A NEW FAUNA FROM THE COLORADO GROUP OF SOUTHERN MONTANA. 

By JoHN B. REESIDE, Jr. 

INTRODUCTION. 

This paper describes a small but interesting 

fauna collected in 1921 by W. T. Thorn, jr., 

Gail F. Moulton, T. W. Stanton, and K. C. 

Heald in the Crow Indian Reservation in 

southern Montana. The locality is in sec. 36, 

T. 6 S., R. 32 E ., Big Horn County, and is 2 

miles east of the Soap Creek oil field. 

The stratigraphic section in the Soap Creek 

oil field was described briefly by Thorn and 

Moulton in a press notice issued by the United 

States Geological Survey December 5, 1921, 

entitled "The Soap Creek oil field, Crow Indian 

Reservation, Mont." It was described also in 

a later and more general paper. 1 The youngest 

beds present near the oil field belong to the 

Niobrara formation, but in the adjacent parts 

of the Crow Reservation to the east and north 

higher formations are present and are in part 

included in the section given below. The part 

of the section from the Cloverly formation to 

the Niobrara formation, inclusive, is derived 

frmn the publications mentioned above and 

from data kindly supplied by Mr. Thorn. The 

thicknesses given for the Eagle sandstone and 

the Telegraph Creek formation apply especially 

to the vicinity of Pryor Creek, some 30 miles 

north of the Soap Creek oil field. The included 

lists of fossils are based on the writer's determinations. 

.Partial section of forma:tions exposed in the Crow Indian 

Reservat-ion, Mont. 

Feet. 

:Eagle sandstone ............................ . ... 200-250 

Sandstones and some shales; at base the massive 

Virgelle sandstone member. This formation contains Scaphites hippocrepis (Dekay), Scaphites n. 

sp. aff. S. aquisgranensis Schlueter, Inoceramus 

aff. I. lobatus Goldfuss, Placenticeras syrtale (Morton), Placenticeras meeki Boehm, Placenticeras 

planum Hyatt, Baculites ovatus Say, Baculites 

asper Morton, Baculites n. sp. aff. B. anceps 

Lamarck, and many other fossils. 

1 Thorn, W. T., jr., Oil and gas prospects-in and near the Crow Indian 

·Reservation, Mont.: U. S. Geol. Survey Bull. 736, pp. 35-53, 1922 

·(Bull. 7313-B) 

Feet. 

Telegraph Creek formation......... . . . . . . . . . . . . . 320-350 

Sandstones and shales. This group of beds contains at places in the upper part a fauna like that 

of the Eagle sandstone, but in the lower beds it 

contains Uintacrinus sp., Marsupites sp. (identified by Frank Springer), Inoceramus dejormis 

Meek var., Ostrea cf. 0. congesta Conrad, Baculites 

sp., Puzosia (Latidorsella) n. sp., and Scaphites n. 

sp. aff. S. geinitzi D'Orbigny. • 

Niobrara formation (top formation of Colorado 

group)"........................................ 400 

Bluish calcareous shale in upper and lower 

parts; dark shale in middle. In the upper part it 

contains Uintacrinus socialis Grinnell (identified 

by Frank Springer), Yoldia sp., Inoceramus, large 

thick-shelled species, Ostrea congesta Conrad, 

Lunatia concinna (Hall and Meek), Tessarolax cf. 

T. hitzi White, Baculites sp., Scaphites vermiformis Meek and Hayden, and fish scales. In the 

middle part it contains Inoceramus aff. I. lamarcki 

Parkinson, Inoceramus umbonatus Meek and Hayden, Inoceramus, large thick-shelled species, 

Pteria aff. P. nebrascensis (Evans and Shumard), 

Anatina aff. A . subgracilis (Whitfield), Veniella 

goniophora Meek, Cardium n. sp., Fusus sp., Volutoderma sp., Baculites aff. B. anceps Lamarck, 

Baculites asper Morton, Scaphites vermiformis Meek 

and Hayden. In the lower part it contains 

Inoceramus, large thick-shelled species, Ostrea 

congesta Conrad, and the basal bed, a zone of large 

yellow concretions, contains Yoldia sp., Nemodon 

sp., Barbatia n. sp., Inoceramus jragilis (Hall and 

Meek)?, Inoceramus (Actinoceramus) n . sp., Veniella goniophora Meek, Callista tenuis (Hall and 

Meek), Corbula cf. C. nematophora Meek, Dentalium sp., Gyrodes aff. G. petrosa (Morton), Turritella aff. T. whitei Stanton, Anchura sp. ,· Nautilus 

sp., Baculites sp., and Scaphites vermiformis Meek 

and Hayden. 

Carlile shale..... . ............................... 425 

This formation may be divided into a number of 

units as follows:. 

Dark shale with whitish septarian nodules containing Inoceramus labiatus (Schlotheim), Ven,iella goniophora Meek, Corbula aff. C. nematophora Meek, Pseudomelania? sp., Fusus sp., 

Prionocyclus wyomingensis Meek. Thickness 50 

feet. 

Zone of large yellowish · sandstone concretions. 

Thickness 5 feet. 

Dark shale. Thickness 35 feet. 

Shale with thin hard rusty red concretions and 

layers containing Inoceramus fragilis Hall and 

25 
26 SHORTER CONTRJBUTIONS TO GENERAL GEOLOGY, 1923. 

Meek, Inoceramus cf. I. lamarcki Parkinson, 

Veniella sp., Volutoderma? sp., Baculites gracilis 

Shumard, Scaphites warreni Meek and Hayden, 

Prionotropisaff. P. woolgari (Mantell). Thickness 

30 feet. · 

Dark shale. Thickness 60 feet. 

Bluish calcareous shale containing in ita lower 

part the fauna described in this paper. Thickness 100 feet. 

Dark shale and bentonite. Thic~ss 145 feet. 

Feet. 

Frontier formation...... . . . . . . . . . . . . . . . . . . . . . . . . . 410 

Chiefly dark shale with bentonite but with a 

zone of thin coarse sandstones near the top. 

Shark teeth the only fossils observed. 

Mowry shale.... . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . 200-300 

Hard bluish-white sha1e with layers of hard dark 

shale. Contains abundant :fish remains but ~ew 

other fossili. 

Thermopolis shale.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 550-800 

Dark marine shale with streaks and lenses of 

light-colored sandstone containing Inoceramus 

labiatus (Schlotheim), Pteria aff. P. nebrascensis 

(Meek and Hayden), Ostrea sp., Entolium sp., Modiola n. sp., Gyrodes aff. G. depressa Meek, fish and 

turtle remains. Middle part of formation of dark 

clay and bentonite ;lowerpartofdarkmarineshale. 

Cloverly formation. . ... . . . . . . . . . . . . . . . . . . . . . . . . 320-425 

An upper member of sandy shale and thin-bedded rusty sandstone that may represent the 

Dakota sandstone of Upper Cretaceous age. 

A middle member consisting of variegated shale 

where exposed along the Big Horn Mountains and 

containing Unio sp. and Viviparusf sp. and a 

basal member of thick coarse-grained conglomeratic sandstone. These divisions may repre- . 

sent the Fuson shale and Lakota sandstone, of 

Lower Cretaceous age. 

THE FAUNA AND ITS RELATIONS. 

The collection described in this paper contains five species of ammonites referred to 

three genera, two species of Inoceramus, an 

ostreid, and a gastropod. 

The species are as follows: 

V ascoceras thomi Reeside, n. sp. 

Vascoceras moultoni Reeside, n. sp. 

Vascoceras stantoni Reeside, n. sp. 

V ascoceras sp. undeterminable. 

Pseudotissotia (Choffaticeras) sp.? 

Helicoceras pariense White? 

Inoceramus labiatus (Schlotheim). 

Inoceramus sp. undetermined. 

Ostrea or Exogyra sp. 

Gastropod, undetermined. 

This fauna is known from only this one 

locality in the Western Interior province of 

North America, and consequently its correlation must rest in large part on its position with 

relation to other faunal zones in the same 

stratigraphic section and in the adjacent 

region. It is therefore of interest to consider 

some of the faunal zones recognizable in the 

Cretaceous deposits of this province. 

A series of more or less widespread and more 

or less distinctly defined faunal zones have 

long been recognized in the Cretaceous deposits of the Western Interior. The lowest 

zone to be considered here is well characterized 

only in the southern part of the province, where 

it contains Exogyra columbella Meek and 

Gryphaea newberryi Stanton as its guide fossils. 

This zone includes the Graneros shale of the 

central Great Plains, the basal part of the 

Mancos shale of New Mexico, Colorado, and 

Utah, and the Thermopolis shale of the north. 

At many places, especially in the north, it is 

nearly barren of fossils, and those present are 

not sufficiently restricted to serve as guide 

fossils. 

Above this zone occurs a zone with an 

abrindance of Inoceramus labiatus (Schlotheim). 

In the central Great Plains region this zone is 

contained in the Greenhorn limestone, and 

very few other fossils than the guide fossil 

have been found in it. In western Colorado 

and the adjacent region it is well marked in 

the lower part of the Mancos shale. It occurs 

in southern and central Wyoming in the 

Frontier formation and in northern Montana 

in the lower part of the Colorado shale. 

Above this zone of Inoceramus labiatuslies a 

zone which contains as its more prominent and 

restricted species Scaphites warreni Meek and 

Hayden, several species each of Prionotropis, 

and Prionocyclus, Inoceramus fragilis Hall and 

Meek, Inoceramus dimidius White, and Ostrea 

lugubris Conrad. It very rarely co~tains 

Inoceramus labiatus (Schlotheim). This zone 

is perhaps the most sharply defined and most 

widely .recognized of the series. It comprises 

the entire Carlile shale of the central Great 

Plains and Black Hills regions, part of the 

Mancos shale of western Colorado and adjacent 

regions, the Carlile shale of Wyoming, and part 

of the Colorado formation of Montana. 

Above the zone of Scaphites warreni comes a 

zone which contains Uintacrinus socialis Grinnell, Inoceramus umbonatus Meek and Hayden, 

Inoceramus deformis Meek, and, especially in 

the north, Scaphites ventricosus Meek and 

Hayden and Scaphites vermiformis Meek and 

Hayden. A very abundant and locally restricted form of this zone is Ostrea congesta 
A NEW FA UN A FROM THE COLORADO GROUP OF SOUTHER.N MONTANA. 27 

Conrad. Inoceramus labiatus is reported in the 

literature as occurring here also, but it has not 

been found in numerous recent collections, and 

its earlier assignment to the fauna of this zone 

is very probably due to the erroneous reference 

of local exposures of the Greenhorn limestone 

to the Niobrara formation inN ebraska, Kansas, 

and elsewhere prior to Darton's work in that 

region. In this zone falls the Niobrara formation of the Great Plains region, part of the 

Mancos shale of western Colorado and the' 

adjacent regions, the Niobrara formation of 

Wyoming, and the upper part of the Colorado 

shale of northern Montana. 

Above this zone of Uintacrinus and Scaphites vermifor'mis comes a zone containing 

Scaphites hippocrepis (DeKay), Scaphites n. sp. 

aff. S. aquisgranensis Schlueter, Placenticeras 

syrtale (Morton) and its allies, Placenticeras 

planum Hyatt, and Inoceramus aff. I. lobatus 

Goldfuss. In New Mexico this zone has 

yielded also Mortoniceras aff. Jf. delawarense 

(Morton). In Montana and in southwestern 

Colorado and adjacent parts of New Mexico 

there is a subzone at the base of this zone which 

lacks Scaphites hippocrepis and Scaphites aff. 

S. aquisgranensis but which contains Scaphites 

n. sp. aff. S. geinitzi D'Orbigny as its most 

distinctive form. The zone of Scaphites hippocrepis is represented by the Eagle sandstone 

and Telegraph Creek formation of southern 

Montana, part of the Cody shale of northern 

Wyoming, part of the Steele shale of central 

and southern Wyoming, and the upper part 

of the Mancos shale of southwestern Colorado 

and adjacent New Mexico. Presumably the 

basal part of the Pierre shale of the central 

• Great Plains and Black Hills regions rep resents 

this zone, though the distinctive· species have 

not been found in it except in northeastern 

New Mexico. Above the zone of Scaphites 

hippocrepis other faunal zones may be recognized but will not be described in this paper. 

The stratigraphic section at the Soap Creek 

oil field and in the adjacent country, as shown 

in the section given on page 25, has afforded 

enough paleontologic data to determine the 

relative position of the fossils described in this 

paper. The beds containing the fauna include 

the highest bed in which Inoceramus labiatus 

occurs abundantly and lie immediately beneath 

beds with the characteristic fauna of the zone of 

Scaphites warreni. They are therefore to be 

correlated with at least the upper part of the 

Greenhorn limestone of the central Great 

Plains, though the occurrence of Inoceramus 

labiatus in beds some 800 feet lower in the 

section raises a doubt whether the beds COJ}-

taining Vascoceras represent all of the Greenhorn limestone as developed at such localities 

as those in eastern Colorado, where the Greenhorn limestone contains the only beds in 

which Inoceramus labiatu~ occurs, is only about 

50 feet thick, and is separated from the Dakota 

sandstone by scarcely 200 feet of Graneros 

shale. It is possible that the relatively great 

thickness of Graneros shale present in the 

Black Hills region beneath the Greenhorn 

limestone is due entirely to greater deposition 

of material to form the shale without an appreciably greater lapse of time and that the 

Greenhorn limestone, which does not change 

much in thickness over the whole region, 

represents approximately the same time interval everywhere. If so, the beds containing 

Vascoceras may represent all the time interval 

of the Greenhorn limestone and its equivalents 

in various parts of the Western Interior. In 

central Montana the Mosby sandstone member 

of the Warm Spring shale 2 occupies a position 

in the section similar to that of the beds containing Vascoceras. Inasmuch as the faunas 

of the two units have in common only Inoceramus labiatus they do not help in deter-

·mining the relations between them. Perhaps 

the only suggestion offered is the occurrence 

of Metoicoceras whitei Hyatt in the Mosby 

sandstone. This species is most abundant 

in and most characteristic of the lower part 

of the Colorado group ' in southern Utah and 

in New Mexico and may indicate that the 

conditions which permitted the northward 

extension of Vascoceras as far as southern 

Montana were the same as those which permitted Metoicoceras to reach central Montana 

and that the Mosby sandstone and the beds 

containing V ascoceras represent the same time. 

The only other occurrence of V ascoceras in 

North America is that at Cerro del Macho, in the 

State of Coahuila, Mexico, described by Bose. 3 

Here the associated fossils are more numerous, 

though none of the species seem to be identical 

with those from Montana, except Inoceramus 

Zabiatus. Bose has given a good summary 

~U.S. Geol. Survey Bull. 736, p.l72, 1922 (Bull. 736-F). 8 Bose, Emil, On a new ammonite fauna of the lower Turonian of 

Mexico: Texas Univ. Bull. 1856, pp. 173-257, 1918. 
28 SHORTER CONT'R.IBUTIONS TO GENERAL GEOLOGY, 1923. 

of the distribution of the Vascoceras fauna and 

of its composition in all its principal occurrences. The fauna in its fullest and most 

typical development contains species of the 

~mmonite genera Fagesia, Vascoceras, Mammites, Pseudaspidoceras, Neolobites, Pseudotissotia, Hoplitoides, and Thomasites. It is 

the Salmurian fauna of the European geologists and is widely distributed in the Mediterranean region. It occurs in the lower and 

middle Turonian of Portugal; the lower 

Turonian of Algeria, Tunis, and Egypt; the 

Turonian of the southern Sahara region; and 

in Brazil, Colombia, Peru, and Mexico. Faunas 

more or less related though not yet reported 

to contain Vascoceras occur in the Turonian of 

southern France, in India, and in Japan. 

A comparison of the faunal succession in the 

Western Interior province with that in western 

Europe suggests the following correlations: 

Western Interior. Europe. 

Z fs h. h" . {Lower Campanian. one o cap ttes tppocreptS. _____ . _ U S t . 

pper an oman. 

Zone of Uintacrinus, Inoceramus}L S t . 

b . d S h. . ower an oman. um onatus, an cap ttes vermt- 0 . . jormis. omac1an. 

Zone of Scaphites warreni. ______ . ____ Upper Turonian. 

Zone of Inoceramus labiatus (Vascoceras at top in Montana) _______ .. _ Lower Turonian. 

Apparently the present occurrence of Vascoceras would agree with the accepted assignment of the other known occurrences to the 

lower Turonian. It might be middle Turonian, 

if such a unit were recognized, but scarcely 

younger. 

DESCRIPTIONS OF SPECIES. 

Genus VASCOCERAS Choffat. 

Choffat's original description4 is in part as 

follows: 

Genus formed by shells more or less thick, sometimes 

globular, with ventral region rounded, ornamented in 

youth by ribs giving rise to tubercles on the flanks and 

to tubercles or elongated swellings on each side of the 

siphon. With some rare exceptions ( Vascoceras subconciliatum), these lines of tubercles disappear in the adult 

stage, those of the umbilical border persisting longer, and 

the ventral region, or even all the visible part of the shell, 

is without ornamentation. . 

The length of the living chamber is from one-half to 

three-fourths of a whorl. 

The suture shows two broad, rounded, weakly incised 

saddles, the third saddle much less important than it 

4 Choffat, Paul, Les a:nmonees du Bellasien, des couches a Neolobites 

vibrayeanus, du Turonien, et du Senonien: Faune cretacique du Portugal, vol. 1, ser. 2,p. 53, 1898. 

would be if the decrease were regular. The lobes are 

broad and divided by small saddles, in general not 

incised. From the position of these saddles the first 

lobe may be ' considered as divided into two or three 

parts. The second lobe is either simple or divided into 

two. [Translated.] 

Choffat proposed four sections of the genus-

(a) monotuberculate forms with wide umbilicus, (b) subglobular forms with rounded 

umbilical border, (c) globular forms with 

angular or subangular umbilical border, (d) 

multituberculate forms. 

Pervinquiere 5 later discussed Vascoceras, 

modifying somewhat Choffat's original description. Pervinquiere's description is as follows: 

Shell more or less thick, sometimes globular, with 

ventral region rounded, ornamented, in youth, by ribs 

bearing umbilical tubercles and marginal tubercles; 

these tubercles become less distinct in the adult stage 

(the umbilical tubercles remain distinct longer) and 

even disappear completely except on one group. There 

is never a median ventral tubercle. Living chamber 

measuring three-fourths of a whorl or even more. * * * 

Suture including two broad, rounded, little incised 

saddles; the third much smaller. Lobes broad and 

divided by small unincised saddles. [Translated.] 

Pervinquiere recognizes only three sections 

of the genus: 

1. Group of V. gamai and of V. douvillei-durandi. 

Monotuberculate forms with wide umbilicus in. the first 

species and more restricted. in the second. There is 

every intermediate form between the two, as regards both 

general form and the greater or lesser rounding of the 

umbilical shoulder. · 

2. Group of V. harttijormis. Globular forms, with 

the umbilicus generally narrow, the umbilical shoulder 

more or less angular. 

3. Group of V. subconciliatum. Multituberculate forms, 

departing notably from the preceding and approaching 

Mammites and the extreme forms of Acanthoceras. 

Pervinquiere points out that Vascoceras 

differs from the nearly related genus Fagesia 

Pervinquiere in general form, in the much 

earlier disappearance of the ribs and tubercles, 

and especially in the suture. The suture of 

Fagesia · has four slender lateral saddles, 

rounded in the upper part and trifid in subdivision; three lateral lobes, of which the :first 

is profoundly bifid, the second less so,' and the 

third pointed. Pervinquiere adds, however, 

that some forms of Vascoceras are difficult to 

distinguish from Fagesia. 

5 Pervinqniere, Leon, Etudes cle paleontologie tunisienne, pt. 1, 

Cephalopodes des terrains secondaires, pp. 331-332, 1907. 
A NEW FAUNA FROM THE COLORADO GROUP OF SOUTHERN MONTANA. 29 

The specimens in hand from Montana are a 

bit c.onfusing in their relations. The general 

form, except perhaps for the width of the umbilicus, would permit an assignment to Fagesia, 

and the proportions and degree of incision of 

the suture fit those of Fagesia better than those 

of Vascoceras. Moreover, the umbilical tubercles are prominent, and there are traces of the 

ventral ribs in even the largest specimens. 

The younger whorls, however, show distinctly 

the umbilical and ventral tubercles of Vascoceras, the umbilicus is wider than shown in 

most of the figured specimens of Fagesia, and 

the suture in every specimen examined shows a 

pointed first and second lateral lobe, not bifid. 

The writer therefore assigns the specimens to 

Vascoceras rathe~ than to Fagesia and further 

would place the first two of the species here 

described under Pervinquiere's section 1 and 

the third under section 2. 

V ascoceras thomi Reeside n. sp. 

Plate XI, figures 1-2 ; Plate XII, figures 1-2; Plate XIII, 

figures 1-2; Plate XIV, figures 1-2 ; Plate XV, figures 

1-7; Plate XVI, figures 1-6. 

Shell stout, coronate. Earlier whorls not 

well shown in the type specimen except for the 

umbilical part, but apparently stout. Whorls 

above 115-millimeter diameter have a moderately depressed, oval cross section. Living 

chamber in type occupies three-fourths of a 

whorl and is apparently incomplete. Maximum diameter of type 165 millimeters. Umbilicus deep but fairly wide-about one-half 

the diameter of the shell in width. Umbilical 

shoulders rounded but well defined. 

Sculpture of earlier whorls of type specimen 

seen only in the umbilicus, where it consists of 

large blunt conical nodes, seven to the whorl. 

On the last whorl of the type faint coarse ribs 

connect the umbilical nodes and a faint flattening on the venter seems to correspond to the 

space between the marginal nodes of the 

younger stages. 

The suture shows a fairly broad ventral lobe 

and four lateral lobes and saddles, only moderately incised. The first later~llobe is bluntly 

pointed, and the first lateral saddle is trifid. 

A very large specimen (see Pl. XIII, figs. 1-2; 

Pl. XIV, figs. 1-2) assigned to this species has 

a maximum diameter of 260 millimeters and 

is apparently almost complete. The inner 

whorls are poorly preserved. The living cham333720-25-3 

ber occupies three-fourths of a whorl; the 

aperture is riot preserved. The suture of this 

specimen has wider saddles than those of the 

suture of the type but is otherwise like it. 

The umbilical nodes and obscure ventral ribs 

persist to the end of the specimen. 

A small specimen assigned to this species 

(see Pl. XV, figs. 1-7) shows the sculpture and 

form of the stages following that at the diameter of 25 millimeters. The whorls to a 

diameter of about 40 millimeters are as high as 

wide and have strong rounded ribs that begin 

at the umbilical nodes, pass with a slight 

forward curve to the margin of the venter, 

where they form an elongated, poorly defined 

node, and then continue unbroken across the 

venter. Two or three ribs start from each 

umbilical node, and there are some intercalated ribs. On the half whorl from the 

diameter of 25 millimeters to the diameter of 

40 millimeters there are four umbilical nodes 

and 15 ventral ribs. Above the diameter of 40 

millimeters the ribs are less and less distinct on 

the venter, and at the diameter of 7 5 millimeters there are only indistinct folds. The 

umbilical nodes, however, remain large and 

blunt. The suture is much like that of the 

type. 

A fourth specimen (see Pl. XVI, figs. 1-6), 

about the size of that just described, is assigned 

with some doubt to this species. The sculpture 

is much weaker than on the specimen · just 

described and less than one would expect to 

find on the type at the same size. The cross 

section of the whorl is somewhat more depressed, and the suture is more incised. The 

specimen is closer to V. thomi than to the 

other species described in this paper and is 

therefore attached to it. 

Vascoceras thomi may be recognized by its 

well-rounded venter and relatively high whorls. 

It differs from V. moultoni Reeside in possessing 

more elevated whorls and in sutural details; 

from V. stantoni Reeside in its much more 

elevated whorls and less angular umbilical 

shoulder It suggests somewhat V. silvanense 

Choffat 6 but is apparently a much larger species 

and has a wider umbilicus and a different 

suture. It also suggests V. adonense Choffat 7 

6 Choffat, Paul, Les ammom\es du Bellasien, des couches a Neolobite 

vibrayeanus du Turonien, et du Senonien: Faune cretacique du Portugal, 

voL 1, ser. 2, p. 57, pl. 8, fig. 5; pl. 21, fig. 9, 1898. 

7 Idem, p. 59, pl. fig. 9, 3; pl. 21, fig. 12. 
30 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 19'23. 

but differs in the retention of the tubercles, 

in the form of the umbilicus, and in suture. 

V ascoceras moultoni Reeside, n. sp. 

Plate XVII, figures 1-2; Plate XVIII, :figures 1-2. 

Shell stout, coronate. Earliest stage seen 'in 

the single specimen available is at diameter of 

80 millimeters. Whorl has broad, depressedoval cross section. Width of umbilicus more 

than half the diameter of the shell. Umbilical 

shoulder bluntly rounded. Living chamber 

and aperture unknown. 

Sculpture of the visible whorls consists 

chiefly of large blunt conical nodes on the 

umbilical shoulders; umbilical wall smooth; 

venter smooth except for ill-defined broad, 

low ribs connecting the nodes. 

Suture little incised; the lobes long and 

slender, the saddles rather broad and open; 

first lateral lobe pointed; first lateral saddle 

trifid. 

Vascoceras moultoni may be recognized by 

the depressed-oval form of the cross section 

of the whorl and the relatively simple suture. 

It has a broader, more depressed whorl and 

simpler suture than V. thomi Reeside and a 

rounded rather than a subangular umbilical 

shoulder as in V. stantoni Reeside. It resembles some of the forms assigned in the literature to V. douvillei Choffat but is distinct 

from all of them in the persistence of the 

umbilical tubercles and in the suture. 

V ascoceras stan toni Reeside, n. sp. 

Plate XIX, figures 1-2; Plate XX, :figures1-3; Plate XXI, 

:figuresl-3. 

Shell stout, coronate. Earliest stage seen, 

at diameter of 35 millimeters, has whorl with 

depressed-ovate cross section. The form of 

the cross section changes little to the stage 

at diameter of 1QO millimeters but thereafter 

becomes a broad pentagon. Width of umbilicus about half the diameter of the shell; umbilical shoulders subangular. Type entirely 

septate. 

Sculpture of the whorl at diameter of 35 

millimeters consists of coarse rounded ribs 

starting in pairs from a high conical umbilical 

node, passing to the margin of the venter, 

where they form blunt elongated nodes, and 

then continuing unbroken across the venter. 

There are four umbilical nodes and perhaps 10 

ventral ribs on the half whorl succeeding the 

diameter of 35 millimeters. At the diameter 

of 70 millimeters, a whorl later, the whorl is 

smooth except for the umbilical nodes, and it 

remains so in all the later stages seen. 

The suture shows four lateral lobes and 

saddles, moderately incised. The first lateral 

lobe is pointed, and the first lateral saddle 

trifid. 

Two other specimens assigned to this species 

show a much later stage of growth than the 

type. The better preserved though less complete specimen (see Pl. XXI, figs. 1-3) would 

have measured about 275 millimeters in diameter. It has the same form of the whorl as the 

type and preserves even at so late a stage the 

umbilical tubercles and traces of the ventral 

ribs. The suture of this specimen was not 

seen. 

Vascoceras stantoni may be recognized by its 

broad whorls with depressed pentagonal cross 

section and subangular umbilical shoulders. 

In the early stages it is not greatly different 

from V. thomi Reeside except that the ribs 

are finer, but in the later stages it departs 

sharply from that species in the . form of the 

whorl. It differs from V. moultoni Reeside in 

its subangular umbilical shoulders and in 

sutural details. It is perhaps closest to V. 

harttiformis Choffat 8 in its general form but 

differs in the persistence of the umbilical 

nodes, in the greater width of the umbilicus, 

and in the suture. 

Vascoceras sp. 

Plate XX, figure 4. 

The young stages of these American· species 

of V ascoceras seem to be missing in most of the 

specimens in hand. · One rather poorly preserved mold shows the exterior of younger 

whorls than any of the other specimens and is 

therefore figured. 

Genus PSEUDOTISSOTIA Peron. 

Subgenus CHOFFATICERAS Hyatt. 

Pseudotissotia (Chotl'aticeras) sp.? 

Plate XII, :figures 3-6. 

A single small specimen of an ammonite 

with sharp venter was obtained in cleaning the 

s Choffat, Paul, op. cit., p. 53, pl. 12, fig. 3; pl. 13, figs. 3--{l; pl. 21, figs. 

22-24, 1898. ' 
A NEW FAUNA FR.OM THE COLORADO GROUP OF SOUT'HER.N MONTANA. 31 

umbilicus of one of the large specimens of 

Vascoceras. This small specimen is nearly 

complete, preserving three-fourths of the last 

whorl unseptate, although only 13 millimeters 

in greatest diameter. The shell is very much 

compressed, discoid. The flanks of the whorls 

curve evenly from the umbilicus to the ventral 

keel. The umbilicus is moderately wide, about 

one-fourth the diameter of the shell, and the 

umbilical margin is rounded. The entire shell 

is smooth, without any trace of ribs or nodes. 

The suture is well preserved and very simple. 

It shows a very broad ventral lobe, a broad 

first lateral saddle with two incipient marginal 

lobes, a broad first lateral lobe with a suggestion of an incipient marginal lobe on the outer 

side, a simple second lateral saddle and lobe, 

and one auxiliary saddle and lobe. 

The generic assignment of this little ammonite is uncertain. On the basis of Hyatt's figures of the sutures of young Metengonoceras 

and Ooelopoceras 9 it c~mld scarcely belong to 

those genera of sharp-ventered ammonites, 

both of which are known to occur in the 

Colorado group of the Interior province of 

North America. Of other genera its suture 

appears to be proportioned more like that of 

Pseitdotissotia than of any other genus, and it 

is therefore tentatively assigned to Pseudo-

. tissotia and to the subgenus Ohoffaticeras because it shows no trace of ventrolateral keels 

or nodes. 

9 Hyatt, Alpheus, Pseudoceratites of the Cretaceous: U.S. Geol. Survey Mon. 44, pl. 10, figs. 1o-12; pl. 27, fig. 13, 1903. 

Helicoceras pariense White? 

Plate XX, figures 5-6. 

A single fragment of a small cephalopod 

that appears to have had an open coil in a 

single plane was uncovered in preparing the 

type of T1 ascoceras tho mi. It suggests very 

strongly young Helicoceras pariense White, 10. 

though the specimen is insufficient to warrant 

an unquestioned assignment to that species. 

The suture is not visible, but the form and 

sculpture agree closely with those of the 

specimen figured by Stanton. 

Hyatt 11 ;referred Helicoceras pariense White, 

to his genus Exiteloceras, but the writer prefers 

to use the more general name here. 

Inoceramus labiatus (Schlotheim). 

Plate XIV, figures 3-5. 

A number of specimens of this widespread 

species accompany the other fossils of the 

collection. They are mostly of small size 

but do not depart in any way from typical 

shells from other localities. 

Inoceramus sp. 

Plate XIV, figure 6. 

A single small specimen of a relatively 

coarse-ribbed, transversely elongated species 

of Inoceramus is contained in the collection. It 

resembles in some respects several different 

species but is hardly sufficient for certain 

identification. 

1o Stanton, T. W., The Colorado formation and its invertebrate fauna: 

U.S. Geol. Survey Bull. 106, p. 164, pl. 35, figs. 2--4, 1893. 

n Hyatt, Alpheus, The phylogeny of an acquired characteristic: 

Am. Philos. Soc. Proc., vol. 32, p. 577, 1894. 
• 

PLATES XI-XXI. 

33 
u. :s. U.t.VLUli!viiL o::>u<<V-"'1 

1 

FOSSILS FROM THE COLORADO GROUP OF SOUTHERN MONTANA. 

2 

Vascoceras thomi Reeside, n. sp. Type specimen (U.S. 1::-at. Mus. catalog No. 32535). 1, Side view; 2, rear view. 
U , S. GEOLOGICAL SURVEY 

,, 

/I ........... __ ./',' 

I I 

I I I I 

I I 

I\ 

'-,\ '~ ,, 

..... , ........ .... __ ; 

I 

, 

I 

\.,, 

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\ 

\ 

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4 .X3 / 

\ 

---~--------------

3 

1 

2 

PROFESSIONAL PAPER 132 PLATE XII 

5 X3 

FOSSILS FROM THE COLORADO GROUP OF SOUTHERN MONTANA. 

1-2. Vascoceras thomi Reeside, n. sp. Type specimen (U.S. Nat. Mus. catalog No. 32535). 1, Cross section at diameter of 165 millimeters; 

2, suture at diameter of 100 millimeters. 

3-6, Pseudotissotia (Choffaticeras) sp.?· 3, Side view; 4, rear view; 5, front view; 6, suture. (U.S. Nat. Mus. catalog No. 32541.) 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 132 PLATE XIII 

1 X Yz 2 X !12 

FOSSILS FROM THE COLORADO GROUP OF SOUTHERN MONTANA. 

Vascoceras thomi Reeside, n. sp. 1, Side view; 2, rear view. (U. S. Nat. Mus. catalog No. 32536.) 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 132 PLATE XIV 

1 

6 

,---...... 

I ' I \ 

I I 

\--.~~ 5 

.,.--...... 

I ' I I \ I 

' ,_._/ I 

2 

FOSSILS FROM THE COLORADO GROUP OF SOUTHERN MONTANA. 

1-2. Vascoceras thomi Reeside, n. sp. 1, Cross section of whorl at diameter of 200 millimeters; 2, parts of three sutures at diameter of 150 millimeters of specimen shown on Plate XIII. (U.S. Nat. Mus. catalog No. 32536.) 

3-5. Inoceramuslabiatus (Schlotheim). (U.S. Nat. Mus. catalog Nos. 32540 and 32543.) 

G. Inoceramus sp. (U.S. Nat. Mus. catalog No. 32542.) 
U . S. GEOLOGICAL SURVEY 

3 4 

6 

---tt -----------

1 

PROFESSIONAL PAPER 132 PLATE XV 

--..... 

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5 

I 

( 

- . I - --- - - - - - - - - /,.... "\,- - - - - - - ' - - I I \ 

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2 

FOSSILS FROM THE COLORADO GROUP OF SOUTHERN MONTANA. 

Vascoceras thomi Reeside, n. sp. 1, Side view of outer whorl; 2, rear view of outer ·whorl; 3, side view of inner whorl; 4, rear view of inner whorl; 

5, cross section at diameter of 75 millimeters; 6, suture at diameter of 55 millimeters; 7, suture at diameter of 30 millimeters. (U. S. Nat. 

Mus. catalog No. 32536.) 
U. S. GEOLOGICAL SURVEY 

1 

3 

_([[ ___________ _ 

5 

PROFESSIONAL PAPER 132 PLATE XVI 

I 

I 

I 

I 

I 

2 

4 

---- -------------~-------------,----- 6 1 x2 J . 

FOSSILS FROM THE COLORADO GROUP OF SOUTHERN MONTANA. 

Vascoceras thomi Reeside, n. sp. 1-3, Entire specimen; 1, side view; 2, rear view; 3, front view; 4, rear view with part of outer whorl removed; 

5, cross section at diameter of70 millimeters; 6, suture at diameter of60 millimeters. (U.S. Nat. Mus. catalog No. 32536.) 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 132 PLATE XVII 

1 

FOSSILS FROM THE COLORADO GROUP OF SOUTHERN MONTANA. 

Vascoceras moultoni Reeside, i:t. sp. Type specimen (U.S. Nat. Mus. catalog No. 32537). 1, Side view; 2, rear view. 
U. '3. GEOLOGICAL SURVEY 

' I 

1 

;""' 

-;--

/ 

f 

I 

PROFESSIONAL PAPER 132 PLATE XVIII 

2 

FOSSILS FROM THE COLORADO GROUP OF SOUTHERN MONTANA. 

Vascoceras moultoni Reeside, n. sp. Type specimen (U.s. Nat. Mus. catalog No. 32537). 1, Cross section of whorl at diameter of 150 millimeters; 

2, suture at diameter of 110 millimeters. 
U . S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 132 PLATE XIX 

1 2 

FOSSILS FROM THE COLORADO GROUP OF SOUTHER~ MONTANA. 

Vascoccras stantoni Reeside, n. sp. T ype specimen (U.S. Nat. Mus. catalog No. 32532). 1, Side view of whole specimen; 2, front view with part of outer whorl removed. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 132 PLATE XX 

X2 

1 

FOSSIIB FROM THE COLORADO GROUP OF SOUTHERN MONTANA. 

1-3. Vascoceras stantoni Reeside, n. sp. Type specimen (U. s. Nat. Mus. catalog No. 32532). 1, Cross section at diameter of 150 millimeters; 

2, suture at diameter of 90 millimeters; 3, suture at diameter of 40 millimeters. 

4. Vascoceras sp. Side view of squeeze showing young whorls. (U.S. Nat. Mus. catalog No. 32538.) 

5-6. Helicoceras pariense White? 5, Side view; 6, rear view. (U.S. Nat. Mus. catalog No. 32539.) 
U. S o GEOLOGICAL SURVEY PROFESSIONAL PAPER 132 PLATE XXI 

·------ -------

2 xY21 1 

FOSSILS FROM THE COLORADO GROUP OF SOUTHERN MONTANA. 

Yascoceras stantoni Reeside, n. sp. 1, Side view; 2, rear view; 3, cross section, slightly reduced, at diameter of 240 millimeters. (U.S. Nat. Mus, 

catalog No. 32533.)