TtHE -FAUNA oF~ .. 'IHE·'·:.,SQ-CALLED DAKOTA FORMATION OF NORTHERN · 

·.· .. - ·'''(JENTRA·L"COLORADO AN:D ITS EQUIVALENT IN 

SOUTHEASTERN WYIMING. . 

By JoHN B. REESIDE, Jr. 

INTRODUCTION. s a h I es .anu I " I d ower san stone member in the 

Thi!] paper describes a small fauria from Boulder[ district and northward may be · the 

beds in northern central Colorado that have time eg_uivalent of · the -Comanche." The 

long been ·designated the Dakota formation, fossils of the northern area are mostly in poor 

often with doubt that all the beds so named con~iti n and are said to include one or more 

were really equivalent to the typical Dakota species pf Ostrea, an Inoceramus indistinguishsandstone of eastern Nebraska. The upper able from I. labiatus Schlotheim, and an 

part of the equivalent beds in southeastern Aviculal closely related t.o A. linguaeformis 

Wyoming was referred by some writers to th~ Evans and Shumard, though -probably not 

Benton shale and the lower part to the Cl~verly identica~. · · · 

.formation. This so-called Dakota formation of Mr. ~tanton made six collections from as 

northern central Colorado and its equivalent many Igcalities in 1906 and others in 1909 and 

in southeastern Wyoming consist of cherty 1.920. .If ~907 Prof. Henderson made a colleccong~omerate, brown quartzose sandstone, and tlon of rhi?h a part was presented .by him to 

dark shale. The .conglomerate is .usually at t~e Ge9IogiCal Surve:y. In . ~~21 larger collecthe base of the series and at many localities is t10ns were made at six local~ties by W. T. Lee. 

overlain by a single shale unit and that in . These ter. collections have supplied ~ore adeturn by a sandstone. At other localities, quate speCimens of most of the species than 

however, there are several alternations of were coFotained in tl;te earlier collections and 

san~stone and shale above the basal conglom- have s~ow? more definitely. th~ relationships 

eratiC layer. The fossi.ls described in this o! the flossils. All the materia,lin. these collecpaper, except one speCimen, were obtained ~IOns haJ1

s,. thr,ough Mr. Stanton s kindness, been 

fro~ the shales of the middle part of the for- In the 'jl'Iter s hands, as w~ll as specimens. for. 

mat10n. The single specimen, an ammonite, compar~son from the ~ ashita fauna of south~ 

came from the uppermost sandstone. ern C?l~ra~o, New Mexi?o, Kansas; and Te;xas 

Fossils from the "Dakota formation" of co?tained In the collectiOns of the GeologiCal 

nor~hern Colorado were first recorded by Prof. Survey. l . 

Junius Henderson, 1 of the University of 

C I . THE FAUNA AND ITS RELATIONS. 

o orado. Henderson states that fossils were 1 

found by T. W. Stanton and himself at almost The fr una of the "middle Dakota shale" of 

every good exposure of the "medial shales" northern Colorado and southern Wyoming infrom a locality 5 miles north of Boulder, eludes srven species, of which ·one is not defiriColo., to Owl Canyon, in northern Larimer itely der erminable, three are assigned to new 

County, thou.gh they were not determinative. species, and thr. ee are assigned to ·species preHe suggests that the presence of Comanche viously described. The list of species is as 

fossils at Canon City and the persistence of a follows: . . 

tripartite division in the "Dakota formation" Inoceramus comancheanus Cragin. · 

indicat'e "that ,at least part of the medial In9ceramus bellvueri.sis Reeside, n. sp: . 

--~------------...:.._· ---- Pteria salinensis White. 

1 Henderson, Junius, The foothills formations of north-central Colorado: Os rea larimerensis Reeside, n. sp. 

Colorado Gool. Survey First Ann. Rept., pp. 172-176, 1908; The Creta- ceous formations of northeastern Colorado and the foothills formations OstJrea noctuensis Reeside, n. sp. 

of north-central Colorado: Colorado Geol. Survey Bun~ 19, pp. 83-85, , Anfhura kiowana Cragin? 

1920. • Ammonite, undetermined. 

1S9 
200 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1922. 

To this list may be added the scales and bones one species after another from the faunal assemof undetermined fish and also teeth collected blage. In the Purgatoire River region of Colonea;ry ~<;:>v~~nd, Co~o., by Prof. ~enderson and rado the fauna lacks a number of Washita 

ideiltified by J. W: Gidley as pt;6bably plesio-: ·species that- are prominent at ~' the ·localities 

saurian.2 Inoceramus ·· comanchea_nus_J_ Pteria farther s~mtheast. In the · .Apishapa River 

salinensis, and Anchura lciowana occur in rocks region still-more species have dropped out of the 

of Washita age in Kansas and other States, and fauna, and at Canon City only two or three are 

their occurrence in the beds here considered known. Such a change. as this may well actherefore supports a correlation of the "ihiddle count · for the paucity of recognized Washita 

Dakota" with the Washita group, although --species in northern central Colorado and southsuch a correlation, based on a single species eastern yY"yoming, though th~ . causes of the 

each of Inoceramus arid Pteria and a somewhat change are entirely 'conjecturaL It has been 

doubtfully identified species of A nchura, has a suggested by Stanton 5 that · the difference berather frail foundation. The other species are tween the fauna of the Purgatoire formation 

not very close to any described forms from the and that of the so-called Dakota formation of 

, Washita group or the Benton shale and have northeastern Colorado is due to a difference iri 

little value in correlation. The absence of such age, the sea in which the Purgatoire formation · 

widespread and abundant species ~s Ostrea was deposited not having reached northern Colquadriplicata Shumard, Gryphaea corrugata orado until Dakota time, when many of the 

Say, · Trigonia em6ryi Conrad, Pholadomya characteristic Washita species had ceased ·to 

sanctisa'Qae Roemer, Cardium lcansasense Meek, exist. The relationship of the beds of Washita 

Protocardia multilin,eata Shumard, Turritella age in Kansas to the overlying Dakota for- · 

seriatim-granulata Roemer, and Pachydiscus mation is so intimate as to preclude any great 

brazoensis (Shumard), which occur in many difference-in age, and the differenee in in,tercollections from the Purgatoire formation and pretation of the fauna is . therefore · not very 

its equivalents,3 is surprising. There is no fea- great. However, it seems to the writer that it 

ture of the sediments that indicates conditions is better to regard the fossils of the so-called 

of deposition in northern Colorado very differ- Dakota formation as of the same age as those 

ent from those in southern Colorado-in fact, of the Purgatoire formation and attribute the·, 

on the contrary, the sediments of the two areas differences between them to some·now unknown 

are so much alike that tentative correlations difference· in the conditions under which the 

betw-een them have been based on the simi- sediments were deposited. The fauna frorri 

larity. It is difficult to explain why conditions northern Colorado, in spite of its paucity, is · 

that would permit the .existence ·of Inoceramus more like that of the Washita group than that 

comancheanus, Pteria salinensis, and an An- of the succeeding Benton shale or that of any 

chura very like A. kiowana would completely known Dakota beds, and a correlation based ·· 

shut out any trace of their usual associates, on the fauna must be a correlation with the 

which are present in southern Colorado, scarcely Washita rather than with· the Benton. The 

200 miles away . . ·Whether these three species fauna is apparently an extension of the known 

were hardier and could endure conditions that range of the late Comanche fauna as far north · 

co~pletely precluded the existenee of the other as southern Wyoming. 

spe.cies can not be determined. The Washita The single ~ ammonite, Pachydiscus? sp., 'from · 

fauna, as shown by Stanton/ suffers a progres- the uppermost sandstone of the "Dakota forsive change northwestward from the Tucumcari mation," is sufficient only to show that this . 

region of New Mexico and. the Cimarron River sandstone is in at least one -locality of marine 

region . of Oklahoma by the disappearance of origin. The specimen might belong to the 

Washita fauna or to a later one. The marine 2 Henderson, Junius, The Cretaceous formations of northeastern Colorado and the-foothills formations of north-central Colorado: Colorado 

Geol. Survey Bull. 19, p. 85, 1920. 

a Stanton, T. W ..• The Morrison formation and its relations with the 

Comanche series and the Dakota formation: Jour. Geology, vol. 13, 

pp. ()57-669, 1905. 

4 Stanton, T. W., idem. 

•) 

origin of the sandstone 'at two other localities 

is indicated by the presence of Halymenites. 

These localities are at ·the month of- Little 

o Stanton, T. "\Y., Some prob:ems connected with the Dakota sand· 

stone: Geol. Soc. America Bull., vol. 33, pp. 265-272, 1922. · 
THE FAUNA - OF -TH:E1 SO-CALL'ED DAKOTA FORMA'TIION. ·'2.01 

Thompson . .Canyon and 10 · miles- north of 

Boulder, Boulder County, Colo.6 

a Henderson, J,uriius; The Creta-Jeous formations ·of northeaste:-n Colorado and the foothills formations of north-central Colorado: Colorado 

Geol.' Survey ~ull. 1!), p. 85, '1920. 

DISTRIBUTION OF' SPECIES . .. I 

Tne . following table and list show the geographic distribution of the species described in 

this paper: . 

Distribution of species from the so-called Dakota formation o.f northern central Colorado and southern Wyoming by 'localities. 

ci 3 7, 8 10 11 12 13 14 15 Hi 

InoceramuscomancheanusCragin .... · .... X------~- X X-------- X X X X X .... X X X 

Inoceramus bellvuensis Reeside ............. ~ . . . . . . . . X . . . . . . . . . . . . . . . . X X X ................... . Pt.eriasalinensisWhite ... · ...... . ........ X X X X ... . X .. . . X X X X ........ X · X 

Ostrea larimerensis Reeside ............................... ." .. X .. .. X X X X ...... . . X ... X 

OstreanoctuensisReeside ... ·······.·· · -- . . ... . .. . ... X .... X X X X X X ............ ---- ... . Anchura kiowana Cragin? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X . . . . X X .. . ................ . Pachydiscus? sp ..... · ..... ~ . :. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X . . . . . . . . . .. . Ammonite, undetermined._ ........... , ......................................... · ...................... X 

Fish scales and bones. . . . . . . . . . . . . . . . . . . . . . . X . . . . . . . . X X X X X X . . . . . . . . . . . . X : X X 

a Numbers refer to the io aliti s given in t:n fo:lowing list. 

1. U. S. G. S. locality 3689. Sixmile Canyon., 4 miles 

north of Boulder, Boulder County, Colo.; sandy shale 

between the "Dakota'' s1tndstones; T. W. St ·nton,' 

collector, 1906: 

. . 

Inoceramus coinancheanus Cragin .. 

Pteria salinensis White. 

Ostrea sp. undetermined. 

2 .• U. S. G. S. locality 3990. Lykins Gulch, 9 miles 

·north of· Boulder, Boulder County, Colo.; 'sandy shale 

between the ' 'Dakota" sandstones; _T·. W. St nton, 

collector, 1906 : 

Pteria salinensis White. 

Ostrea sp. undetermined. 

Fish remains. 

3. U. s: G. S. locality 3685. South end of abbit 

Mountain, 7 miles northwest of Longmont, Boulder C unty, 

Colo.; shales between the "Dakota" sandst-Ones~ . W. 

Stanton, collector; 1906: · . 

Inoceramus sp. undetermined. 

Pteria salin(msis white. · 

Ostrea sp. undeterinined. 

4:. U. S. G. S. loca:Iity 3686. Lykins ranch, at· 

of canyon of Little Thompson Creek, Boulder ·Co n~y, 

Colo.; sandy shale between the "Dakota" sands on~; 

T. W. Stanton, collector, 1906: _ 

Inoceramus comancheanus Cragin. 

Inoceramus bellvuensis Reeside. 

Pteria salinensis White. 

Ostrea noctuensis Reeside. 

5. U. S. G. S. locality 10631. Handy ditch, c nyon 

west of Lo-veland, Larimer County 1 Colo.; sandy 

beneath the "upper Dakota',· san~stone; W. T. Lee, 

collector, 1921: · · 

Inoceramus comancheanus Cragin. 

Fish remains. 

6. U. S. G. S. locality 10657. Handy ditGh, c 

west of Loveland, Larimer County, Colo.; middle of 

between the "Dakota'' sandstones; W. T. Lee; ·coil ctor, 

1921. 

Inoceramus sp. ~uidetermined. 

Pteria salinensis White. 

Ostrea larimerensis Reeside. 

Ostrea noctuensis Reeside 

Fish remains. 

7. U. S. G. S. locality 3688. Eight miles northwest 

of Loveland and 2 mUes north of the junction of Big 

Thompson and BuckhorJ;J. creeks, Larimer County, Colo.; 

sandy shale between ~he '~Dakota'' sandstones; T. W. 

Stanton, collector, 1906: 

Ostrea noctuensis Reeside . 

Fish · remains. 

8. U. S. G. S, locality 10659. Soldier Canyon, west 

of Fort Collins,. Larimer County, CoJo.; middle of shale of 

"middle Dakota"; W. T. Lee, collector, 1921: 

Inoceramus comancheanus Cragin. 

Pteria salinensis ~ite. · 

Ostre~ larimerensis Reeside. · 

Ostrea noctuensis Reeside. 

Anchura kiowana Cragin? _ 

Fish remains. 

9. U. S. G. S. locality 3687. Ditch bank on north side 

of Cache la Potidre Riv~r, 9'miles nortl:l:West·of Fort Collins 

and 2 miles above Laporte,_ Larimer, County, Colo.; shale 

between the ''Dakota'' hogbacks; T. W_. Stanton, collector, 

1906. 

Inoceramus -comancheanus Cragin .. 

Inoceramus bellvuensis Reeside. 

Ostrea larimerensis Reeside. 

Ostrea noctuensi~ Reeside, 

Fish remains. 

10. U. S. G. s.· locality .10660. Ditch on ."Dakqta" 

ridge in sec._12, T. 8 N., R ... 7.Q W.,, north of Bellvue, Larimer County, Colo.; upper part of "middle Dakota"; 

W. T. Lee, collector, 1921: 

' Inoceramu·s comancheanus Cragin. ' 

Inoceramus bellviuensis Reeside. 

Pteria salmensis White. 

Ostrea larimerens~s Reeside. 

Ostrea noctuensis Reeside. 

Anchurakiowana ·.Cragin? -

Fish remains . . · · 

-!'·.' 

11. U. 'S. G. ·S. locality 5401. Owl Canyon iJ12 miles 

north .of Fort Collins, Lari~er County, Colo.; · wdd1e 

Dakota''.; Junius Henderson, collector, 1907~ 

Inoceramus comancheanus Cragin. 

.Inoceramus bellvuensis Reeside . . 

. Pteria salinensis White. , · 

Ostrea. larimerensis Reeside. 
202 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1922. 

Ostrea noctuensia Reeside. 

Anchura kiowana Cragin? 

12. U. S. G. S. locality 10375. Two miles southeast of 

Greenacre ranch, 20 miles north of Fort Collins, Larimer 

County, Colo.; dark shale beneath the "upper Dakota'' 

hogback; T. W. Stanton, collector, 1920: 

Inoceramus coma11cheanus Cragin. 

Pteria salinensis White. 

13. U. S. G. S. locality 10375a. Same locality as 10375; 

upper sandstone of the "Dakota'' hogback, above the dark 

shales; T. W. Stanton, collector, 1920: 

Pachydiscus? sp. 

14:. U. S. G. S. locality 10662. Schoolhouse near Box 

Elder Qreek, southeast of Greenacre ranch , Larimer 

County, Colo.; upper part of "middle Dakota''; W. T. 

Lee, collector, 1921: 

- Inoceramus comancheanus Cragin. 

Ost!ea larimerensis Reeside. 

Fish bone. 

15. U. S. G. S. locality 5863. Horse Creek, 30 miles 

northwest of Cheyenne, Laramie County, Wyo.; shale 

beneath the upper ledge of the "Dakota''; T. W. Stanton, 

collector, 1909: 

Inoceramus comancheanus Cragin. 

Pteria salinensia White. 

Gastropod, undetermined. 

Fish remains. 

16. U. S. G. S.locality 10670. Gap of Chugwater Creek 

at Iron Mountain, Laramie County, Wyo. ; "middle 

Dakota'' shale; W. T.' Lee, collector, 1921: 

Inoceramus comancheanus Cragin. 

Pteria salinensis White. 

Ostrea larimerensis Reeside. 

Ammonite, undetermined. 

Fish remains. 

DESCRIPTIONS OF SPECIES. 

Genus INOCERAMUS Sowerby. 

Inoceramus comancheanps Cragin. 

Plate XLV, figures 1-7 

1895. Inoceramus comancheana Cragin, Colorado Coli. 

Studies, 5th year, pp. 53-55. 

1901. Inoceramus comanchean us Cragin. Hill, U. S. Geol. 

Survey Twenty-first · Ann. Rept., pt. 7, pl. 35, 

fig. 4. 

1920. Inoceramus comancheawus Cragin. Adkins and 

Winton, Texas Univ. Bull. 1945, p. 73, pl. 17, 

fig. 1-3. 

Cragin's original description is as follows: 

Shell equivalve, broadly and obliquely rhombic-ovate, 

more gibbous than that of I. labiatus Schlotheim, the axis 

of greatest dimension diverging from the hinge line much 

more widely than in the latter species; alar outline 

rounded; anterior margin descending steeply in a nearly 

straight line for a considerable distance on front of the 

beaks, then curving rather suddenly away toward the 

somewhat prominently co:qvex distal part of the basal 

outline, anterior and posterior margins making nearly a 

right angle with each other; beaks placed opposite the 

anterior extremity of the hinge, moderately inflated and 

moderately elevated above the hinge line, anteriorly 

flattened but not abruptly so; hinge plat~ rather short, 

broad, the liganiental grooves crowded, more numerous 

and longer than in I. labiatus, though ample and shallow; 

valves thin, ornamented with numerous concentric 

riblike folds, which on the distal and ventral parts are 

quite strongly elevated and much narrower than the 

intervals between them. 

Height 82, length 95, breadth 54, axis of greatest dimension 107 milimeters. In some examples the species 

attains considerably larger dimensions. 

The writer has in hand a number of fairly 

good specimens of an Inoceramus indistinguishable from specimens of I. comancheanus. This 

species is characterized by its elongate form, 

the axis of elongation making an angle of 50° 

to 70° with the hinge line; moderately coarse, 

rounded, concentric ribs without finer sculpture 

between; ribs somewhat irregular; umbo 

rather slender; anterior margin straight or 

slightly concave, making an angle of 70° to 100° 

with the hinge line. It differs from the later 

I. labiatus, as pointed out by Cragin, in the 

greater angle between the axis of elongation 

and the hinge line. It is also less elongated, 

has stronger sculpture and less smoothly ovate 

concentric ribs, and lacks the fine striae l?etween 

the concentric ribs. It somewhat resembles 

an undescribed species associated with I. 

labiatus and related to I. lamarclci var. cuvieri 

Sowerby, though it differs in having a more 

elongate form and much finer sculpture. 

Inoceramus anglicus Woods, of the Gault; I. 

crippsi Mantell, of the Cenomanian; and I. 

pictus Sowerby, of the Cenomanian, are related species. I. anglicus has more regular 

concentric ribs and a broader curvature and 

is a wider shell. I. crippsi 4as a greater angle 

between the anterior margin and the hinge 

line (140°), a thicker · umbo, .and fine striae 

between the concentric ribs. I. pictus differs 

chiefly in possessing finer sculpture. These 

comparisons are based largely on figures by 

Woods 7 and might not hold in an actual . 

comparison of specimens, but so far as the 

writer is able to determine, I. comancheanus is 

closer to I. crippsi and I. pictus than to the 

other species mentioned. 

Occurrence: Many localities in Texas, 

Kansas, Okl~homa, and southern Colorado. 

In northern Colorado: Sixmile Canyon, Lykins 

ranch, canyon west of Loveland, ,Soldier 

Canyon, Cache la Poudre River, north of 

1 Woods, Henry, A monograph of the Cretaceous Lamellibranchia of 

England, vol. 2, pt. 7, pp. 264, 27"3, 279, text figs. 29, 33-36; pl. 45, figs. 

8-10; pl. 48, figs. 2, 3; pl. 49, figs. 5, 6, 1911. 
THE FAUNA SO-CALLED DAKOTA', FORMATION. 203 

.Bellvue, Owl Canyon, 2 miles southe st of 

Greenacre ranch, Boxelder Creek. In W yoming: Horse Creek and Iron Mountain. 8 

Inoceramus bellvuensis Reeside, n. sp. 

Plate XLVI, figures 1-3. 

Shell apparently equivalve, very inequilateral. Outline of valve subquadrate; anterior 

part moderately convex; posterior part flattened, forming an ilf-defined wing dorsally. 

Anterior margin nearly straight; ventral margin broadly convex; posterior margin nearly 

straight. Anterior margin makes an angle of 

120° with the hinge line: Sm·all part of hinge 

line preserved shows ligament pits small and 

shallow. Umbones nearly terminal. Ornamentation · of ·somewhat irregular narrow coneentric ribs with . unsymmetrical curvature; 

ID.terspaces wider than ribs, concave. 

· This species is marked by its broad subquadrate valves, small convexity, and' sculpture. It is perhaps closer to Inoceramus_ 

crippsi Mantell th~n to any other -species but 

shows no trace of the fine striae between the 

ribs that are present on that species. 

The specific name is derived from Bellvue, 

Colo., near which the type was collected. 

Occurrence: Lykins ranch, Cache la Poudre 

River, north of Bellvue, and Owl Canyon, 

Colo. 

Genus PTERIA Scopoli. 

Pteria salinensis White. 

Plate XLVII, figures 1-5. 

1880. Pte:ria (Oxytoma) salinensis White, U. S. Nat. Mus. 

Proc., vol. 2, pt. 2, pp. 296, 297, pl. 5, figs. 1, 2 ... 

1883. Pte:ria (Oxytoma) salinensis White, U. S. Geol. and 

Geog. Survey Terr. Twelfth Ami. Rept., pt. 1, 

pp. 15, 16, pl. 16, figs. 2a, b. 

'?1893. Pte:ria salinensis White. Cragin, Texas Geol. Survey Fourth Ann. Rept., p. 211. 

White's original description is as follows: 

Shell rather large fo; a Cretaceous Pter{a; the body, 

exclusive of the wings, obliquely subovate, broad at the 

base, moderately gibbous, distinctly but not very greatly 

inequivalve; the left valve, as usual, more convex than 

the right and its beak more prominent; the convexity of 

the valves somewhat uniform but increasing toward the 

~bonal region in each, where it is greatest; anterior wing 

moderately large, defined from the body of the shell by 

being laterally compressed but not by any distinct auricular furrow, the byssal sinus under the anterior wing of 

the right valve having the usual size and shape common 

B Th3 full des ription of all these lo alities is given on pages-_-

to Oxytoma; posterior wing not proportionately large and . 

not distinctly defined from the body of the ,shell except 

by a somewhf!.t gradual lateral compression; its posteriQr angle not greatly produced; hinge line less than the 

axial length ' of the shell; posterior adductor scars not 

distinct; antbrior adducto~ scars distinct and deep for a 

shell of. this! genus, placed immediately in front of the 

beaks that f the left valve being more distinct than the 

other.' * * * . 

It is know to have reached an axial length of more than 

60 millimete s, a transverse width near its base of at least 

50 millimete s and a thickness of about 25 millimeters 

when both v l~es we~e in natural position. 

The chara ter of the surface is not known, but it was 

evidently ne rly smooth, as is usual with Oxytoma. 

The wri~er h~s in hand a number of specimens tha include both valves of a smoothshelled Pt ria. Such simple shells are somewhat unsa isfactory material for comparisons, 

as very sirilar species occur at a number of 

very distil}ct horizons, from the Paleozoic on. 

However, 'n comparison with species from the 

Washita, {)olorado, and Montana groups the 

specim. ens ib hand are so close toP. ~alin~nsis that 

it is difficuit to pick out an essential difference. 

P. gastrod4s (Meek) of the Benton i's a lar~el 

stout, nea~ly equivalve shell with the ?uthne 

of the valjves well rounded, the anterwr ear 

short propcbrtionately, and the axis of the shell 

only mol rately oblique. P. linguaeformis 

(Evans a d Shillnard) is a proportionately 

small ine uivalve shell, with valves rather ' . elongated . nd oblique, . and the anterwr ear 

small. P. salinensi~ has ~ less elongated fori? 

than P.li~uaeform~s an. d Is muc. h larger, but It 

is not nea ly so stout and rounded asP. gastrades. It has also a relatively long a:q.d narrow anter~· r ear and is nearly equivalve. · 

Occurre ce: Washita group of Texas and 

· rocks of s me age in Kansas and southern 

Colorado. In northern Colorado: Sixmile Canyon, Lyki s Gulch, Lykins ranch, south end 

of Rabbit ountain, canyon west of Loveland, 

Soldier Ca on, north of Bellvue, Owl Canyon, 

arid 2 miles southeast of Greenacre ranch. In 

Wyoming: orse Creek and Iron Mountain. 

Genus OSTREA Linnaeus. 

Plate XL VII, figures 6-12. 

thin, flattened, acutely triangular 

in outline; mall, an average specimen attaining a lengt of 60 millimeters. Beak narrowly 

tapered; b se of valve smoothly rounded. 
204 S:H:ORTER CONTRIBUTIONS TO GENERAL : GEOLOGY, 1922. 

Ma~gins of the valves smooth. Surface irregu- Genus ANCHURA Conrad . . 

Lrfy and fuiely wrinkled, especially near the Anchura kiowana Cr~ght? 

beak. Internal cast reflects the larg- er wrinkl_ es, ~ ' ·. 

Plate XLVIII, figures 6-8. 

but otherwise smooth. Hinge not seen; prob1 ll 1895. Anchura kiowana Cragin, Coiorado Coli. "Studies,. 5th ub y sma and weakly developed. 

h year, pp. 66, 67. T e writer has hesitated to apply names to 

this and the following species of Ostrea. Both Cragin's original ~escripti~n is as folio":"~ ; 

belong to a type of simple oyster that appears Shell small, consisting of six convex whorls; spire elein many faunas from Jurassic to Recent time, vated; suture impressed; wing of moderate si2je, consisting 

d 1 h h d'ff of a proximal flangelike part, continued posteriorly across an a t oug 1 erences may be pointed out half or more of the first spire whorl, and a carinated fa:Icithe variability of the shells is so great that no form process; carina gradually arising at the base of the 

differences seem to hold good, and separation falciform process and traversing the latter to the ~xtrem}ty; -

into species is more or less arbitrary. However: 'falciform process much shorter and less upturned distally 

there appear to be no described forms in the than that of the som~what similar species A. ruida White, 

equivalent or adJ. acent faunas of the region that _ not rising to the lowest level of the suture between the 

body whorl and the first spire whorl but having its point 

may be compared with these, and as a matter directed outward and-somewhat upward so as to make a. 

of convenience names are here applied. large angle with the axis-of the spire, extero-inferior outThe specific name of 0. larimerensis is derived line of wing rounded and the border between this and 

from Larimer County, Colo. the canal sinuous, margin of upper (flange) part of wing 

Occurrence: Canyon west of Loveland, Sol- describing a slightly concave to sigmoid outline and more or less thickened and reflexed; inner lip provided With a. 

dier Canyon, Cache la Poudre River, north of moderately broad and·prominent callous; canal short and 

Bellvue, Owl Canyon, and ·Box Elder Creek, obliquely truncated; spire whorls and posterior half, t() 

Colo.; Iron Mountain, Wyo. two-thirds of body whorl ornamented with narrow c1.1rv.ed, 

subvertical ribs or folds, of which there are about 24 o~ the· 

Ostrea noctuensis Reeside, n. sp. 

Plate XLVIII, figures 1-5. 

Shell very thin, gently arched, subquadrate, 

of medium size, an average individual attaining 

a length of 80 or 90 millimeters. Beak bluntly 

rounded, basal. part of shell broadly rounded. 

:Margins of valves smooth. · Surface of most of 

the specimens marked by fine, rather regular 

concentric lines and a few broad, obscure folds. 

Surface of other specimens irregularly wrinkled, 

much as in 0. larimerensis. Internal cast 

smooth except for the reflection of the broad 

folds. Hinge small and weak. 

This species may possibly be :=: :t1ly a veriant 

of 0. larimerensis, as it is of the same general 

type, but its broad outline is distinct, and _so is 

· its sculpture in most of the specimens. 

· The specific name is derived from the locality 

of the type, Owl Canyon · (noctuus =owl). 

Occurrence: Lykins ranch, . canyon west _of 

Loveland, northwest of Loveland, Soldier 

Canyon,· Cache la Poudre River, north of Bellvue, and Owl Canyon, Colo. -

first spire whorl, and with numerous revolving striae, ·-the 

latter ornamentation gradually becoming prominent ·and 

superseding the ribs on the lowest third to half of the body 

whorl. 

Height 19, breadth of body whorl, including e{CCl,lTsion 

of the wing, 15 millimeters; angie of spire slopes abou~ ~ 

in A. ruida White. * * * This species is distinguish~d 

from Anchura ruida White by the vertically costate ·body 

whorl, by the shorter, . differently directed falciform 

process, and by having the alar carina confined directly t() 

the wing and nearly to the falciform process instead of 

rcing common to the wing and part of the body whorl. 

The writer has six specimens of a sipall 

species of Anc.hura, all poorly -preserved but 

showing enough of the details to indica~e a 

close relationship to ·A. kiowana, as defined by 

Cragin's description and by good specimens. 

One specimen preserves a mold of the exterior 

_of 'the wing, and although fine details are lacking it is· clear that the wing has the form of that 

of A. kiowana and that the carina is confined 

practically to the wing. The presence of 

vertical ribs is also indicated on the body whorl 

of this specii.Uen. Another specrrn:en pres~rvi~g 

a mold · of the spire and perhaps part p'f t~~ 

body whorl shows a strong sculpture like that 
'THE "FAUNA. OF 'THE SO-CALLED DA OTA, FORMATION. 205 

on A. kiowana. Th(e material ·available - is 

inadequate for certain id.en.tification, but the 

differences :from A. ·.ruioo White and other 

species of equivalent ·and adjacent formations 

and the resemblances to A. kiowana make a 

tentative :assignment to that species justifiable 

Occurrence: Kiowa shale of Kansas. Soldier 

Canyon, north of Bellvue, and Owl Canyon, 

Colo. 

Genus PACHYDISCUS Zittel. 

Pachydiscus? sp. 

Plate XLIX, figure 1. 

A single specimen of an ammonite, much 

weathered and preserving few details but suggesting strongly the genus Pachydiscus, is contained in the collections. ' It might well be a 

weathered specjmen of P. brazoensis (Shumard), 

but it might equally well belong to some later 

species, and even a certain generic assignment 

must await better material. 

The stratigraphic position of this specimen is 

a little higher than that of the remainder of the 

fossils described in this paper. It came from 

the upper sandstone of the "Dakota" hogback, 

above the dark shales, and not from the shales 

themselves, as did the other fossils. 

Occurrence: Two miles .southeB.st of Greenacre ranch, Colo. 

Ammonite, genus and species undetermined. 

Plate XLIX, fi:gur.e 2. 

A single small specimen of an ammonite preserving few distinctive features is contained in 

91048°--23----14 

the colle1tions. The shell is clearly- that of a 

much coif-pressed species with very small umbilicus a~d truncated but unchanneled venter. 

The earlirr part of the shell preserved shows; 

coarse, awparently rounded ribs, but the later 

part is prl1 ctically smooth. The greatest diam-· 

eter of th shell is 30 millimeters, and the width 

of · the tr mea ted venter a little more than 1 

millimete . The shell might be a species of 

Engonoce as, Knemiceras, Metoicoceras, or SOill&. 

other genus. · 

Occurr 1

nce: Iron Mountain, Wyo. 

Fi scales and bones, undetermined. 

Plate L, figures 1-11. 

les and bones occur at several of thelocalities [rom which ·. fossils are described in. 

this papi. Some of them resemble Leuchichthyops. vagans Cockerell/ and others re- , 

semble L hthyodectes sp. Cockerell. 10 A few 

specimens are figured for the sake of more completely ill strating the known fauna. 

Occurre ce: Lykins Gulch, canyon west of 

Loveland, northwest of Lo-veland, Soldier 

Canyon, ache la Poudre River, north of Bellvue, and ox Elder Creek, Colo.; Horse Creek 

and Iron ~ountain, Wyo. . 

9 Cockerell, T~. A., Some American Cretaceous fish scales: U. S. 

Geol. Survey P of. Paper 120, p. 180, pl. 35, figs. 1-15, 1919. 

10 Idem, p. 17 , pl. 34, figs, 3, 4. 
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PLATES XLV-IJ. 

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U. S. GEOLOGICAL SURVEY 

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PROFESSIONAL PAPER 131 PLATE XLV 

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FOSSILS OF THE SO-CALLED DAKOTA FORMATION OF NORTHERN CENTRAL COLORADO AND 

SOUTHEASTERN WYOMING. 

Inoceramus comanchean us Cragin, north of Bellvue, Colo. 1-3, Left valves of three specimens (U. S. Nat. Mus. catalog No. 32513); 

4-7. right valves of four specimens (U. S. Nat. Mus. catalog No. 32513). 

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PROFESSIONAL PAPER 131 PLATE XLVI 

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FOSSILS OF THE SO-CALLED DAKOTA FORMATION OF NORTHERN CENTRAL COLORADO AND 

SOUTHEASTERN WYOMING. 

Inoceramus bellvuensis Reeside, n. sp., north of Bellvue, Colo. 1, Type specimen (X ~), left valve (U.S. Nat. Mus. catalog No. 32514); 

2, 3, left valves of two specimens (U.S. Nat. Mus. catalog No. 32515). 
U. S. GEOLOGICAL SURVEY 

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PROFESSIONAL PAPER 131 PLATE XLVII 

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FOSSILS OF THE SO-CALLED DAKOTA FORMATION OF NORTHERN CENTRAL COLORADO AND 

SOUTHEASTERN WYOMING. 

1-5. Pteria salinensis White, north of Bellvue, Colo. 1-3, Left valves of three specimens (U.S. Nat. Mus. catalog No. 32516}; 4,5, right 

valves or two specimens (U.S. Nat. Mus. catalog No. 32516). 

6-10. Ostrea larimerensi~ Reeside, n. sp., Soldier Canyon, Colo. 6, Small complete valve, selected as the type (U. S. Nat. Mus. catalog 

No. 32517): 7, 8, apical part of two valves, showing the sculpture (U. S. Nat. Mus. catalog No. 32518);, 9,10, two larger specimens, 

partly exfoliated (U.S. Nat. Mus. catalog No. 32518). 

11,12. Ostrea larimerensis Reeside, n. sp., north of Bellvue, Colo. 11, Internal cast of an unusually convex specimen (U.S. Nat. Mus. 

catalog No. 32519); 12, a nearly complete valve retaining the shell (U. S. Nat. Mus. catalog No. 32.119). 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 131 PLATE XLVIII 

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FOSSILS OF THE SO-CALLED DAKOTA FORMATION OF NORTHERN CENTRAL COLORADO AND 

SOUTHEASTERN WYOMING. 

1, 2. Ostrea noctuensis Reeside, n. sp., Owl Canyon, Colo. l, Type specimen (U.S. Nat. Mus. catalog No. 32520); 2, Apical part of another specimen (U. S. Nat. Mus. catalog No. 32521). 

3, 4. Ostrea noctuensis Reeside, n. sp., north of Bellvue, Colo. 3, Specimen retaining most of the shell (U. S. Nat. Mus. 

catalog No. 32522); 4, specimen retaining only the apical part of the shell (U. S. Nat. Mus. catalog No. 32522). · 

5. Ostrea noctuensis Reeside, n . sp., Soldier Canyon, Colo. Internal cast. (U. S. Nat. Mus. catalog No. 32523.) 

6, 7. A nchura kiowana Cragin?, Soldier Canyon, Colo. Two specimens (X 2). (U. S. Nat. Mus. catalog No. 32524.) 

8. A nchura kiowana Cragin; typical example from Kansas for comparison. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 131 PLATE XLIX 

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FOSSILS OF THE SO-CALLED DAKOTA SANDSTONE OF NORTHERN CENTRAL COLORADO AND SOUTHEASTERN WYOMING. 

1. Pachydisws~ sp., 2 miles southeast of Greenacre ranch, Colo. (U.S. Nat. Mus. catalog No. 32525). 

2. Ammonite, undetermined, Iron Mountain, Wyo. (U.S. Nat. Mus. catalog No. 32526). 
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U. S. GEOLOGICAL SURVEY PROFE~SIONAL PAPER 131 PLATE L 

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FOSSILS OF THE SO-CALLED DAKOTA SANDSTONE OF NORTHERN CENTRAL COLORADO AND 

SOUTHEASTERN WYOMING. 

1-7. Fish scales and bones, north of Bellvue, Colo. (U.S. Nat. Mus. catalog No. 10771). 

8-10. Fish scales and bone, Iron Mountain, Wyo. (U.S. Nat. Mus. catalog No. 10772). 

11. Fish bone, Horse Creek, Wyo. (U.S. Nat. Mus. catalog No. 10773).