Late Bajocian Ammonites 

From the Cook Inlet 

Region, Alaska 

By RALPH W. IMLAY 

JURASSIC AMMONITES FROM SOUTHERN ALASKA 

GEOLOGICAL SURVEY PROFESSIONAL PAPER '418-A 

Description and illustrations of cephalopods· 

of Middle Jurassic (late Ba;'ocian) age 

I:IBRARY 

tHJRfAU OF MIN£1 ~18RARV 

SPOI\ANl. ~ASH. 

JUN 31971 

PlfASf lfTtJIN 

TO l18RAIY 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1962 
r 

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___________________________________________ A-1 Comparisons with other faunas ______________________ _ 

Introduction ________ -- ________ ----_---------------- North America, exclusive of Alaska ______________ _ 

Arctic region __________________________________ _ 

Biologic analysis _________________ -- ___ - ---- --------- 1 Eurasia and north Africa _______________________ _ 

Stratigraphic summary ______________________ - ____ --- 2 

North side of Cook inlet____ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2 

Australasia and Indonesia _______________________ _ 

Geographic distribution _____________________________ _ 

Systematic descriptions _____________________________ _ 

Talkeetna Mountains____________________________ 2 References-----------------------------------------

Age of the fauna____________________________________ 2 Index ____________________________________________ _ 

ILLUSTRATIONS 

[Plates follow index] 

PLATE 1. Lissoceras, Spiroceras?, and Calliphylloceras. 

2. Oppelia (Li-roxyites). 

3. Megasphaeroceras. 

4. Dettermanites. 

5. Sphaerocems, Leptosphinctes, and Macrophylloceras. 

Page 

A-3 

3 

3 

4 

4 

4 

5 

13 

15 

Page 

FIGURE 1. Index map showing the principal areas of upper Bajocian (Jurassic) rocks in the Cook Inlet region, Alaska______ A-7 

2. Index map showing occurrences of upper Bajocian (Jurassic) fossils in the Talkeetna Mountains, Alaska________ 8 

3. Index map showing occurrences of upper Bajocian (Jurassic) fossil in the Tuxedni Bay area, Alaska____________ 9 

4. Index map showing occurrences of upper Bajocian (Jurassic) fossils in the northern part of the lniskin Peninsula, 

Alaska------------------------------------------------------------------------------------------- 10 

TABLES 

Page 

TABLE 1. Ammonite genera and subgenera from beds of late Bajocian age in the Cook Inlet region, Alaska, showing biological relationships and relative numbers available for study______________________________________________ A-1 

2. Localities where megafossils were collected from upper Bajocian strata in the Cook Inlet region, Alaska________ 5 

3. Geographic distribution of the upper Bajocian ammonites from the Cook Inlet region, Alaska _____________ -___ 6 

III 
JURASSIC AMMONITES FROM SOUTHERN ALASKA 

LATE BAJOCIAN AMMONITES FROM THE COOK INLET REGION, ALASKA 

By RALPH w. IMLAY 

ABSTRACT 

Jurassic ammonites of late Bajocian age occur in the Cook 

Inlet region, Alaska, along the west side of Cook Inlet, and in the 

southeastern part of the Talkeetna Mountains. The dominant 

genera are Liroxyites, a subgenus of Oppelia, M egasphaeroceras, 

n.nd Dettermanites. These have not been recorded outside the 

Cook Inlet region. The ammonites also include a fair number of 

specimens of M acrophylloceras, Calliphylloceras, and Lissoceras, 

but only n, few specimens of Leptosphinctes. Lytoceras, Spiroceras?, and Sphaeroceras are represented by single specimens. 

These ammonites along the west side of Cook Inlet occur only 

in the lower part of the Bowser member of the Tuxedni formation. 

This lower part is overlain unconformably by the upper part, 

which is characterized by Cranocephalites of probable Bathonian 

age. The lower part is underlain abruptly but conformably by 

the Cynthia Falls sandstone member of the Tuxedni formation, 

which has furnished the middle Bajocian ammonites Chondroceras and Normannites from its lower and middle parts. Beneath 

the Cynthia Falls sandstone member follows an unnamed siltstone member that has furnished many ammonite genera characteristic of the European zone of Stephanoceras hurnphriesianum. 

The ammonites from the lower part of the Bowser member are 

dated as late Bajocian mainly because they include Sphaeroceras; 

Spiroceras?, and Leptosphinctes that are typically late Bajocian, 

becu.use they do not include any genera that are typical of the 

Bathonian or middle Bajocian of Eurasia and north Africa; and 

because they occur above beds that contain many middle Bajocian ammonites such as Chondroceras, Norrnannites, Telocert;ts, 

Stemmatoceras, Zemistephanus, Stephanoceras, and Witchellia. 

The presence of Leptosphinctes itself is good evidence for a late 

Bajocian age, but its association with Sphaeroceras and an uncoiled n.mmonite that is probably Spiroceras is excellent confirmatory evidence. Furthermore, the resemblance of the Alaskan 

Leroxyites u.nd Dettermanites to the European Oxycerites and 

Polyplectites, respectively, indicates an age not older than late 

Bajocian. Such an age for the lower part of the Bowser member 

is in line with the presence of Cranocephalites in the overlying 

beds, as that genus appears to represent much of the Bathonian, 

according to recent studies in Alaska, Montana, and Greenland. 

The dominance of the ammonites Liroxyites, ll1 egasphaeroceras, and Dettermanites in the upper Bajocian rocks of Alaska 

contrasts with their absence in the Tethyan region. Similarly 

the upper Bajocian rocks of the Tethyan region have furnished 

many ammonite genera that have 110t yet been found in Alaska. 

These differences indicate that faunal developments were somewhat different in the two regions during Bajocian time. 

INTRODUCTION 

The n.rn1nonites described herein have been studied 

primarily to demonstrate that rocks of late Bajocian 

age are present in Alaska above beds containing middle 

Bajocian ammonites typical of the Tethyan region and 

below beds characterized by the amrnonite Cranocephalites, which is known elsewhere only frorn the Arctic 

region and the western interior of the United States. 

The evidence sets a lower limit to the age of the Cranocephalites beds. The late Bajocian ammonite faunule 

is also unusually interesting because the dominant amrnonite genera and subgenera present have not been 

found in other parts of the world. 

The fossils fron1 the upper Bajocian rocks of the Cook 

Inlet region, Alaska, were collected by G. S. Martin in 

1913, A. A. Baker in 1921, L. B. Kellun1 and Hehnuth 

Wedow, Jr. in 1944, R. W. Imlay and D. J. Miller in 

1948, Arthur Grantz in 1951 and 1953, L. F. Fay in 

1953, and R. L. Detterman in 1957 and 1958. 

Many thanks are due Arthur Grantz and R. L. Detterman for preparing locality maps and descriptions 

and for furnishing and checking all the stratigraphic 

information. The position of the lower boundary of 

the Bowser rnember of the Tuxedni fonnation shown 

on the index rnaps (figs. 3, 4) is based on an unpublished map prepared by R. L. Dettennan. 

BIOLOGIC ANALYSIS 

The Alaskan Jurassic amn1onites of late Bajocian age 

described herein include 154 speci1nens. Their distribution by genera, subgenera, subfamilies, and families is 

shown in table 1. The table shows that the Sphaero('eratidae and the Oppeliid'ae are the do1ninan t families; 

TABLE 1.-Ammonite genera and subgenera from beds of late 

Bajocian age in the Cook Inlet region, Alaska, showing biological 

1·elationships and relative numbers available for study 

Family Subfamily 

Phylloceratidae_____ Phylloceratinae_ ------ Calliphylloceratinae.-- Lytoceratidae_ _ ____ Lytoceratinae ________ _ 

Spiroceratidae_ __ __ _ _ ____ ------------------

1-laploceratidae _____ ------------------------ Oppeliidae__________ Oppeliinae_ ----------- Stephanoceratidae _________________________ _ 

Sphaeroceratidae ___ -----------· ------------

Perispbinetidae_____ Leptosphinctinae ____ _ 

Genus and subgenus 

Macrophylloceras _________ _ Calliphylloceras ___________ ·_ 

Lytoceras __ __ -------------- Spiroceras? ___________ -----

Lissoceras __ --------------- Oppelia (Liroxyites) _______ _ Dettermanites ____ _________ _ Meoasphaeroceras _______ --- Sphaeroceras ______ ________ _ 

Leptosphinctes ___ --- _ -- ___ _ 

L. (Prorsisphinctes?) ______ _ 

L. ?-----------------------

A-1 

Number 

of specimens 

10 

8 

1 

1 

7 

50 

10 

63 

1 

1 
A-2 JURASSIC AMMONITES FROM SOUTHERN ALASKA 

the Phyl1oceratidae, Haploceratidae, and Stephanoceratidae are much less con1mon; and the Lytoceratidae, 

Spiroceratidae, and Perisphinctidae are of minor importance. The most common and characteristic am-

~ monites are Liroxyites, Megasphaeroceras, and Dettermanites. These have not been recorded outside of the 

Cook Inlet region, Alaska, although they resemble the 

ammonites Oxycer-ites, Sphaeroceras, and Polyplectites 

respectively of the Tethyan region. Their presence 

supports the idea of Arkell (1956, p. 609, 614) that the 

Pacific region developed as a faunal province, distinct 

from the Tethyan and Boreal faunal provinces, during 

Bajocian time. The other genera and subgenera listed 

are common in the Middle Jurassic of the'Tethyan region. 

STRATIGRAPHIC SUMMARY 

NORTH SIDE OF COOK INLET 

Fossils of late Bajocian age have been found along 

the west side of Cook Inlet only in the lower part of 

the Bowser me1nber of the Tuxedni formation (figs. 

1, 3, 4). This lower part consists of 600 feet, or'less, 

of interbedded dark-gray siltstone, sandy siltstone, 

and claystone that contains many ash beds and weathers reddish brown or rusty. · Locally it contains small 

fossiliferous concretions. It rests abruptly on the massive sandstone of the underlying Cynthia ·Falls sandstone member of the Tuxedni formation and is overlain 

abruptly by the lowest 1nassive siltstone and sandstone 

in the upper part of the Bowser. This 1nassive siltstone and sandstone overlaps southward across the 

underlying rusty beds and at the south end of the 

Iniskin Peninsula rests directly on the Cynthia Falls 

sandstone n1en1ber (written communication, R·. L. 

Detterman, May 15, 1959). 

All the late Bajocian fossils fron1 the lower part of · 

the Bowser. me1nber appear to have been obtained 

fr01n concretions. They consist 1nostly of ammonites 

and the pelecypod Inoceramus ambiguus Eichwald. 

In addition they include belmnnite fragments, the 

gastropod Amberleya, the pelecypod Pleuromya, and 

terebratulid brachiopods. 

TALKEETNA MOUNTAINS 

Fossils of late Bajocian age have been found in the 

Talkeetna Mountains at two places (fig. 2). At one 

place near Boulder Creek (Mesozoic loc. 8572), the 

fossils appear to have been obtn.ined from concretions 

and consist only of ammonites.· At the second place 

near the head of Sheep Creek (Mesozoic loc. 24821) 

the fossils are preserved in a dark-gray coarse-grained 

pebbly sandstone that contains n1any fossils other than 

amn1onites. These include in particular · belen1nite 

fragn1ents, the gastropod Amberleya, the pelecypods 

Oxytoma, Lima (Plagiostoma), Isocyprina?, and Astarte. In addition, worm tubes oc.cur in the sandstone 

matrix, on the internal mold of the pelecypod Lima, 

and also in close association with belemnite fragn1ents 

that are corroded and rounded. 

Stratigraphically, Mesozoic locality 24821 is near the 

top of the Tuxedni formation (Arthur Grantz, written communication, Nov. 14, 1960). Mesozoic locality 

8572 is near Mesozoic locality 8573 (Martin, 1926, p. 

225, 228) which has furnished the ammonite Cranocephalites. This an1monite elsewhere in the Talkeetna 

Mountains has been found in a sandstone a few hundred feet below the Chinitna formation (Arthur 

Grantz, written communication, Apr. 8, 1959). It 

occurs alo.ng the west side of Cook Inlet in the upper 

part of the Bowser member of the Tuxedni formation, 

directly above the amn1onites herein described. Judging by these occurrences all the late Bajocian ammonites in the Talkeetna Mountains are probably from 

near the top of the Tuxedni formation. Their exact 

stratigraphic position is possibly determinable in the 

sequence exposed along the northwest side of Boulder 

Creek where a1nmonites ranging in age from middle 

Bajocian (Mesozoic loc. 8567) to Callovian (Mesozoic 

loc. 8571) have been found. 

AGE OF THE FAUNA 

The ammonite fauna in the lower part of the Bowser 

member of the Tuxedni formation on the west side of 

Cook Inlet and in equivalent beds in the. Talkeetna 

Mountains (table 1) is considered to be of late Bajocian 

age primarily because it includes the genera Sphaeroceras, Spiroceras?, and Leptosphinctes. Of these, Sphaeroceras in Europe and in the Tethyan region ranges from 

the zone of Stephanoceras humphn'es'ianum to the top of 

the Bajocian (Westermann, 1956a, p. 24-35; Arkell, 

1952, p. 77; Arkell, 1956, p. 32, 50, 100, 142, 262, 278); 

Sp'iroceras ranges from the late Bajocian to the late 

Bathonian (Arkell, 1957, p. L206); and Leptosphinctes is 

typically late Bajocian. There is a possible occurrence 

of Leptosphinctes in the middle Bajocian of Argentina 

(Jaworski, 1926, p. 262, pl. 2, fig. 4; Westermann, 1956b, 

p. 268; Arkell, 1956, p. 585), but the report of L.eptosphinctes in the middle Bajocian of Alaska (Imlay, 1952, 

p. 979) was based on specimens now referred to Parab?:gotites Imhty (1961, p. 471, pl. 64, figs. 1-3). 

Associated with Sphaeroceras, Spiroceras?, and Leptosphinctes in Alaska are other ammonites that suggest a 

late Bajocian or Bathonian age. These include Oppelia 

(Liroxyites), which resembles Oppelia (Oxycerites), and 

Dettermanites, which resembles Cadomites in size, coiling, 

and ornamentation but bears elongate lateral lappets as 

in Polyplectites. With these also occur the genus Megasphaeroceras, whose resemblance to Sphaeroceras suggests an age not younger than Bajocian, and the genus 

Lissoceras, which ranges from middle Bajocian to early 
LATE BAJOCIAN AMMONITES FROM THE COOK INLET REGION A-3 

Bathonian. Significantly the ammonite faunule in the 

lower part of the Bowser member of the Tuxedni forillation does not contain any genera that n,re characteristic of the middle Bajocian, althou'gh such genera occur 

in the underlying beds along the north side of Cook 

Inlet. Thus the immediately underlying Cynthia Falls 

sandstone 1nember contains Ohondroceras and Normannites, t"Lnd the next underlying unnamed siltstone member contains these genera plus Teloceras, Zemistephanus, 

Stephanoce·ras, Oppelia (Oppelia), Witchellia, and Sonn~n~a. Most pi·obably some of these genera would occur in the lower part of the Bowser member, if it were 

as old as middle Bajocian. 

In sun1mation, the ammonite fauna characterizing the 

lower part of the Bowser member of the Tuxedni formation contains certain genera that are typical of the 

late Bajocian, others that could be either late Bajocian 

or Bathonian, and two that range from the middle Bajocian into the Bathonian or Callovian. The fauna does 

not include ar'ly genera characteristic of the middle Bajocian but overlies beds that contain such ammonites. 

All these facts constitute strong evidence that the ammonite fauna is of late Bajocian age. 

Such an age assignn1ent for the ammonites in the 

lower part of the Bowser member of the Tuxedni formation is in harmony with the presence in the overlying 

beds of another a1nmonite fauna characterized by Oranocephal?:tes, of probable Bathonian age. This Bathonian assignment was made by Imlay (1952, p. 980, 981) 

on the basis of faunal associations and stratigraphic 

relations and has been supported by his recent studies 

in Alaska and Montana. Additional information was 

furnished by Call om on (1959), who claims that the 

Oranocephalites beds of East Greenland not only are of 

Bathonian age, but probably represent the entire early 

Bathonitul and possibly at their base represent some of 

the Bajocitul. Callon1an, of course, did not know of all 

the ft"Lunal evidence, presented herein, for the presence 

of late Bnjocian in Alaska nor that the lower and upper 

parts of the Bowser n1ember are separated by an unconformity (see stratigraphic summary) that may represent 

part of the Bajocinn or part of the Bathonian, or both. 

Nevertheless, he presents a strong argument that the 

Oranocephalites beds in East Greenland are equivalent 

to the lower Bathonian of the European and the Tethyan region. By implication, any faunas beneath the 

Oranocephalites ·beds are older than Bathonian. 

It seems reasonable, therefore, both stratigraphically 

n.nd faunn1ly to correlate the lower part of the Bowser 

member of the Tuxedni formation with the upper Bajocian. 'rhere is no positive evidence, however, whether 

that part represents all, or only part of the upper Bajocian. Considering that 3 ammonites zones are recognizable in western Europe (Arkell, 1956, p. 31, 32) and 

only 1 is recognizable in the lower par.t of the Bowser 

1nen1ber perhaps only part of the upper·. Bajocian is 

represented in the Bowser n1ember.. It:is ·also possible 

that the upper third of the Cynthia Falls sandstone 

n1ember, which has not yielded any am1nonites, may be 

equivalent to part of the upper Bajocian. 

COMPARISONS WITH OTHER FAUNAS 

NORTH AMERICA, EXCLUSIVE OF A~ASX:A 

Fossils of definite late Bajocian age have not been 

identified in Canada or in the conterminous United 

States south of Alaska. However, some anunonites 

from northern Alberta that Frebold (1957, p. 54-56, 

pl. 28, figs, 1 a, b, 2; Arkell, 1956, p. 542, 609) compared 

with species of Oppelia (Oxycerites) from the lower 

Bathonian of Europe have very broad, falcoid ribs 

greatly resen1bling those on. Oppelia (Liroxyites) kellumi 

I1nlay from Alaska. This resemblance suggests that 

the Canadian specimens may be of late Bajocian rather 

than of Bathonian age, but their exact age will have to 

await the discovery of other an1monites that are better 

preserved or belong to genera that have a more restricted range. 

The late Bajocian is probably represented faunally 

in the States of Oaxaca and Guerrero in southern 

Mexico, according to statements by Arkell (1956, p. 

565) and Erben (1956, p. 27-29, 78, 79,-82-87, 92, 93), 

but the published evidence is not conclusive. The 

amn1onite fragment that Burckhardt (1927, p. 90, pl. 

16, figs. 10, 11, 16) described as Oosmoceras (Strenoceras) 

aff. 0. bifurcatum (Quenstedt [not Zieten]) was cited by 

hin1 (1927, p. 94; 1930, p. 26) as evidence of a late 

Bajocian age. The same a1nmonite, however, was 

referred questionably to Garantiana by Arkell (1956, 

p. 565) who noted that it could be late Bajocian or 

Bathonian. The associated fossils listed by Erben 

include Oppelia aff. 0. subradiata (Sowerby), 

Stephanoceras?, Perisphinctidae (Leptosphinctinae ?) , 

nnd Sphaeroceras. These identifications are stated to 

be prelin1inary and therefore, do not afford evidence 

for a close age determination. 

ARCTIC REGION 

Ammonite faunules of n1iddle or late Bajocian age 

resembling those in the Tethyan region on a generic 

level have not been identified in the Arctic region 

(Arkell, 1956, p. 609), although Callomon (1959, p. 507-

511) speculates that smne of the lowest Oranocephalitesbearing beds in East Greenland are possibly of late 

Bajocian age. His arguments for such an age are 

based partly on the resemblance of Oranocephalites to 

the n1iddle Bajocian genus Chondroceras and partly on 

the presence of seven amn1onite zones below beds that 

he considers earliest Callovian. His knowledge of the 
A-4 JURASSIC AMMONITES FROM SOUTHERN ALASKA 

relative duration of ammonites n1akes hin1 doubt that 

all seven zones can be accommodated in the Bathonian 

stage. He ad1nits that the lowest Cranocephalites beds 

do not contain any amn1onite genera typical of the 

Tethyan Bajocian but neither do the overlying Cranocephalites beds, which are assigned to the Bathonian 

on a stratigraphic basis, contain any genera in common 

with the Tethyan Bathonian. These faunal differences 

with the Tethyan province are explained, following 

Arkell (1956, p. 609, 614), by the separation of ammonites into faunal provinces during the middle Bajocian. 

The writer's recent studies of the Cranocephalites 

faunules in western Montana and in the Cook Inlet 

region, Alaska, show that those faunules are probably 

of Bathonian age and have much more in common 

faunally with the Callovian than with the Bajocian. 

Furthermore, the fact that in Alaska the Cranocephalites beds rest unconformably on beds containing the 

typical late Bajocian ammonite Leptosphinctes, described herein, makes a late Bajocian age unlikely for 

any beds containing Cranocephalites. 

EURASIA AND NORTH AFRICA 

Upper Bajocian a1nmonites of the Tethyan region 

have been recorded at many places in northern Africa, in 

western Europe south of the Baltic sea, in southern 

U.S.S.R. in Europe, in the Middle East, and in southwestern Asia (Arkell, .1956, p. 31, 50, 77, 122, 142, 

176, 208, 240, 249, 263, 278, 291, 300, 325, 355, 362, 

364, 371, 377, 474, 483, 487, 515). The most common 

ammonites are the Parkinsoniidae, including such genera 

as Parkinsonia, Garantia, and Strenoceras, and the Leptosphinctinae, including such genera as Bigotites and 

Leptosphinctes. Genera that are known only from the 

upper Bajocian include Bigotites, Leptosphinctes, Cleistosphinctes, Vermisphinctes, Prorsiphinctes, Strenoceras, 

Pseudogarantia, Caumontisphinctes, and Ermoceras. 

Genera that range from the upper Bajocian into the 

Bathonian include Spiroceras, Cadomites, Polyplectites, 

Morphoceras, Garantia, and Parkinsonia. Genera and 

subgenera that range from the upper Bajocian into the 

Callovian include Oxycerites and Oecotraustes. Genera 

that range from the middle into the upper Bajocian 

include Strigoceras, Cadomoceras, Oppelia s. s., Sphaeroceras, Stephanoceras, Teloceras, and Normannites. The 

genus Lissoceras ranges from middle Bajocian into 

lower Bathonian. There are also a few genera that are 

either uncommon or are known from only a small part 

of the Tethyan region, such as Thamboceras, Trimargina, and Magharina from the Middle East. 

In general, assemblages of these ammonites from the 

Tethyan region are easily recognized and distinguished 

from middle Bajocian or Bathonian assemblages in that 

region. Furthermore, in parts of western Europe 

detailed studies have shown the upper Bajocian may be 

subdivided into three ammonite zones (Arkell, 1956, 

31, 32, 50, 77, 142) based on the ranges of certain genera 

and species. Interestingly, such genera as Teloceras, 

Stephanoceras, and Normannites that are typical of the 

middle Bajocian have been found locally in beds of late 

Bajocian age (Arkell, 1956, 63, 99, 100, 122, 142, 176, 

232, 263, 264, 278, 300, 483). Many of these occurrences are in the lower part of the upper Bajocian, but 

some are in the middle part (Arkell, 1956, p. 483), and 

some have not been placed exactly within the substage. 

The upper Bajocian ammonite assemblages in the 

Tethyan region show faunal relationships with the upper 

Bajocian ammonites in the Cook Inlet region, Alaska, 

primarily through the genera Spiroceras, Sphaeroceras, 

and Leptosphinctes. Otherwise marked differences 

exist. There are as yet no known representatives of the 

Parkinsoniidae in Alaska, and many other genera that 

are common in the upper Bajocian of the Tethyan 

region are unknown in Alaska. Futher1nore, the dominant ammonites in the upper Bajocian of Alaska belong 

to Dettermanites and Megasphaeroceras, which are 

unknown outside Alaska, although they resemble 

Polyplectites and Sphaeroceras respectively. 

AUSTRALASIA AND INDONESIA 

In New Guinea and in the Sula Islands (Pulau-pulau 

Sula) the upper Bajocian is represented, according to 

Arkell (1956, p. 439, 446, 448), by Cadomites daubenyi 

(Gemmellaro) (Boehm, 1912, p. 148, pl. 34, figs. 5a, b), 

although he admits that the genus ranges at least as 

high as middle Bathonian. These occurrences are in 

the eastern part of the Tethyan realm or region as 

defined by Arkell (1956, p. 614). 

Elsewhere on the lands within or surrounding the 

Pacific Ocean, except in Alaska, marine upper Bajocian 

has not been identified, or is missing according to the 

evidence presented by Arkell (1956, p. 382-462, 542, 

555, 585). This is rather surprising considering that 

marine middle Bajocian has been identified at many 

places in this region, but is in harmony with the general 

distribution of marine Bathonian in the san1e region 

(Arkell, 1956, fig. 98 on p. 608). In many places, however, not enough is known about the geology to prove 

definitely that the upper Bajocian is missing. 

GEOGRAPHIC DISTRIBUTION 

The occurrence by area and locality of the megafossils 

described in this report is indicated in table 3. The 

positions of the various areas are shown in figures 1 to 

4. Descriptions of the individual localities are shown 

as follows in table 2. 
LATE BAJOCIAN AMMONITES FROM THE COOK INLET REGION A-5 

TABLE 2.-Localities where megafossils were collected from upper Bajocian strata, Cook Inlet region, Alaska 

Locality on Geological 

Survey 

figures 2-4 Mesozoic 

locality 

1 _______________ 24821 

2 _______________ 8572 

3 _______________ 21282 

4 _______________ 22709 

5 _______________ 22710 

6 _______________ 11034 

6--------------·· 19934 

6 _______________ 21314 

7 _______________ 11036 

1--------------- 19943 

7 _______________ 21313 

7 _______________ 21315 

8--------------- 26593 

9 _______________ 11035 

1.0 ______________ 20001. 

11. ______________ 2131.8 

1.1 ______________ 27099 

Collectors' field Nos. 

53AGz144 ____ 

13AM2L _____ 

48AI8L ______ 

51AGz140 ____ 

51AGz14L ___ 

21ABF-42 ____ 

44AWWF-3 __ 

48AI30 _______ 

21ABF-43 ____ 

44AWWF-12_ 

48AI29 _______ 

48AI3L ______ 

57 ADT5 _____ 

21ABF-44 ____ 

44AWWF-68_ 

48AI35 .. ______ 

58ADt2 ______ 

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

Arthur Grantz and L. F. Fay, 1953. Talkeetna Mountains, Anchorage D-2 quad., on Sheep Creek. Lat 61 °59'17" N., long 147°38'35" W., Tuxedni formation, near top. 

G. C. Martin, 1913. Talkeetna Mountains, at altitude of 4,200 ft on ridge west of 

creek that enters the main Boulder Creek from the north, 3 miles above its junction with the East Fork. Tuxedni formation. 

R. W. Imlay and D. J. Miller, 1948. Tuxedni Bay area, on tributary entering 

Bear Creek from the southeast, 4.75 miles S. 22° W. of Fossil Point. Bowser 

member of the Tuxedni formation, 300ft above base. 

Arthur Grantz, 1951. Tuxedni Bay area, about 0.3 mile above mouth of tributary 

entering Bear Creek from southeast at a point 2.53 miles from Tuxedni channel. 

Bowser member of the Tuxedni formation, about 1.00 ft above base. 

Arthur Grantz, 1951. Tuxedni Bay area, about 0.5 mile above mouth of same tributary described under Mesozoic loc. 22709. Bowser member of the Tuxedni 

formation, about 260 ft above base. 

A. A. Baker, 1921. Iniskin Peninsula, on right fork of Cliff Creek about 2, 700 ft 

above junction with left fork and 2.46 miles S. 15° W. of mouth of Fitz Creek. 

Bowser member of the Tuxedni formation, about 1.00 ft above base. 

Helmuth Wedow, Jr., 1944. Iniskin Peninsula, small tributary on right side of 

Cliff Creek about 5,100 ft above junction with Fitz Creek and 2.42 miles S. 14° W. 

of mouth of Fitz Creek. Bowser member of the Tuxedni formation, about 85 ft 

above base. 

R. W. Imlay and D. J. Miller, 1948. Iniskin Peninsula, on Cliff Creek 3.66 miles 

N. 87° E. of Tonnie Peak. Same location as Mesozoic locs. 11034 and 1.9934. 

Bowser member of the Tuxedni formation, from 10 to 100 ft above base. 

A. A. Baker, 1.921. Iniskin Peninsula, on right fork of Cliff Creek about 8,000 

ft above junction with Fitz Creek and 2.58 miles S. 15° W. of mouth of Fitz 

Creek. Bowser member of Tuxedni formation, 125 to 175ft above base. 

Helmuth \Vedow, Jr., 1.944. Iniskin Peninsula, on Cliff Creek about 200ft downstream from a prominent cascade, 1}~ miles above junction with Fitz Creek and 

3.35 miles east of Tonnie Peak. Bowser member of the Tuxedni formation, 125 

to 17 5 ft above base. 

R. W. Imlay and D. J. Miller, 1948. Iniskin Peninsula, on Cliff Creek just below a cascade. Same location and stratigraphic position as Mesozoic locs. 11036 

and 19943. 

R. W. Imlay and D. J. Miller, 1948. Iniskin Peninsula, on Cliff Creek near Mesozoic locs. 21313 and 19943. Bowser member of the Tuxedni formation, float 

from lower 175 ft. 

R. L. Detterman, 1957. Iniskin Peninsula, on Cliff Creek near location of Mesozoic 

loc. 21313, lat 59°4.9'20" N ., long 153°11'00" W. Bowser member of the Tuxedni 

formation, 200 ft above base. 

A. A. Baker, 1921. Iniskin Peninsula, on right fork of right fork of Cliff about 

9,000 ft above junction with Fitz Creek and 2.68 miles S. 16° W. of mouth of 

Fitz Creek. Bowser member of Tuxedni formation, lower part. 

Helmuth Wedow, Jr., and L. B. Kellum, 1944. Iniskin Peninsula, on northeast 

side of Tonnie Creek about 200 ft downstream from top of a cascade which 

is 0.9 mile S. 48° E. of Tonnie Peak, Bowser· member of the Tuxedni formation, 

about 100 ft above base. 

R. W. Inllay and D. J. Miller, 1948. Iniskin Peninsula, on Tonnie Creek 1.00 to 

1.05 miles S. 51° E. of Tonnie Peak. Same location as Mesozoic loc. 27099. 

Bowser member of the Tuxedni formation, from 50 to 125ft above base. 

R. L. Detterman, 1958. Iniskin Peninsula, on Tonnie Creek 0.81 mile N. 55° W. 

of Iniskin Bay Association No. 1 well. Lat 59°4.5'30" N., long 153°15'05" W. 

Same location as loc. 21318. Bowser member of the Tuxedni formation, 75 to 

100 ft above base. 

SYSTEMATIC DESCRIPTIONS 

Genus MACROPHYLLOCERAS Spath, 1927 

Macrophylloceras ·cf. M. grossicostatum Imlay 

ribbing on the smaller whorls at diameters of about 

60 nun. 

Figured specimen.-USNM 130903. 

Plate 5, figures 6, 7 

Ten septate specimens fr01n the Bowser n1e1nber of 

the Tuxedni fonnation are closely similar to Macrophylloce1'as g1'0SS'icostatum In1lay (1953, p. 74, pl. 25, 

figs. 11-13, 15, 16) fron1 the Chinitna formation of 

Alaska in shape, coiling, and ribbing on the larger septate whorls. They appear to have slightly coarser 

604333 0-62-2 

Occurrence.-Lower part of Bowser member of the Tuxedni 

formation, Iniskin Peninsula, at USGS Mesozoic locs. 11035, 

21313, 21314, and 26593. Talkeetna Mountains from upper part 

of the Tuxedni formation at Mesozoic loc. 24821. 

Genus CALLIPHYLLOCERAS Spath, 1927 

Calliphylloceras sp. 

Plate 1, figure 8 

The genus is represented by eight internal molds that 
A-6 JURASSIC AMMONITES FROM SOUTHERN ALASKA 

TABLE 3.-Geographic distribution of the upper Bajocian ammonites from the Cook Inlet Region, Alaska 

[Numbers 1-11 refer to numbers on figs. 2-4. Higher numbers are Geological Survey Mesozoic locality numbers] 

North side of Cook Inlet 

~~~~~~si----------,,-----------------------------------·------------ Tuxedni Bay I 

Tuxedni 

formation 

---- ...... !;; C'l 

00 

""' 00 C'l 

3 

--

C'l 

00 

~ C'l 

4 

---- 0> 

j2 ;2 ""' M 

C'l 

C'l C'l 

C'l ~ 

Iniskin Peninsula 

Bowser member (lower part) of Tuxedni formation 

6 8 9 10 11 

""' ~ <.0 M ~ ~ M lQ § ;:s 0> M M ""' 0> M 0> 0> ~ ~ 0> ~ ~ lQ 

~ ~ ~ ~ ~ <.0 C'l C'l C'l C'l ~ C'l 

-----------------------------1-----------------------------------

Macrophylloceras cf. M. grossicostatum Imlay- ---------------------------------- X . --- - ---- ---- ---- ---- ---- X ---- - --- X ---- X X __ -- _______ _ Calliphylloceras sp __ -------------- _------- X - _-- ---- __ - ___ - _ - _.,. _ _ _ _ _ X _ _ _ _ _ _ _ _ _ _ _ _ X _ _ _ _ _ _ _ _ X X ___ _ Lytoceras sp _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X 

Spiroceras? sp ____________________________________ X _______________________________________________________ _ 

Lissoceras bakeri Imlay, n. sp ______________________ X X X X X X ____________ X ___________________ _ 

Oppelia (Liroxyites) kellumi Imlay ______________ ---- X ________________ X X X X X ____ X X X X 

M egasphaeroceras rotundum Imlay__________ X _ _ _ _ X _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X X X X X X X _ _ _ _ X X 

M. cf. M. rotundum Imlay _________________________________________ X -.--- ____________ X ____________ X ___ _ 

M. SP~------------------- --------------- --.-- ---- ---- ---- ____ · ---- ---- ---- ---- ---- ---- ---- ---- ---- X ---- ---- Sphaeroceras talkeetnanum Imlay, n. sp __________ X ___________________________________________________________ _ 

Dettermanites vigorosus Imlay_ _ _ _ _ _ _ _ _ _ _ _ _ _ X X _ _ _ _ _ _ _ _ _ _ _ _ X X X X _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X _ _ _ _ X ___ _ Leptosphinctes cliffensis Imlay, n. sp ________________________________________________ X _______________________ _ L. (Prosisphinctes?) delicatus Imlay, n. sp _______________________________________________________________ X ___ _ 

L.? sp __________________________________ ---------------------------- X ------------------------------------ Belemnite fragments ______________________ X ________________________ X ________________________ X X ___ _ 

Amberleya cf. A. densinodosa Huddleston ____ X ____ X ____ X ________ X ________ X ____________ X X X 

Oxytoma sp _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ 

Inoceramus ambiguus Eichwald'"'------,------ X ____________________ X X X X X ____________ X X X 

Lima (Plagiostoma) sp _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X _______________________________________________________________ _ Astarte sp _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ Isocyprina? sp ___________________________ X ________________________________________________________ -------- Pleuromya sp ________________________ ~ __________________ -. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X ___ _ Brachiopods undet_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ X _ _ _ _ _ _ _ _ _ _ _ _ X X ___ _ Worm tubes _____________________________ X ________________________________________ .---- ___________________ _ 

bear sigmoidal constrictions and faint traces of sigmoidal lirae. Fragments of shell, preserved on the specimen illustrated, show that the constrictions are confined 

to the internal molds. Compared with Calliphylloceras 

freibrocki Imlay (1953, p. 73, pl. 26, figs. 7-11), the 

constrictions are rnore strongly sigmoidal.· 

Figured specimen.-US NM 130906. 

Occurrence.-Lower part of Bowser member of the Tuxedni 

formation, Iniskin Peninsula, at USGS Mesozoic locs. 20001, 

21314, 21315, and 21318. Talkeetna Mountains from upper part 

of the Tuxedni formation at Mesozoic Joe. 24821. 

Genus LYTOCERAS Suess, 1865 

Lytoceras sp. 

The genus is represented only by one septate fragn1ent 

of an internal mold that shows traces of growth lines 

spaced from 2 to 3 mm apart. 

Occurrence.-Lower part of the Bowser member of the Tuxedni 

formation at USGS Mesozoic loc. 22709. 

Genus SPIROCERAS Quenstedt, 1858 

Spiroceras1 sp. 

Pl.ate 1, figure 7 

One fragment of a small uncoiled ammonite is similar in lateral view to the small specimens of Spiroceras 

from the upper Bajocian of western Europe (Roman 

and Petourand, 1927, pl. 3, figs. 13-31, pl. 4, pl. 5, 

·figs. 6-11, 15-19; Potonie, 1929, pl. 17, figs. 4-12). 

A definite generic identification cannot be made, however, because the venter is not preserved. The flanks 

bear high widely spaced forwardly inclined ribs that 

are swollen at about three-fifths of the height of the 

flanks. The ribs ventral to these swellings weaken 

slightly and then terminate in conical tubercles on 

the venter. On the dorsmn the ribs are broader and 

lower than on the flanks. 

Figured specimen.-USNM 130908. 

Occurrence.-Lower part of Bowser member of the Tuxedni 

formation, Tuxedni Bay area, USGS Mesozoic loc. 21282. 

Genus LISSOCERAS Boyle, 1879 

Lissoceras bakeri Imlay, n. sp. 

Plate 1, figures 1-6, 9-12 

This species is represented by seven specirnens. 

The shell is compressed and involute. The whorls 

are subovate, much higher than wide, widest at about 

one-third their height, and embrace about two-thirds 

of the preceding whorls. The flanks are slightly convex and converge. in the upper two-thirds to a narrowly 
LATE BAJOCIAN AMMONITES FROM THE COOK INLET REGION A-7 

IFI ocE 

FIG URI~ 1.-lndox map showing tho principal aroas or uppor Bajocian (Jurassic) rocks in the Cook Inlet region, Alaska. (1) Eastern part of the Talkeetna Mountains; 

(2) Tuxodni Bay aroa; (3) northern part of the Iniskin Peninsula. 

arched venter. 'rhe umbilicus is fairly narrow, step:. 

like; wall fairly low, vertical, rounding evenly into 

flanks. 'rhe incomplete body cluunber comprises at 

len,st half a whod. 

The shell bears fine gently flexuous growth lines · 

that become slightly stronger ventrally. These incline 

forward on the lower pn,rt of the flanks, recurve backward just nbove the rniddle of the flanks, and then 

curve forward again. 1'he suture line is characterized 

by the second latm:al saddle, being rnuch higher than 

the first. The first lateral lobe is n1uch longer than 

the ventral lobe. 

Most of the specin1ens are too crushed or incomplete 

for accurate rneasuretnents. One srnall specin1en at a 

diarneter of 37 111111 has a whorl height of 19 mn1, a 

whorl thickness of 13 rnm, and an urnbilicaf width 

of 7.5 nun. 

This species is distinguished from all described 

species of Lissoceras by its larger size and more highly 

frilled suture line. L. oolithicum (d'Orbigny) (184.6, 

p. 383,' pl. 126, figs. 1-4; Rmnan and Petourand, 192.7, 

p. 48, pl. 5, figs. 12-14) .fronl the upper Bajocian of 

Europe is probably :the· rn6st sin1ilar, but it has rnore 

convex flanks, inclined instead. of vertical·- urnbilica\ 

wall, and a more narrow second lateral saddle. ·.', - ' 

This species is named in honor of Arthur A. Baker 

of the Geological Survey, who collected the holotype 

specin1en. 

Types: Holotype USNM 130891; paratypes, USNM 130892, 

130893a, b, 130894. 
A-8 JURASSIC AMMONITES FROM SOUTHERN ALASKA 

148°30' 14a·oo· 147"30' 147•oo· 

10 MILES 

61°45' tt==============:±================±===::±===========tJ FIGURE 2. -Index map showing occurrences of upper Bajocian (Jurassic) fossils in the Talkeetna Mountains, Alaska. (N urn bers on map refer to those given in the locality list (table 2) and in the distribution table.) 

Occurrence: Lower part of Bowser member of the Tuxedni 

formation, Iniskin Pen_insula, at USGS Mesozoic locs. 11034, 

19934, 21282, 21314, 21315; Tuxedni Bay area at Mesozoic 

locs. 22709 and 22710. 

Genus OPPELIA Waagen, 1869 

Subgenus LIROXYITES Imlay, 1961 

The original description of this subgenus (Imlay, 

1961, p. 469) is as follows: 

This subgenus resembles Oxycerites Roilier in its highly involute 

coiling, discoid shape, sharp venter, and presence of numerous 

auxiliary lobes in its suture line. It differs by its falcoid ribs 

being much broader and more closely spaced, by the presence 

of conspicious falcoid striae, and by the ribs and striae persisting 

well onto the adult body chamber instead of fading.· Other 

possible distinctions are the weak crenulations on the keel formed 

by the continuations of the ribs and the striae; the presence on 

some specimens of two raised spiral bands instead of a single 

median spiral band; and the development of eccentric coiling 

on the adult body chamber. The type species of Liroxyites is 

Oppelia (Liroxyites) kellumi Imlay, n. sp. 

Oppelia (Liroxyites) kellumi Imlay 

Plate 2, figures 1-12 

?Oppelia (Oxycerites) ex gr. jallax Gueranger. Frebold, 1957, 

Canada Geol. Survey Mem. 287, p. 54-56, pl. 28, fig. 2 

[not figs. Ia, b]. 

Oppelia (Liroxyites) kellumi Imlay, 1961, Jour. Paleontology, 

v. 35, no. 3, p. 470, pl. 63, figs. 5, 7-9. 

The original description is as follows: 

This species is represented by 50 specimens of which most 

retain some shelly material. The shell is a discoidal, highly 

involute compressed oxycone. The coiling becomes slightly 

eccentric on the body chamber. The lower parts of the flanks 

are subparallel, but the upper parts converge toward the venter. 

The venter is acute and bears a narrow open keel that is generally 

slightly pinched at its base and, wherever the shell is preserved, 

is marked by faint continuations of the ribbing. The umbilicus 

is extremely small on the septate part of the shell but widens on 

the body chamber. The umbilical wall is low, vertical, and 

rounds rather· abruptly into the flanks. The body chamber 

occupies half a whorl. The aperture terminates abruptly in a 

gentle, forwardly inclined falcoid curve. 
LATE BAJOCIAN AMMONITES FROM THE COOK INLET REGION 

152"50' 152"45' 152"40' :l52.35' 

MILES 

Base of Bowser member 

of Tuxedni formation 

FrounE 3.-Index mnp showing occurrences of upper Bajocian (Jurassic) fossils in the 'l'uxedni Day area~ Alaska. (Numbers on map refer to those given in the locality list 

(table 2) and in the distribution table.J 

The ornamentation consists of weak to moderately strong 

fn.lcoid ribs, falcoid striB.e and faint, broad spiral bands. The 

falcoidribs are low n.nd nearly as broad as the interspaces. They 

are barely visible at a din.meter of 22 mm and gradually become 

higher and brottder during growth except near the aperture of 

the adult where they weaken. They arise near the middle of 

the flanks as bundles of striae, become stronger ventrally, weaken 

considerably at the keel and arc faintly indicated 011 the keel 

wherever the shell is preserved. On internal molds, however, 

the ribs end abruptly at the keel. They do not split into sccond1\.I'Y ribs. The fn.lcoid striae cover the entire surface of the shell 

pn.mllcl to the ribs but unlike the ribs are not visible on the iHternal molds. On some specimens a faint spiral band occurs at 

about two-fifths of the height of the whorl and a11other at threefifths of the height of the whorl. 

The suture line is finely frilled, has a longer ve11tral than 

latcmllobe, and has seven auxiliary lobes that diminish regularly 

toward the urnbilicttl scam. 

Most of the specirncns arc too imperfect for accurate measurements. However, the specimen shown on plate 6:3, figure 9 at 

a diarncter of 62 mm has a whorl height of :35 mm, a whorl 

thickness of 13 mm, and an umbilical width of 4 mm. 

This species bears broad falcoid ribbing closely similar to that 

of an n.mmonite from the Fernie group of Alberta, Canada, 

described by Frcbold (1957, p. 54-56, pl. 28, fig. 2) as Oppelia 

(Oxyceriles) ex. gr. fallax Guem11gcr a11d it may be identical 

specifically. However, it differs from the Europea11 Oppelia 

(Oxycerites) fallax (Gucmnger), as described by Arkell (1951, p. 

604333 0-62--3 

56-60, pl. 5, figs. 1-:3; pl. 8, figs. lla, b; text-figs. 15, 16) by having broader, lower, and more closely spaced falcoid ribs that persist onto the adult body chamber. The large smooth adults of 

the European species of Oxycerites contrast markedly with the 

ribbed adult whorls of Oppelia (Liroxyites) kellumi Imlay, n. sp. 

from Alaska. 

The eccentric coiling of the Alaskan species. contrasts also 

with the tight coiling of most species of Oxycerites, but does occur 

on Oxycerites knapheuticus (Buckman) (1924, pl. 479) from the 

lower Bathonian of England and on Oxycerites tilli (Loczy) (1915, 

pl. 4, fig. :3) from the Callovian of Hungary. 

The weak spiral banks on the Alaskan species are not nearly 

as well developed as the spiral grooves and ridges on Strigoceras 

(Arkell, 1957, p. L272) and are not accompained by fine furrows 

and ridges, or by a hollow keel, as in that genus. 

This species is named in honor of Lewis B. Kellum of the University of Michigan who collected some of the type specimens. 

Types.-Holotype, USNM 1:30886; paratypes, USNM 130887a, b, 

13088~ 1:30889a-~ 130890. 

Occurrence.-Lower part of the Bowser member of the Tuxedni 

formation, Iniskin Peninsula, at USGS Mes. locs. 110:35, 11036, 

1994:3, 20001, 21282, 21:313, 21314, 21315, 21:318, and 27099. 

Genus MEGASPHAEROCERAS Imlay, 1961 

The original description of this genus (Imlay, 1961, 

p. 4 70) is as follows: 

This genus resembles Sphaeroceras Bayle in its globular shape, 

tiny umbilicus, sharp, wiry ribbing, and a tendency for the inter-
A-10 JURASSIC AMMONITES FROM SOUTHERN ALASKA 

FIGURE 4.-Index map showing occurrences of upper Bajocian (Jurassic) fossils in the northern part of the In is kin Peninsula. (Numbers on map refer to those gi veu in the 

locality list (table 2) and in the distribution table.) 

nal mold to be smooth or nearly smooth. It differs markedly, 

however, by the adult body .cham,ber . remaining tightly coiled, 

enlarging adorally instead of contracting, and bearing much 

weaker ribbing than the septate~' ~h();ls.· .. Furthermore, the 

apertural constriction is followed by· a weak swelling rather than 

by a flared collar and the adults are much larger than in any 

described species of Sphaeroceras. The suture line has moderately broad lobes and saddles, has an irregularly trifid first lateral lote that is slightly longer than the ventral lobe, and bears 

a general resemblance to that of the genqs Labyrinthoceras 

Buckman (1919, pls. 134, 135). 

The type species of M egasphaeroceras is M egasphaeroceras 

rotundum Imlay, n. sp. 

Megasphaeroceras rotundum Imlay 

Plate 3, figures 1, 4-12 

Megasphaeroceras rotundum Imlay, 1961, Jour. Paleontology, 

v. 35, no. 3, p. 471, pl. 63, figs. 1-4, 6. 

The original description of this species is as fol1ows: 

The species is represented by about 60 specimens. The shell 

is stout to moderately stout and is tightly coiled. The whorls 

are depressed, wider than high, widest on the lower fourth of the 

flanks, becoming more depressed with growth, embracing preceding whorls nearly completely. The flanks and venter are 

evenly convex. The umbilicus is extremely small. The umbilical wall is low, vertical at base, and rounds fairly abruptly into 

flanks. The body chamber is represented by three-fifths to 

three-fourths of a whorl. The aperture curves strongly forward 

and terminates abn.wtly. It is marked on the internal mold by 

a broad constriction followed by a weak swelling that is not 

apparent where the shell is preserved. At the apertural constriction there is a slight contraction of the body whorl. 

The ribbing on the septate part of the shell is sharp and gently 

flexuous. The primary ribs are radial on the umbilical wall and 

curve forward on the lower fourth of the flank where some of them 

bifurcate. From 1 to 3 secondary ribs arise freely near the zone 

of furcation between the primary ribs. All secondary ribs 

become higher and sharper ventrally, curve forward on the flanks, 

and cross the venter with a slight forward arching. 

The ribbing on the adult body chamber weakens considerably 

but persists adorally to near the aperture as low broad ribs and 

striae. The shell at the apertural constriction is marked only 

by striae. 

The ribbing on the internal molds of the septate whorls is much 

weaker than on the shell, but the greatest weakening occurs on 

the internal molds of the adult body chamber where the ribbing 

becomes very weak and on some specimens is indistinct. 

The suture line is rather finely divided and has moderately 

broad saddles and lobes. The first lateral lobe is irregularly 

trifid and slightly longer than the ventral lobe. The second 

lateral saddle is broader and lower than the first lateral saddle. 

The general sutural pattern is similar to that of Labyrinthoceras 
LATE BAJOCIAN AMMONITES FROM THE COOK INLET REGION A-ll 

intricat1t1n Buckman (1919, pl. 135). The suture line of Sphaeroceras brongniarti (J. Sowerby) illustrated by Westermann (1956a, 

text-fig. 6 on p. 31) has a broader first lateral lobe and a narrower 

second lateral saddle. 

The dimensions of the type specimens in millimeters are as 

follows: 

Whorl Whorl 

Specimen Diameter height thickness 

Pttratype 130899c_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 92 ? 53 ? 

Holotype 130898_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 62 33 42 ? 

Parn.type 130899tL_______________ 63 35 ? 

Paratype :t.30899d_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 48 30 34 

Paratype 130899b_~------------- 41 25 25 

This species shows considerable variation in the density and coarseness of i~s ribbing, in the persistence of 

the ribbing on the body charnber, in the ilnprint of the 

ribbing on the internal 1nold, and in the stoutness of 

its whorls. All these characteristics vary independently of each other and consequently separation of the 

species into subspecies has not been possible. Although certain specin1ens differ rnarkedly frmn other 

specimens in stoutness of whorls or in coarseness of 

ribbing, there are many other specimens that are intermediate in appearance between the extrmne variants .. 

7'ypes.-holotype USNM 130898; paratypes USNM 130899ad, 130900. 

Occ1trrence.-Lower part of Bowser member of the Tuxedni 

formation at USGS Mesozoic locs. 11035, 11036, 19943, 21282, 

21313, 21314, 21315, 21318, 22709, 26593. Talkeetna Mountains from the Tuxedni formation at Mesozoic loc. 24821. 

Megasphaeroceras cf. M. rotundum Imlay 

Plate 3, figures 2, 3 

Several adult specimens bearing considerable shell 

material differ fr01n M. rotundum Imlay by having 

n1uch finer denser ribbing that disappears at an earlier 

growth stage. Their shells exh{bit faint ribbing on the 

adapical end of the body whorl but the body chambers 

are marked only by weak forwardly curved striae. 

The internal molds of the body chambers are quite 

srnooth. 'I'hese specimens possibly represent a finely 

l'ibbed Vl1t·in.nt of lvl. rotundum ImJay in which the 

body chamber becomes almost smooth. 

Ji'igw·ed specimen.-USNM 130904. 

Occ'!trrence.-Lower part of Bowser member of the Tuxedni 

formu.tion at USGS Mesozoic locs. 19934, 21315, and 21318. 

Genus SPHAEROCERAS Boyle, 1878 

Sphaeroceras talkeetnanum Imlay, n. sp. 

Plate 5, figures 1-4 

The genus Sphae1'0ceras is represented in the Geologicnl Survey collections fro1n Alaska by one speci1nen 

th1~~ shows only the adult body whorl. The septn.te 

pm·:t of this whorl is globose and tightly coiled. The 

body chamber includes n.bout three-fifths of a whorl, is 

seniicirculn.r in section, u.nd becomes depressed neu.r the 

aperture. Its u.dornl part is abruptly contracted frmn 

the septate part of the shell so that the ·umbilical seam 

trends radial and then bends forward at a right· angle 

near the aperture. The aperture terminates in a pronounced flared collar that is followed by a constriction, 

then by a n1inor swelling, and then by a nearly smooth 

area that is projected forward ventrally. 

The body whorl is marked by about 38 primary and 

89 secondary ribs. These are high and sharp where the 

shell is preserved but are low and weak on the internal 

mold. The prin1ary ribs are slightly stronger than the 

secondary ribs, are radial on the septate part of the shell, 

and incline forward near the aperture. Bifurcation 

occurs Inainly a little above the middle of the flanks. 

Son1e secondary ribs arise freely on the upper parts of 

the flanks. 

The suture line is too poorly exposed to be traced 

u.ccura tely. 

About one-fifth of a whorl behind the aperture the 

specirnen has a n1aximun1 dian1eter of 49 n1n1 and an 

estin1ated thickness of 36 mm. At the adapical end of 

the body chamber the whorl height is about 16 nun and 

the whorl thickness to 33 min. Half a whorl adorally 

the san1e din1ensions are 26 and 34 mm respectively, but 

the specin1en is son1ewhat con1pressed laterally. Near 

the apertural flare the san1e di1nensions are 19 and 32 

n1n1 respectively. . 

This Alaskan specimen is assigned to Sphaeroceras 

because of its extrernely narrow umbilicus, fine superficial ribbing, its abruptly contracted body charnber, 

flared collar, and deep terminal constrictions. The 

genus Sphaeraceras has been discussed in detail by 

Western1ann (1956a, p. 24-35, pl. 14), who shows that it 

differs frmn Chondroceras mainly by hu. ving a s1naller 

umbilicus, a niore _abruptl)i- contracted body chmnber, 

generally finer sharp"er ribbing on the adult body chainher, and generally .. ·a fess strongly flared collar. He 

notes that the genus in western Europe ranges frmn the 

1niddle Bajocian zone of Stephanoceras humphriesianum 

to the end of the Bajocian, but is n1ost conunon in the 

lower part of the upper Bajocian. This range is supported by Arkell (1957, p. L292), but 1nost of the individual occurrences listed by him (1952, p. 77; 1956, p. 

32, 50, 142) are from the lowei· prtrt of the upper Bajocin.n. One possible middle Bn.jocian occurrence is listed 

(Arkell, 1956, p. 268) from north Africa. 

Concerning species of Sphaeroceras, Wester1nann 

recognizes only S. brongniarti (J. Sowerby) and two 

subspecies. He places S. globus Buckman (1927, pl. 

725) in synonyn1y with S. brongniarti and suggests that 

S. tutthum Bucknuw (1921, pl. 258) is possibly synonyJnous. 

The Alaskan specin1en compares closely in shape and 

ribbing with S. brongniarti (J. Sowerby) as figured by 

Arkell (1952, fig. 20, p. 77) and Westermann (1956n,, pl. 
A-12 JURASSIC AMMONITES FROM SOUTHERN ALASKA 

14, figs. 1-6). The only conspicuous difference is its 

considerably larger size and its more strongly flared 

collar. A few specin1ens.of S. brongniarti (J. Sowerby) 

(Rorr1an, 1938, pl. 18, fig. 187; Buckman, 1927, pl. 725; 

Westermann, 1956a, fig. 4, p. 30) have a n1oderately 

prominent ventral flare of similar shape, but on n1ost 

specimens the flare is not as promin"ent. 

Type.-Holotype USNM 130902. 

Occurrence.-Upper part of Tuxedni formation in the Talkeetna Mountains at USGS Mesozoic loc. 8572. 

Genus Dettermanites Imlay, 1961 

The original description of this genus (Imlay, 1961, 

p. 4 71 ), is as follows: 

This genus resembles Stephanoceras in coiling, shape, ornamentation and sutural pattern, but differs by having elongate 

lateral lappets. In this respect it is similar to Polyplectites, but 

it differs by being much larger, by developing coarser ribbing on 

its body chamber, and by its ventral lobe being appreciably 

longer than its first lateral lobe. In Polyplectites these lobes as 

illustrated by Westermann (1954, p. 337, 341, 345) are nearly of 

the same length. The genus N ormannites, whose long lateral 

lappets somewhat resemble those of Dettermanites, has fewer 

secondary ribs that are much stronger relative to the primary 

ribs. Both ribbing and sutural pattern indicate an assignment 

of Dettermanites to the Stephanoceratidae rather than to the 

Otoitidae. · 

The type species of Deltermanites is D. vigorosus Imlay, n. sp. 

This genus is named in honor of Robert L. Detterman of the 

U.S. Geological Survey. 

Dettermanites vigorosus Imlay 

Plate 4, figures 1-9 

Dettermanites vigorosus Imlay, 1961, Jour. Paleontology. v. 35, 

no. 3, p. 472, pl. 64, figs. 1-3. 

The original description' of this species is as follows: 

This species is represented by 10 specimens preserved in concretions that with 3 exceptions reveal only one side of the specimen. The whorls are nearly coronate in section, much wider 

than high, and embrace the preceding whorls nearly one-half. 

The body whorl is slightly contracted from the penultimate 

whorl. The umbilicus is moderately wide. Its wall is steeply 

inclined and rounds evenly into the flanks. The' body chamber 

occupies about three-fourths of a whorl. The aperture bears 

lateral lappets. It is marked on internal molds by a constriction, 

followed by a collar, and then by lappets. 

The ribbing consists of prominent widely-spaced primary ribs 

that incline forward slightly and terminate near the middle of 

the flanks in acute tubercles. From these pass bundles of two, 

or rarely three, much weaker secondary ribs that incline forward 

on the flanks and cross the venter transversely. Many rib 

bundles are separated by single ribs that arise freely along the 

zone of furcation. Both ribs and tubercles become gradually 

stronger and sparser during growth. 

The suture line is characterized by its ventral lobe being 

appreciably longer than the first lateral lobe and by the second 

lateral lobe being much shorter. The first lateral lobe is irreggularly trifid. 

The holotype at a diameter of 89 mm, has a whorl height of 

32 mm, an estimated whorl thickness of 36 mm, and an umbilical 

width of 41 mm. 

This species has much coarser ribbing than any described 

species of Polyplectites except possibly P. dorni (Roche) (1939, 

p. 222; Dorn, 1927, p. 240, pl. 5, fig. 6; Westermann, 1954, p. 342, 

pl. 32, figs. 4a, b) which is much smaller and apparently less 

evolute. 

Types-Holotype, USNM 130895; paratypes, USNM 130896, 

130897a, b. 

Occurrence-Lower part of Bows~r member of the Tuxedni 

formation, Iniskin Peninsula, at USGS Mesozoic locs. 11034-

11036, 19934, 21314 and 21318. Talkeetna Mountains at USGS 

Mesozoic locs. 8572 and 24821. 

Genus LEPTOSPmNCTES Buckman, 1920 

Leptosphinctes cliffensis Imlay, n. sp. 

Plate 5, figures 10, 11 

One internal mold exhibits highly evolute coiling, a 

con1pressed whorl section, and an incon1plete body 

chan1ber that occupies about four-fifths of a whorl. 

The septate whorls bear deep constrictions and fairly. 

strong, forwardly inclined primary ribs that ter1ninate 

in acute tubercles high on the flanks. The ribbing on 

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

inner whorls is not exposed. However, the ventral 

area on the adoral half of the outermost septate whorl 

and the adjoining part of the body chamber is marked 

by fairly weak secondary ribs that arise in pairs fr01n 

the lateral tuberch~s and incline strongly forward. 

Adorally on the body chamber all ribs become much 

weaker, the venter becomes nearly smooth, and the 

tubercles disappear. The body chamber bears two 

deep, forwardly inclined constrictions and several weak 

constrictions. 

The suture line is only partly exposed near the middle 

of the outermost septate whorl. It appears to be less 

frilled and to have a stockier first lateral lobe than on 

the described European species of Leptosphinctes, 

although showing s01ne resen1blance to the suture line 

of L. coronarius Buck1nan (1921, pl. 202). 

As only one side of the speci1nen is preserved, accurate measurements cannot be made. At a dian1eter 

of about 80 mn1, the whorl height is 22 n1n1, and the 

umbilical width is 46 nun. 

This speci1nen resembles Leptosphinctes (Vermisphinctes) vermijormis (Bucknutn) (1920, pl. 162) in 

coiling, strength of ribbing, and presence of deep constrictions. It is distinguished by the presence of 

lateral tubercles, by somewhat sparser ribbing, and by 

the secondary ribs arising higher on the flanks of the 

body whorl. Compared with L. leptus Buckn1an (1920, 

pl. 160) it is more evolute, has sparser ribbing, and 

probably has a lower whorl section. Cmnpared with 
LATE BAJOCIAN AMMONITES FROM THE COOK INLET REGION A-13 

L. co1·onaTius Buclonan (1921, pl. 202), its lateral 

tubercles n,ppear to be 1nuch higher on the fln,nks and 

its coiling more evolute. 

Ty7Je.-Holotype USNM 130907. 

Occurrence.-Lower part of the Bowser member of the Tuxedni 

formation at USGS Mesozoic loc. 21313. 

Leptosphinctes (Prorsisphinctes1) delicatus Imlay, n. sp. 

Plate 5, figures 8, 9 

One laterally crushed internal 1nold of which only 

one side is preserved consists of 1}~ septate whorls and 

11bout tluee-fifths of a body. cha1nber. The coiling is 

highly evolute. 'rhe whorls are ovate and compressed. 

The septate whorls bear deep constrictions and fairly 

weak forwardly inclined pri1nary ribs that extend to 

near the rniddle of the flanks and do not bear tubercles. 

FrOJn then1 pass pairs of 1nuch weaker secondary ribs 

that incline strongly forward. The body whorl bears 

deep constrictions and low forwn,rdly inclined primary 

ribs that fade out on the venter. 

The ventral lobe is longer than the first lateral lobe. 

The second lateral lobe is a little shorter. The saddles 

are nulCh wider than the lobes. The first lateral saddle 

is unevenly divided into a large outer branch n,nd a 

s1nall inner branch. 

At a dia1nete.r of 94 m:m, the whorl height is 24 nun 

and the umbilical width is 52 1nn1. 

'I'his specimen shows considerable resmnblance to 

Glyphosphinctes glyphus Buclonan (1925, pl. 544) which 

Arkell (1958, p. 168) provisionally assigns to the 

subgenus PTtJTsisphinctes. It differs in its sparser and 

wen,ker ribbing that tends to fade n1ore on the venter 

of the larger whorls. In this respect it shows more 

resemblance to Leptosphinctes davidsoni Buckn1an 

(1921, pl. 201), but it differs by having slightly stronger 

ribbing and by lacking tubercles on its outer septate 

whorls. As its innern1ost whorls are not preserved, 

the presence or absence of tubercles cannot be denlonstrated, ttnd hence the subgeneric assignment to 

P·rorsisphinctes is u 11 certain. 

Ty11e.-Holotype USNM 130901. 

Occurrence.-Lower part of the Bowser member of the Tuxedni 

formation at USGS Mesozoic loc. 21318. 

Leptosphinctes 1 sp. 

Plate 5, figure 5 

One internal 1nold of an immature ammonite has 

much coarser ribbing than the other specimens of 

Leptosphinctes described herein. It is highly evolute, 

bears several weak constrictions per whorl, and the 

pri1nary ribs tenninate in tubercles just below the 

mnbilical seam. From these pass pairs of secondary 

ribs. The characteristics of the middle part of the 

venter are unknown. The coarseness of the ribbing 

is comparable with that on Bigotites hennigi Bentz 

(1925, p. 180, pl. 9, figs. 1-4) from northern Germany. 

Figured specimen.-USNM 130905. 

Occurrence.-Lower part of the Bowser member of the Tuxedni 

formation at USGS Mesozoic loc. 21314. 

REFERENCES 

Arkell, W. J., 195Q-58, English Bathonian ammonites: Palaeont. 

Soc. Pub., 264 p., 33 pis., 83 figs. 

--- 1956, Jurassic geology of the world, 806 p., 46 pls. 28 

tables, 102 figs. 

--- 1957, in Arkell, W. J., Kummel, Bernhard, and Wright, 

C. W., Mesozoic Ammonoidea: Treatise on Invertebrate 

Paleontology, Part L, Mollusca 4, 490 p., illus. 

Bentz, Alfred, 1925, Die Garantienschichten von Norddeutschland mit besonderer Berucksichtigung des Brauneisenoolith 

horizontes von Harzburg: Preuss. Geol Landesanstalt 

Jahrb., v. 45, p. 119-193, pls. 4-9. 

Boehm, Georg, 1912, Beitrage zur Geol. von Niederlandischen 

Indien, Abt. 1 Die Si.idki.isten der Sula-Inseln Taliabu und 

Mangoli, Abschnitt 4, Unteres Callovien: Palaeontographica, Supp. 4, p. 123-179, pls. 32-44. 

Buckman, S. S., 1909-30, Type ammonites: London, private 

pub., 7 v. 

Burckhardt, Carlos, 1927, Cefalopodos del Jurasico de Oaxaca 

y Guerrero: Inst. geol. Mexico Bol. 47, 108 p., 34 pis. 

Burckhardt, Carlos, 1930, Etude syntheque sur le Mesozoique 

Mexicain: Abh. Schweizer. Palaeont. Gesell., v. 49, p. 

1-123; v. 50, p. 125-280. 

Callomon, J. H., 1959, The ammonite zones of the middle 

Jurassic beds of East Greenland: Geol. Mag., v. 96, no. 

6, p. 505-513, pls. 17, 18. 

Dorn, Paul, 1927, Die amm_oniten fauna der Parkinsonienschichten bei Thalmassing (Frankenalb): Preuss. Geol. 

Landesanstalt Jahrb., v. 48, p. 225-251, pls. 4-7. 

Erben, H.K., 1956, El Jurasico Medio y el Calloviano de Mexico: 

Internat. Geol. Cong., 20th, Mexico, D. F. 

Frebold, Hans, 1957, The Jurassic Fernie group in the Canadian 

Rocky Mountains and foothills: Canada Geol. Survey Mem. 

287, 197 p., 44 pls., 5 figs. 

Imlay, R. W., 1952, Correlation of the Jurassic formations of 

North America, exclusive of Canada: Geol. Soc. America 

Bull., v. 63, p. 953-992, 2 correlation charts. 

--- 1953, Callovian (Jurassic) ammonites from the United 

States and Alaska. Part 2. Alaska Peninsula and Cook 

Inlet regions: U.S. Geol. Survey Prof. Paper 249-B, p. 

41-108, pls. 25-55, figs. 3-9, 6 tables. 

--- 1961, New genera and subgenera of Jurassic (Bajocian) 

ammonites from Alaska: Jour. Paleontology, v. 35, no. 

3, p. 467-474, pls. 63-64. 

Jaworski, Erich, 1926, La Fauna del Lias y Dogger de la Cordillera Argentina en Ia parte meridional de la Provincia 

de Mendoza: Aetas Acad. Nac. Cienc. (Cordoba), v. 9, 

nos. 3, 4, p. 138-319, pl. 1-4. 

Loczy, Ludwig von, 1915, Monographie der Villanyer Callovien-Ammoniten: Geologica Hungarica (Budapest), v. 1, 

pt. 3, 4, p. 255-502, pls. 1-14. 
A-14 JURASSIC AMMONITES FROM SOUTHERN ALASKA 

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

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

Orbigny, Alcide d', 1842-51, Paleontologie de FranQaise: Terrains Jurassiques, v. 1, 642 p., 234 pls. 

Potonie, Robert, 1929, Die ammonitischen Nebenformen des 

Dogger (Apsorroceras, Spiroceras, Parapatoceras) : Preuss. 

Geol. Landesanstalt Jahrb., v. 50, p. 216-261, pls. 17-19. 

Roche, Pierre, 1936, Aalenien et Bajocien du Maconnais: Lyon 

Univ. Lab. geologie, Travaux, pt. 35, Mem. 29, 355 p., 

13 pls. 

Roman, Frederic, 1938, Les Ammonites Jurassiques et 

Cretacees, 554 p., 53 pls. 

Roman, Frederic, and Petourand, C., 1927, Etude sur la fauna 

du Bajocien superieur du Mont d'Or Lyonnais (Ciret), 

Cephalopodes: Lyon Univ. Lab. geologie Travaux, pt. 11, 

Mem. 9, p. 5-55, pls. 1-7. 

Westermann, Gerd. 1954, Monographie der Otoitidae (Ammonoidea): Beihefte zum Geol. Jahrb., No. 15, 364 p., 

33 pls. 

--- 1956a, Monographie der Bajocien Gattungen Sphaeroceras und Chondroceras (Ammonoidea): Beihefte zum 

Geol. Jahrb., No. 24, p. 1-122, pls. 1-14, 67 figs., 4 tables. 

--- 1956b, Phylogenie der Stephanocerataceae und Perisphinctaceae des Dogger: Neues Jahrb. Geologie u. 

PaHi.ontologie Abh. 103, p. 233-279, 9 figs., 2 tables. 
Page 

A mberleya •••• ------ ________ . -----.----... •• •. A-2 

ambigmts, Inoceramus ..•.• --- __ --------------. Astarte •••••• ---••• ______ •. ____ .--------•.•... 

bakeri, Lissoceras ____________________________ 6; pl. 1 

blfttrcatnm, Cosmoceras ••• _ ------------------- 3 

Bigotites. __ •••• --------•• ----- _______ --- ____ .. 4 

hennigi.. --------------------------------- 13 

brongniarti, S7Jhaeroceras •••• -----•••••• ----.• • 11 

Cadomites •• _ •••••••••. ---------.. __ • ------... 2, 4 

da?tbenyi. ••.•• ---------•••••. ____ . --.---.. 4 

Cactomoceras .•••..••• _______________ •. --.• •. . . 4 

Calli·phylloceras freibrockL. .•... __ -----•••.. --. 6 

SP-------------------------------------- 6; pl. 1 

Cattmontis1Jhinctes ••••• ---- __________ .• ------- 4 

ChlniLna foi'IIHLtion ... ------------------------ 2, 5 

Chonctroceras •••••••.••. -----------.----------- 3, 11 

Cleistos1Jhinctes •• ------------.----------...... 4 cliffensis, Leptos1Jhinctes ____________________ 113; pl. 5 

coronarins, Le1JtOS1Jhinctes .•• ------------------ 12, 13 

Cosmoceras bif?trcat·~tm________________________ 3 

(Strenoceras) •••.•••• ------•• ----. .• •• •• . . . 3 

Cranoce1Jhalites •• -------------------••• --•.. 1, 2, 3, 4 

ctcmbenyi, Caclomites ••••• _______________ ---- __ . 

da11idsoni, Le1Jtosphinctes ••••..• _______________ 13 

clclicatns, J~eptos1Jhinctes (Prorsis1Jhinctes) ... 13; pl. 5 

Dettermanites ••••• ------•••... ______ •.. ----.. 2, 4, 113 

vigorostts.------------------------------ 113; pl. 4 

ctorni, PolU1Jlectites •••• --------- ______ --------- 12 

lET'lnoceras. _ ---•••••• --.-----------•• ---------

fcdla:t, 07Jpelia (Oxycerites) .. ------------------

freibrocki, Calli1Jhylloceras.--------•••• -----... 6 

Garantia ••• -----------------------------------

Garantiana ••. -------------------------------- globus, S7Jhaeroceras •••. --.••••••... ------..... 11 

GlU1JhOs1Jhinctes gly7Jh1ts ••.••..... --.• --------- 13 

gly7Jhns, GlU1JhOs1Jhinctes .. -------.------------ 13 

grossicostat?tm, A1"acro1Jhylloceras •••.. -------- 6; pl. 5 

:Hnplocoratlduo .•••••••.•• ------.. __ ---------. 2 

hennigi, Bigotites •• ------------------·--------- 13 

htt7117Jhriesimmm, Ste7Jhanoceras ... ------------ 2,11 

Inoceram·~ts ambigmts •••••• ____ •••• ----------. 

intricatnm, Labyrinthoceras ••.. ---------------- 10, 11 

Isocy1Jrina •• ------•.•• -----------••.••••• --.-- 2 

INDEX 

[Italic numbers indicate descriptions] 

Page 

kellumi, Oppeiia (Liroxyites).-------- A-3, 8, 9; pl. 2 

knapheuticus, Oxycerites ..• -------------------- 9 

Labyrinthoceras intricatum .. ------------------ 11, 12 

Leptosphinctes .. -------------------------- 2, 4, 113, 13 

cli/fensis ... ---------------------------- 113; pl. 5 

davidsoni.. ..... --------------------------- 13 

coronarius .. _____ .. ______ . ---------------- 12, 13 

leptus ------------------------------------- · 12 

SP------------------------------------- 13; pl. 5 

(Prorsisphinctes) delicatus.------------- 13; pl. 5 

(Vermisphinctes) vermiformis______________ 12 

Lcptosphinctinae ... -------------------------- 3. 4 

leptus, Leptosphinctes.------------------------ 12 

Lima .. __________________ --------------------- 2 

(Plagiostoma) .. --------------------------- 2 

Liroxyites ... ___________ --·. -----.------------- 2, 8 

(Liroxyites) kellumi, Oppelia ____________ 3, 8, 9; pl. 2 

Oppelia ... -------------------------------- 2, 8 

Lissoceras ..... -------------------------------- 2, 4, 7 

bakeri ... -------------------------------- 6; pl. 1 

oolithicum ____ ---------------------------- 7 

Lytoceras sp ... ___ . _______ ----.---------.----- 6 

Lytoceratidac. __ -----------------------------

Macrophylloceras grossicostatum _____________ 6; pl. 5 

Magharina .... -------------------------------- 4 Megasphaeroceras _____________________________ 2, 4, 9 

rotundum ... ------------------------ 10, 11; pl. 3 

Morphoceras ___________ -- _-- ----.------------. 4 

Normannites •.. ------------------------------ 3, 4, 12 

Oecotraustes _____ -------.. ------.-------------- 4 

oolithicum, Lissoceras ___ . __ ------- __ . --------. 7 

Oppelia ____ -- __ ---- ___________ ------.--------- 4 

subradiata. __ . _________ ------------- _ -- __ - 3 

(Liroxyites) ______ . ___________ ---- _______ -- 2, 8 

kellumi_ ________________________ 3, 8, 9; pl. 2 

( Oppelia) __________ ---------------------- _ 3 

(Oxycerites).------------------------------ 2, 3, 8 fallax _ ----- _ __ _ __ _ _ __ __ __ __ __ __ ____ _ _ _ 9 

(Oppelia), Oppelia ________________ ------------ 3 

Oppcliidac ____ ------------------------------- 1 

Oxycerites ... ---------------------------------- 4, 8, 9 

knapheuticus _______ ___ -- __ ---- _ ___ _ __ __ __ _ 9 

tilli_-------------------------------------- 9 

(Oxycerites) fallax, Oppelia .. ------------------

Oppelia ... -------------------------------- 2, 3, 8 

Oxytoma ____ ------- ________ . ------------------ 2 

Oxycerites ... --- ____________ ----------.• ------- 2 

Page 

Parabigotites ..•. ----------- __ ----------------. A-2 

Parkinsonia. _. ------------------------------- 4 

Parkinsoniidae. _ ----------------------------. 4 

Perisphinctidae _____ . ---------------. __ ------- 2, 3 

Phylloceratidae _____ ------ ____ . ______ -------.. 2 

(Plagiostoma), Lima_________________________ 2 

Pleuromya ____ _ ........ _ ........ _- _.--.-------

Polyplectites. -------------------------------- 2, 4,12 

dorni. _ ----------------------------------- 12 

Prorsisphinctes --- _............................ 4 

(Prorsisphinctes) delicatus, Leptosphinctes ..• 13; pl. 5 

Pseudogarantia ... --------- _________ . __ . ------ 4 

rotundum, Megasphaeroceras. ----------- 10, 11; pl. 3 

Sonninia. _ ----------------------------------- 3 

Sphaeroceras •. ------------------------ 2, 3, 4, 9, 10, 11 

brongniartL---------------------.. ------- 11 

globus __ . __ --------------------. ___ ------- 11 talkeetnanum ___________________________ 11; pl. 5 

tutthum _______ --- ____ --------------------. 11 

Sphaeroceratidae .. __ -------------------.---.. 

Spiroceras .... -------------------------------- 2, 4, 6 

sp. ---------------------------------.. ·-- 6; pl. 1 

S piroceratidae. _. _ ... _. _. __ .. _ .......... __ •... 2 

Stephanoceras .•. ------------------------------ 3, 4 humphriesianum__________________________ 2, 11 

Stephanoceratidac .. ----- ___ • ----------------- 2 

Strenoceras ___ ----------.----------------... -- 4 

(Strenoceras), Cosmocl}ras __ ------------------- 3 

Strigoceras. -------- _________________ ---------- 4, 9 

subradiata, Oppelia. -------------------------- 3 

talkeetnanum, Sphaeroceras _________________ 11; pl. 5 

Teloceras .. ----------------------------------- 3, 4 

Thamboceras ... __ -----.-.- __ ------ __ ----------. 4 

tilli, Oxycerites _ ------------.. -------.--------- 9 

Trimargina_ --------------- ______ ~- ----•.. ---. 

tutthum, Sphaeroceras.------------------------ 11 

Tuxedni formation, Bowser member---------- 2, 3, 5 

Cynthia Falls sandstone member--------- 2, 3 

vermiformis, Leptosphinctes ( Vermisphinctes) _ _ 12 

Vermisphinctes .. ----------------------------- 4 

( Vermisphinctes) vermiform is, Leptosphinctes.. 12 

vigorosus, Dettermanites .. ------------------ 113; pl. 4 

Witchellia .. -------------- -----~---- ----------. 3 

Zemistephanus ••.. -~ ___ -- __ ------------------- 3 

A-15 
PLATES l-5 
PLATE 1 

[Figures natural size unless otherwise indicated] 

FIGURES 1-6, 9-12. Lissoceras bakeri Imlay, n. sp. (p. A-6). 

1, 2. Paratype USNM 130894 from USGS Mesozoic loc. 22709. 

3. Paratype USNM 130893a from USGS Mesozoic loc. 21282. Offset marks beginning of crushed body chamber. 

4, 6. Paratype USNM 130893b from USGS Mesozoic loc. 21282. Offset marks beginning of crushed body chamber. Suture line (X 2) 

drawn at whorl height of 31.5 mm. 

5, 9, 11, 12. Holotype USNM 130891 from USGS Mesozoic loc. 

11034. Suture line (X 2) drawn at whorl height of 47 mm. A 

small part of the large septate whorl has been removed to show the 

next inner whorl. 

10. Paratype USNM 130892 from USGS Mesozoic loc. 19934. Shows 

slightly more than half a whorl of the body chamber. 

7. Spiroceras? sp. (p. A-6). 

Figured specimen USNM 130908 from USGS Mesozoic loc. 21282. 

Side view. 

8. Calliphylloceras sp. (p. A-5). 

Figured specimen USNM 130906 from USGS Mesozoic loc. 21315. 
GEOLOGICAL SURVEY 

1 2 

(' 

' 

. ' 

3 

PROFESSIONAL PAPER 418- A PLATE I 

( 

\ 

4 

LISSOCERAS, SPIROCERAS ?, AND CALLIPHYLLOCERAS 
PLATE 2 

[Figures natural size unless otherwise indicated] 

FIGuRES 1-12. Oppelia (Liroxyites) kellumi Imlay (p. A-8). 

1-4. Sutured paratype USNM 130888 from USGS Mesozoic loc. 19943. 

Apertural, lateral, and ventral views. 

5. Suture line (X 2) of paratype USNM 130889a from USGS Mesozoic 

loc. 21318 drawn at whorl height of 28 mm. 

6. Holotype USNM 130886 from USGS Mesozoic loc. 20001. Shows 

complete body chamber occupying half a whorl and eccentric coiling. 

7, 8. Paratype USNM 130889b from USGS Mesozoic loc. 21318. 

9. Suture line (X 2) of paratype, USNM 130889c from USGS Mesozoic 

loc. 21318. 

10, 12. Paratypes USNM 130887a, b from USGS Mesozoic loc. 20001. 

Show eccentric coiling of adult body chamber. Fig. 10 shows crenulations oil the keel. 

11. Paratype USNM 130890 from USGS Mesozoic loc. 11035. Shows 

ribbing of an inmature specimen. 

e 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 418- A PLATE 2 

4 

OPPELIA (LIROXYJTES) 
PLATE 3 

[Figures natural size unless otherwise indicated] 

FIGURES 1, 4-12. Megasphaeroceras rotundum Imlay (p. A-10). 

1. Paratype USNM 130899a USGS Mesozoic loc. 21314. Shows constriction and contraction of body whorl at aperture. Note how the 

sharpness of the ribbing where shell is preserved contrasts with the 

weak ribbing on the internal mold. 

4, 7, 9. Holotype USNM 130898 from USGS Mesozoic loc. 21314. Note 

smoothness of internal mold on body chamber. Suture line (X 2) 

drawn at whorl height of 31 mm about one-quarter of a whorl from 

the body chamber. 

5, 6. Paratype USNM 130899b from USGS Mesozoic loc. 21314. Shows 

the sharp ribbing typical of the shell of most immature specimens. 

8. Paratype USNM 130900 from USGS Mesozoic loc. 21318. Shows 

finer denser ribbing than most immature specimens of the species. 

10. Paratype USNM 130899c from USGS Mesozoic loc. 21314. Shows 

the weak ribbing on the internal mold of a large adult whorl. 

11, 12. Paratype USNM 130899d from USGS Mesozoic loc. 21314. 

Shows ribbing intermediate in coarseness between that shown on figs. 

6 and 8. Note absence of ribbing where the shell is removed. 

2, 3. Megasphaeroceras cf. M. rotundum Imlay (p. A-ll). 

Figured specimen USNM 130904 from USGS Mesozoic loc. 19934. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 418-A PLATE 3 

MEGASPHAEROCERAS 
PLATE 4 

[Figures natural size unless otherwise indicated] 

FIGURES 1-9. Dettermanites vigorosus Imlay (p. A-12). 

1-3. Paratype USNM 130897a from USGS Mesozoic loc. 11036. Shows 

ornamentation of inner whorls and beginning of body chamber. 

4, 7, 8. Holotype USNM 130895 from USGS Mesozoic loc. 21318. The 

suture line (X 2) was drawn at a whorl height of 18.5 mm about onethird of a whorl from the adoral end of the outermost septate whorl. 

5, 6. Paratype USNM 130896 from USGS Mesozoic loc. 8572. Shows 

half a whorl of the adult body chamber from which a small part has 

been removed. 

9. Paratype USNM 130897b from USGS Mesozoic loc. 11036. 
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[Figures natural size unless otherwise indicated] 

FIGURES 1-4. Sphaeroceras talkeetnanum Imlay, n. sp. (p. A-11). 

Holotype USNM 130902 from USGS Mesozoic loc. 9572. Lateral, ventral (2 views) and apertural views. The sinuous ventral margin of the 

aperture is shown on fig. 2. 

5. Leptosphinctes? sp. (p. A-13). 

Figured specimen USNM 130905 from USGS Mesozoic loc. 21314. 

6, 7. M acrophylloceras cf. M. grossicostatum Imlay (p. A-5). 

Figured specimen USN M 130903 from USGS Mesozoic loc. 21313. Partial 

suture line drawn at whorl height of 29mm. 

8, 9. Leptosphinctes (Prorsisphinctes?) delicatus Imlay, n. sp. (p. A-13). 

Holotype USNM 130901 from USGS Mesozoic loc. 21318. Suture line 

(X 2) drawn at whorl height of 14 mm. 

10, 11. Leptosphinctes clijfensis Imlay, n. sp. (p. A-12). 

Holotype USNM 130907 from USGS Mesozoic loc. 21315. Suture line 

(X 2) drawn at whorl height of about 13 mm near middle of outermost 

septate whorl. 
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SPHAEROCERAS, LEPTOSPHINCTES, AND MACROPHYLLOCERAS