genera and subgenera 

are represented by 1 to 4 specimens. Ammonites are 

actually more difficult to find in the area than these 

figures suggest, considering that 1 locality (Mesozoic 

loc. 27317) accounts for 120 specimens, and 3 localities 

(Mesozoic Iocs. 719, 901, and 27313) account for 

another 45 specimens. The biological distribution of 

the ammonites by subgenera, genera, subfamilies, and 

families is shown in table 1.

STRATIGRAPHIC SUMMARY

The fossils dealt with herein are from an irregular 

belt of metamorphosed Jurassic rocks, 10 to 25 miles in 

width, that crop out near the western base of the Sierra 

Nevada from Butte County on the north to western 

Madera County on the south. A number of formational names have been proposed for the rocks within 

this belt, but the validity of most of the names has 

not been firmly established. -~

For an isolated area of Jurassic rocks east of Oroville, 

in southeastern Butte County, the term Monte de Oro 

formation was proposed by Turner (1896, p. 548, 549). 

This formation consists mostly of dark carbonaceous 

clay slates similar to those of the Mariposa formation 

but includes some sandstone and conglomerate. It 

has furnished plant fossils, some marine pelecypods, 

and one ammonite.

For the main mass of Jurassic sedimentary rocks 

extending from the Colfax-Grass Valley area southward to Madera County, the term Mariposa slate was 

proposed by Becker (1885, p. 18-23). This term was

restricted by J. P. Smith (1910, chart facing p. 217) to 

the slate and associated rocks in the metamorphic 

Gold Belt (mother lode) area that are characterized by 

the pelecypod Buchia (formerly called Aucella) and by 

the ammonite now referred to Amoeboceras dubium 

(Hyatt).

For the rocks in the southwestern part of the Colfax 

quadrangle that had been called Mariposa slate by 

Becker, Smith (1910, p. 217) proposed the term Colfax 

formation. These rocks, as described by Lindgren 

(1900), consist of interbedded shale, slate, sandstone, 

tuff, and conglomerate. He noted that most of the 

slate is not very fissile, which feature is a possible distinction from the slates of the Mariposa formation. 

In naming the Colfax formation, Smith appears to 

have been influenced by the lack of the pelecypod 

Buchia and by presence of Ammonites colfaxi Gabb, 

which he considered to be of Portlandian age.

Subsequently N. L. Taliaferro and his students made 

extensive studies of the Jurassic in the foothills of the 

Sierra Nevada from Eldorado County southward to 

Madera County. As a result of these studies the 

Mariposa slate was raised by Taliaferro (1933, p. 149) 

to the rank of a group and divided into the Mariposa 

slate above and the Indian Gulch agglomerates below.

Beneath the Mariposa group, Taliaferro recognized 

(1933, p. 149) some thousands of feet of Jurassic rocks 

that had previously been included partly in the Mariposa slate, partly in the Paleozoic Calaveras group, 

and partly in intrusive rocks of unknown age. For 

these older Jurassic rocks the term Amador group was 

proposed (Taliaferro, 1942, p. 89, 90). This group in 

the northern part of its known extent in Eldorado, 

Amador, and Calaveras Counties, as described by 

Taliaferro (1943, p. 282-284), is about 7,100 feet thick, 

rests uncomfortably on the Paleozoic, and consists of 

the Cosumnes formation below and the Logtown 

Ridge agglomerates at the top. Near the southern 

part of its extent, south of Calaveras County, the group 

is at least 14,000 feet thick, its base is not exposed, 

and it consists of five formations. On the Merced

TABLE 1. Ammonite genera and subgenera from Late Jurassic beds in the western Sierra Nevada, Calif.

Family Subfamily Genus and subgenus

Phylloceratidae _____________ Phylloceratinae__ ______________ Phylloceras.----------------

Oppeliidae____________________ Taramelliceratinae____________ Taramellicerasf (Proscaphitesf)

Kosmoceratidae. ______________________________________________ Kepplerites (Seymourites) _____

(Gowericeras}- ______--_

Cardioceratidae ___________ Cadoceratinae___ __._-_-__.__- Pseudocadoceras _ ____________

. . Cardioceratinae_-__-___-____-__ Amoeboceras (Amoebites} ______

Perisphinctidae. _______________ Pseudoperisphinctinae____ _______ Grossouvria. ________________

Perisphinctinae_ _ _ ____________ Perisphinctes"? _ ______________

Perisphinctes (Discosphinctes} _ 

(Dichotomosphinctes') _ _ _ _ _

(Dichotomosphinctesl} 

Idoceratinae___________________ Idoceras ________________----

Idocerasf _______-_______----

. Virgatosphinctinae______ ________ Subdichotomocer'as? ___________

Asipidoceratidae. ______________ Peltoceratinae__ ______________ Peltoceras (Metapeltocerast) _ _ _

Number of 

specimens

2

4

12

1

125

25

1

1

14

1

6

1

1

4

1
JURASSIC AMMONITES, SIERRA NEVADA D-3

River from oldest to youngest these formations include: 

(a) Lower volcanic rocks; (b) pillow basalt; (c) Hunter 

Valley chert; (d) Penon Blanco volcanics; and (e) 

Agua Fria slate. Taliaferro correlated the Penon 

Blanco agglomerate with the Logtown Ridge agglomerate and the Hunter Valley chert with part of the 

Cosumnes formation. Type localities for these formations were not designated.

During and after World War II, the Jurassic rocks 

in and near the Mother Lode area were studied by 

geologists of the U.S. Geological Survey. According 

to Lorin Clark (oral communication, October 1958), 

the five formations proposed by Taliaferro for the 

Merced River area are difficult to recognize with the 

exception of his Penon Blanco volcanics. In contrast 

the Cosumnes and Logtown Ridge formations, particularly as exposed along and near the Cosumnes River, 

are definitely mappable units. The sequence along 

the Cosumnes River, described briefly by Heyl (1948, 

p. 15-17) and Lorin Clark (written communication, 

January 1960), may be summarized as follows: 

Mariposa slate:

5. Mostly dark-blue-gray to black clay slate that weathers 

pale green to olive brown. Includes some siltstone, 

graywacke, conglomerate lenses, and locally volcanic 

rocks. Thickness unknown but evidently several 

thousand ft. Differs from the Cosumnes formation 

containing much less conglomerate.

Logtown Ridge formation of Taliaferro:

4. Mostly tuffs, andesitic agglomerates, and volcanic 

breccia. Includes two units of pillow lava. Thickness several thousand ft. Idoceras cf. I. planula (Heyl) 

in Zeiten, described herein, is reported to have been 

found near the top of the formation.

Cosumnes formation of Taliaferro:

3. Thin-bedded green gray and black tuff, in part slatey; 

some hundreds of ft. thick. Contains Pseudocadoceras 

grewingki (Pompeckj) (Mesozoic Iocs. 24710, 27317) in 

abundance about 600-700 ft above base.

2. Graywacke and dark clay slate.

Pseudocadoceras ? sp. (Mesozoic loc. 22175) was found 

about 500 ft below top. Thickness unknown.

1. Conglomerate and sandstone in alternating units. 

Contains debris of underlying Paleozoic Calaveras 

formation. Thickness unknown.

Calaveras formation.

The combined thickness of the Logtown Ridge 

formation and the Cosumnes formation along the 

Cosumnes River is indicated by Heyl to be between 

7,000 and 8,000 feet. The Cosumnes formation is 

reported to be about 3,600 feet thick and the Logtown 

Ridge formation about 4,300 feet thick by Lorin Clark 

(written communication, January 1960). Howeverthe 700 feet or more of thin-bedded tuff that Heyl 

placed at the top of the Cosumnes formation (unit 3

above) are transitional into the Logtown Ridge formation and, for convenience in mapping, are now placed 

in that formation by Clark (oral communication, 

October 1958). As mapped by Clark, the Logtown 

Ridge formation consists entirely of volcanic rocks, 

and the Cosumnes formation consists of interbedded 

sedimentary and volcanic rocks.

The sequence of the Logtown Ridge formation and 

Cosumnes formation exposed along the Cosumnes 

River is particularly interesting because the outcrops 

are nearly continuous, the formational boundaries are 

well exposed, there appear to be no great structural 

complications, and ammonites have been found at 

three places whose relative stratigraphic positions can 

be determined. As a result, the Logtown Ridge formation and the upper part of the Cosumnes formation 

along the Cosumnes River are dated fairly closely.

These conditions contrast with those found generally 

throughout the belt of Jurassic rocks under discussion. 

According to Lorin Clark (written communication, 

Nov. 16, 1959)

the stratigraphy of the Jurassic in the western Sierra Nevada 

is extremely complicated. Volcanic formations intertongue 

with sedimentary formations, and both change thickness and 

character markedly within distances of 20 miles or less.

Such lithologic changes within short distances imply 

that formational boundaries do not remain time 

planes for many miles. These changes, in conjunction 

with the repetition of apparently identical rocks at 

different parts of the Jurassic sequence, probably 

explain why most of the fossil collections from the 

belt of Jurassic rocks have not been closely located 

stratigraphically.

AGES AND CORRELATIONS 

COSUMNES FORMATION

The Cosumnes formation at its type locality on the 

Cosumnes River is at least in part of Callovian age 

because it grades upward into the Logtown Ridge 

formation whose basal beds have furnished many 

specimens of the Callovian ammonite Pseudocadoceras 

(figs. 1, 2). The only ammonite from the Cosumnes 

formation proper is a crushed specimen obtained about 

500 feet below the top of the formation on the Cosumnes 

River. This specimen (see pi. 2, fig. 23) was at one 

time compared by Imlay (1952, p. 975) with the 

Callovian genus Grossouvria, but its coiling is too 

involute for that genus, and it is now referred tentatively 

to Pseudocadoceras on the basis of coiling and rib pattern. 

The specimen is of some significance because it suggests 

that the upper part of the Cosumnes formation is 

not older than Callovian.
D-4 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

EUROPEAN

STAGES

(Arkell, 1956

1957)

TAYLORSVILLE

AREA, 

CALIFORNIA

COOK INLET 

REGION, 

ALASKA

WESTERN 

SIERRA 

NEVADA

SOUTHWESTERN 

OREGON

EAST-CENTRAL 

OREGON

WESTERN 

CALIFORNIA

Knoxville 

formation

Mariposa

formation

and equivalent

beds

Logtown Ridge

formation

and equivalent

beds

Rogue 

formation 

(no fossils

known)

Foreman 

formation

Chinitna 

formation

Lonesome formation 

Dothan of Lupher, 1941

formation 

(no fossils

known)

Cosumnes

formation

(age of lower

part unknown)

Trowbridge formation 

of Lupher, 1941

Snowshoe formation

of Lupher, 1941

(upper part)

Hinchman 

sandstone

Tuxedni formation 

upper part

FIGUEE 1. Correlation of the Late Jurassic formation in the Pacific coast region.
31-3

I

European stages 

(Arkell, 1946, 

1956, 1957)

Purbeckian

Portlandian

Kimmeridgian

Oxfordian

L

Gallovian

1

 a 

3

wnian

1

;

I

§3

1

1

i

1

Standard zones in northwest Europe 

(Arkell, 1946, 1951, 1956; 

Callomon, 1955)

Titanites giganteus

Glaucolithites gorei

Zaraiskites albani

Pat'lot'ia pallasiodes

Pavlovia rotunda

Pectinatites pectinatus

Subplanites wheatleyensis

Subplanites spp.

Gravesia gigas

Gravesia gravesiana

Aulacostephanus pseudomutabilis

Rasenia mutabilis

Rasenia cymodoce

Pictonia baylei

Ringsteadia pseudocordata,

Decipia decipiens

Perisphinctfs cautisnigrae

Perisphinctes plicatilis

Cardioceras cordatum

Quenstedtoceras mariae

Quenstedtoceras lamberti

Peltoceras athleta

Erymnoceras coronatum

Kosmoceras jason

Sigaloceras calloviense

Macrocephalites macrocephalus

Characteristic fossils in the 

Western Interior region 

(Imlay, 1953)

No fossil evidence

Vetulonaia spp. and 

Gyraulus veternus

Buchia coneentrica 

in northwestern Montana

Cardioceras spp.

Cardioceras spp.

Cardioceras cordiforme

No fossil evidence

Kepplerites mclearni

Kepplerites tychonis

Gowericeras subitum

Gowericeras costidensum

Arcticoceras codyense

Characteristic fossils in the Alaska 

Peninsu a and Cook Inlet regions 

(Imlay, 1953)

No fossi evidence

Buchia piochii

Buchia rugosa and 

Buchia mosquensis

Buchia 

coneentrica 

and Amoeboceras 

Buchia (Prionodoceras) 

spitiensis spiniferum

Cardioceras distans

Cardioceras mart.iw

Pseudocadoceras

 S ^

| K Paracadoceras 

S 'i^ ancl 

g, Go vericeras

^ Xenocephalites 

and Kheraiceras

Characteristic fossils in northwestern Washington

Buchia piochii

Buchia rugosa 

and 

Buchia mosquensis

No fossil evidence

Characteristic fossils in California 

and Oregon

:s Buchia fischeriana substeuer

.§ oceras, Protacanthodiscus, 

^ and Proniceras

^ Kossmatia dilleri 

and Durangites

No fossil evidence

Amoeboceras (Amoebites) 

dubium 

 % and 

"a Subdichotomoceras!

8 Discosphinctes 

|g virgulatiformis 

| and 

Dichotomosphinctes 

muhlbachi

No fossil evidence

Peltoceras (Metapeltocerasl)

Pseudocadoceras grewingki

Kepplerites (Gowericeras), 

Lilhettia, Choffatia, 

and Xenocephalites

Kepplerites and Choffatia

FIGURE 2. Correlation of the Late Jurassic faunas in the Pacific coast region.
D-6 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

LOQTOWN RIDQB FOEMATION

The Logtown Ridge formation at its type locality 

on the Cosumnes River ranges in age from Callovian 

to late Oxfordian, or early Kimmeridgian. Evidence 

for a Callovian age consists of the presence of the 

ammonite Pseudocadoceras in the basal 600 feet of the 

formation. This genus in Europe ranges from the 

basal part of the zone of Sigaloceras calloviense into the 

zone of Peltoceras athleta (Callomon, 1955, p. 255), 

and is absent from the highest and lowest parts of the 

Callovian stage. A similar range is indicated in 

southwest Alaska where Pseudocadoceras occurs only 

in the upper two-thirds of the Chinitna formation 

associated with other ammonites that are correlated 

with the Erymoceras coronatum, Kosmoceras jason, and 

the upper part of the Sigaloceras calloviense zones of 

Europe (Imlay, 1953b, p. 48-54). Significantly, Pseudocadoceras is absent in the lower 1,000 feet of the 

Chinitna formation (Imlay, 1953b, p. 51-53) and in 

the upper 800 to 1,500 feet of the underlying Bowser 

member of the Tuxedni formation, although these 

parts have furnished early Callovian ammonites. This 

absence of Pseudocadoceras in the lower part of the 

Alaskan Callovian is comparable to its absence in the 

Macrocephalites macrocephalus zone at the base of the 

European Callovian. It follows, therefore, that the 

presence of Pseudocadoceras in the lower part of the 

Logtown Ridge formation in California shows not 

only that the lower part is Callovian but that it is 

younger than the earliest Callovian of Europe and 

Alaska (figs. 1, 2).

Further evidence concerning the age of the lower 

part of the Logtown Ridge formation is furnished by 

the particular species of Pseudocadoceras that are present. These include P. grewingki (Pompeckj) and probably, also, P. crassicostatum (Imlay, 1953b, p. 94, pi. 

49, figs. 19, 20, 22-24). Of these species, P. grewingki 

(Pompeckj) in Alaska is the longer ranging, but its 

lowest occurrence is in beds that are correlated with 

the upper part of the Sigaloceras calloviense zone. P. 

crassicostatum Imlay has been found only in the upper 

part of the range of P. grewingki (Pompeckj) in beds 

that are correlated with the Kosmoceras jason and 

Erymoceras coronatum zones of Europe (Imlay, 1953b, 

p. 51-53). By comparisons with Alaska, therefore, 

the species of Pseudocadoceras that are present in the 

lower part of the Logtown Ridge formation suggest a 

middle rather than an early Callovian age.

The upper part of the Logtown Ridge formation is 

dated as latest Oxfordian or early Kimmeridgian by 

the presence of the ammonite Idoceras aff. I. planula 

(Heyl) in Zeiten. This species belongs to a group of 

species that in Mexico has been found only in the early

Kimmeridgian (Burckhardt, 1912, p. 102; 1930, p. 64; 

Imlay, 1939, p. 21). In Europe, however, the group 

occurs also in beds of latest Oxfordian age (Wegele, 

1929, p. 76-78; Arkell, 1956, p. 114, 115) at the top of 

the zone of Epipeltoceras bimammatum. A late Oxfordian age for the upper part of the Logtown Ridge formation is favored by the resemblance of the specimen of 

Idoceras present to a species in the late Oxfordian of 

Europe and to the fact that the apparently stratigraphically higher Mariposa formation in Calaveras, 

Mariposa, and Eldorado Counties has furnished ammonites that likewise are as old as late Oxfordian. It is 

possible, of course, that beds that are mapped as the 

Mariposa formation in one county are the lateral 

equivalents of beds mapped as the Logtown Ridge 

formation in another county.

Dating the upper part of the Logtown Ridge formation on the Cosumnes River as latest Oxfordian to 

early Kimmeridgian, based on the ammonite Idoceras, 

appears to be contradicted by the presence of a large 

specimen of Peltoceras of late Callovian age, described 

herein, from the Mariposa formation on nearby Big 

Indian Creek. It is questioned, however, whether 

Peltoceras actually was collected from the Mariposa 

formation or whether it came from some beds within 

the Logtown Ridge formation. When the Peltoceras 

was discovered in 1914, the term Logtown Ridge had 

not been defined, and it seems probable that any beds 

from Amador County that furnished Jurassic ammonites would have been referred to the Mariposa formation. Furthermore, the Logtown Ridge formation is 

exposed immediately west of Indian Creek and would 

seem to be a more likely source for a large ammonite 

than the relatively softer slates of the overlying Mariposa formation. A stratigraphic position for Peltoceras near the middle of the Logtown Ridge formation 

appears likely, provided that the specimen of Idoceras 

was actually obtained from the upper part of that 

formation, as is indicated by the matrix of the specimen.

COLFAX FORMATION OF SMITH, 1910

The Colfax formation of Smith crops out near Colfax 

in the southwestern part of the Colfax quadrangle, 

Placer County, and has furnished several ammonites of 

Callovian age. These include, in particular, Ammonites 

colfaxi Gabb, which Smith (1910, chart facing p. 217) 

considered to be of Portlandian age but which is herein 

identified with the Callovian genus Grossouvria. This 

dating is upheld by the presence of Kepplerites lorinclarki Imlay, n. sp., and K. (Gowericeras} lindgreni 

(Hyatt) from other localities near Colfax.

In Europe Kepplerites and its subgenus Qowericeras 

range through the lower two-thirds of the early Callovian zone of Sigaloceras calloviense (Callomon, 1955,
JURASSIC AMMONITES, SIERRA NEVADA D-7

p. 255) except for two possible occurrences of Kepplerites in the zone of Macrocephalites macrocephalus 

(Arkell, 1953, p. 117, 119; 1956, p. 120). The subgenus Seymourites in the Boreal region and in the 

western interior of North America has a similar range 

(Spath, 1932, p. 138, 139, 145, 146; Imlay, 1953a, p. 7, 

8, 17, 18). In the Cook Inlet region, Alaska, Seymourites occurs rarely in the lower part of the range of 

Pseudocadoceras in beds that are correlated with the 

Kosmoceras jason and the upper part of the Sigaloceras 

calloviense zones of Europe. Gowericeras likewise occurs 

rarely with Pseudocadoceras in beds that are correlated 

with the upper part of the Sigaloceras calloviense zone. 

Both subgenera are more common, however, below the 

range of Pseudocadoceras (Imlay, 1953b, p. 50, 52) 

in the basal part of the Cbinitna formation which is 

correlated with the lower part of the Sigaloceras calloviense zone.

By comparisons, the occurrences of Kepplerites and 

Gowericeras in the Colfax formation of Smith near Colfax, Calif., might be as young as the Pseudocadoceras 

beds at the base of the Logtown Ridge formation, but 

most probably are somewhat older and equivalent to 

some part of the Cosumnes formation. In particular, 

the resemblance of Kepplerites (Gowericeras) lindgreni 

(Hyatt) to K. (Gowericeras) sp. from Alaska (Imlay, 

1953b, p. 100, pi. 53, figs. 6, 7, 10), favors a correlation 

with the basal part of the Chinitna formation well below 

the range of Pseudocadoceras. Similarly, the greater 

resemblance of Kepplerites lorinclarki Imlay, n. sp., to 

species of Kepplerites from the basal Callovian of 

Europe (Buckman, 1922, pis. 286, 289a, b; Arkell, 1954, 

p. 118, and 1956, p. 120) than to any described North 

American species of Kepplerites suggests a very early 

Callovian age, perhaps corresponding to the Macrocephalites macrocephalus zone of Europe.

MARIPOSA FORMATION

The Mariposa formation proper and similar slatey 

beds, extending from Eldorado County southward to 

Madera County, have furnished the pelecypod Buchia 

at many places. The specimens of Buchia present 

have all been referred by Imlay (1959, p. 157) to B. 

concentrica (Sowerby), which in Eurasia ranges from the 

upper Oxfordian zone of Perisphinctes cautisnigrae to 

the lower Kimmeridgian zone of Aulacostephanus 

pseudomutabilis.

A similar age for the Mariposa formation is shown by 

some of the ammonites that are associated with Buchia. 

These are listed by localities as follows:

Taramellicerasf (Proscaphites 1}) denticulatum (Hyatt) Mesozoic loc. 901.

Amoeboceras (Amoebites) dubium (Hyatt) Mesozoic loc. 719.

Perisphinctes (Discosphinctes) virgulatiformis Hyatt Mesozoic 

loc. 901.

P. (Dichotomosphinctes) cf. P. muhlbachi Hyatt Mesozoic loc. 901. 

Subdichotomoceras! aff. S. filiplex (Quenstedt) Mesozoic Iocs. 

902, 903, 904.

Other ammonites from the Mariposa formation, not 

associated with Buchia, are:

Perisphinctes (Dichotomosphinctes) muhlbachi Hyatt, Mesozoic

loc. 27517. 

P. (Dichotomosphinctes) cf. P. muhlbachi Hyatt, Mesozoic loc.

27460. 

P. (Dichotomosphinctest) spp. Mesozoic Iocs. 490, 24317.

Concerning the Eurasian ranges of these ammonites, 

Taramelliceras ranges through the Oxfordian and 

Kimmeridgian, and the subgenus Proscaphites is 

typically Oxfordian (Arkell, 1957, p. L 280-281). 

Amoeboceras ranges through the upper Oxfordian and 

the lower Kimmeridgian. The subgenus Amoebites 

is known only from the lower Kimmeridgian (Arkell, 

1957, p. L 306-307; Spath, 1935, p. 30-36). Dichotomosphinctes ranges through the Oxfordian (Arkell, 

1957, p. L 322) and occurs rarely in the lower Kimmeridgian (Arkell, 1937, p. 61). Discosphinctes in 

central and southern Europe ranges through the zones 

of Gregoryceras transversarium and Epipeltoceras bimammatum of the upper Oxfordian (Arkell, 1937, p. XLVII, 

p. 61) and appears to be transitional to Lithacoceras 

of the lower and middle Kimmeridgian (Arkell, 1937, 

p. LII). Subdichotomoceras ranges through the Kimmeridgian (Arkell, 1957, p. L 328), but is most characteristic of the lower and middle Kimmeridgian.

Judging from the ranges of these ammonite genera, 

the Mariposa formation might be equivalent to the 

entire Oxfordian and Kimmeridgian stages of Europe. 

However, the association of certain ammonites with 

other ammonites, or with Buchia concentrica (Sowerby) 

indicates that only the late Oxfordian and the early 

Kimmeridgian are represented by fossils in the Mariposa 

formation.

Thus the late Oxfordian is represented by the faunule 

at USGS Mesozoic locality 901, which contains Perisphinctes (Discosphinctes) virgulatiformis Hyatt, P. 

(Dichotomosphinctes) cf. P. muhlbachi Hyatt, Taramelliceras'? (Proscaphites^.) denticulatum (Hyatt), and 

Buchia concentrica (Sowerby). Of these, the presence 

of Buchia is evidence of an age not older than late 

Oxfordian, both Dichotomosphinctes and Proscaphites 

are much more likely to be Oxfordian than Kimmeridgian in age, and Discosphinctes is typical of the 

late Oxfordian. Furthermore, the perisphinctid ammonites present are closely similar to species in the 

late Oxfordian of Cuba and Mexico. P. (Discosphinctes) virgulatiformis (Hyatt) is nearly identical 

with Perisphinctes (Discosphinctes) carribeanus Jaworski 

from the late Oxfordian of Cuba (Jaworski, 1940, p. 

109, pi. 3, figs. 1, 2; pi. 4, fig. 5 ; pi. 7, fig. 6) and Mexico
D-8 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

(Burckhardt, 1912, p. 35, pi. 7, figs. 4-14). P. (Dichotomosphinctes) muhlbachi Hyatt greatly resembles 

P. (Dichotomosphinctes) durangensis Burckhardt (1912, 

p. 16, pi. 3, figs. 1, 2) from Mexico.

The early Kimmeridgian is equally strongly represented by the subgenus Amoebites at USGS Mesozoic 

locality 719 judging by the range of that ammonite 

in Eurasia and Greenland. It is probably represented 

also by the ammonites referred to the Kimmeridgian 

genus Subdichotomoceras from USGS Mesozoic localities 

902, 903, and 904 as those ammonites are associated 

with Buchia concentrica (Sowerby) of late Oxfordian 

to early Kimmeridgian age.

None of the fossil collections from the Mariposa 

formation afford any evidence of an age younger than 

the early Kimmeridgian. An age as old as early Oxfordian is possible for those collections containing 

Perisphinctes (Dichotomosphinctes) muhlbachi Hyatt at 

USGS Mesozoic locality 27517 and comparable ammonites at USGS Mesozoic localities 490, 24317, and 

27460 that are not associated with Buchia. Such 

an age seems unlikely, however, considering that the 

ammonites in question are closely similar to P. (Dichotomosphinctes} durangensis Burckhardt from the 

upper Oxfordian of Mexico.

Fossils other than Buchia and the ammonites listed 

above are scarce in the Mariposa formation. They are 

poorly preserved and have not been studied carefully 

and probably would not be useful in dating the formation. Such fossils include l( Belemnites" pacificus 

Gabb (USGS Mesozoic Iocs. 490, 901, 903, 904, 1982, 

25638), Avicula? sp. (USGS Mesozoic loc. 901; see 

Hyatt, 1894, p. 429), Entolium? aurarium (Meek) 

(USGS Mesozoic Iocs. 904, 1983), Entolium? sp. 

(USGS Mesozoic loc. 18937), Nucula? sp. (USGS 

Mesozoic loc. 18937), Lima? sp. (USGS Mesozoic 

Iocs. 27398, 27459), Cerithium? sp. (USGS Mesozoic 

loc. 901), and Turbo? sp. (USGS Mesozoic loc. 901).

In summation, the Mariposa formation, if dated on 

the basis of ammonites and the pelecypod Buchia, 

is of late Oxfordian and early Kimmeridgian age. 

The evidence shows that some of the beds are locally 

as old or perhaps slightly older than the upper part 

of theLogtown Ridge formation on the Cosumnes River.

Conceivably some of the Mariposa formation that 

has not furnished fossils could be younger than early 

Kimmeridgian. This seems unlikely, however, considering that the Geological Survey geologists have found 

Buchia concentrica (Sowerby) at 16 localities and that 

the collections in the museums in California contain 

this species from many other localities, but nowhere 

in the western part of the Sierra Nevada has a specimen 

of the younger Buchia rugosa (Fischer) been discovered.

Similarly in the Galice formation in southwestern 

Oregon, which formation is lithologically and faunally 

similar to the Mariposa formation, Buchia concentrica 

(Fischer) has been found at 18 localities, but not a 

single specimen of Buchia rugosa (Fischer) has been 

found. This contrasts with the abundance of Buchia 

rugosa (Fischer) from northwestern Washington northward into northern Alaska. Furthermore, in southwestern Oregon, the Galice formation is overlain with 

angular unconformity by the Riddle formation that contains ammonites and Buchia piochii (Gabb) of Portlandian-late Tithonian ages (Imlay and others, 1959, 

p. 2780). The time represented by the unconformity 

seems to correspond with the middle and upper Kimmeridgian and perhaps the early Portlandian, which 

is the time represented in Alaska and the Arctic region 

by Buchia rugosa (Fischer). It seems, therefore, that 

failure to find this species of Buchia in southwestern 

Oregon and in Claifornia is related to diastrophism and 

not to an unfavorable environment or to insufficient 

collecting.

MONTE DE OHO FORMATION

The Monte de Oro formation (Turner, 1896, p. 548, 

549) contains mollusks of late Oxfordian age to early 

Kimmeridgian age (figs. 1, 2). The evidence consists 

mostly of one fairly well preserved specimen of the ammonite Perisphinctes (Dichotomosphinctes) (see pi. 4, 

figs. 4, 7) that is similar to P. (Dichotomosphinctes) 

elisabethaeformis Burckhardt (1912, p. 31, pi. 6, figs. 

1-5) from the late Oxfordian of Mexico and of two 

crushed specimens of Buchia (see pi. 5, figs. 7, 8) that 

bear very fine radial striae and probably belong to 

Buchia concentrica (Sowerby).

The specimens of Buchia were obtained along the 

western side of some plant-bearing beds on the north 

bank of the Feather River from 3 to 4 miles northeast 

of Oroville (USGS Mesozoic loc. 4801). With them 

occur the pelecypods Ostrea, Modiolus, Trigonia, 

Meleagrinella, Lima, Chlamys?, Tancredia, a gastropod, 

belemnites, and plant fossils. Most of the molluscan 

genera are represented by only a few specimens, but 

Meleagrinella occurs in abundance.

The association of Buchia with Meleagrinella is 

interesting as Meleagrinella became scarce after the 

appearance of Buchia (Imlay, 1959, p. 156) in the 

late Oxfordian. The fact that Meleagrinella is represented by many specimens and that Buchia is represented by only two specimens suggests, therefore, 

that the beds containing these genera represent the 

time during which Buchia first appeared as a distinct 

genus. It is possible, however, that the relative 

abundance of the two genera is related to environmental conditions.
JURASSIC AMMONITES, SIERRA NEVADA D-9

In contrast to the evidence afforded by the mollusks, 

the flora in the Monte de Oro formation has furnished 

a correlation with the Bajocian of Europe (Ward, 

1900, p. 340-377; Fontaine, 1905, p. 48-145; Knowlton, 

1910, p. 39, 43, 44). Furthermore, some plant-bearing 

beds in Douglas County, Oreg. that contain the same 

plant species have been referred also to the Bajocian 

(Knowlton, 1910, p. 33-64). These beds in Douglas 

County, Oreg., all occur, however, within sequences 

that contain Buchia piochii (Gabb) (Diller, 1908a, p. 

376-383; Imlay and others, 1959, p. 2781), a fossil 

that is characteristic of the latest Jurassic (PortlandianTithonian) (Imlay, 1959, p. 159). Because of this 

association in Oregon, the comparable plant-bearing 

beds in the Monte de Oro formation near Oroville 

were at one time referred also to the Portlandian 

(McKee and others, 1956, p. 3). However, the discovery of Buchia cf. B. concentrica (Sowerby) within 

the same beds as the plants near Oroville and of Dichotomosphinctes in associated beds shows that the Monte 

de Oro formation is considerably older; that is, late 

Oxfordian to early Kimmeridgian. Therefore, on the 

basis of the mollusks, the plant species in question 

range from late Oxfordian to Portlandian, inclusive, 

and are much younger than the Bajocian.

A middle Late Jurassic age for the Monte de Oro 

formation is not out of harmony with the plant evidence 

because many species of plants have long ranges. Also, 

such an age means that the Monte de Oro formation 

is correlative, at least in part, with the Mariposa slate 

farther south, which correlation fits very well with 

present knowledge concerning the Jurassic paleogeography of California. A Portlandian age for the 

Monte de Oro formation does not fit because beds of 

that age are not known anywhere on the east sides 

of the Sacramento and San Joaquin Valleys.

COMPARISONS WITH OTHER FAUNAS 

TAYLORSVILLE AREA, CALIFORNIA

Beds of Callovian age are represented near Taylorsville by the Hinchman tuff, Bicknell sandstone, and 

Foreman formations of Diller (1892, p. 370-394) on 

Mount Jura; by the North Ridge formation of Crickmay (1933b, p. 896, 901) on Mount Jura; and by the 

Kettle formation of Diller (1908b, p. 84) near Hosselkus 

Creek east of Mount Jura. In the Hinchman tuff and 

Bicknell sandstone occur corals and mollusks that Hyatt 

(in Diller, 1908b, p. 49-52) and Crickmay (1933b, 

p. 901) considered to be of Callovian age. In the North 

Ridge formation of Crickmay, which overlies the 

Hinchman tuff, was found the ammonite Choffatia 

hyatti (Crickmay) (1933b, p. 901, 913, 914, pi. 32, fig. 3,

583565 0 61 2

pl. 33) that Arkell (1956, p. 554) said resembled European species from the Macrocephalites macrocephalus 

zone. From the lower part of the overlying Foreman 

formation, was obtained Reineckeia (Reineckeites) dilleri 

(Crickmay) (1933b, p. 902, 914, pl. 32, fig. 2, pl. 34, 

figs. 1-5). Fragments of the same subgenus occur 

likewise in a collection from the Foreman formation 

made by Diller (1908b, p. 56, USGS Mesozoicloc. 3143). 

From talus near the middle of the Foreman formation, 

Vernon McMath, University of Oregon, collected specimens of Pseudocadoceras (identified .by Imlay). These 

ammonites show that the lower and middle parts of the 

Foreman formation are of Callovian age not older than 

the European zone of Sigaloceras cattoviense or younger 

than the zone of Peltoceras athleta.

From the Kettle meta-andesite near Hosselkus Creek, 

Vernon McMath and the writer obtained specimens of 

Pseudocadoceras schmidti (Pompeckj), P. cf. P. grewingki (Pompeckj), and Choffatia sp. (USGS Mesozoic 

loc. 26784). Some hundreds of feet higher stratigraphically were obtained Cadoceras sp. juv., Xenocephalites? sp., Paracadoceras? sp., and Pseudocadoceras 

cf. P. grewingki (Pompeckj) (USGS Mesozoic Iocs. 

26785, 26786). These ammonites indicate an early 

middle Callovian age comparable with that of the lower 

part of the middle third of the Chinitna formation in the 

Cook Inlet region, Alaska (Imlay, 1953b, p; 53). If 

Paracadoceras and Xenocephalites are correctly identified, the age of the beds is probably not younger than 

the Sigaloceras calloviense zone of Europe.

On the basis of these ammonites, the lower and middle parts of the Foreman formation and a considerable 

thickness of the Kettle meta-andesite of the Taylorsville area may be correlated with the lower part of the

Logtown Ridge formation and probably the adjoining

transitional upper part of the Cosumnes formation on 

the Cosumnes River. Stratigraphically, the North 

Ridge formation of Crickmay, the Hinchman sandstone, and the Bicknell sandstone, all of Callovian age, 

could be correlative with part of the Cosumnes formation beneath the beds containing Pseudocadoceras. 

Faunal evidence is lacking for the existence of Oxfordian or younger Jurassic beds in the Taylorsville 

area. Crickmay (1933b, p. 902, 903) described some 

new formations above the Foreman formation and 

assigned them a middle Late Jurassic to Tithonian age, 

but he did not publish any evidence. Taliaferro 

(1942, p. 100) considered that the Foreman formation 

was equivalent to the Mariposa formation but that 

could be true only for the upper part that has not furnished fossils. The fact that the Foreman formation 

includes slates similar to those in the Mariposa formation is not a sound basis for correlation because similar
D-10 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

slates occur in the beds of Callovian age near Colfax 

and locally in the Cosumnes formation, which are both 

appreciably older than the Mariposa formation.

CENTRAL OREGON

Lower Callovian ammonites have been found in the 

Izee-Suplee area of central Oregon throughout about 

9,000 feet of beds ranging from the upper part of the 

Snowshoe formation of Lupher (1941) to within 300 

feet of the eroded top of the Lonesome formation of 

Lupher (1941), which is the youngest Jurassic formation 

exposed. The collections from the basal part of 

Lupher's Trowbridge shale have been mentioned by 

Lupher (1941, p. 264, 265). They include Lilloettia 

buckmani (Crickmay) and Kepplerites (Gowericeras) 

cf. K. spinosum (Imlay). Ammonites from the upper 

part of the Snowshoe formation, as mapped by William 

Dickenson of Stanford University, include Chqffatia sp., 

Xenocephalites vicarius Imlay, Lilloettia sp., and Gowericeras cf. G. spinosum Imlay (USGS Mesozoic Iocs. 

26778-26780). Ammonites from the Lonesome formation, obtained at various levels from near the base to 

within 1,000 feet of the top, belong mostly to the genus 

Xenocephalites, and some are identical with X. vicarius 

Imlay (USGS Mesozoic Iocs. 26781, 26782, 27372, 

27373). One small ammonite obtained 300 feet below 

the top of the Lonesome formation is probably an immature specimen of Xenocephalites (USGS Mesozoic 

loc. 27383). The ammonite Pseudocadoceras is probably represented in the Lonesome formation in a 

collection from the southeast corner of sec. 25, T. 19 S., 

R. 28 E.

Judging from these collections, most of the Callovian 

in central Oregon represents only the lower part of the 

Callovian stage and is comparable to the lower half of 

the Chinitna formation and to the upper part of the 

Bowser member of the Tuxedni formation in the Cook 

Inlet region, Alaska (Imlay, 1953b, p. 51-53). The 

presence of Pseudocadoceras? in the Lonesome formation of Lupher (1941) suggests that some part of that 

formation is as young as the Foreman formation of the 

Taylorsville area and the lower part of the Logtown 

Ridge formation of the Cosumnes River area in California.

SOUTHWESTERN OREGON

The Callovian has not been identified faunally in 

southwestern Oregon. If present, it is possibly represented by the Dothan formation (Diller, 1907, p. 

407-411) and the overlying Rogue formation (Wells and 

Walker, 1953) that lithologically bear considerable resemblance to the California Cosumnes formation and 

Logtown Ridge formation, respectively. In contrast, 

the late Oxfordian to early Kimmeridgian has been

identified faunally in the Galice formation (Diller, 1907, 

p. 403-407), which consists mostly of slates similar to 

those of the Mariposa formation of California. The 

faunal evidence consists of the presence of the pelecypod 

Buchia concentrica (Sowerby) at 18 localities and of 

perisphinctid ammonites at 4 localities. Most of these 

ammonites are fragmentary, but one laterally crushed 

specimen (see pi. 4, fig. 2) from the Almeda mine on 

the Rogue River, 3 miles below the mouth of Galice 

Creek (USGS Mesozoic loc. 3326), is a typical representative of the subgenus Dichotomosphinctes and 

is similar in appearance to Perisphinctes (Dichotomosphinctes) wartaeformis Burckhardt (1912, p. 25, 

pi. 5, figs. 1-4, 6) and to P. (Dichotomosphinctes) aff. 

P. (D.) plicatilis d'Orbigny in Burckhardt (1912, pi. 

4, figs. 2-4) from the upper Oxfordian beds of northern 

Mexico. This ammonite constitutes excellent evidence 

that part of the Galice formation is of late Oxfordian 

age,

WESTERN BRITISH COLUMBIA

In the Harrison Lake area the ammonites Cadoceras 

catostoma Pompeckj, Paracadoceras harveyi Crickmay, 

and Pseudocadoceras schmidti (Pompeckj) are listed 

from the middle of the Mysterious Creek formation of 

Crickmay (1930, p. 55-57). This association of species and genera in Alaska (Imlay, 1953b, p. 50-53) 

occurs in beds that are correlated with the Sigaloceras 

cattoviense zone of Europe. It is probably about the 

same age as the faunule found in the Kettle metaandesite on Hosselkus Creek in the Taylorsville area, 

previously discussed herein. It could be of the same 

age as the basal part of the Logtown Ridge formation 

on the Cosumnes River, but the presence there of 

coarsely ribbed specimens of Pseudocadoceras comparable to P. crassicostatum Imlay (1953b, p. 50, 94) suggests a slightly younger age probably equivalent to the 

middle Callovian.

In the Queen Charlotte Islands an ammonite faunule 

from the upper part of the Yakoun formation consists 

of species of Kepplerites (Seymourites) (McLearn, 1929, 

p. 4-12) identical with species in the lower and middle 

thirds of the Chinitna formation in the Cook Inlet 

region, Alaska (Imlay, 1953b, p. 50-53, 95-99). The 

fact that Kepplerites on the Queen Charlotte Islands 

is not associated with Cadoceras or Pseudocadoceras 

suggests correlation with only the lower third of the 

Chinitna formation. These occurrences are mentioned 

because Arkell (1956, p. 554) suggested that Kepplerites (Gowericeras) lindgreni (Hyatt) from near Colfax, 

Calif., is similar to species of Kepplerites from the 

Queen Charlotte Islands. The present studies show, 

however, that the species is quite different, and resembles species in Alaska from the very base of the Chi-
JURASSIC AMMONITES, SIEKRA NEVADA D-ll

nitna formation (Imlay, 1953b, p. 31, pi. 22, figs. 10-13) 

and in the western interior from the zone of Gowericeras costidensum (Imlay, 1953a, p. 6, 7, 31, pi. 22, 

figs. 10-13) which zone lies below the lowest known 

occurrence of Kepplerites (Seymourites). Also, the 

fact that the new species of Kepplerites, described herein, from near Coif ax differs considerably from any 

described species of K. (Seymourites) from British Columbia suggests that the beds near Colfax are probably 

of slightly different age.

ALASKA PENINSULA AND COOK INLET REGIONS, 

ALASKA

The lower and middle Callovian are well represented 

by a varied succession of ammonites in the Alaska 

Peninsula and in the Cook Inlet region except possibly 

for the lowest European zone of Macrocephalites 

macrocephalus (Imlay, 1953b, p. 51-55). That zone 

may be represented by the upper part of the Bowser 

member of the Tuxedni formation, which includes such 

typical Callovian ammonites as Grossouvria, Kheraiceras, Xenocephalites, and Kepplerites along with the 

long-ranging ammonites Phylloceras, Macrophylloceras, 

and Calliphylloceras. The species that are present all 

range up into the lower part of the Chinitna formation, 

so that the upper part of the Bowser member cannot be 

much older. In fact the presence of one specimen of 

Kepplerites similar to K. tychonis Kavn suggests that 

at least part of the Bowser member is equivalent to 

the lower part of the Sigaloceras calloviense zone of 

Europe (Imlay, 1953b, p. 53). Nevertheless, the absence of such ammonites as Lilloettia, Cadoceras, Paracadoceras, Pseudocadoceras, Gowericeras, and Cosmoceras 

from the upper part of the Bowser member implies a 

position low in the Callovian.

The succession of Callovian ammonites that has been 

established for Alaska cannot yet be demonstrated for 

California and Oregon because of meager collections 

and complicated structure. It is implied, however, by 

the fact that many of the Callovian ammonites that 

have been found in California and Oregon are identical 

specifically with the Callovian ammonites of Alaska. 

Assuming that the succession is approximately the same 

in all three States, certain correlations may be made, 

as discussed in the section dealing with "Ages and correlations." Thus the beds near Colfax, Calif., that contain Kepplerites and Gowericeras are correlated with 

the basal part of the Chinitna formation and the highest part of the Tuxedni formation of Alaska and hence 

with the European Sigaloceras calloviense zone and possibly the Macrocephalites macrocephalus zone. The 

beds containing Pseudocadoceras at the base of the Logtown Ridge formation contains species identical with 

those in the middle to upper thirds of the Chinitna formation and are correlated with the middle Callovian of 

Europe. In contrast, the ammonite Peltoceras from 

the Logtown Ridge (?) formation on Big Indian Creek 

in Amador County, Calif., has no counterpart in Alaska where the upper Callovian is missing as it is generally throughout the Arctic region.

The Oxfordian and Kimmeridgian stages in Alaska 

are represented mostly by a succession of species of the 

pelecypod Buchia (Imlay, 1955, p. 83-86). However, 

the lower Oxfordian, present locally in the Najknek formation of the Cook Inlet region and the Alaska Peninsula, is represented by the ammonite Cardioceras 

(Reeside, 1919, p. 9, 18, 24, 25, 27) that is 4>t associated with Buchia. The overlying beds in the lower 

part of the Naknek formation contain an abundance of 

Buchia concentrica (Sowerby) that is associated with 

the typical late Oxfordian ammonites Arftoeboceras 

(Prionodoceras) (Reeside, 1919, p. 30) and Perisphinctes 

(Dichotomosphinctes). (See pi. 4, fig. 6.) I^ear the 

middle of the Naknek formation, Buchia concentrica 

(Sowerby) is associated for several hundred feet with 

B. rugosa (Fischer) and B. mosguensis (vofn Buch). 

The last two species continue upward for ir^any hundreds of feet to the top of the Naknek formation. 

Their range in Alaska cannot be dated accurately because of lack of associated ammonites other than 

Phylloceras and Lytoceras, but by comparisons with 

their ranges in Eurasia and Mexico, they do not occur 

lower than the lower Kimmeridgian zone of Aulacostephanus pseudomutabilis or higher than the lower Portlandian (Imlay, 1955, p. 74, 75, 85; 1959, p. 165).

The lower part of the Naknek formation in Alaska 

shows faunal relations to the Mariposa formation in 

northeastern California and to the Galice forknation in 

southwestern Oregon and northwestern California. As 

in those formations, Buchia concentrica (Sowerby) is 

the most common fossil. Associated with this species 

in all three formations is the ammonite Perisphinctes 

(Dichotomosphinctes). The species of this subgenus 

present in the Naknek formation (USGS Me^ozoic loc. 

10796) may be identical with Perisphinctes (Dichotomosphinctes) muhlbachi Hyatt from the Maijiposa formation. The genus Amoeboceras occurs rarely both in 

the lower part of the Naknek formation and in the 

Mariposa formation but is represented by different subgenera of slightly different ages. The species of Phylloceras that ranges throughout most of the Naknek 

formation, but is particularly common in its lower part, 

is identical specifically with the Phylloceras in the Galice 

formation (USGS Mesozoic Iocs. 3322, 3335) and possibly includes some fragmentary specimens of Phylloceras in the Mariposa formation (USGS Mesozoic loc. 

27318).
D-12 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

In contrast, the upper part of the Naknek formation 

has nothing in common faunally with the Mariposa 

formation and the Galice formation except for the 

ammonite PhyUoceras. The pelecypod Buchia rugosa 

(Fischer), which is common in the upper part of .the 

Naknek formation, has not been found in the Pacific 

coast south of northwestern Washington. Its absence 

in Oregon and California is in harmony, however, with 

the absence in those States of any ammonites of middle 

Kimmeridgian to early Portlandian age.

MEXICO

The only Callovian ammonities from Mexico that 

have been described are from the southern part of the 

country in the states of Oaxaca and Guerrero (Burckhardt, 1927; 1930, p. 26, 32, 35, 36, 43; Arkell, 1956, p. 

564). Most of them are different from any ammonites 

that have been found in the Callovian of California. 

There are relationships, however, on the generic level. 

Thus the species of Reineckeia (Reineckeites) described 

by Burckhardt (1927, pi. 16, pi. 17, pi. 18, figs. 1, 2, 7) 

from Mexico resemble R. (Reineckeites) dilleri (Crickmay) (1933b, pi. 32, fig. 2, pi. 34) from the Taylorsville 

area, in California. Chqffatia waitzi Burckhardt (1927, 

p. 75, pi. 30, figs. 2-5) is too small for comparison with 

Chofatia hyatti (Crickmay) (1933b, pi. 33) from the 

Taylorsville area. Xenocephalites nikitini (Burckhardt) 

(1927, pi. 16, figs. 4-9) recalls the presence of a questionable example of the genus in the Kettle metaandesite of the Taylorsville area. The species of 

Peltoceras described by Burckhardt (1927, pi. 32, pi. 

33, figs. 4-7, pi. 34) differ considerably from the specimen of Peltoceras from Indian Creek, Amador County, 

Calif., but possibly have significance paleogeographically 

as no other occurrence of Peltoceras, or of late Callovian 

fossils, are known in North America.

The Mexican Callovian has no representatives of 

such ammonites as Cadoceras, Paracadoceras, Pseudocadoceras, Kepplerites, and Gowericeras that occur in the 

Callovian from California to Alaska along withReineckeia (Reineckeites), Chqffatia, and Xenocephalites. It 

appears, therefore, that except for the presence of 

Peltoceras, the Callovian of California is much more 

similar faunally to that of Alaska than to that of Mexico. 

This does not imply, of course, that there was any 

physical barrier between the seas in California and those 

in Mexico.

The Oxfordian ammonites of Mexico that have been 

described mostly from the area of San Pedro del Gallo, 

Durango (Burckhardt, 1912, p. 1-40, 203, 204, 209-213, 

pis. 1-7). At this place the upper 100 meters of Oxfordian strata have furnished the ammonites Ochetoceras, Taramelliceras (Proscaphites), Perisphinctes (Discosphinctes), and Euaspidocerds, which probably represent the Epipeltoceras bimmamatum zone of central 

and southern Europe (Burckhardt, 1912, p. 213; 

Arkell, 1956, p. 563). From the underlying 150 meters 

of strata have been obtained ammonites belonging to 

Creniceras, Taramelliceras, and Perisphinctes (Dichotomosphinctes). This faunule is correlated with the 

Perisphinctes plicatilis zone of northwest Europe 

(Arkell, 1956, p. 563) and with the Gregoryceras transversarium zone of central and southern Europe (Burckhardt, 1930, p. 64; Arkell, 1956, p. 114).

From these Oxfordian strata the ammonite Amoeboceras cf. A. alternans (von Buch) has also been 

recorded, from about 4 kilometers north of San Pedro 

del Gallo north of Potrero de las Tunas (Burckhardt, 

1930, p. 66). This occurrence is the southernmost 

record of the genus in North American and perhaps 

in the world, being much further south than the 

Amoeboceras from northern Italy recorded by Arkell 

(1956, p. 175).

The faunal sequence at San Pedro del Gallo is of 

considerable interest in determining the age of the 

Mariposa formation and of equivalent formations on 

the Pacific coast. One of the ammonites, Perisphinctes (Discosphinctes) carribeanus (Jaworski) (Burckhardt, 1912, p. 35, pi. 7, figs. 4-14) from the upper 

100 meters of the Oxfordian sequence at San Pedro del 

Gallo may be identical with P. (Discosphinctes) virgulatiformis Hyatt (1894, p. 422) from the Mariposa 

formation. Another ammonite, Perisphinctes (Dichotomosphinctes) durangensis Burckhardt (1912, p. 16, pi. 

3, figs. 1, 2), from the lower 150 meters of the Oxfordian 

at San Pedro del Gallo is apparently identical with P. 

(Dichotomosphinctes) muhlbachi Hyatt (1894, p. 426) 

from the Mariposa formation and with a specimen of 

P. (Dichotomosphinctes) (pi. 4, fig. 6) from the lower 

part of the Naknek formation, Alaska. P. (Dichotomosphinctes) elisabethaeformis Burckhardt (1912, p. 31, 

pi. 6, figs. 1-5) from the same lower beds at San Pedro 

del Gallo resembles a specimen of Dichotomosphinctes 

from the Monte de Oro formation near Oroville, 

Calif, (pi. 4, figs. 4, 7). Finally, P. (Dichotomosphinctes) wartaeformis Burckhardt (1912, p. 25, pi. 5, 

figs. 1-4, 6) resembles a specimen of P. (Dichotomosphinctes) (pi. 4, fig. 2) from the Galice formation of 

southwestern Oregon.

The Kimmeridgian ammonite faunas of Mexico are 

varied, well described (Burckhardt, 1906, 1912, 1919, 

1921; Imlay, 1939, p. 21, 22, tables 4-7), and obviously 

have little in common with the fossils from the Mariposa 

formation in California. They do not contain a 

single representative of the genus Amoeboceras. They 

do contain a few representatives of Svbdichotomceras 

(Burckhardt, 1906, pi. 31, figs. 1-4; Imlay 1939, pi. 

10, figs. 1-3, 13) that are similar to Subdichotomocerast
JURASSIC AMMONITES, SIERRA NEVADA D-13

aff. S. filiplex (Quenstedt) from the Mariposa formation. They do contain Buchia concentrica (Sowerby) 

which was found by Burckhardt (1930, p. 67, 80) near 

Mazapil, Zacatecas, in a thin bed lying above beds 

characterized by species of Idoceras similar to /. 

balderum (Oppel) and below beds containing Glochiceras fialar (Oppel). This occurrence was confirmed by 

collections made by C. L. Rogers and others (1956, p. 

23) in his unit B. Associated with this species of 

Buchia is another species that Burckhardt (1930, p. 67) 

compares to Aucella pallasi var. plicata Lahusen but 

which probably belongs to B. rugosa (Fischer). (See 

Imlay, 1955, p. 84; 1959, p. 158-159.)

The stratigraphic occurrence of these species of 

Buchia is interesting because the overlying beds containing Glochiceras fialar (Oppel) are correlated with 

the European zone of Aulacostephanus pseudomutabilis 

(Burckhardt, 1930, p. 64; Imlay, 1952, pi. 2) and the 

underlying beds containing Idoceras balderum are 

correlated with the European zone of Rasenia mutabUis. By comparison with the Jurassic of California, 

the absence of Buchia rugosa (Fischer) from the 

Mariposa formation would suggest that that formation 

is older than the beds in Mexico that contain Glochiceras fialar (Oppel). This is supported also by the 

absence of Buchia mosguensis (von Buch) from the 

Mariposa formation, as that species is present in the 

Glochiceras fialar beds near San Pedro del Gallo, 

Durango (Burckhardt, 1912, p. 216, 217).

GEOGRAPHIC DISTRIBUTION

The occurrence by county and locality of the species 

described in this report is indicated in table 2. The 

general position of each locality is shown on figure 3. 

Detailed descriptions of the individual localities are 

shown in table 3.

SUMMARY OF RESULTS

1. The Jurassic ammonites from the western part of 

the Sierra Nevada include 12 genera and subgenera and 21 species. Only one species is 

described as new. Seymourites and Gowericeras 

are considered subgenera of Kepplerites. Discosphinctes and Dichotomosphinctes are considered 

subgenera of Perisphinctes.

2. These ammonites are all of Late Jurassic age and 

in terms of European stages, represent the early 

to late Callovian, the late Oxfordian, and the 

early Kimmeridgian.

3. The exact stratigraphic positions of most of the 

fossils relative to formational boundaries is 

not known because of complicated stratigraphy 

or inexact field descriptions. However, the 

faunal evidence is sufficient to show the exact

ages of the formations at certain spots and the 

approximate age range of the formations locally.

4. The Jurassic beds near Coif ax, Placer County, 

have furnished the Callovian ammonites Grossouvria coljaxi (Gabb), Kepplerites torinclarki 

Imlay, n. sp., and K, (Gowericeras), lindgreni 

(Hyatt). An early Callovian age is indicated 

by the presence of Kepplerites and by the close 

resemblance of K. lindgreni (Hyatt) to a species 

in Alaska that occurs considerably below beds of 

middle Callovian age.

5. The Cosumnes formation at its type locality on 

the Cosumnes River is at least in part of Callovian 

age as it has furnished an ammonite, \Pseudocadocerasf, about 500 feet below its top, and its 

highest beds are transitional into the Logtown 

Ridge formation.

6. The Logtown Ridge formation on the Cosumnes 

River has furnished the Callovian ammonite 

Pseudocadoceras grewingki (Pompeckj) in its 

lower part about 600 to 675 feet abovs its base. 

With this species is associated a coarsely ribbed 

species that is probably identical with P. crassicostatum Imlay. By comparisons with Alaska, 

these ammonites indicate a correlation with the 

upper third of the Chinitna formation and 

thence with the middle part of the Callovian 

stage. The presence of Pseudocadoceras itself 

is evidence of an age not older than the late 

early Callovian zone of Sigaloceras calloviense. 

The Logtown Ridge formation is probably represented also by the ammonite Peltoceras ihdt was obtained at, or near, Indian Creek. This ammonite 

is excellent evidence of a late Callovian age.

The upper part of the Logtown Ridge formation on 

the Cosumnes River has furnished the ammonite 

Idoceras of latest Oxfordian to early Kimmeridgian age.

7. The Mariposa formation and similar slatey units 

containing Buchia concentrica fSowe^by) have 

furnished a number of ammonites of late Oxfordian to early Kimmeridgian age. The late 

Oxfordian is represented by Perisphinctes (Dichotomosphinctes) muhlbachi Hyatt a|nd by P. 

(Discosphinctes) virgulatiformis Hydtt, which 

are essentially identical with species in Mexico 

and Cuba. The early Kimmeridgian is represented by Amoeboceras (Amoebite$) dubium 

(Hyatt) and probably by Subdichotomocerast 

aff. S. filiplex (Quenstedt). This age range is 

confirmed by the presence of Buchia \concentrica 

(Sowerby) at a number of places in the Mariposa 

formation from near its base to at least several 

thousand feet above its base. The late Oxfordian ammonites from the Mariposa formation
D-14 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

TABLE 2. Geographic distribution oj Late Jurassic megafossils in the western Sierra Nevada, Calif.

[Numbers 1-31 refer to numbers on fig. 3. Most of the larger numbers refer to Mesozoic collections in the U.S. Geological Survey. Collection numbers from the University 

of California at Berkeley are preceded bv the letters UC; from Leland Stanford Junior University by the letters SU; and from the Museum of Comparative Zoology 

at Harvard University by the letters MCZ]

Phylloceras sp. ___ __

Taramelliceras? 

(Proscaphites?) 

denticulatum 

(Hyatt) ----- --

Kepplerites lorindarki 

Imlay, n. sp __ -

(Oowericeras) lindgreni (Hyatt) 

Pseudccadoceras grewingki (Pompeckj) _

cf. P. grewingki 

(Pompeekj). ...

cf. P. crassicostatum 

Imlay ..........

P.?SP ..

Amoeboceras 

(Amoebites) dubium 

(Hyatt) 

Qrossouvria colfaxi 

(Qabb)..... .....

Perisphinctes? sp---.-..

Perisphinctes (Discosphinctes) 

virgulatiformis 

Hyatt- __ ---.

(Dichotomosphinctes) muhlbachi 

Hyattcf. P. muhlbachi 

Hyatt 

cf. P. elisabethaeformis Burckhardt.---------

(Dichotomosphinctes?) spp._- . ... .

Idoceras cf, /. planula 

(Heyl) in Zeiten....

Idoceras? sp... _ _ ...

Subdichotomoceras? aff. 

S. filiplex 

(Quenstedt).--. __

Peltoceras (Metapeltoceras?) sp .. -.-.

"Belemnites" pacificus 

Oabb. .............

Turbo? sp ._ ... ___

Cerithium? sp _ -

Gastropods undet _ ...

Pinna sp _ --_..-. _ ..

Modiolus sp----- _ --..

Mytiluss-p.. ...........

Avicula? sp ____ . ...

Meleagrinella sp_- -- ...

Meleagrinella? sp.....

Buchia concentrica

cf. B. concentrica 

(Sowerby) ....

Chlamys? sp _ - ....

Entcliuml aurarium 

(Meek)............

sp 

Lima sp __ .... _ ....

Lima"! sp __ ... _ __ .

Ostrea sp.-... .._..

Trigonia sp ______ .

Tancredia? sp_. ------- .

Corbis? sp.. ---.---.

Rhynchonellid braehiopod-.... _ _ ....

Eehinoid fragments.---

Butte County

Monte de Oro 

formation

1

>o

X

V

2

n

X

X

3

i

X

X

X

£S 

w

X

1

X

X

X

X

X

v

X

V

<M§Tt<

X

SU9063

X

Placer 

County

Colfax 

formation 

of Smith

4

m 

S

(N

X

X

5

MCZ5287

<o

is

IM

Eldorado County

"Mari- posa" 

formation

6

tSIM

X

7

1

X

8

IM

X

v

00

X

Logtown 

Ridge formation

9

t> 02

v

10

!

d

t>

v1

11

o

i

v

t»

RIM

V

Cosumnes formation

12

S 

3

X

Amador County

Logtown 

Ridge(?) formation

13

SU9062

X

"Mari- posa" 

formation

14

&

Z

X

X

Formation unknown

15

t»

1

X

........

Calaveras 

County

Mariposa 

formation

16

t»

1

--

17

a> 

t~

X

I

v

v

X

v

«

--

18

i

v

V

X

Tuolumne County

Mariposa (?) formation

19

"5

g

IM

1IM

....

Mariposa 

County

Mariposa formation

20

*O

R «

X

X

--

I

--

X

!> 

8 

55

X

X

X

--

21

i

v

v

v

X

X

v

X

-

oc

C- S

X

-

22

X

X

23

S

1

X

-

1

X

X

-

24

1IM

X

X

-

25

i

X

X

1

X

--

26

c< 

1

X

-

27

CO>o

<N

X

-

28

<N

1

X

--

-

-

2930

ll

X-

-X

X--
JURASSIC AMMONITES, SIERRA NEVADA D-15

NEVADA

I S A C R A M E/N T 0 j

San Andreas 

O

\ CALAVERAS

^ Copperopolis o 77X^^X20 O Sonor

\

Stockton

3NTRA C 0 S T A < SAN /JOAQUIN

Camp O ~x 2.4 

Jacksonville

FIGUKE 3. Index map of Jurassic localities in the western Sierra Nevada, Calif.
D-16 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

TABLE 3. Descriptions of the Late Jurassic fossil localities in the western Sierra Nevada, Calif.

Locality on 

fig. 3

1 __ .-----.

2_ _ ..__.._

3_____ ____-.

3 ._--_--_

3__ -.-___.__

3.. _________

3 ._-._--.

4___. _______

5 -__-_--.

5 _ ___..__

6 _ _______

7 -_-_--_-

8_._________

8_______,___

9___________

10______.___

ll___-___.__

Geological 

Survey 

Mesozoic 

localities

16625

3990

3991

3992

4801

4802

27313

27516

27517

490

25638

27318

24710

Collector's field Nos.

5-l-_--__-______.

5-2-_-________.___

5-3-__.__________

5-l7_-_-___-___._

5-16_-_-__-_..___

LC-53-282. ______

LC-55-30. _______

LC-53-283____._

Localities of other institutions

Stanford Univ. Mus. Paleontology 9063.

MCZ-5287 Harvard. ____

Paleontology 9065.

Univ. Calif. Berkeley

A-4996.

Collector, year of collection, description of locality, and stratigraphie 

assignment

V. T. Alien, 1927. From hydraulic mine north of

Oroville and about 3 miles southwest of fossil locality 

near Banner Mine, Oroville quad., Butte County, 

Monte de Oro formation. 

James Storrs, 1906. North bank of Feather River a

quarter of a mile below mouth of Morn^ Ravine and 

3 miles above Oroville, SE. cor. sec. 32, T. 20 N., 

R. 4 E., Oroville quad., Butte County, Monte de 

Oro formation. 

James Storrs, 1906. North bank of Feather River,

about 4 miles above Oroville, at mouth of ravine 

west of Banner Mine, probably NW. cor. sec. 3, T. 

19 N., R. 4 E., Oroville quad., Butte County, Monte 

de Oro formation. 

James Storrs, 1906. Along stage road a quarter of a

mile southwest of Banner mine, probably east central 

part of sec. 33, T. 20 N., R. 4 E., Oroville quad., 

Butte County, Monte de Oro formation. 

James Storrs, 1907. Western part of the plant-bearing

beds and north side of the Feather River from 3-4 

miles above Oroville, probably SEtf sec. 33, T. 20 

N., R. 4 E., Oroville quad., Butte County, Monte de 

Oro formation. 

James Storrs, 1907. Near eastern part of plant beds

on north side of the Feather River from 3-4 miles 

above Oroville, probably SE# sec. 33, T. 20 N., R. 4 

E., Oroville quad., Butte County, Monte de Oro 

formation. 

R. S. Creely, 1956. From north bank of Feather River

just north of Sycamore Hill, about 3 miles northeast 

of Oroville, 450 ft south of NE. cor. sec. 4 near its east 

edge in T. 19 N., R. 4 E., Oroville quad., Butte 

County, Monte de Oro formation. 

L. D. Clark, 1953. Road cut on west side of U.S.

Highway 40, 0.1 mile north of Midget Auto Court 

and 0.85 mile northeast of road turnoff to Grass 

Valley, NW}£ sec. 26, T. 15 N., R. 9 E., Colfax 

quad., Placer County, Colfax formation of J. P. Smith. 

J. D. Whitney. "From railroad cut at station 2777,

sec. 53, 1 mile west of Colfax, 14 ft below surface 

of ground." Colfax quad., Placer County, Colfax 

formation of J. P. Smith.

Colfax and a quarter of a mile west of railroad station, 

Colfax quad., Placer County, Colfax formation of 

J. P. Smith.

town quad., Eldorado County, "Mariposa" formation. 

G. W. Kimble and H. W. Turner, probably 1884.

Slates Big Canyon about 2 miles north of Placerville, 

SWK sec. 36, T. 11 N., R. 11 E., Georgetown quad., 

Eldorado County, "Mariposa" formation. 

L. D. Clark and N. K. Huber, 1955. South bank of

Cosumnes River 0.1 mile east of the Michigan Bar 

bridge in the SEK sec. 36, T. 8 N., R. 8 E., Folsom 

quad., Sacramento County, "Mariposa" formation. 

R. W. Imlay, 1958, same as Mesozoic loc. 25638.

J. C. Heald. Nashville, Placerville quad., Eldorado

County, probably from Logtown Ridge formation.

andesitic tuff. "Presumably from a building stone 

quarry near the Huse bridge over the Cosumnes 

River about 6 miles north of Plymouth." Placerville quad., either southern Eldorado County, or 

northern Amador County, Logtown Ridge formation, near top. 

L. D. Clark and E. H. Pampeyan, 1953. North bank

of Cosumnes River, 4,550 ft S. 55° W. of Huse bridge, 

at point where river bends sharply southward for 

half a mile, south central part of sec. 15, T. 8 N., 

R. 10 E., Fiddletown ^/.-min quad. Eldorado County, 

Logtown Ridge formation, about 600-675 ft above 

base.
JURASSIC AMMONITES, SIERRA NEVADA D~17 

TABLE 3. Descriptions of the Late Jurassic fossil localities in the western Sierra Nevada, Calif. Continued

Locality on 

fig. 3

11.

12.

13.

14.

15.

16.

17. 

IT17.

18.

19.

19.

20. 

20.

20.

21. 

21.

Geological 

Survey 

Mesozoic 

localities

27317

22175

18937

27387

24317

719

904

27566

903

27395

27396

27315

27394

27397

901

27568

Collector's field Nos.

I-58-9-28A.

Heyl 1.

LC-52-260.

292.

293.

263.

294.

LC-59-101.

Localities of other institutions

Stanford Univ. Mus. 

Paleontology 9062.

Collector, year of collection, description of locality, and s^ratipraphie 

assignment

R. W. Imlay, 1958. Fossils obtained 100-3QO ft above 

Cosumnes River at same place as Mesozoic loc. 

24710 in thin-bedded tuffs from 600-640 ft above 

base of Logtown Ridge formation.

J. H. Eric and A. A. Stromquist, 1949. About 600 ft 

west of base of Logtown Ridge formation on right 

bank of Cosumnes River about 2 miles below the 

Huse Bridge and 1,850 ft east of west edge of Fiddletown 7/l 2 min quad., lat 38°31'50" N., long 120°51'00" 

W., NW}£ sec. 22, T. 8 N., R. 10 E., Eldorado County, 

Consumnes formation, upper part, about 500 ft 

below top.

F. M. N. Hamilton, 1914. Big Indian Creek, southwest 

corner of Placerville 30-min quad., Amador County. 

Probably from Logtown Ridge formation.

G. R. Heyl, 1944. Small gulley three-fourths of a mile 

NNW of Plymouth, Sutter Creek 15-min quad., 

Amador County "Mariposa" formation .

Collector and year of collection unknown. Mokolumne 

River downstream from Middle Bar Bridge, T. 5 N.,

R. 11 E., Sutter Creek quad., Amador or Calaveras

County, formation unknown.

L. D. Clark and D. B. Tatlock, 1952. Cherokee Creek, 

sec. 22, T. 3 N., R. 12 E., San Andreas qijiad., Calaveras County loose boulder in stream be^d along a 

major fault zone. "Mariposa" formation.

G. F. Becker, probably 1890. Texas Ranch, in valley 

of Angels Creek near north edge of sec. 28 or 29, T. 

2 N., R. 13 E., Copperopolis quad., Calaver&s County, 

Mariposa formation.

Cooper Curtice, 1891. Six miles from Coppkropolis on 

road to Sonora and on grade to Angels Creek near 

center of sec. 33, T. 2 N., R. 13 E., Copperopolis 

quad., Calaveras County, Mariposa formation.

Cooper Curtice, probably 1891. Wagon ro^id 2 miles 

west of Reynolds Ferry and 1 mile west of ^otherlode, 

Copperopolis quad., Calaveras County, Calif., Mariposa 

formation. ' Cooper Curtice, 1891. West bank of Stanislaus River 

opposite mouth of Bear Creek near center sec. 11, 

T. 1 N., R. 13 E., Copperopolis quad., Calaveras 

County, Mariposa formation, about 1,000 ft above

A. A. Stromquist, 1940-50. About 0.7 mile north of 

Mormon Creek and 0.5 mile east of Stanislaus River 

in NE#SE# sec. 25, T. 2 N., R. 13 E., Sonora quad., 

Tuolumne County, Mariposa (?) formation.

A. A. Stromquist, 1940-50. Soldiers Gulch north of 

Mormon Creek, SE^NE^ sec. 25, T. 2 N., R. 13 E., 

Sonora quad., Tuolumne County, MariposA(?) formation.

A. A. Stromquist, 1940-50. Mormon Creek, probably 

near east boundary of sec. 36, T. 2 N., R. 13 E., 

Sonora 15-min quad., Tuolumne County, Mariposa 

formation.

A. A. Stromquist, 1940-50. About 0.4 mile south of 

Mormon Creek in SW^SWtf sec. 31, T. 2 N., R. 14 E. 

Sonora 15-min quad., Tuolumne County, Mariposa 

formation.

A. A. Stromquist, 1940-50. On fault cutting metavolcanic rock north of Mormon Creek, SE^SWH sec. 

30, T. 2 N., R. 14 E., Sonora 15-min quad., Tuolumne 

County, Mariposa (?) formation.

Cooper Curtice, 1891. On trail opposite Bpsticks Bar 

near Reynold's Ferry across the Stanislaus River, 

SE*4 sec. 34, T. 2 N., R. 13 E., Copperoplois quad., 

Tuolumne County, Mariposa formation.

L. D. Clark, D. L. Jones, and N. J. Silberling, 1959. 

From placer sluiceway trench on north bank of 

Stanislaus River about 15 ft above low-water mark of 

Melones Reservoir in the NW#NW# sec. 3, T. 1 N., 

R. 13 E., Copperopolis quad., Tuolumne County, 

Calif., Mariposa formation, about 1,000 feet above 

base.
D-18 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

TABLE 3. Descriptions of the Late Jurassic fossil localities in the western Sierra Nevada, Calif. Continued

Locality on 

fig. 3

22 _-___

23 _______

23 - -----

24 -_--_

25 --.

25 ------

26 _______

27 --__.

28 _____

29 -L-._

30 ----.

31 _______

Geological 

Survey 

Mesozoic 

localities

20554

27459

27398

902

27311

27312

253

1982

243

27460

1983

Collector's field Nos.

Heyl 255_ _ _____

183--------------

LC-53-42A ____

LC-53-280- ____.-

Localities of other institutions

leontology 9064.

Collector, year of collection, description of locality, and stratigraphic 

assignment

Vander Hoof. From Wood Canyon (?) near Sonora,

Sonora quad., Tuolumne County, Mariposa formation. 

George Heyl, 1947. Woods Creek Canyon, 3 miles

northwest of Jacksonville, sec. 2 or 3, T. 1 S., R. 14 E., 

Sonora 15-min quad., Tuolumne County, Mariposa 

formation. 

G. F. Becker, probably 1884. Woods Creek, northwest

of Jacksonville, Sonora 15-min quad., Tuolumne 

County, Mariposa formation. 

G. R. Heyl, 1946. Crest of Woods Creek Ridge 1 mile

northwest of Jacksonville, sec. 12, T. 1 S., R. 14 E., 

Sonora 15-min quad., Tuolumne County, Mariposa 

formation, 2,000-3,000 ft above base. 

Cooper Curtice, 1891. South bank of Tuolumne River

at Moffat Bridge, SW. cor. sec. 18, T. 1 S., R. 15 E., 

Sonora quad., Tuolumne County, Mariposa formation. 

L. D. Clark and R. Pack, 1953. Moffat Bridge site

near Jacksonville. Railroad cut on south side of 

Tuolumne River, 200-225 ft east of contact between 

Mariposa formation and mafic volcanic breccia. 

SW. cor. sec. 18, T. 1 S., R. 15 E., Sonora 15-min 

quad., Tuolumne County, Mariposa formation, 200 ft 

above base. 

L. D. Clark, 1953. North bank of Merced River,

NW. cor. sec. 26, T. 3 S., R. 16 E., Coulterville 

quad., Mariposa County, Mariposa formation, about 

1,000 ft above base. 

H. W. Turner, G. F. Becker, and C. A. White, 1884.

Left bank of Merced River a quarter of a mile below 

Bagby (formerly called Bentons Mills), sec. 6?, T. 

4 S., R. 17 E., Coulterville 15-min quad., Mariposa 

County, Mariposa formation. 

H. W. Turner, 1892. Hell Hollow, north of Bear Valley

in northwest part of T. 4 S., R. 17 E., Coulterville 

quad., Mariposa County, Mariposa formation. 

H. W. Turner, 1884. Mariposa estate near Pine Tree

Mines, about half a mile east of head of Hell Hollow, 

T. 4 S., R. 17 E., lat 37°36' N., long 120°07' W., 

Coulterville quad., Mariposa County, Mariposa 

formation, probably 3,000-4,000 ft above base. 

W. D. McLearn, received at Natl. Mus. May 3, 1922.

Bullion Mountain. Coulterville quad., Mariposa 

County, Mariposa formation.

(Bullion Mountain post office), probably Mariposa 

quad., Mariposa County, Mariposa formation.

indicate that its lower part locally is of approximately the same age as the upper part of the 

Logtown Ridge formation on the Cosumnes 

River where a specimen of Idoceras was obtained.

The Monte de Oro formation is of late Oxfordian to 

early Kimmeridgian age. The evidence consists of 1 ammonite similar to Perisphinctes 

(Dichotomosphinctes) elisabethaeformis (Burckhardt) from the late Oxfordian of Mexico and 

of 2 crushed specimens of Buchia that probably 

belong to Buchia concentrica (Sowerby).

The affinities of the Callovian ammonites in the 

western part of the Sierra Nevada are mainly 

with those of British Columbia and Alaska as 

indicated by the presence of such ammonites as 

Cadoceras, Paracadoceras, Pseudocadoceras, 

Kepplerites, and Gowericeras. Ammonites in

common with both Alaska and southern Mexico 

include JReineckeia, Choffatia, and Xenocephalites. Peltoceras occurs in common with 

Mexico but not with Alaska. In Alaska, however, late Callovian beds that might contain 

Peltoceras have never been found and in the Cook 

Inlet region, the late Callovian is represented by 

an unconformity.

10. The affinities of the late Oxfordian ammonites from 

California are mostly with Mexico and Cuba, 

but astonishingly one of the ammonites, Perisphinctes (Dichotomosphinctes) miihlbachi Hyatt 

is essentially identical both with P. durangensis 

Burckhardt from Mexico and with a specimen 

from the Alaska Peninsula.

11. Among the early Kimmeridgian ammonites from 

California, the presence of Amoeboceras in-
JURASSIC AMMONITES, SIERRA NEVADA D-19

dicates affinities with Alaska and the Boreal 

region. The ammonite Subdichotomoceras has 

not been found in Alaska but has been found in 

Mexico and in many other parts of the world. 

12. The ammonite faunas that existed in California 

from early Callovian to early Kimmeridgian 

times appear to have had free marine connections 

northward to Alaska and southward to southern 

Mexico, but during Callovian time the Alaskan 

influence was dominant.

SYSTEMATIC DESCRIPTIONS

Class CEPHALOPODA 

Genus PHYLLOCERAS Suess, 1865

Phylloceras sp.

The genus is represented by fragmentary external 

and internal molds of a single specimen that has been 

crushed laterally. The external mold shows that the 

species has a very small umbilicus and very fine dense 

flexuous ribs that are grouped in low broad folds on the 

lower part of the flanks. There is no trace of sigmoidal 

constrictions.

The folds on the lower part of the flanks appear to be 

much less pronounced than in a species of Phylloceras 

from the Galice formation of southwestern Oregon 

(USGS Mesozoic Iocs. 3322, 3335) or from the Naknek 

formation of Alaska, but the poor preservation of the 

specimens makes specific identification impossible.

Nonfigured specimen: USNM 130784.

Occurrence: "Mariposa" formation at USGS Mesozoic loc. 

27318.

Genus TARAMELLICERAS Del Campana, 1904 

Subgenus PROSCAPHITES Rollier, 1909

Taramelliceras? (Proscaphites?) denticulatum (Hyatt) 

Plate 1, figures 9-11

Oecotraustes denticulata Hyatt, 1894, Geol. Soc. America Bull.,

v. 5, p. 427. 

"Oecotraustes" denticulata Hyatt. Crickmay, 1933a, U.S. Geol.

Survey Prof. Paper 175-B, p. 58, pi. 17, figs. 11-13.

This species is characterized by a compressed shell, 

a narrow venter, a very narrow umbilicus, a row of midventral serrations, and by weak gently flexuous ribs 

that become stronger ventrally on the flanks but weaken 

on the venter and do not extend to the median ventral 

serrations.

The suture line is poorly exposed. It has been described and illustrated adequately by Crickmay (1933a, 

pi. 17, figs. 12, 13).

This species was compared by Hyatt with Ammonites 

lochensis Oppel (1863, p. 207, pi. 54, figs, la-d) from the 

late Oxfordian of Germany. It appears to be similar 

in most respects, but has somewhat sparser ribbing. 

It also shows some resemblance to Ammonites pichleri

Oppel (1863, p. 212, pi. 51, figs. 4a-c). That species 

differs by having fine ribs and many intercalated ribs 

of which all extend to the midventral serrations (Jeannet, 1951, pi. 29, figs. 7a, b; pi. 30, figs. 2a, b). These 

species from Europe have been placed by Jeaiknet (1951, 

p. 95, 96) in a new genus Eicheiceras, which Arkell 

(1957, p. L281) considers to be a synonym of Proscaphites, a subgenus of Taramelliceras.

Similar appearing species of Taramelliceras from the 

late Oxfordian of Mexico (Burckhardt, 1912, p. 12-14, 

pi. 2, figs. 5-12) all have somewhat finer ribbing than 

the California species. Interestingly the Mexican 

species are associated with species of Discosphinctes and 

Dichotomosphinctes similar to those associated with 

Taramelliceras^ denticulatum (Hyatt).

Types: Cotypes USNM 30206.

Occurrence: Mariposa formation at USGS Mesozoic loc. 901.

Genus KEPPLERITES Neumayr and Uhlig, L892

Kepplerites lorinclarki Imlay, n. sp.

Plate 1, figures 1-8

Twelve fragmentary molds represent a species that 

is characterized by being fairly small and by having 

unusually prominent ribbing for the genus. It has 

stout ovate whorls and evenly rounded flanks. Its 

venter is poorly exposed but is probably evenly rounded. 

The umbilicus is fairly narrow on the inner khorls but 

widens considerably on the body whorl. The body 

chamber is represented by about half a wjiorl. The 

aperture is marked on the internal mold by a broad 

forwardly inclined constriction that is nearly smooth. 

The external mold shows that the aperture is marked 

by an abrupt constriction that is followed by a flattened area bearing weak riblets.

The ribs on the body whorl are high, triangular in 

section, and sharp topped. They trend backward on 

the umbilical wall and curve forward strongly on the 

flanks. The primary ribs are thicker and higher than 

the secondary ribs and terminate at about one-third of 

the height of the flanks in prominent tubercles. From 

the tubercles pass pairs of secondary ribs that are separated from adjoining pairs by single ribs that "begin at 

or above the zone of furcation. The nearly complete 

whorl shown on plate 1, figure 7, has about 23 primary 

ribs. The suture line cannot be- traced.

This species has sharper, sparser, and coarser ribbing 

than any species of Kepplerites at a comparable size 

that has been described from North America. It 

shows a little resemblance to Kepplerites (Seymourites) 

kuzuryuensis Kobayashi (1947, p. 29, pi. 7, fig. 3) 

from Japan, but that species has much finer ribbing, 

more secondary ribs, and attains a much larger size. 

Among European species it shows considerable resem-
D-20 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

blance in ribbing, whorl shape, and coiling to the inner 

whorls of Kepplerites keppleri (Oppel) as figured by 

Buckman (1922, pi. 289a, b) and somewhat less resemblance to K. cereale (Buckman) (1922, pi. 286; Arkell, 

1954, fig. 42 on p. 118). It differs from these species 

by having fewer secondary ribs, by having prominent 

ribs and tubercles on its body chamber, and by its 

much smaller size. This species is named in honor of 

Lorin Clark of the Geological Survey who collected the 

type specimens.

Types: Holotype USNM 130777; paratypes USNM 130778. 

Occurrence: Colfax formation of Smith at USGS Mesozoic 

loc. 27313.

Subgenus GOWERICERAS Buckman, 1921

Kepplerites (Gowericeras) lindgreni (Hyatt)

Plate 1, figures 12, 14

Olcostephanus lindgreni Hyatt, 1894, Geol. Soc. America Bull.,

v. 5, p. 427. 

"Galilaeiceras" lindgreni (Hyatt). Crickmay, 1933a, U.S.

Geol. Survey Prof. Paper 175-B, p. 57, pi. 17, figs. 9, 10.

This species is known only from one specimen that 

has been somewhat elongated and crushed. Allowing 

for deformation, the whorl appears to be ovate in 

section and probably higher than wide. The flanks 

and venter are evenly rounded. The coiling is evolute, 

the umbilicus fairly wide, and the outer whorl does not 

retract appreciably from the remainder of the shell. 

The body chamber includes at least half a whorl.

The ribs curve backward on the umbilical wall, 

curve forward on the flanks, and apparently cross the 

venter transversely. The primary ribs are sharp and 

moderately spaced. At about two-fifths of the height 

of the flanks they pass into fascicles of weaker secondary ribs that outnumber the primary ribs 4 or 5 to 1. 

Most of the furcation prints are swollen and were probably originally tuberculate. Some of the secondary 

ribs appear to rise freely near the middle of the flanks. 

The suture line cannot be traced accurately. Details 

of the dimensions have been published by Crickmay 

(1933a, p. 57).

"Olcostephanus" lindgreni Hyatt was considered by 

Crickmay (1933a, p. 57) to be close to Galilaeiceras 

Buckman (1922, pis. 290, 291), which Arkell (1957, 

p. L298) regards as a synonym of Gowericeras in the 

family Kosmoceratidae. This general assignment 

seems reasonable as the species bears many resemblances to Gowericeras costidensum Imlay from the 

western interior region (Imlay, 1953a, p. 31, pi. 22, 

figs. 10-13) and to Gowericeras snugharborensis Imlay 

from Alaska (Imlay, 1953b, p. 99, pi. 53, fig. 9). It 

shows even closer resemblances to a specimen of Gowericeras from the Talkeetna Mountains (see pi. 1, 

fig. 13), and is possibly identical specifically. Specific

identification will be difficult, however, until other 

specimens of 0. lindgreni Hyatt are found in California 

that show the characteristics of the species better than 

the holotype.

"Olcostephanus" lindgreni Hyatt was identified as 

Kepplerites (Gowericeras? or Seymourites) (?) lindgreni 

Hyatt by Arkell (1956, p. 554) who said the species 

seems "to be much like Seymourites figured from 

Canada by McLearn (1929, pis. 1-8)."

The writer considers, however, that "Olcostephanus" 

lindgreni Hyatt has more evolute coiling and a wider 

umbilicus than any of the species of Seymourites including Yakounoceras and Yakounites) described by 

McLearn and that it greatly resembles certain species 

from Alaska and the western interior region described 

under the generic name Gowericeras in the sense used 

by Spath (1932, p. 81, 94). In this sense Gowericeras 

Buckman (1921, p. 54, pi. 254; 1922,-pis. 287, 288, 404) 

includes Galilaeiceras Buckman (1922, pis. 290, 291), 

Galileanus Buckman (1922, pi. 293, and Galilaeites 

Buckman (1922, pi. 309).

Recently Arkell (1957, p. L289) placed Gywericeras 

in synonymy with Kepplerites without explanation and 

this assignment apparently is supported by Callomon 

(1955, p. 235). Nevertheless, the group of species that 

have been included under Gowericeras as defined by 

Spath differ from typical Kepplerites and its subgenus 

Seymourites by having more evolute coiling and by the 

body chamber not retracting appreciably from the 

septate whorls. In addition it differs from typical 

Kepplerites by earlier loss of ventral flattening and by 

the persistence of tubercles on the flanks of the body 

chamber. In conformity with the scaled-down classification used by Arkell (1940, p. LXVI; 1950, p. 354, 

355), Gowericeras probably would rank as a subgenus 

under Kepplerites at least as different from typical 

Kepplerites as the subgenus Seymourites.

A number of features by which the European species 

ol Gowericeras may differ from the American species 

assigned to that genus have been mentioned by Donovan (1953, p. 132; 1957, p. 135). These include bituberculate primary ribs, strongly curved primary ribs, 

an abrupt backward bend of the secondary ribs near 

their junction with the primary ribs, and the presence 

of a tabulate venter on the inner whorls. An examination of various illustrations of European species of 

Gowericeras suggests, however, that these are not constant features on all the species and are, therefore, 

probably not of generic or subgeneric importance (compare J. de C. Sowerby, 1827, pi. 549; Buckman, 1921, 

pi. 254; 1922, pis. 288, 290, 291, 293, 294, 309; 1923, 

pi. 404; Corroy, 1932, pi. 24, figs. 3, 4; Douville, 1915, 

p. 29, pi. 8, figs. 1, 4, pi. 9, figs. 1,5). Even a flattened 

venter on the inner whorls is not known to be present
JURASSIC AMMONITES, SIERRA NEVADA D-21

in all European species that have been assigned to 

Gowericeras.

Similarly in all the species of Gowericeras from Alaska 

and in most of those from the western interior of the 

United States, the characteristics of the inner whorls 

are unknown. Some of the species may have tabulate 

venters on their inner whorls as do some of the European species. As far as the outer whorls are concerned 

the assignment of certain species from North America 

to Gowericeras seems reasonable and has been confirmed by Arkell (1956, p. 550).

Types: Holotype USNM 30205.

Occurrence: USGS Mesozoic loc. 27516 from the Colfax formation of Smith half a mile south of Colfax and a quarter of a 

mile west of the railroad, Placer County, Calif.

Genus PSEUDOCADOCERAS Buckman, 1918 

Pseudocadoceras grewingki (Pompeckj) 

Plate 2, figures 1-8, 11-13

For synonomy see Imlay, 1953b, U.S. Geol. Survey 

Prof. Paper 249-B, p. 93.

Nearly 80 molds of Pseudocadoceras have been 

collected from thin beds of tuff in the lower part of 

the Logtown Ridge formation on the north bank of the 

Cosumnes River. Most of these are from a stratigraphic interval of about 40 feet, but one of the largest 

specimens (see pi. 2, fig. 7) was obtained about 75 feet 

above the others. Most of the specimens are so 

crushed and deformed that they cannot be identified 

specifically, but at least 12 specimens may be identified 

on the basis of ornamentation and coiling with P. 

grewingki (Pompeckj) from Alaska (Imlay, 1953b, 

p. 93, pi. 49, figs. 1-12). (See pi. 2, figs. 11-13.)

This species is characterized by its narrowly rounded 

venter, fairly wide umbilicus, and strong sharp ribs 

that coarsen anteriorly and incline forward on the 

venter. Bifurcation occurs fairly regularly a little 

below the middle of the flanks, but on the body whorl 

the branches tend to be loosely united with the primary 

ribs. Some ribs remain unbranched.

Pseudocadoceras grewingki (Pompeckj) in Alaska 

is much more common than the other species of the 

genus and has a longer range. It ranges through most 

of the upper two-thirds of the Chinitna formation 

(Imlay 1953b, table 2 on p. 50) and through the middle 

part of the Shelikof formation. In the upper part of 

its range it is associated locally with other species of 

Pseudocadoceras of which 2 have much finer and denser 

ribbing and 1, P. crassicostatum Imlay (1953b, p. 94, 

pi. 49, figs. 19, 20, 22-24), has coarser and sparser 

ribbing. The beds containing P. grewingki (Pompeckj) 

in Alaska are correlated with the European zones 

of Erymnoceras coronatum, Cosmoceras jason, and the

upper part of the Sigaloceras calloviense zone. (Imlay, 

1953b, p. 53).

Types: Plesiotypes USNM 130779,130781. 

Occurrence: Logtown Ridge formation at USGS Mesozoic 

Iocs. 24710 and 27317.

Pseudocadoceras cf. P. grewingki (Pompeckj) 

Plate 2, figure 22

Five crushed ammonite fragments from the Mokulumne River show all the characteristics of jiie genus 

Pseudocadoceras. In particular the largest bud least 

crushed fragment, herein illustrated, greatly resembles 

the adult body chamber of P. grewingki (Pompeckj). 

It bears sharp fairly widely spaced primary ribs that 

bifurcate a little below the middle of the flanks. The 

secondary ribs are sharp, a little broader than the 

primary ribs, and arch forward on the venter,

Figured speciemen: USNM 130783.

Occurrence: From unknown stratigraphic positioii at USGS 

Mesozoic loc. 27387.

Pseudocadoceras cf. P. crassicostatum Imlay 

Plate 2, figures 14-21

Associated with Pseudocadoceras grewingki (Pompeckj in the basal part of the Logtown Ridge formation 

on the Cosumnes River are 15 specimens of the genus 

that have much coarser and more widely spaced ribbing and probably belong to P. crassicostatum Imlay 

(1953b, p. 94, pi. 49, figs. 19, 20, 22-24) from Alaska 

(See pi. 2, figs. 9, 10). The specimens are so deformed 

and fragmentary, however, that the identification is 

not positive. They could be a coarse variant of P. 

grewingki (Pompeckj).

Figured specimen: USNM 130780. : Occurrence: Logtown Ridge formation, lower parj., at USGS 

Mesozoic loc. 27317.

Pseudocadoceras? sp. 

Plate 2, figure 23

One ammonite from the upper part of the Cosumnes 

formation on the Cosumnes River probably belongs to 

Pseudocadoceras although it is too corroded for positive 

identification. It has moderately evolute coiling and 

strong closely spaced primary ribs most of which bifurcate at or below the middle of the flanks. At one 

place the secondary ribs curve backward on the upper 

part of the flanks, but at other places they curve forward. Because of this backward curvature the ammonite was once compared by Imlay (1952, p. 975) with 

the perisphinctid genus Grossouvria of Callovian age. 

However, its coiling is not nearly evolute enough for 

it to belong to Grossouvria and it does resemble the 

genus Pseudocadoceras in both coiling and rib pattern.
D-22 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

The local backward curvature of the secondary ribs 

on the flanks could be a result of deformation.

This ammonite is significant because it is the only 

ammonite known from the upper part of the type section of the Cosumnes formation and is the only evidence that that part is of Callovian age.

Figured specimen: USNM 130782.

Occurrence: Cosumnes formation, upper part, at USGS Mesozoic loc. 22175.

Genus AMOEBOCERAS Hyatt, 1900 

Subgenus AMOEBITES Buckman, 1925

Amoeboceras (Amoebites) dubium (Hyatt) 

Plate 2, figures 24-28

Cardioceras dubium Hyatt, 1894; Geol. Soc. America Bull., v. 5, 

p. 420-422.

^Cardioceras whitneyi Smith, 1894, Geol. Soc. America Bull., v. 

5, p. 253, 254.

Amoeboceras dubium (Hyatt). Reeside, 1919, U.S. Geol. Survey Prof. Paper 118, p. 38, pi. 24, figs. 5-8. 

(Hyatt). Crickmay, 1933a, U.S. Geol. Survey Prof. Paper 

175-B, p. 56.

Amoeboceras (Amoebites} dubium (Hyatt). Spath, 1935, Meddelelser om Gronland, v. 99, no. 2, p. 34.

Amoeboceras dubius (Hyatt). Hanna and Hertlein, 1941, California Dept. Nat. Res., Div. Mines Bull. 118, pt. 2, p. 

166, fig. 60(23).

The original type lot contains 15 molds^of which all 

have been crushed laterally. The species is characterized by fairly straight sharp mostly simple moderately to widely spaced ribs that incline slightly forward 

on the flanks and terminate on the ventrolateral margin 

in prominent clavate tubercules. On several specimens two adjoining ribs terminate in a single tubercle. 

A few ribs fade out on the upper part of the flanks 

below the zone of tubercles. The tubercles curve 

strongly forward and terminate at shallow grooves. 

The midline of the venter bears a stout low serrated 

keel whose serrations outnumber the tubercles nearly 

2 to 1.

This species was referred to Amoebites by Spath 

(1935, p. 34) because some of its ribs disappeared on 

the flanks below the tubercles. He compared three 

specimens from Greenland (see Spath, 1935, pi. 3, fig. 

1, pi. 5, figs. 1, 6) with both A. dubium (Hyatt) and 

A. (Amoebites} elegans Spath (1935, p. 33, pi. 4, figs. 

1-3) and noted that the holotype of A. elegans Spath 

differs from A. dubium (Hyatt) by having denser more 

regularly spaced ribbing near the umbilicus. It appears, also, that A. dubium (Hyatt) may be distinguished by having fewer secondary ribs and by developing stronger tubercles on the larger whorls.

Types: cotypes USNM 30201.

Occurrence: Mariposa formation at USGS Mesozoic loc. 719.

Genus GROSSOUVRIA Sieminadzki, 1898

Grossouvria colfaxi (Gabb) 

Plate 2, figure 29; plate 3, figures 13-17

Ammonites colfaxi Gabb, 1869, Am. Jour. Conch., v. 5, pt. 1,

p. 7, 8, pi. 4, fig. 2 [and v. 4, pi. 16]. 

Perisphinctes colfaxi (Gabb). Hyatt, 1894, Geol. Soc. America

Bull., v. 5, p. 424, 425.

The species is represented by a nearly complete internal mold and by part of an external mold of a single 

specimen. Both molds have been stretched considerably, but before stretching the whorls were probably nearly circular in section. The coiling is evolute 

and the whorls embrace each other about one-fifth. 

The umbilicus is. very wide and shallow. The body 

chamber is represented by slightly more than half a whorl 

and is probably nearly complete. Its adoral end is 

slightly flexuous and is curved forward near the middle 

of the flank, but is not sufficiently well preserved to 

show if the specimen had a lateral lappet.

The ornamentation on the inner whorls consists of 

variably strong variably spaced forwardly inclined ribs 

and constrictions. On the adoral half of the penultimate whorl the ribs are alternately single and forked. 

On the earlier formed whorls single ribs outnumber 

forked ribs. Most of the forked ribs are coarser and 

higher than single ribs. Bifurcation of the ribs occurs 

at various heights below the middle of the flanks.

The ornamentation of the body whorl is similar to 

that on the penultimate whorl, but single ribs become 

more common toward the aperture. Bifurcation occurs 

at various heights, but mostly below the middle of the 

flanks. The bifurcation points are particularly prominent but probably were not tuberculate. The ribs on 

the internal mold are high and sharp. On the external 

mold they are high and round. Most ribs are curved 

backward on the upper part of the flanks and on the 

venter and appear to weaken somewhat on the venter. 

On the body chamber some of the secondary ribs arise 

freely high on the flanks and others are indistinctly connected with primary ribs.

Parts of a simple suture line are preserved near the 

adoral end of the last septate whorl. The ventral lobe 

is not exposed. The first lateral lobe is slender and 

trifid. The second lateral lobe is much shorter than ths 

first. The auxiliaries are weakly developed and are 

somewhat distorted owing to deformation.

This species is assigned to Qrossouvria because of the 

highly irregular and variable ribbing on its inner 

whorls, the presence of many constrictions and single 

ribs, the backward curvature of the secondary ribs on 

the body whorl, its rounded whorl section, and the characteristics of the suture line. Except for the irregular 

ornamentation on the inner whorls, the presence of
JURASSIC AMMONITES, SIERRA NEVADA D-23

many deep constrictions, and its round whorl section, 

it could be assigned to Siememdzkia. Arkell (1957, p. 

L 319; 1958, p. 212) notes, however, that the Bathonian 

Siemeradzkia is replaced by the Callovian Grossouvria 

and that the two are difficult to separate generically 

"except on stratigraphic grounds."

Grossouvria colfaxi (Gabb) differs from most species 

of Grossouvria and Siemeradzkia by having stronger 

ribbing and by attaining a larger size. G. anomala 

(Loczy) (1915, p. 386, pi. 8, figs. 8-11, pi. 14, fig. 5; 

Neumayr, 1871, pi. 12, figs. 2a, b; Spath, 1931, p. 364, 

pi. 60, fig. 8) is probably the most similar but has somewhat weaker ribbing. G. pseudocobra Spath (1931, 

p. 371, pi. 48, figs. 7a, b) has finer ribbing on its inner 

whorls. G. leptus Gemmellaro figured by Corroy (1932, 

pi. 23, figs. 1, 2) is as large as G. colfaxi (Gabb), but has 

more secondary ribs and fewer unbranched ribs. 

Siemeradzkia de-mariae Parona and Bonarelli (1895, 

p. 147; Neumayr, 1871, pi. 12, figs. 4a, b, 5) is similar 

in size and appearance but is more involute, has fewer 

simple ribs, fewer constrictions, and the ribbing on its 

inner whorls is more regular.

Most species of Ohojfatia and Subgrossouifria differ 

from G. colfaxi (Gabb) by having more regular ribbing 

on their inner whorls, by developing more distant primary ribs on their outer whorls, and by not having 

backwardly curved secondary ribs. A possible exception is Choffatia (Grossouvria^.} aurita Spath (1931, p. 

362, pi. 40, figs. (6a, b) from India.

G. colfaxi (Gabb) shows some resemblance to the 

genus Rursiceras Buckman (1919, pi. 145), but its 

ribbing is more irregular in strength and spacing, single 

ribs are more common, and its secondary ribs do not 

curve backward on the venter nearly as strongly. It 

may be compared, also, to Parapeltoceras annulosum 

(Quenstedt) (1886-87, pi. 88, fig. 22; Jeannet, 1951, 

p. 164, pi. 75, figs. 3a, b) but is readily distinguished 

by its deep constrictions, by its variable ribbing, and 

by some of its ribs bifurcating low on the flanks.

Type: Holotype 5287, Mus. Comparative Zoology, Harvard 

College.

Occurrence: Colfax formation of Smith "From railroad cut at 

sta. 2777, sec. 53, 1 mile west of Colfax, 14 ft. below surface of 

ground," Placer County, Calif.

Genus PERISPHINCTES Waagen, 1869

Perisphinctes? sp.

Plate 5, figure 4

One small ammonite bears sharp, nearly straight 

primary ribs that incline forward on the flanks. Most 

of them bifurcate at or below the middle of the flanks 

into slightly weaker secondary ribs that cross the venter transversely. Several short ribs are intercalated

on the upper part of the flanks. Two constrictions 

are present.

The preservation of this specimen does not permit 

positive generic or even family identification It appears to be a perisphinctid ammonite, although its ribs 

branch lower than in most genera of the Perisphinctidae. 

Its rib pattern shows some resemblance to that in 

Reineckeites of the family Reineckeiidae, but the ventral ends of the primary ribs are not swollen or tuberculate.

Figured specimen: Stanford Univ. Mus. Paleontology 9065.

Occurrence: The label accompanying the specimen states 

"Mariposa formation, Nashville, Eldorado County." The lithologic features of the specimen suggest that it was obtained from 

the Logtown Ridge formation instead of from the Mariposa 

formation.

Subgenus DISCOSPHINCTES Dacque, 1914

Perisphinctes (Discosphinctes) virgulatiformis Hyatt 

Plate 3, figures 1-10

Perisphinctes virgulatiformis Hyatt, 1894, Geol. Soq. America

Bull., v. 5, p. 422, 423. 

Virgatosphinctoides virgulatiformis (Hyatt). Crickm&y, 1933a,

U.S. Geol. Survey Prof. Paper 175-B, p. 56, 57, pi. 16,

figs. 24-25, pi. 17, figs. 1-8. 

?Perisphinctes virgulatus Quenstedt. Burckhardt, 1912, Inst.

geol. Mexico Bol. no. 29, p. 35-38, pi. 7, figs. 4-14. 

?Perisphinctes (Planites) virgulatus Quenstedt var. ,carribeana

Jaworski, 1940. Neues Jahrb., Beilage-Band, Abt. B,

p. 109-114, pi. 3, figs. 1-2, pi. 4, fig. 5, pi. 7, fig. 6. 

?Discosphinctes cf. D. virgulatus (Quenstedt) of Burckhardt,

Imlay, 1945, Jour. Paleontology, v. 19, p. 274, pi. 41,

figs. 9-11. 

?Discosphinctes carribeanus (Jaworski). Arkell, 1956, Jurassic

Geology of the World, p. 573, London.

The shell is compressed, discoidal. The whorls are 

flattened, higher than wide, and embrace the preceding whorls considerably. The umbilicus is fairly 

narrow for a perisphinctid ammonite.

The ornamentation consists of narrow closely spaced 

forwardly inclined ribs and of weak forwardly inclined 

constrictions. The primary ribs curve backward on 

the umbilical margin and curve forward gently on 

the flanks. Many of them remain simple but many 

others bifurcate between the middle and the upper 

third of the flanks. Trifurcating ribs are present 

locally near constrictions. (See pi. 3, fig. 3.) The 

secondary ribs are not interrupted on the venter.

The suture line is similar to that of Pefisphinctes 

(Discosphinctes) carribeanus (Jaworski) figured by 

Burckhardt (1912, pi. 7, fig. 8). The first lateral 

lobe is long and trifid. The second lateral lobe is 

much shorter. There are three small auxiliary lobes. 

The second lateral saddle is as high as the first.

This species is placed in the subgenus Discosphinctes 

Dacque as defined by Arkell (1937, p. XLVIII-XLIX)
D-24 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

because of its high whorls, involute coiling, dense 

forwardly inclined ribs, and weak constrictions. It 

shows no tendency to develop bundles of ribs as in 

Lithacoceras. Virgatosphinctoides, which Arkell (1957, 

p. L 329) considers a synonym of Subplanites, has 

more evolute coiling and the primary ribs become 

coarse and widely spaced. Dichotomosphinctes has 

more e volute coiling, deeper constrictions, and nearly 

radially trending ribs of which most bifurcate regularly 

on the ventral margin.

Perisphinctes (Discosphinctes) virgulatiformis Hyatt 

appears to be identical with P. (Discosphinctes) carribeanus Jaworski (see pi. 3, figs. 11, 12) from the late 

Oxfordian of Cuba (Jaworski, 1940, p. 109, pi. 3, figs. 1, 

2; pi. 4, fig. 5, pi. 7, fig. 6) and Mexico (Burckhardt, 

1912, p. 35, pi. 7, figs. 4-14) as far as the fragmentary 

condition of the type specimens of the California 

species permits comparison. Until better 'preserved, 

or more complete specimens of P. virgulatijormis are 

found, the exact specific relationship cannot be determined.

Types: USNM 30204.

Occurrence: USGS Mesozoic loc. 901 from the Mariposa 

formation.

Subgenus DICHOTOMOSPHINCTES Buckman, 1926 

Perisphinctes (Dichotomosphinctes) miihlbachi Hyatt 

Plate 4, figure 8

Perisphinctes miihlbachi Hyatt, 1894, Geol. Soc. America Bull.,

v. 5, p. 426. 

Dichotomoceras! miihlbachi (Hyatt). Crickmay, 1933a, U.S.

Geol. Survey Prof. Paper 175-B, p. 57, pi. 18, figs. 1, 2. 

?'Perisphinctes durangensis Burckhardt, 1912, Inst. geol. Mexico

Bol. 29, p. 16, pi. 3, figs. 1, 2, pi. 4, fig. 6.

The holotype, represented mostly by an external 

mold, is characterized by evolute coiling, by moderately 

spaced high narrow ribs that bifurcate above the line 

of involution, and by deep constrictions. The primary 

ribs curve backward at the edge of the umbilicus, and 

incline forward gently on the flanks. The secondary 

ribs, exposed at one place on the penultimate whorl 

where the suture line is preserved (see Crickmay, 1933, 

pi. 18, fig. 1), arise in pairs from the primary ribs and 

curve gently backward on the flanks. The dorsal ends 

of the secondary ribs are likewise exposed on part of the 

outermost whorl. Some of these arise in pairs from the 

primary ribs and others arise indistinctly from or alternate with the primary ribs. A few of these secondary ribs curve backward at their junction with the 

primary ribs.

One external mold of an ammonite (pi. 4, fig. 3) from 

the Stanislaus River opposite Bosticks bar (Mesozoic 

loc. 901) shows the ribbing typical of Dichotomosphinctes and matches very well with the inner whorls

of P. (Dichotom.osphinctes) miihlbachi (Hyatt) at a comparable size. The specimen was referred to Perisphinctes sp.? by Hyatt (1894, p. 423) who notes that

The whorl is broader at the same age than is any other species 

mentioned in this paper; there are consequently fewer whorls at 

the same age. The lateral costae are single and very long, the 

bifurcations occurring well up on the abdomen.

The immature growth stage of P. miihlbachi Hyatt is 

possibly represented also, by one small specimen (pi. 

4, fig. 5) from Mount Boullion (Mes. loc, 27460). It 

bears ribs and constrictions a little coarser and sparser 

than those on the inner whorls of the holotype. The 

venter is somewhat worn, but is clearly marked by deep 

forwardly arched constrictions and by faint continuations of the flank ribs. Some of the primary ribs appear to bifurcate at the margin of the venter, but others 

appear to remain simple.

P. miihlbachi Hyatt was assigned by Crickmay 

(1933a, p. 57) tentatively to Dichotomoceras on the 

basis of its suture line. That genus as defined, however, does not have constrictions and its ribs generally 

bifurcate at or below the line of involution. Except 

for these features P. miihlbachi Hyatt greatly resembles 

the genotype of Dichotomoceras (Buckman, 1919, v. 

3, pi. 139A). In shape and ornamentation P. miihlbachi 

Hyatt likewise greatly resembles Orthosphinctes, but it 

differs by having a higher point of rib branching and 

by lacking trichotomous ribs.

Considering all its features P. miihlbachi Hyatt 

shows more resemblances to Dichotomosphinctes than 

to the other genera mentioned and it greatly resembles 

several described species of Dichotomosphinctes. For 

example, P. durangenis Burckhardt (1912, p. 16, pi. 

3, figs. 1,2), from Durango, Mexico, is nearly identical 

in appearance. P. plicatiloides O'Connell from Cuba 

(O'Connell, 1920, p. 670, pi. 36, figs. 1, 2; Jaworski, 

1940, pi. 4, fig. 4, pi. 5, figs. 5 a, b, pi. 6, figs. 1 a, b) 

and Mexico (Burckhardt, 1912, pi. 3, figs. 3-6) has 

somewhat sparser ribbing. P. antecedens Salfeld (in 

Arkell, 1938, p. 83, pi. 15) and P. rotoides Ronchadze 

(in Arkell, 1938, p. 90, pi. 16, figs. 1-7) from Europe 

appear to differ only in minor details of ribbing.

The assignment of P. miihlbachi Hyatt to the subgenus Dichotomosphinctes is strengthened also by its 

apparent identity with a well-preserved specimen of 

Dichotomosphinctes from the Naknek formation of 

Alaska shown on plate 4, figure 6. Unfortunately 

the holotype of P. miihlbachi Hyatt is not sufficiently 

preserved to show all the features necessary for a 

positive specific identification.

Types: Holotype USNM 30203; comparable specimen from 

Mount Boullion, USNM 130786; comparable specimen from Reynolds Ferry, USNM 103460; comparable specimen from 

Alaska, USNM 130789.
JURASSIC AMMONITES, SIERRA NEVADA D-25

Occurrence: "Mariposa" formation at USGS Mesozoic loc. 

27517. Possibly present in the Mariposa formation at Mesozoic 

Iocs. 901 and 27460.

Perisphinctes (Dichotomosphinctes) cf. P. elisabethaeformis 

Burckhardt

Plate 4, figures 4, 7

One external mold shows parts of three evolute 

whorls that bear fine ribbing similar to that on the 

inner whorls of P. elisabethaeformis Burchkardt (1912, 

p. 31, pi. 6, figs. 1-5) from the upper Oxfordian of 

Mexico. The primary ribs begin at the line of involution, are nearly straight on the flanks, incline 

slightly forward, and generally bifurcate on the upper 

fourth of the flanks. A few primary ribs remain 

simple and some of the secondary ribs are indistinctly 

connected with the primary ribs. Several weak constrictions are present.

This species has much denser ribbing than the specimen of P. (Dichotomosphinctes) from the Galice formation of southwestern Oregon. (See pi. 4, fig. 2.)

Figured specimen: Stanford Univ. Mus. Palentology 9063.

Occurrence: Monte de Oro formation. North Bank of Feather 

River just north of Sycamore Hill, about 3 miles northeast of 

Oroville, and from 450 ft south of NE. cor. of sec. 4, T. 19 N., 

R. 4 E., Butte County, Calif.

Perisphinctes (Dichotomosphinctes?) spp. 

Plate 4, figure 1; plate 5, figures 5, 6

Several ammonites are so crushed and stretched that 

their correct subgeneric position cannot be determined. 

The coarseness of the ribs and the positions at which 

the ribs divide into secondary ribs seem to vary as a 

consequence of stretching. Nevertheless the ammonites exhibit evolute coiling and moderate to coarse 

ribbing. Nearly all the ribs bifurcate along a zone 

somewhat above the middle of the flanks and the secondary ribs incline forward. A few ribs remain simple 

and none of the ribs trifurcate. Weak constrictions 

are present.

The bifurcation points appear to be much lower on 

the flanks than is typical of Dichotomosphinctes, but 

that may be a result of deformation. If it is normal, 

however, an assignment of the specimens to Torquatisphinctes would seem more probable as that genus differs from Dichotomosphinctes by having more simple 

ribs and somewhat lower points of rib furcation.

The specimen shown on plate 5, figure 5, was mentioned by Hyatt (1894, p. 426) as being closely related 

to Perisphinctes muhlbachi Hyatt. It appears, however, to have much finer ribbing and lower points of 

rib furcation.

Figured specimens: USNM 103461, 103787, 103788. 

Occurrence: Mariposa formation at USGS Mesozoic Iocs. 490, 

27566, and 24317.

Genus IDOCERAS Burckhardt, 1906

Idoceras aff. I. planula (Heyl) in Zeiten 

Plate 5, figures 12-16

The genus Idoceras in California is represented by 

one specimen that has been crushed laterally. It includes an external mold of the inner whorls and an internal mold of the outer whorls.

On the inner whorls the amount of involution is 

about two-fifths. On the body whorl it is about onethird. The whorls are subquadrate in section and a 

little higher than wide. The flanks and venter are 

nearly flat. The umbilicus is fairly wide. The umbilical wall is low, vertical, and rounds evenly into the 

flanks. The body chamber is incomplete, but is represented by three-fifths of a whorl.

On the inner whorls the ribs are high, fahjly sharp, 

closely spaced, and incline strongly forward o|n the upper part of the flanks. The primary ribs bifurcate 

just above the middle of the flanks into slightly weaker 

secondary ribs and are slightly swollen along the zone 

of furcation. The secondary ribs become thicker but 

slightly lower ventrally. Most forked ribs are separated by short ribs that begin at the line of furcation. 

The characteristics of the ribbing along the midline of 

the venter are not well preserved. One deep constriction is present.

On the penultimate whorl the primary ribs are sharp 

and moderately spaced. Most of them bifurcate at 

about two-thirds of the height of the flanks, but some 

remain simple and there are a few short ribs on the 

upper part of the flanks. The secondary ribs broaden 

ventrally, incline gently forward, and terminate at a 

nearly smooth zone along the midline of tfye venter. 

Several constrictions are present.

On the body chamber the primary ribs become more 

widely spaced and curve forward strongly on the flanks. 

Most ribs bifurcate fairly high on the flanks and virgatoid branching occurs at two places. The secondary 

ribs are somewhat higher and broader than the primary 

ribs. The midline of the venter, exposed at) only one 

place, appears to be nearly smooth. The body whorl 

has about 37 primary ribs.

This species is assigned to the genus Idoceras because 

it has perisphinctid ribbing that is projected forward 

on the upper parts of the flanks and on the venter and 

is interrupted along the midline of the venter. It 

belongs to the group of Idoceras characterized by 

/. planula (Heyl) in Zeiten and /. balderum pppel) as 

defined by Burckhardt (1912, p. 102). Thife group is 

generally very evolute, has simple perisphinctid ribbing 

at all growth stages and commonly has generally pronounced constrictions. It may have some simple ribs
D-26 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

but rarely trichotomous ribs. It attains its greatest 

development in Mexico where it is confined to beds of 

early Kimmeridgian age (Burckhardt, 1930, p. 64, 

tables 4-6; Imlay, 1939, p. 21, table 4). In Europe, 

however, it occurs both in beds of early Kimmeridgian 

and of late Oxfordian age (Arkell, 1957, p. L 323). In 

Mexico it is succeeded in slightly younger early Kimmeridgian beds by a group characterized by /. durangense Burckhardt. That group is generally less 

evolute, commonly has trichotomous and bidichotomous 

ribbing, and the ribs in the adult become swollen near 

the umbilicus and on the venter but become feeble or 

indistinct on the middle of the flanks (Burckhardt, 

1912, p. 102).

The California specimen of Idoceras is similar to the 

Mexican species /. soteloi Burckhardt (1906, p. 52, pi. 9, 

figs. 9-12), /. laxevolutum Fontannes in Burckhardt 

(1906, p. 48, pi. 10, figs. 1-3), and /. neogaeum Burckhardt (1906, p. 51, pi. 11, figs. 5-8) from Zacatecas, 

Mexico. Of these, /. soteloi Burckhardt has somewhat 

stronger ribbing on its inner whorls and ventral weakening occurs only on the adoral end of the body whorl. 

/. laxevolutum Fontannes in Burckhardt has more 

closely spaced ribs that are less inclined on the flanks 

and that become trichotomous near the adoral part of 

the body chamber. Many of its secondary ribs are 

indistinctly united with the primary ribs. /. neogaeum 

Burckhardt appears to have weaker secondary ribs on 

its outer whorls and coarser ribbing on its inner whorls. 

The density of the ribbing on the inner whorls of the 

California specimen resembles that on the inner whorls 

of I.figueroae Burckhardt (1906, p. 60, pi. 10, figs. 4-7) 

but the ribbing on the outer whorls is sparser and apparently sharper. The ribbing on the California specimen would appear less sharp, however, if some shell 

layers were present as on most of the illustrated Mexican 

specimens.

Compared with Idoceras planula (Heyl) in Zeiten 

from the ] ate Oxfordian of Europe (Quenstedt, 1888, 

p. 974, pi. 108, figs. 1-5; Wegele, 1929, p. 76, pi. 9, 

fig. 3) the California specimen is less evolute and has 

fewer simple and intercalated ribs on its body whorl, 

but the spacing and sharpness of the ribs are closely 

similar. 1. schroederi Wegele (1929, p. 77, pi. 9, fig. 6) 

has denser ribbing and more simple ribs. I. balderum 

(Oppel) (1863, p. 242, pi. 67, fig. 2; Loriol, 1877, p. 95, 

pi. 15, fig. 7; Wegele, 1929, p. 78, pi. 9, fig. 7) is more 

involute and has weaker and broader primary ribs. 

The specimen figured as /. laxevolutum (Fontannes) 

by Ziegler (1959, p. 28, pi. 1, fig. 6) appears to have 

coarser and straighter primary ribs.

Figured specimen: Univ. of California [Berkeley] Mus. Paleontology 32724.

Occurrence: Logtown Ridge formation at Univ. of California 

(Berkeley) loc. A-4996. The field description is as follows: 

"from a building stone quarry on Logtown Ridge, near the Huse 

Bridge over the Cosumnes River about six miles north of 

Plymouth. Ammonite occurs in a metamorphosed andesitic 

tuff."

Idoceras? sp.

Plate 5, figures 10, 11

One small specimen consists of an external mold of 

three inner whorls and a fragment of an internal mold 

of the next larger whorl. The three inner whorls are 

depressed ovate in section. They are marked by 

prominent forwardly inclined primary ribs and constrictions. Most of the primary ribs bifurcate slightly 

above the middle of the flanks, but some remain 

simple. The secondary ribs arch forward on the venter.

On the next larger whorl the venter bears a strong 

constriction that is preceded by a swollen rib. The 

ventral ribs arch forward strongly in a chevronlike 

manner as in the genus Idoceras.

Figured specimen: Stanford Univ. Mus. Paleontology 9064. 

Occurrence: The field label states "Mariposa formation, Wood 

Canyon? near Sonora."

Genus SUBDICHOTOMOCERAS Spath, 1925 

Subdichotomoceras? aff. S. filiplex (Quenstedt)

Plate 5, figures 1-3, 9 

Perisphinctes filiplex Quenstedt?. Hyatt, 1894, p. 423, 424.

This species is characterized by evolute coiling and 

by high sharp fairly widely spaced primary ribs of 

which most bifurcate at about three-fifths of the 

height of the flanks. A few primary ribs remain 

simple. The secondary ribs are nearly as prominent 

as the primary ribs and incline forward slightly. 

Some of the secondary ribs are indistinctly connected 

with the primary ribs or arise freely high on the flanks. 

Several deep constrictions are present on the inner 

whorls of one fragmentary specimen, but constrictions 

are not present on any of the outer whorls.

Hyatt's comparison of the California species with 

"Ammonites" filiplex Quenstedt (1888, p. 1090, pi. 

126, fig. 3) from the middle Kimmeridgian of Europe 

was apt, but the presence of several simple ribs suggests 

an even greater resemblance with Subdichotomoceras 

inversum Spath (1931, p. 521, 522, pi. 84, figs. 7a, b, 

pi. 85, fig. 4) from the middle Kimmeridgian of India. 

Another species with ribbing nearly identical with 

that of the California species occurs in the upper 

Kimmeridgian near Mazapil, Zacatacas, Mexico (Burckhardt, 1906, p. 114, pi. 31, figs. 1-4; Arkell, 1956, p. 

562). Also, similar appearing specimens of Subdichotomoceras are known from the Kimmeridgian of
JURASSIC AMMONITES, SIERRA NEVADA D-27

southern Coahuila, Mexico (Imlay, 1939, p. 35, 

pi. 10, figs. 1-3, 13).

The California species is placed in Subdichotomoceras 

rather than in Dichotomosphinctes because of the coarse 

ribbing on its inner whorls and its rather low point of 

rib furcation. Compared with Perisphinctes (Dichotomosphinctes) miihlbachi Hyatt, its ribs are coarser 

and more widely spaced at comparable sizes and 

bifurcation occurs much lower on the flanks.

Figured specimen: USNM 30203, 130785.

Occurrence: Mariposa formation, USGS Mesozoic Iocs. 902, 

903, and S04.

Genus PELTOCERAS Waagen, 1871

Subgenus METAPELTOCERAS Spath, 1931

Peltoceras (Metapeltoceras?) sp.

Plate 6, figure 1

The Stanford University collections contain a plaster 

cast of a large ammonite that is characterized by 

evolute coiling, perisphinctid ribbing on its inner 

whorls, and bituberculation on the outer whorls. 

The inner whorls are not well preserved, but at one 

place at a diameter of 25 mm they show two blunt 

tubercles from which arise pairs of strong ribs that 

trend transversely on the venter. At diameters 

greater than 50 mm, two rows of tubercles are present 

and both become very prominent adorally. Apparently 

the inner tubercles develop first and are stronger 

than the outer tubercles on the largest whorls, but 

this appearance may be deceptive because the cast 

is poorly preserved, the original mold was crushed 

and distorted, and the venter of the largest whorl 

is not preserved. No trace of the suture line is visible.

This specimen is assigned to Peltoceras because it 

has two rows of massive lateral tubercles on its outer 

whorls, perisphinctid ribbing on its inner whorls, 

and evolute coiling. As the inner rows of tubercles 

appear to have developed before the outer, the specimen is provisionally assigned to the subgenus Metapeltoceras Spath (1931, p. 552. 559, 560, 574-578; 

Arkell, 1940, p. LXX; Jeannet, 1951, p. 170). However, blunt lateral tubercles appear on the inner 

whorls at a smaller diameter than in any of the species 

of Metapeltoceras from India figured by Spath (1931, 

pi. 110, figs. 4a, b, 8a, b; pi. 114, figs, la, b; pi. 105, 

figs. 8a, b; pi. 110, figs. 5a, b; pi. 90, figs. 6a, b; pi. 

118, figs. 6a, b; pi. 105, figs. 2a, b; pi. 106, figs. 4a-c), 

or from Switzerland figured by Jeannet (1951, pi. 

72, fig. 5; pi. 73, figs. 5-6, 8; pi. 74, fig. 1; pi. 89, fig. 

l; pi. 90, fig. 1,2; pi. 91, fig. 1,2).

Figured specimen: Stanford Univ. Mus. Palentology 9062.

Occurrence: The back of the plaster cast bears the statement, 

"Ammonite from Mariposa slate in Big Indian Creek, Amador 

County south of Nashville, Eldorado County, Calif. Mold 

collected by F. M. N. Hamilton, State Mineralogist, May, 1941."

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D-28 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY

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 1955, Characteristic Jurassic mollusks from northern 

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10 p.

Loczy, Ludwig, 1915, Monographic der Villanyer CallovienAmmoniten: Geologica Hungarica, v. 1, pts. 3-4, p. 255- 

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INDEX

[Italic numbers indicate descriptions]

Page

Ages and correlations of formation______ D-3-9 

Agua Fria slate..________________ 3 

Alaska Peninsula and Cook Inlet regions,

Alaska--.-------------........... 11

atternans, Ammonites............______ 12

Amoeboceras................______ 12

Amador group..._______________. 2 

.Ammonites colfaxi,..................... ____ 2,6,22

filiplex..--................................ 26

lochensis.---......................___. 19

pichleri... _____________________ 19

Amoebites----................. ________ 7,8,22

(Amoebites), Amoeboceros-..........__..... 2

dubium Amoeboceras...------.-... 13,14,22,pi.2

elegans, Amoeboceras____________-_ 22

Amoeboceras.--.... ______...._.... 7,11,12,18,22

atternans-..--. __.___._____________ 12

dubium.......... _______________.. 2,22

dubius...........--------................. 22

(Amoebites)-..... .--.___.--__.____.__. 2

(Amoebites) dubium. __________ 13,14, %t, pi. 2

(Amoebites) elegans^-..................... 22

(Prionodoceras). .... ____._._______ 11

annulosum, Parap»ltoceras... _._________ 23

anomala, Grossouvria-................. ______ 23

antecedent, Perisphinctes-..................... 24

Aspidoceratidae__._. _____.. 2

athleta, Peltoceras-... __-__-_----_._____... 6,9

Aucella ........ _____________________ 2

pallasi plicata_ _____..._____________ 13

Aulacostephanus pseudomutabilis___.__... 7,11,13 

aurorium, Entolium- ________________.._.. 8,14

aurita, Choffatia (Grossouvria)._ ________ 23 

Avicula sp..._..._____________________ 8,14

B

balderum, Idoceras .............______. 13,25,26

Belemnites pacificus.^..__.-_______. 8,14 

sp.._ ._ _ 14

Bicknell sandstone________._.______ 9

Big Indian Creek..._________._.-..______.___- 6,11

bimammatum, Epipeltoceras____________ 6,7,12

Biologic analysis____.________________ 2

Bowser member, Tuxcdni formation_____ 6,10

Buchia.............................. 2,7,8,11,13,18

cancentrica-....... ___ 7, 8, 9,10,11,13,14,18, pi. 5

mosquensis ______________________ 11,13

piochii.......... __________________ 8,9

rugosa........ .____________ 8,11,12,13

buckmani, Lilloettia.............. .____.... 10

C

Cadoceras............................... 10,11,12,18

catostoma................_________ 10

sp. juv.-________..._____ 9

Cadoceratinae_-..._._._______._. 2

Calaveras formation___________ ____ 3 

Calaveras group.._____......____.... 2

Cattiphylloceras.-........ ___________ 11

callovitnse, Sigaloceras.. _____ 6,7,9,10,11,13,21 

Cardioceras-.---.............................. 11

dubium................................... 22

whitneyi-................................. 22

Cardioceratidae._-..._.____.___ 2

Page

Cardioceratinae..._______________ 2 

carribeanus, Discosphinctes- ________ 23

Peris phinctes (Discos phinctei)--- 7,12,23, 24, pi. 3 

catostoma, Cadoceras-... ______......__ 10

cautisnigrae, Perisphinctes...-------.-......... 7

Central Oregon___________.______.._ 10

Cephalopoda..__---...___.__..._... 19 

cereale, Kepplerites........ _._________ 20

Cerithium sp______.-...____.__.. 8,14

Chinitna formation_________ 6, 7, 9,10,11,13, 21 

Chlamys-................... __________ 8,14

Choffatia-...-............................ 12,18,23

hyatti..................................... 9,11

waitzi.................................... 12

(Orossouvria) aurita .......__._____. 23

sp______________________ 9,10

Coif ax formation of Smith----------... 6-7,16,21,23

colfaxi, Ammonites.....----------..-.-------- 2,6,22

Grossouvria.- ............... 13,14,**, 23, pis. 2,3

Perisphinctes. __________________.__ 22

Comparisons with other faunas.________ 9-13

concentrica, Buchia---...- 7,8, 9,10,11,13,14,18, pi. 5 

Corbis sp-_--------____-..__- ____ 14

coronatum, Erymoceras- ...................... 6,21

Cosmoceras------...... _-_____..___-- 11

jason. ___________-_______----------.--__-- 21

costidensum, Gowericeras---------------------- 11,20

Cosumnes formation ________ 2,3-6,9,10,13,17,21,22

Cosumnes River. _...... 3,8, 9,10,13,16,17,18, 21,26

crassicostotum, Pseudocadoceras _. 6,10,13,14, 81, pi. 2 

Creniceras.-------... ___.._.____-__--_-. 12

de-mariae, Siemeradzkia.......... _____.._. 23

denticulata, Oecotraustes....................... 19

denticulatum, Taramelliceras_______._____. 19

Taramelliceros (Proscaphites) ..._._ 7,14, 19, pi. 1 

Dichotomoceras.---------------------------- ._ 24

muhlbachi--...... ____-----_____.. 24

Dichotomosphinctes........... 7, 9,10,13,19, 24, 25, 27

(Dichotomosphinctes) durangensis, Perisphincta.__._._ -------_-.------.----. 8,12,18

elisabethaeformis, Perisphinctes.. 8,12,18, SB, pi. 4 

muhlbachi, Perisphinctes...--- ........ 7

8,11,12,13,14,18, #4,27, pi. 4 

Perisphinctes-. ................. 2,8,11,12,25

plicatilis, Perisphinctes...............-.... 10,12

wartaeformis, Perisphinctes__----------- 10,12

spp., Perisphinctes................. 7,35, pis. 4,5

dilleri, Reineckeia (Reineckeites)............... 9,12

Discosphinctes...... .................. 7,13,19,23

carrileanus.............. .... 23

virgulatus........ - 23

(Discosphinctes) carribeanus, Perisphinctes.... . 7,

12,23,24, pi. 3 

Perisphinctes---.............. .......... 2

virgidatiformis, Perisphinctes.............. 7

12,13,14,03,24, pi. 3

Dothan formation._.______..__..-- - 10 

dubium, Amoeboceras......................... 2,22

Amoeboceraa (Amoebites)....--... 13,14,22,pi. 2

Cardioceras.- ______.. -..._... 22 

dubius, Amoeboceras.......................... 22

durangenae, Idoceroa.......................... 26

durangensis, Perisphinctes..................... 24

Perisphinctes (Dichotomosphinctes). i.... 8,12,18

E

elegans, Amoeboceras (Amoebites)........ .... 22

elisabethaeformis, Perisphinctes.. 14,25

Perisphinctes (Dichotomosphinctes) 8,

12,18, IS, pi. 4

Entolium aurarium. 8,14

sp.. _._.... - . ... 8,14

Epipeltoceras bimammatum.................. 6, 7,12

Erymoceras coronatum...........-.-..-....... 6,21

Euaspidocfras. ------------- --------------- 12

fialar, Glochiceras.............. ..r 13

figueroae, Idoceras........... 26

filiplex, Ammonites........-------- 26

Perisphinctes.--- 26 

Subdichotomoceras... ------ 7, fo, 14,06, pi. 5

Foreman formation of Diller.... 9-10

G 

Galice formation. _-.. - 8,10,11,12,19,25

Galilaeiceras.. ........... .----- 20

lindireni - - - 20

Galilaeites _ - . - - -- 20

Galileanus........... ... ----- 20

Geographic distribution-. .-.. 13 

Glochiceras fialar.. ....... .. -- 13

Gowenceras.. . 7, li, 12,13,18,20 

costidensum..... --- 11,20

snugharborensis........ ------- 20

spinosum..... 10

Kepplerites......... . 10

(Gowericeras) Kepplerites.- 2,20 

lindgreni, Kepplerites..- 6,7,10,13,14, 80, pi. 1 

sp., Kepplerites---- 7, pi. 1

(Gowericeras or Seymourites) Undgreni\, Kepplerites. ..-----.... 20

Gtegoryceras transversarium...... 7,12

grewingki, Pseudocadoceras......3, 6,9,13,14, XI, pi. 2

Qrossoworia-.... 2,3,6,11,21,22

anomala...........-------------------- 23

colfajci-.-...----------- 13, 14, K, 23, pis. 2, 3

leptus-...- - --------. -- 23

pseudocobra...............-------------- 23

(Grossouvria) aurita, Choffatia...... 23

H

harveyi, Paracadoceras. 10 

Hinchman tuff... 9 

Hosselkus Creek. ---------- - - T - -- 9,10

Hunter Valley chert- 3 

hyatti, Choffatia-..---. . --------- 9,11

Idoceras............ 2,6,13,18,25,26

balderum.... . 13,25,26

durangense 26

^(/weroae -------------------------- -- 26

laxevolutum.- ---------------------------- 26

neogaeum............- ---------- 26

planula ....... ...... - 3, 6, 14, 25, 26, pi. 5

schroederi.............. 26

soteloi- . - -- - - - 26 

sp.. H W, Pi- 5

D-29
D-30 INDEX

Idoceratinae .-______. 

Indian Gulch agglomerates.. 

inversion, Subdichotomoceras _

Page 

2 

2 

26

keppleri, Kepplerites- ......_- ... -

Kepplerites--- .................. 7,11,12,13,18,

cereale.--- ___________- .._

keppleri______________________--------_

lorinclarki -------... 6, 7, 13, 14, 19,

tychonis________._____--._. ..

(Gowerice ras)...... __________ ___-----_ 

lindnreni - - 6, 7, 10, 13, 14, SO, 

spinosum.. ......-________--.. .

sp.--________________________ 7,

Kepplerites (Gowriceras or Seymourites) lindgreni--... ____________ _ _-

Kepplerites (Seymourites)---------- _________ 2,

(Seymourites} ku:uryvengis...-.... -. 

Kettle formation of Diller__________________

Kettle meta-andesite.____________________ 9,

Kosmoceras iason.............................

Kosmoceratidae. _____________________________

kuzvryvensis, Kepplerites (Seymourites)-------

L

laxevolutum, Tdoceras. 

leptus, Grossoueria--- 

Lilloettia- ---------

buckmani--------

sp_._____________

20 

19,20

20

20 

pi. 1

11

2,20 

pi. 1

10 

pi. 1

20

10.11

19

9

10.12

6,7

2

19

26

23

11

10

10

sp.

lindgrem, Galilaeiceras-... 

Kepplerites (Gowencer

...._ 8,14

______________ 20

_____-__-___-. 6,7,

10,13,14, .0, pi. 1 

(Gowericeras or Seymourites)---------- 20

Olcostephamis-- _____________________ 20

Literature cited___________________._____ 27-28

Lithacoceras _________________________________ 7, 24

lochensis. Ammonites______________________ 19

Logtown Ridge agglomerates. _____ 2,3 

Logtown Ridge formation..______ 3, 6, 7, 8, 10, 11,

13,16,17,18, 21,23,26 

Lonesome formation of Lupher_____________ 10

lorinclarki, Kepplerites---------- 6, 7, 13, 14, 19, pi. 1

Lytoceras. __________________________________ 11

IN I 

Macrocephalites macrocephalus _________________

Macrocephalites macrocephalus zone of Europe.

macrocephalus, Macrocephalites __ ______________

Macrophylloceras _____________________________

Mariposa formation_________________ 2,6,7-8,

12,13-18,23, 24, 

Mariposa slate-_______________________________

Meleagrineila.------------------ ____________

sp_

6,7 

7,

9,11 

6,7 

11

9,10, 

25, 27

.. _ __ 2,3,9 

________________.___ 8 

 14

Metapeltoceras-------- ______________________ 27

(MetTpeltoc'ras), Pe.foceras________________ 2

sp., Peltoceras-- ____________________ 14, 81, pi. 6

Mexico_______________________ 12-13

Modiol us-------------_--_-.--_-__-_._.-_-____ 8

sp________________________________________ 14

Mokulumne River____________________ 21

Monte de Oro formation.__________ 2,8-9,16,18, 25

mosquensis, Buchi</_-_---__ ______..____ 11,13

muhtbachi, Dichotomoceras __________._ 24

Perisphinctes---------- _________________ 24, 25

(Dichotomosphinctes) _______ 7, 8, 11, 12,

13, 14, 18, 84, 27, pi. 4

mutatilis, Rasenia___. ______________. 13

Mysterious Creek formation of Crickmay.._ 10 

Mytilussp ---...-------._-. .----_-.-.-._ 14

N 

Naknek formation______________ 11,12,19,24

neogaeum, Idoceras--... .______...___.__. 26

nikitini, Xenocephalites_____________

North Ridge formation of Criekmay. 

Nucula sp---------------------------

Page 

12

O

Ochetoceras... ______.

Oecotraustes denticulata. 

Olcosfephanus lindgreniOppeliidae___._-_._. 

Ostrect- _________________

sp ___________________ ________________ 14

pacificus, Belemnites. - - ____________ 8,14

pallast plicata. Aucella.------ ... _ ____ _ _ _ 13

Paracadoceras ____ _ __ ____ _ ____________ 11, 12, 18

harvpyi- ___ ___ __ __________-_-__-. __ ____ 10

sp_.-- ----- - ---------------- 9

Parap-ltoceras annulosum,-- __________________ 23

Feltoceras...... .................... 6, 11, 12, 13, 18, 27

atMeta. ................................... 6,9

(Aletapeltoceras} ________ __________________ 2

sp.---- --- ----- --. 14, 47, pi. 6

Peltoceratinae. __ -_-_____-___-_________. _ _ 2

Penoii Blanco agglomerate_---___-______-_____ 3

Penoii Blanco volcanics_-_______ __ .______.- 3

Perisphinctes--.-.- __ __ _______ -___ _ 2, 13,23

anteccdens-.-- .... __-_.__ __ _ . _ _ _ __ 24

cautisnigrae ------------------------------- 7

colfa.d- ________________________________ _ 22

durange nsis _____________________________ 24

elisabethaeformis- ------------------------- 14,25

fiHplex --------------------------------- 26

muhlbachi 24, 25

phcatiloides --------------------- ______ 24

rotoides- ---------------------------------- 24

virgulatiformis- ............. ___ _ _______ 23,24

virnulatus ---------------------- --- ------ 23

(Dichotomosphinctes) ----------- 2,8,11,12.25

durangensis-------- _ -___ __- 8,12, 18

elisabethaeformis- ______ __ 8, 12. 18, 2\ pi. 4

mu\lbachi.. 1, 8, 11,12, 13, 14, 18, 24, 27, pi. 4 

Dlicatilis -- --- - - 10, 12 

loartaeformis-------------------------- 10, 12

spp. _ .. _ _ _ _______ _ __ 7, 25, pis. 4, 5

(Discos phinctes) ______ ... _ _-_-_. 2

carribeanus- ________________ 7, 12, 23, 24, pi. 3

virgulatiformis- ....... 7, 12, 13, 14, £ ,, 24, pi. 3

(Planites} virgulatus.... ............... 23

sp_ _. . 14, 23, 24, pi. 5

Perisphinctidae.- -------------------------- 2,23

Perisphinctinae----- _ __ _ ___-_-----------_- 2

Phylloceras... ---- -- 2,11,12,19

sp........... ---- ----.- - 11,19

Phylloceratidae_. __ __ __________

Phylloceratinae... ----------.---_--

richleri, Ammonites. -------------

Pinna sp_. _--__-.--_----_----_----

piochii, Buchia ___ ________ ______-_

(Planites) virgulatus, Perisphinctes-

_ 2 

__ 2

- 19

----- 14

- -_ 8,9

---- 23

planula, Idoceras.- - 3, 6, 14, .5, 26, pi. 5

plicata, Aucella pallasi------------------ __---_ 13

plicatilis, Perisphinctes (Dichotomosphinctes}-- 10,12 

plicatiloides, Perisphinctes--------------------- 24

(Prionodoceras), Amoeboceras ________________ 11

Pr oscaphites-.-------------------------------- 7, 19

(Proscaphites) dtnticulatum, Taramelliceras ___ 7,14,

19, pi. 1 

Taramelliceras--------- - ----------------- 2, 12

Pseudocadoceras 2, 3, 6, 7, 9, 10, 11, 12, 13, 18, 21 

crassicostatum 6, 10, 13, 14, SI, pi. 2

grewinyki. ------------ 3, 6, 9, 13. 14, SI, pi. 2

schmidti--. - ---- --- 9, 10

sp 3, 14, 81, pi. 2

pseudocobra, Grossouvria.. --------------------- 23

pseudomutabilis, A ulacostephanus--. ________ 7, 11, 13

Pseudoperisphinctinae__---- ------------------ 2

R

ffasenia mutabilis. 

Reineckeia--------

(Fteineckeites). 

dilleri -

13

18

12

9,12

Page 

Reineckeiidae.-_.__.___.________---___-_--_-_ 23

Peineckeites----------- ________________________ 23

(Reineckeites) dilleri, Reineckeia. ________ 9,12

Reineckeia_._____._____--..___ 12

Picheiceras_-- __.____________________ 19

Riddle formation______ ___________ 8

Rogue formation_--___________.__.________._. 10

rotoides, Perisphinctes-- _____________..____ 24

rugosa, Buchia_______________________ 8,11,12,13

Ffursiceras___________________ 23

S

schmidti, Pseudocadoceras ______.____. 9,10 

schroederi, Idoceras- ___________________________ 26

Seymourites-- __________________ 7,13,20

(Seymourites), Kepplerites------ ___.____ 2,10,11

kuzuryuensis, Kepplerites-------- _______ 19

Shelikof formation________ ________ 21

Siemeradzkia,---.- _____________________________ 23

de-mariae- _________________________ 23

Sigaloceras eff?Zor.fw*e_-___________ 6, 7, 9.10,11,13, 21

Snowshoe formation of Lupher---__-------_ 10

snuqharborensis, rjotvericeras------------.---.- 20

soteloi, Tdoctras------------------------------- 26

Southwestern Oregon_____-__.____-_. __._-. 10

spinosum, ^owericeras- _______ _______________ 10

Kepplerites (r'-owericeras) --_____________-- 10

Stratigraphic suramary____-__________ ___ 2-3

Subdichotomoceras,- _____________ 2,7,8,12,19,26,27

filiplex 7, 13, 14, 86, pi. 5

inversum -------------------------------- 26

Subgrossouvria _________________ .___ _. 23

Subplanites--.-------------------------------- 24

Summary of results ____________________ 13

Systematic descriptions-_______.__-__--_ - 19-27

T 

Tancredii------------------------------------ 8

sp - 14

Taramelliceras_____ _ _ __________._ _- 7,12,19

dtnticulatum_________________ ________ 19

(Proscaphites)---- ___._______-_-___ 2,12

denticulatum-__________ 7,14, 19, pi. 1 

Tararnellit) "ratinae__---__--__--------_------_ 2

Taylorsvillc area, Galifornia_ _ __ _ _____ 9-10,12

Torijiintisphinctes----------------------------- 25

transversarium, '-regor^ceras------------------- 7,12

Trigonia_____________________--------------- 8

sp 14

Trowbridge shale of Lupher._____-___---_ _ 10

Turbo sp-_-_-__-___-_ 8,14 

tychonis, Kepplerites---------------- -. 11

V

vlcarius, Xenocephalites--- __-.__ __ __ 10 

Virgatosphinctoides virgulatiformis- ... -__ 23 

virgulatiformis, Perisphinctes------------------ 23,24

Perisphinctts (Discosphinctes)-- -_-_ _ 7,

12,13,14, 83, 24, pi. 3

Virgatosphinctoides ---------------------- 23

virgulatus, Discosphinctes--......-------------- 23

Perisphinctts----------------------------- 23

(Planites) 23

Virgatosphinctinae-_-____------_------------- 2

1'irgatosphinctoides---------------------------- ^4

W 

waitzi, Choffaiia------ -____-----_---------- 12

wartaeformis, Perisphinctes (Dichotomosphinctes) 10,12

Western British Columbia.-,----.----------- 10-11

whitneyi, Cardioceras------------ _-_-----_-_ 22

X

Xenocephalites------------- -- 10,11,12,18

nikitini----------------------------------- ^

vicarius-------- _ -_--- _-- --- 10

sp__ __--_- -- --- --- 9

Yakoun formation. ___ -- - 10

Yakounites-------- -_ _ -__ - 20

Yakounoceras _ _ ----- -- --- 2"

U. S. GOVERNMENT PRINTING OFFICE : 1961 O -583565
PLATES 1-6
PLATE 1

[All figures natural size]

FIGURES 1-8. Kepplerites lorinclarki Imlay, n. sp. (p. 19).

1-3, 8. Holotype, USNM 130777 from USGS Mesozoic loc. 27313. Figs. 1-3 are from rubber casts of an 

external mold of the body chamber. Figs. 2 and 3 together represent the same view as fig. 1 but are lighted 

to emphasize ribbing and tubercles. Fig. 8 is an internal mold of the body chamber of holotype. 

4-7. Paratypes, USNM 130778 from USGS Mesozoic loc. 27313. Figs. 4-6 are from rubber casts of 

external molds. Fig. 4 represents part of an penultimate whorl. Fig. 5 shows the apertural constriction. Fig. 6 shows the strong primary ribs and tubercles on the penultimate whorl. Fig. 7 is an internal 

mold. 

9-11. Taramellicerasl(Proscaphites?) denticulatum (Hyatt) (p. 19).

Cotypes, USNM 30206 from USGS Mesozoic loc. 901. Note ventral serrations of figs. 9 and 10. Fig. 11 

shows gentle ribs on the flanks. Compare with same view published by Crickman, 1933, Prof. Paper 

175-B, pi. 17, figs. 12, 13. 

12, 14. Kepplerites (Gowericeras) lindgreni (Hyatt) (p. 20).

Holotype, USNM 30205 from USGS Mesozoic loc. 27516. 

13. Kepplerites (Gowericeras} sp.

Specimen, USNM 130791 from USGS Mesozoic loc. 24793 in the Talkeetna Mountains, Alaska. This 

specimen is illustrated for comparison with Kepplerites (Gowericeras) lindgreni (Hyatt).
GEOLOGICAL SURVEY PROFESSIONAL PAPER 374 PLATE 1

14

KEPPLERITES, GOWERICERAS. AND TARAMELLICERAS^
PLATE 2

[All figures natural size]

FIGURES 1-8, 11-13. Pseudocadoceras grewingki (Pompeckj) (p. 21).

1-7. Rubber casts of plesiotypes, USNM 130779 from USGS Mesozoic loc. 27317; 8. rubber cast of plesiotype, USNM 130781 from USGS Mesozoic loc. 24710; 11-13. plesiotypes, USNM 108114, 108116, 108115 

respectively, from Alaska included for comparisons with specimens from California shown on figs. 1-8. 

9, 10. Pseudocadoceras crassicostatum Imlay (p. 21).

Plesiotypes, USNM 108118 and 108119 from Alaska included for comparisons with specimens from

California shown in figs. 14-21. 

14-21. Pseudocadoceras cf. P. crassicostatum Imlay (p. 21).

Rubber casts of specimens, USNM 130780 from USGS Mesozoic loc. 27317. Ventral view shown on 

fig. 20 shows forward curvature of ribs.

22. Pseudocadoceras cf. P. grewingki (Pompeckj) (p. 21).

Specimen USNM 130783 from Mesozoic loc. 27387. Note low point of rib branching and forward curvature 

of ribs on venter.

23. Pseudocadoceras? sp. (p. 21).

Specimen USNM 130782 from USGS Mesozoic loc. 22175. 

24-28. Amoeboceras (Amoebites) dubium (Hyatt) (p. 22).

Cotypes, USNM 30201 from USGS Mesozoic loc. 719. 

29. Grossouvria colfaxi (Gabb) (p. 22).

Holotype, Harvard University Museum of Comparative Zoology 5287 from near Colfax, Placer County, 

Calif.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 374 PLATE 2

PSEUDOCADOCERAS, AMOEBOCERAS (AMOEBITES), AND GROSSOUVRIA
PLATE 3

[Figures natural size unless otherwise indicated]

FIGURES 1-10. Perisphinctes (Discosphinctes) virgulatiformis Hyatt (p. 23).

Cotypes, USNM 30204 from USGS Mesozoic loc. 901. Fig. 6 shows venter with its adoral end pointed 

downward. Fig. 9 shows suture lines (X 3) drawn from internal mold of specimen represented by fig. 7. 

Figs. 1, 2, 4, 5, 7, 8, and 10 are from rubber casts of external molds. 

11, 12. Perisphinctes (Discosphinctes) carribeanus Jaworski.

Plesiotypes, USNM 130792 from USGS Mesozoic loc, 26382 at Pan de Azucar, Pinar del Rio Province, Cuba.

Illustrated for comparison with P. (Discosphinctes) virqulatiformis Hyatt. 

13-17. Grossouvria colfaxi (Gabb) (p. 22).

Holotype, Harvard Mus. Comp. Zoology 5287, from railroad cut 1 mile west of Colfax, Calif. 13. Suture 

lines (X 2) drawn near adoral end of last septate whorl; 14, 17. Ventral and lateral views of internal 

mold; 15, 16. Rubber cast of external mold showing ribbing under different lighting. Arrows on fig. 15 

and 16 show position of same forked rib as that illustrated at the bottom of fig. 17. Compare fig. 17 with 

fig. 29 on pi. 2 to note differences in appearance under different conditions of lighting.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 374 PLATE 3

17

PERISPHINCTES (DISCOSPHINCTES) AND GROSSOUVRIA
PLATE 4

[All figures natural size] 

FIGURE 1. Perisphinctes (Dichotomosphinctesl) spp. (p. 25).

Specimen, USNM 130788 from USGS Mesozoic loc. 24317. 

2. Perisphinctes (Dichotomosphinctes) sp. (p. 25).

USNM 130790 from USGS Mesozoic loc. 3326. From the Galice formation at the Almeda mine on the Rouge River 3 miles below Galice Creek, Josephine 

County, Oreg.

3. 5. Perisphinctes (Dichotomosphinctes) cf. P. D. muhlbachi Hyatt (p. 24).

Rubber cast of external mold, USNM 103460 from USGS Mesozoic loc. 901. 

Internal mold, USNM 130786 from USGS Mesozoic loc. 27460.

4. 7. Perisphinctes (Dichotomosphinctes} cf. P. elisabethaeformis Burckhardt (p. 25).

Stanford University Mus. Paleontology 9063 from north bank of Feather River 3 miles northeast of Oroville, Butte County, Calif. Two views of same specimen under different conditions of lighting. 

6. Perisphinctes (Dichotomosphinctes) cf. P. (D.) muhlbachi Hyatt (p. 24).

Laterally crushed body chamber of specimen, USNM 130789 from USGS Mesozoic loc. 10796 from the Naknek formation 3% miles southeast of Mount Lee,

Alaska Peninsula. Note close resemblance to P. muhlbachi Hyatt shown on fig. 8. 

8. Perisphinctes (Dichotomosphinctes) muhlbachi Hyatt (p. 24).

Rubber cast of external mold of holotype, USNM 30202 from USGS Mesozoic loc. 27517.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 374 PLATE 4

PERISPHINCTES (DICHOTOMOSPHINCTES)
PLATE 5

[All figures natural size]

FIGURES 1-3, 9. Subdichotomoceras? aff. AS. filiplex Quenstedt (p. 26). 

1, 3. USNM 30203a from USGS Mesozoic loc. 902. 

2. USNM 30203b from USGS Mesozoic loc. 903. 

9. USNM 130785 from USGS Mesozoic loc. 904. 

Figs. 1, 2, and 9 are from rubber casts of external molds. 

4. Perisphinctes? sp. (p. 23).

Stanford Univ. Mus. Palentology 9065 from near Nashville, Eldorado County, Calif. View of rubber cast of

external mold 

5, 6. Perisphinctes (Dichotomosphinctes?) sp. (p. 25).

Rubber cast of external mold, USNM 103461 from USGS Mesozoic loc. 27566. 

Partly internal and partly external mold, USNM 130787 from USGS Mesozoic loc. 490. 

7, 8. Buchia cf. B. concentrica (Sowerby) (p. 8).

Internal molds bearing traces of fine radial striae, USNM 130793 from USGS Mesozoic loc. 4801. 

10, 11. Idoceras? sp. (p. 26).

Stanford Univ. Mus. Paleontology 9064. Fig. 10 is an internal mold showing venter of a whorl next larger than

the largest shown on fig. 11 which is a rubber cast of an external mold. 

12-16. Idoceras aff. /. planula (Heyl) in Zeiten (p. 25).

Holotype, Univ. of California (Berkeley) Mus. Paleontology 32724 from loc. A-4996. 12. Rubber cast of external mold of inner whorls shown in figs. 13 and 15. 13, 14. Lateral and ventral views of plaster replica of 

complete holotype showing three-fifths of a whorl of body chamber. 15, 16. Lateral and ventral views of holotype without body chamber. A nearly smooth midventral area is shown on fig. 16.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 374 PLATE 6

13 % - 14 -*ft*»WUUH&*<"" 15 16 

SUBDICHOTOMOCERAS1, PERISPHINCTES1, DICHOTOMOSPH1NCTES1, IDOCERAS, AND BUCHIA
PLATE 6

[Figure natural size]

FIGURE 1. Peltoceras (Metapeltocerast) sp. (p. 27).

Stanford Univ. Mus. Paleontology 9062 from Indian Creek, Amador County, Calif. Plaster cast of external mold that 

is probably now lost. Note presence of ribbing on innermost whorls and two rows of tubercles on the outer whorls.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 374 PLATE 6

PELTOCERAS (METAPELTOCERAS1?)