Brachiopod Fauna of 

Saturday Mountain Formation 

Southern Lemhi Range 

Idaho 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 294-L 
Brachiopod Fa una of 

Saturday Mountain Formation 

Southern Lemhi Range 

Idaho 

By REUBEN J. ROSS, ]R. 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 294-L 

Descriptions and stereopho~ographic 

illustrations of I9 species of brachiopods, 

and correlations with other 

Ordovician formations 

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

FRED A. SEATON, Secretary 

. GEOLOGICAL SURVEY 

Thomas B. Nolan, Director 

For sale· by the Superintendeiif of Docuni'ents, U. S. Government Printing Office 

· Washington 25, D. C. 
CONTENTS 

Page 

Abstract------------------------------------------------------------------------------------------------------ 441 

Introduction-------------------------------------------------------------------------------------------~------ 441 Scope of the investigation ________________________ -- _____________________________________________ --- __ ---____ 441 

Acknowledgments----------------------------------------------------------------------------------------- 441 

Stereophotography of the specimens__________________________________________________________________________ 441 

Fossil collecting localities _____ .______________________________________________________________________________ 441 

Dating of Saturday Mountain formation based on previous evidence--------------------------------------------- 443 

Composition and significance of the brachiopod fauna______________________________________________________________ 44.4 

Composition of the fauna___________________________________________________________________________________ 444 

Ageofthefauna------------------------------------------------------------------------------------------- 444 Ecologic significance of the fauna _____________________________ -______________________________________________ 445 

Systematic descriptions of the brachiopods________________________________________________________________________ 446 

Class Articulata------------------------------------------------------------------------------------------- 446 

Superfamily Orthacea---------------------------------------------------------------------------------- 446 

Family Plectorthidae------------------------------------------------------------------------------- 446 Subfamily Platystrophiinae ______________________________ .., _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 446 

Genus Platystrophia------------------------------------------------------------------------ 446 Family Hesperorthidae ___________________________________ .., _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 446 

Subfamily Hesperorthinae_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 446 

Genus Lordorthis, new genus________________________________________________________________ 446 

Subfamily Glyptorthinae------------------------------------------------------------------------ 448 

Genus Glyptorthis------------------------~------------------------------------------------- 448 

Family Dinorthidae-------------------------------------------------------------------------------- 449 Genus Plaesiomys___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ ___ _ _ _ _ _ _ _ _ __ _ _ __ _ _ __ _ _ __ _ _ _ _ _ _ _ 449 

Genus A ustinella ______________________________________________________ ~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 454 

Superfamily Rhynchonellacea_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 456 

Superfamily Spiriferacea ___ ----- _ _ __ _ _ ___ _ _ __ __ _ _ __ _ _ ___ _ _ _ __ _ _ __ _ _ ____ _ _ __ _ _ _ __ _ _ _ __ _ _ _ _ __ _ ___ _ _ _ _ _ _ _ _ _ 456 

Genus Zygospira----------------------------------------------------------------------------------- 456 Superfamily Strophomenacea__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 458 

Genus Thaerodonta--------------------------------------------------------------------------------- 458 Superfamily Da~manellacea_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 458 

Genus Diceromyonia _____ ___ ------ _________________ -·- _ _ _ __ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ 458 

References cited ________________________________________________ ...:______________________________________________ 458 

IndeX-------------------------------------------------------------------------------------------------------- 461 

ILLUSTRATIONS 

[Plates 54-56 follow p. 463) 

PLATES 54.-56. Brachiopod fauna of Saturday Mountain formation. 

Page 

FIGURE 145. Fossil collecting localities in the Saturday Mountain formation, southern Lemhi Range, Idaho_______________ 442 

146. Scatter diagram of length: width in Plaesiomys subquadratus. Specimens of other species and subspecies plotted 

for comparison___________________________________________________________________________________ 450 

147. Scatter diagram of length: width in Plaesiomys subquadratus, brachial valves onlY-------------------------- 451 

148. Scatter diagram of length: width in P. subquadratus subsp. idahoensis, brachial valves onlY--------~--------- 451 

149. Scatter diagram of length: width in P. subquadratus, pedicle valves onlY----------------------------------- 451 

150. Scatter diagram of length: width in P. subquadratus subsp. idahoensis, pedicle valves only___________________ 451 

151. Scatter diagram of hinge width: total width in Plaesiomys subquadratus----------------------------------- 452 

152. Scatter diagram of hinge width: total width in P. subquadratus subsp. idahoensis-------------·-----------·--- 452 

153. Scatter diagram of number of costellae in 10 mm at front of valve: length of valve in mm for Plaesiomys subquadratus--------------------------------------------------------------------------------------- 452 

154. Scatter diagram of number of costellae in 10 mm at front of valve: length of valve in mm for P. subquadratus 

subsp. idahoensis-------------------------------------------------------------------------------- 452 

TABLES 

TABLE 1. Distribution of brachiopod species ______ .:.____________________________________________________________ 445 

2. Measurements of Plaesiomys subquadratus and related forms-------------------------------------------- 453 

III 
SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

BRACHIOPOD FAUNA OF SATURDAY MOUNTAIN FORMATION, SOUTHERN LEMHI 

RANGE, IDAHO 

By REUBEN J. ROSS, JR. 

ABSTRACT 

Silicified brachiopods occur in the Saturday Mountain formation of the southern Lemhi Range, Idaho, in great numbers, 

but not in great variety. Nineteen species have been identified. 

Poor sorting by size or shape of shells at most localities suggests accumulation under quiet bottom condition. A.ws,tineZla 

and the new genus Lordorthis are the most abundantly represented genera. Most of the fauna shows affinities with Late 

Ordovician species, but Middle Ordovician elements are present. 

INTRODUCTION 

SCOPE OF THE INVESTIGATION 

The present study of brachiopods from the Saturday 

Mountain formation resulted from the geologic investigations of C. P. Ross in the southern Lemhi Range, 

Idaho. His early collections indicated that a well-preserved, silicified fauna might be obtained. In 1955 P. E. 

Cloud, ,Jr., MacKenzie Gordon, and I accompanied 

Ross in five days of rewarding collecting. 

Several thousand brachiopod specimens have been 

dissolved from the enclosing dolomitic limestone, but 

only a small percentage of these were unbroken. The 

Saturday Mountain formation has been involved in 

much structural deformation with adverse effects on 

most of the enclosed shells. 

Use of formic acid on small samples of the rock 

has yielded conodonts and specimens of the bryozoan 

Soeptropora fCUJ'Illa Ulrich replaced by iron oxide, in addition to other silicified bryozoans and a few corals. 

Only the braqhiopods are described here. 

ACKNOWLEDGMENTS 

The present work has been greatly assisted by loans 

of type specimens. C. 0. Dunbar, Yale Peabody 

Museum, lent the types and topotypes of Zygospira 

jupiterensis Twenhofel and Z. aequivalvis Twenhofel ; 

N. D. Newell, American Musemn of Natural History, 

lent the types of Plaesiomys subquadratus (Hall) and 

Zygospira reourvirostris (Hall); C. F. Kilfoyle, New 

York State Museum, lent topotype material of Z. reourvirostris (Hall); and R. E. Sloan, University of 

Minnesota, lent topotype material of A ustinella whitfieldi (Winchell). Robert Morris gave critical advice 

on proper handling of stereophotography which was 

put into practice by F. B. Rowell. T .. G. Lovering gave 

valuable advice on statistical problems. 

STEREOPHOTOGRAPHY OF THE SPECIMENS 

Stereophotographs presented in this paper were taken 

with an ordinary view camera of old vintage. To obtain paired photographs, each specimen was placed on 

a sliding base and moved between exposures so that the 

distance between images on the film was 50 mm. This 

is a proper average distance for use with an ordinary 

2 X pocket stereoscope. 

Vertical exaggeration is not the same for all the 

photographs, and it will differ with differences in interpupillary distance of each observer. 

For an average interpupillary distance of 62 mm the 

present photographs will have approximate vertical exaggerations of 0.9 for Xl, of .6 for X2, and of .75 :for 

X 3 magnifications, when viewed through a conventional pocket stereoscope. 

FOSSIL COLLECTING LOCALITIES 

Fossils on which this report is based were collected 

from about twenty localities on the west side of the 

southern end of the Lemhi Range. Because there is 

no land grid by which localities can be accurately designated, reference to approximate longitude and latitude 

is accompanied by brief topographic descriptions. A 

topographic map prepared for C. P. Ross is reproduced 

here (fig. 145) with the localities indicated. 

Probably every locality listed from which I, personally, have collected is less than 75 feet stratigraphically above the base of the formation. These localities 

are D234 CO, D235 CO, D236 CO, D237' CO, D238 CO, 

and D240 CO. At some localities there is a thin quartzite layer within the formation according to C. P. Ross 

(written communication). If this is everywhere so, I 

may have mistaken it for the top of the l(innikinic 

quartzite. 

441 
442 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

FIGURE 145. Fossil collecting localities in the Saturday Mountain formation, southern Lemhi Range, Idaho. 
BRACIDOPOD FAUNA OF SATURDAY MOUNTAIN FORMATION 443 

USGS localitu Descriptio-n 

D203 CO South of south fork of South Creek, elev 7,800 ft. 

N. 43°55'48", W. 113°00'26". 

D234 CO North side of North Creek Canyon, 150ft above 

valley floor and 150 ft east of Kinnikinic 

contact. N. 43°59'01", W. 113°01'00". 

D235 CO North side of North Creek Canyon, 140ft above 

valley floor and 150 ft east of Kinnikinic 

contact, elev 7,200 ft. N. 43°59'01", 

w. 113°01'00". 

D236 CO North side of North Creek Canyon, 135ft above 

valley floor and 150 ft east of Kinnikinic 

contact, elev 7,200 ft. · N. 43°59'01", 

w. 113°01'00". 

D237 CO East side of Black Canyon, elev 7,200 .ft. 

N. 43°53'48.5", W. 112°58'40". D237a, 

9 ft above base of formation. D237b, 21 

ft above base. D237 c, 30 ft above base. 

D2.38 CO West side of Black Canyon, elev 8,500 ft. 

N. 43°54'46", W. 112°59'43". 

D240 CO On ridge between Black Canyon and South 

Creek, just north of divide, elev 8,800 ft. 

N. 43°55'28", W. 112°59'42.5". 

D302 CO South of south fork of Badger Creek, elev 10,000 

ft. N. 44°05'31", W. 113°06'39.5~'. 

D304 CO On ridge west of Black Canyon, elev 8,000 ft. 

N. 43°53'50", W. 112°.59'45". 

D306 CO East side of Black Canyon, elev 7,500 ft. 

N. 43°53'53.5", W. 112°.58'38". 

D308 CO West side of Black Canyon, elev 8,600 ft. 

N. 43°54'49", W. 112°59'43". 

D309 CO On ridge N'\V of Black Canyon, elev 8,900 ft. 

N. 43°55'17", W. 112°59'46". 

D311 CO Southwest side of south fork of South Creek, 

elev 8,100 ft. N. 43°55'39", W. 

112°59' 40.5". 

D312 CO Close to creek on north side of south fork of 

South Creek, elev 7,700 ft. N. 43°58'33", 

'\V. 112°59'42.5". 

D313 CO South of Black Canyon, elev 7,700 ft. N. 

43°53'40", w. 112°59'40". 

D314 CO South of south fork of South Creek, elev 7,300 ft. 

N. 43°55'59", W. 113°00'30". 

D316 CO About halfway between North and South 

Creeks, elev 8,350 ft. N. 43°57'49.5", 

w. 113°00'26". 

3831 SD North side of south fork of Badger Creek, elev 

7,800 ft. N. 44°06'28.5", W. 113°06'41.5". 

(May be erosion remnant of Laketown 

dolomite or equivalent strata) 

DATING OF THE SATURDAY MOUNTAIN FORMATION 

BASED ON PREVIOUS EVIDENCE 

The Saturday Mountain formation was named and 

described (C. P. Ross, 1934, p. 952-956 ; 1937, p. 18-22) 

for its exposures in the Bay horse region, Idaho. In 

1947 Ross (p. 1104-1105) noted its presence in the 

Borah Peak quadrangle. In both reports the formation was dated as Late Ordovician, and in the Bayhorse area it was correlated with the Fish. Haven 

dolomite and the upper part of the Bighorn dolomite. 

In the Bay horse quadrangle, Borah Peak quadrangle 

and southern end of the Lemhi Range the Saturday 

Mountain formation overlies the Kinnikinic quartzite, 

which until 1947, was thought to be of Middle Ordovician age. Ross at that time (p. 1104} cited G. A. 

Cooper as the authority for correlating the quartzite 

with the Fernvale formation "of early Upper Ordovician age." This required that the Saturday Mountain be younger than the Fernvale. 

None of the Receptaculites, Maclurites, or large 

cephalopods that characterize the Red River formation, 

the lower member of the Bighorn, and the Whitewood 

dolomite, have been reported from it-suggesting that 

the Saturday Mountain formation should not be corre-

.lated with these units. Correlation with the Hanson 

Creek formation of Nevada is not as firmly established 

as might be hoped. 

Lithologically much of the Hanson Creek formation, 

particularly on Mount Hamilton (Pancake Summit 

quadrangle, Nevada), cannot be distinguished from the 

Fish Haven dolomite. The two are probably parts of 

a single unit of wide extent. If the Saturday Mountain is correlative with the Fish Haven dolomite, it 

should be equivalent to the Hanson Creek also. 

The silicified brachiopods obtained on Mount Hamilton (Locality D283 CO) were tpo poorly preserved to 

he identified as to species. However, the dinorthids 

and dalmanellids that comprise most of the fauna are 

not identical with those of the Saturday Mountain for- · 

mation, nor are they the same as those from the uppermost Bighorn dolomite. Unfortunately, preservation 

is so poor that only this negative evidence is available 

and I a.m unable to determine what fa.una specimens 

f~mn the Hanson Creek resemble most closely. Therefore, exact correlation of the Saturday Mountain formation with the Hanson Creek of central Nevada. is 

no~ yet possible on the basis of brachiopods. 

One collection from the Saturday Mountain strata of 

the Bayhorse region contained graptolites (Ross, C. P., 

1934, p. 954-955; 1937, p. 21) which were identified by 

Ruedema.nn. The listed graptolites n1ay be expected 

to indica.te correlation with the Lower Caradoc; this 

is considerably older than the brachiopod and coral 

fauna seems to indicate. C. P. Ross (1937, p. 22) 

noted the discrepancy but so far as I know no explanation has ever been offered for it. 

In the Bayhorse area the Saturday Motmtain has 

been considered younger than the Ramshorn slate 

(Ross, C. P. 1937, p. 16-22}, considered "Deepkill" in 

age, i. e. Arenig to Llanvirn and older than Caradoc. 

However, one collection from an isolated area of out-

. crop (T. 8 N., R. 18 E.) includes ·specimens "probably 

~eferruble to Monograptus," an exclusively Silurian 

genus. According to C. P. Ross (1937, p.17) lithologic 

similarity indicated that this outcrop should be mapped 

as Ramshorn slate, not as Silurian Trail Creek forma-
444 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

tion. Therefore, the Ramshorn slate could range from 

Arenig to Silurian in age. 

If so, the Ramshorn slate is equivalent in age and 

facies to the Phi Kappa formation of the Wood River 

district. The Saturday Mountain formation on the 

other hand would be equivalent in age only to a part 

of the Ramshorn slate and in facies would contrast 

strongly with it. The geographic distribution of Ramshorn and Saturday Mountain strata within the Bayhorse area (Ross, C. P., 1934, plate 1), their contrasting 

lithologies, but partly correlative ages indicate either 

that the two are examples of a peculiar facies change 

or that they have been placed in juxtaposition tectonically. Tectonic activity might easily explain the presence within the geographic bounds of the Saturday 

Mountain formation of shales of Caradoc age, derived 

from the Ramshorn slate. 

Nolan, Merriam, and Williams (1956, p. 33) note the 

occurrence of graptolites in the Hanson Creek formation. This fauna has been identified and dated by 

Ruedemann (Merriam and Anderson, 1.942, p. 1686; 

Ruedemann, 1947, p. 108) as correlative with the Polk 

Creek shale of Arkansas and the Sylvan shale of Oklahoma, both! of which are supposedly of Ashgill age. 

This indicates that the Hanson Creek is younger thano 

the graptolite-bearing beds of Caradoc age assigned 

by C. P. Ross (1937,. p. 18-22) to the Saturday Mountain formation. There is evidence from locality 3831-

SD (p. 245) that the Saturday Mountain formation as 

mapped by C. P. Ross (written communication, 1957) 

is locally of Silurian age or that a loc;:tl remnant of 

Silurian strata rests between Ordovician and Devonian 

units. Therefore, the Ashgillian beds of the Hanson 

Creek may correlate with part of it. 

In Nevada the Hanson Creek is locally in juxtaposition with correlative Ordovician rocks of the Vinini 

formation. These are graptolite-bearing shales of an 

entirely different facies thrust in from the west (Nolan, 

Merriam, and Williams, 1956,. p. 34). In Idaho, though 

not in the southern Lemhi Range, similar black shales 

of the Phi Kappa formation are- in close proximity to 

the Saturday Mountain formation (Umpleby, Westgate, and Ross, 1930, p. 18-23, pl. 1). The age of the 

beds of the Phi Kappa seems to range from Llandeilo 

to Ashgill. Studies on graptolites from the Valmy 

and Vinini formations of Nevada lead me to conclude 

that it ranges from Arenig through Ashgill in age. 

It therefore seems evident that the concept of a Western Ordovician facies should now be considered for 

Idaho, just as it has been accepted for Nevada. As 

stated above this concept might also clarify the interrelations of the Saturday Mountain and Ramshorn 

strata of the Bayhorse area. The eastern time equivalents of the Phi Kappa axe the Kinnikinic quartzite 

and Saturday Mountain formation; its southern time· 

and rock equivalents are the Vinini and Valmy formations. 

COMPOSITION AND SIGNIFICANCE OF THE 

BRACIDOPOD FAUNA 

COMPOSITION OF THE FAUNA 

The brachiopod fauna of the Saturday Mountain 

formation in the southern Lemhi Range is little varied. 

Specimens are silicified and therefore can be obtained 

in abundance, but only 19 species have been collected 

(see table 1). 

Distribution of these species by locality is shown in 

table 1. Because collections from many of the localities were merely small field samples, distribution cannot be considered entirely reliable. Fo~ example, the 

sample from locality D302 CO; submitted for identification .}ate in 1955, contained a single specimen of 

Lepidoayalus. Additional collecting would probably 

yield other species at that locality. 

AGE OF THE FAUNA 

Most of the genera listed above are found both in 

Middle and Upper Ordovician rocks. A ustiJtella occurs both in the Waynesville shale of the Richmond 

group and the Maquoketa shale. Until recently it was 

generally accepted as a Richmond index fossil. Sinclair (1956, p. 128) questioned the value of Austinella 

in this respect, suggesting that it may occur in beds 

of Trenton age. Flower (written communication, June 

11, 1956) is convinced of the Red River age of the 

Burnam limestone of Texas in which Austinella also 

is prese~t (Barnes, Cloud, and Duncan, 1953, p. 1037). 

It is Flower's conviction (1952, p. 25-26) that the Red 

River fqrmation is more likely to be of Trenton than of 

Richmo~d age, because many genera of Red River 

cephalopod associations "are appearing in strata of unquestionably late Trenton age." Flower (1952, p. 27) 

places emphasis on the cephalopods from the Terrebonne formation in the vjcinity of Montreal. These 

forms he states are related to the Red River fauna, 

but the strata of the Terrebonne are considered by Clark 

(1952, p. 62, 74) to be of late Trenton age. 

L01'dorthis variabilis Ross n. gen. and sp. bears a 

strong resemblance to Dolerorthis of Silurian age and 

may be fairly closely related to some Silurian species 

of Hesperorthis (pl. 54, fig. 26) (Whittard and Barker, 

1950). Zygospira putilla adds a Silurian element to 

the fauna but Z. cf. Z. airaularis Cooper and Z. cf. Z. 

lebanonensis Cooper are closer to forms of Middle Ordovician age. The specimens of Austinella compare very 

closely with topotype material of A. whitfieldi from 

the Maquoketa shale of Minnesota. The bryozoan · 
BRACHIOPOD FAUNA OF SATURDAY MOUNTAIN FORMATION 445 

TABLE !.-Distribution of brachiopods and one coral species 

Species Locality 

D203 D234 D235 D236 D237 D238 D240 D302 D304 D306 D308 D309 D311 D312 D313 D314 D316 

---------------·-----------------------------------

Platystrophia cf. P. equiconvexa Wang_______ X X X ---- X X X ---- X X X X ---- ---- X ---- X 

Lordorthis variabilis, n. gen. and sp. Ross____ X X X X X X X ---- X X X X X X X X X Glyptorthis cf. G. pulchra Wang ________ - _- _ _ _-- _- __ - ____ - _ _ X X X _ _ _ _ _ _ _ _ X _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __________ _ 

Plaesiomys subquadratus subsp. idahoensis 

Ross, n. subsP------------------------- X ---- X X X X X ---- ____ X ---- X ____ ---- ---- X X cf. P. bellilamellosus Wang _____________ ------------ X ---- _______________________________________________ _ 

A ustinella aff. A. whitfieldi Winchell & 

Schuchert----------------------------- X X X X X X X ---- X X X X X X X X ---- Undet. rhynchonellid, immature ____________ ---------------- X ____ X _______________________________________ _ 

Lepidocyclus? cf. L. rectangularis Wang______ X ---- ---- ---- ---- ---- ____ X ____ ____ ____ ____ X _______________ _ Hypsiptycha SP-----------.,---------------- ---- ---- ---- ---- ---- ____ ____ ____ ____ ____ ____ ____ X _______________ _ Zygospira cf. Z. recurvirostris Ha.L _________ ---- ---- ---- ---- X ____ X ____________________ ---~ _______________ _ putilla Hall and Clarke _______________ X ---- ---- ------------ ________________________________ X _______ _ aff. Z. putilla Hall and Clarke _________ ---------------- X ____ X _______________________________________ _ 

cf. Z. circ'ltlaris Cooper ________________ -------- X ---- X ---- X ____ X ____ X ________ ---- ---- ---- ---- cf. Z. lebanonensis Cooper _____________ -------- X ---- X ---- X ____________ X ____ X -------- ---- ---- Thaerodonta sp. (small) ____ --------------- X ---- ---- ---- X X X _ _ _ _ _ _ _ _ _ _ _ _ X _ _ _ _ X _______________ _ 

Rafi~~;g~!:~)s_p~~======================= Strophomena sp ___________ - __ -- ____ ------ ---- ==== ==== X ==== ---- ---- ==== ==== _ _ _ _ _ _ _ _ X ==== ~ ==== _______________________________________ ==== ==== :::: ==== ==== -~- ==== ==== ==== _ Diceromyonia cf. D. tersa (Sardeson) ________ ---- X X X ---- X X ____ ____ ____ X ____ X X ____ X ___ _ Streptelasma (Grewinkia) robustum (Coral) ___ X X X ---- ---- X ____________________________ X X ____ X 

Sceptropor·a facula Ulrich, important because it is 

known only from the Richmond, Maquoketa and Stony 

Mountain formations and from the correlative uppermost beds of the Bighorn dolomite, is present in some 

of the collections. 

The previous Late Ordovician dating of the Saturday Mountain formation is not as clearly substantiated 

as might be desired. 

If the Fernvale formation is truly of Late Ordovician age and if the brachiopod fauna of the Kinnikinic 

is indisputably correlative with that of the Fernvale, 

the overlying Saturday Mountain must be of Late Ordovician and (or) Silurian age. On Badger Creek, 

C. P. Ross (oral communication, February 24, 1958) 

collected Silurian fossils (USGS Loc 3831-SD) from 

talus which n1ay have been derived from the topmost 

beds of the Saturday Mountain formation and (or) 

from a local remnant of Laketown dolomite. 

North o£ Badger Creek, in the Bayhorse region (C. P. 

Ross, 1934, p. 954-955; 1937, p. 21), graptolites that I 

consider to be of early Caradoc (Middle Ordovician) 

age have been reported from the Saturday Mountain 

formation. I£ these are not in Ramshorn slate tectonically mixed with the Saturday Mountain formation, 

the latter seems to have been deposited during Middle 

and Late Ordovician (and possibly some of Silurian) 

time. 

The presently known brachiopod fauna is not clearly 

of Middle or Late Ordovician age. Fossils that suggest a Late Ordovician age are : 

Sceptropora facula (bryozoan) 

Platystrophia cf. P. eq1ticonve(l)a Wang 

467782-59--2 

Glyptorthis cf. G. pulchra Wang 

Plaesiomys subquadratus idahoensis Ross n. subsp. 

P. bellilamellosus Wang 

.A.ustinel.la aff . .A.. whitfieldi Winchell and Schuchert 

Lepidocyclust cf. L. rectangularis Wang 

Thaerodonta sp. 

Diceromyonia cf. D. tersa (Sardeson) 

Six of these nine species compare closely with but are 

not necessarily identical to previously known Late 

Ordovician forms. 

Three species of a single genus have Middle Ordovician affinities: Zygospira c£. Z. recurvirostris, Z. c£ .. 

Z. circularis, and Z. c£. Z. lebanonensis. Yet these are 

associated ·with a Silurian index fossil, Z. putilla. 

Questions raised about the significance of A ustinella 

have been mentioned above. 

' Comparison with known Late Ordovician brachiopod 

faunas of North America is hampered by the complete 

lack of monographic studies on any collections from 

the western United States. , Cooper (1956, p. 6) notes 

that Middle Ordovician strata in Nevada should receive 

additional attention although his own recent study 

. (1956) is the only one on brachiopods of Middle 

Ordovician age west of the Black Hills. 

At present it seems wise to state orrly that the 

brachiopod fauna described here has more Late than 

Middle Ordovician affinities, and that its exact correlatives cannot yet be determined. 

ECOLOGIC SIGNIFICANCE OF THE FAUNA 

The brachiopod shells seem to have been moved little 

by bottom currents or waves. The ocean bottom in this 

area may have been quiet. Evidence for this conclusion is given below. 
446 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

About the same number of brachial and pedicle valves 

occur in the collections, suggesting little sorting according to different hydrodynamic behaviour of the 

valves. There are more articulated shells thap. usual 

in similarly etched silicified deposits, indicating little 

movement by waves. Immature growth stages of 

several species are abundant; however they do ·not outnumber mature specimens, as might be expected if 

there had been no sorting whatsoever according to size. 

Large shells of Lordorthis variabilis (pl. 54, fig. 13) 

generally have poorly preserved ribs. This might be 

interpreted as the result of abrasion. However, immature specimens of this species have ornamentation 

preserved in the finest detail (pl. 54, figs. 31, 36) and as 

shown by two of the illustrated specimens (pl. 54, figs. 

1, 9, 13) ribbing seems to deteriorate at major growth 

lines. There is good evidence that poorness of ribbing 

is normal in this species after shells have reached 

lengths of 10-15 mm. 

Certain expectable elements of 1\iiddle and Late 

Ordovician faunas are missing or scarce; these include 

the large rhynchonellids, such as Lepidooyolus oapam, 

and htrge strophomenids. Representatives of each of 

these are found but they are rare. The reason for their 

scarcity is not apparent. 

SYSTEMATIC DESCRIPTION OF THE BRACHIOPODS 

Class ARTICULATA 

Superfamily ORTHACEA 

Family PLECTORTHIDAE Schuchert and Cooper, 1931 

Subfamily PLATYSTROPHIINAE Schuchert, 1929 

Genus Platy.strophia King, 1850 

Platystrophia cf. P. equicon.vexa Wang 

Pia te 56, figures 1, 2, 5-8 

This species is not well represented in tl}.e collections. 

All of the mature specimens are broken or deforn1ed, 

and observations must be based on imperfect and immature specimens. These belong to the "low fold subgroup of the triplicate group" of McEwan ( 1920, p. 

390). 

The outline is subrectangular and hinge extremities 

are essentially right-angled; they may be slightly obtuse, or slightly acute. The dorsal valve has convex 

flanks. Pedicle flanks are equally convex on half the 

specimens at hand, and a little less so on the others. 

There are four costae on the fold and three in sinus, 

all of about the same size as those on the flanks. The 

largest specimen in the collections has 12 costae on the 

flanks and 1 or 2 additional incipient ribs in the postero-lateral corners. A similar number are present on 

one much smaller specimen. One small specimen has 

10 costae on one flank and eight on the other. The fold 

is 4.7 mm wide and 3.6 mm high at the front of a valve 

11.2 mm wide. The fold is a little more prominent than 

,in P. equiaonvewa (Wang, 1949, pl. 4B, fig. 4). 

The small specimens of this species are easily confused with P. ewtensa McEwan in which the pedicle 

valve has the more convex flanks (McEwan, 1920, pl. 

42, fig. 40). They also resemble P. elegantula var. 

triplicate McEwan which possesses distinctly obtuse 

postero-lateral angles (McEwan, 1920, pl. 43, fig. 48). 

I have discovered no practical way to distinguish immature specimens of the Saturday Mountain species 

from P. amoena McEwan, but the adults are readily distinguished by the greater number of flank costae, larger 

size, and relatively higher fold. P. oolbiensi8 Foerste 

is very similar in outline. McEwan (1920, p. 414) 

states that there are 9-11 costae on its flanks, but her 

illustr~tions (McEwan, 1920, pl. 44, figs. 8-11) and 

Foerste's (1910, p. 55-56, pl. 4, fig. 2) original description indicate that there are 8 or 9'. P. oolbiensis has a 

fold even lower than those of immature specimens of 

the Saturday Mountain species. 

Since all of the species compared above are of Middle Ordovician age it is fortunate that collections were 

not limited to immature specimens by which erroneous 

dating could have been suggested. 

Mature specimens closely resemble P. anniea'J'IJJW 

Foerste which, however, has concave flanks on the pedicle valve and a longer hinge line. P. olarksvillensis 

Foerste has a longer hinge line and fewer 'costae on 

the flanks. From P. equioonvewa Wang the specimens 

at hand differ in having a more prominent fold and 

deeper sulcus. Th~ strong convexity of the pedicle 

valve is not a consistent feature, but the observed 

range of variation includes the holotype of P. equiconvewa (Wang, 1949, pl. 4B, figs. 3, 4, 5). 

If better material were available it might be possible 

to determine whether the specimens belong toP. equioonvewa or to a new species. 

Figured specimens : USNM 133259-133261 

Localities: D203 CO, D234 CO, D235. CO, D237 CO, 

D238 CO, D240 CO, D304 CO, D306 CO, D308 CO, 

D309 CO, D313 CO, D316 CO. 

Family HESPERORTHIDAE Cooper, 1956 

Subfamily HESPERORTHINAE Schuchert and Cooper, 1931 

Genus Lordorthis Ross, new genus 

Essentially this genus includes resupinate species that 

would otherwise be assigned to H esperorthis. At present it is monotypic. 

In immature stages the shells are planoconvex and 

some immature specimens of the type species indicate 

that the brachial valve may be slightly concave. Mature brachia] valves are convex anteriorly. Pedicle 
BRACHIOPOD FAUNA OF SATURDAY MOUNTAIN FORMATION 447 

valves in immature stages are hemipyramidal but become anteriorly concave or flattened. A chilidium like 

that of H esperorthis may be present, but is preserved 

probably only rarely. The delthyrium is partly closed 

by an apical plate or pseudodeltidium also comparable 

to that of H esperorthis. The pedicle cardinal area is 

apsacline and wider than long. In adult specimens the 

angle between sides of the delthyrium is approximately 

60 degrees; in immature specimens it may be considerably less. 

The brachiophores are bladelike and the cardinal 

process simple. The definition of the median septum 

of the brachial valve is variable in the type species. In 

the pedicle valve the muscle field is typically that of 

H esperorthis. 

Type species.-Lordorthis variabilis Ross, n. sp. 

Discussion.-Lordorthis closely resembles B oreadorthis ( Opik, 1934, p. 184-186) and Dolerorthis; both of 

these genera have convex brachial and flattened pedicle 

valves. The resemblance to Boreadorthis is the closer 

because that genus also possesses H esperorthis-like 

cardinalia~ a chilidium and pseudodeltidium. Neither 

Boreadorthis nor Dolerorthis passes through a planoconvex or concavo-convex stage of growth and as a 

result their brachial valves possess continuously convex lateral profiles. In Lordorthis on the other hand, 

brachial valves are initially flat or concave (plate 54, 

figs. 6, 20, 22, 36); the mature valves, though convex, 

always have an initial concave profile close to the interarea (plate 54, fig. 2). 

The stout brachiophores of Dolerorthis and its lack 

of chilidium and deltidium also serve to distinguish 

that genus from Lorclorthis. 

Until its shells are over 6.0 mm long Lordorthis 

variabilis, the type species, can be unquestionably classified with H esperorthis. Thereafter the shells become resupinate. 

Lordorthis variabilis Ross, n. sp. 

Plate 54, figures 1, 2, 4-6, 8-11, 13-17, 19-25, 27-28, 31-32, 35, 36 

This species is the most abundant of all brachiopods 

in the Saturday Mountain formation of the Lemhi 

Range. Over 100 specimens are at hand and these show 

considerable variation, especially in outline of the 

shells. 

Eroterior.-The outline is variable, being subsemicircular, subsemiellipitical or subrectangular. The 

brachial valve is gently convex with a faint median 

sulcus that fades out anteriorly. The pedicle valve is 

gently convex at the umbo, flattening anteriorly; in old 

specimens it is slightly resupinate toward the margin. 

The dorsal area is anacline and short, while the pedicle 

interarea is apsacline, plane to very slightly curved, 

about a third as long as wide. 

A few specimens of brachial valves show thin uplifted edges on the inside of the notothyrium (pl. 54, 

fig. 21). These and a single small specimen with an 

arched plate in place indicate that there was a delicate chilidium with the general shape of those in H esperorthis (compare pl. 54, fig. 35 with Schuchert and 

Cooper, 1932, pl. 4, figs. 17, 18, 29). The pseudodeltidium is essentially as in H esperm·this; a few specimens 

have an arched rather than flat plate (pl. 54, figs. 14, 

16) and a very few have the pseudodeltidium isolated 

by conjoining adventitious material added to the sides 

of the delthyrium. In these last the pseudodeltidium 

seems to have been built· forward beneath the adventitious material (pl. 54, figs. 23, 24). 

Specimens in which the edges of the delthyrium are 

raised in the same manner as the edges of the notothyria 

mentioned above are fairly numerous; these originally 

led me to surmise that an arched deltidium must have 

been present. Addition of material along the edges of 

the delthyrium is common in the Hesperorthinae 

(Schuchert and Cooper, 1932, p. 85). 

The ribbing is more highly variable than other features of the shells. There is a definite tendency for external ribbing to become obscure after shells have 

reached a length of 15 mm. Some are paucicostate, 

others multicostate. Counts made at an arbitrary 

. median length of 18 mm from the umbo of the pedicle 

valve indicate that simple costae average 7 in 10 mm 

of width, and may be expected statistically to number 

as low as 4 and as high as 10. For shells in which 

smaller ·ribs are intercalated between the costae the total 

count at 18 mm from the pedicle beak may be expected 

to range as high as 14 in 10 mm of width. 

Interior of the ventral valve.-The description of the 

pedicle interior follows almost exactly that given by 

Schuchert and Cooper (1932, p. 88) for the genus 

Dolerorthis, but most of the differences which they 

considered interspecific are here clearly variations 

among individuals of the one species. The distinctness 

with which the median ridge and two pallial trunks are 

developed is highly variable; this cannot be attributed 

entirely to mode of preservation. (Compare pl. 54, 

figs. 4, 14, 19, 24.) 

Interior of the brachial valv.e.-The brachial interior 

is essentially that of H esperorthis. Not one of the 

large brachial valves shows the muscle scars well enough 

to differentiate the anterior from the posterior adductors, a condition illustrated by Opik ( 1934, fig. 43) 

for B oreadorthis; this leads me to consider the possibility that the posterior scars are the larger and that 

the anterior pair may be so small that they are insig-
448 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

nificant-a condition approached by Dolerorthis rustioa 

osiliensis ,(see Schuchert and Cooper, 1932, pl. 5, fig. 

23). One immature brachial valve does show a faint 

transverse ridge between anterior and posterior pairs 

so that they are almost equal in size ; the posterior pair 

is only slightly larger. In this immature characteristic, 

as in several others, Lordorthis variabilis strongly resembles B esperorthis. 

The most obvious variation in this species is found 

in the ratio between the lengths and widths of valves; 

this is particularly obvious in pedicle valves and is illustrated by specimens in plate 54, figures 4, 8, 13, and 

19. Because there are variants between the extremes 

of subrectangular and subsemicircular shells they all 

obviously belong to the same species. 

Shells which are subrectangular tend to have fine 

costae intercalated between the coarse primary costae 

(see pl. 54, fig. 4). Those which are subsemicircular 

have few if any intercalated .parvicostae (pl. 54, fig. 

13). The difference is probably a reflection of the difference in peripheral distance around shells of two 

shapes, there b.eing room for more ribs on a rectangle 

than on a semicircle of comparable size. The specimen 

illustrated in plate 54, figure 13, belongs in the subsemicircular group. Fortunately it shows growth 

lines, and it will be noted that when the median length 

was about 17 mm this was a subrectangular shell. 

Immature oharaoteristios.-Immature specimens of 

this species have several features in common with 

H esperorthis. Small specimens (pl. 54, figs. 22, 25, 28, 

32) have nearly flat brachial valves and strong simple 

costae, and some of them I previously identified as 

H esperorthis in preliminary study of the collections. 

Still smaller specimens (pl. 54, figs. 27, 31, 26) show 

the manner in which many of these seemingly simple 

ribs are intercalated and also show the strongly lamellose nature of the surface in the immature stages. 

The smallest specimen found (pl. 54, figs. 6, 10) is 

a brachial valve. It possesses the brachiophores and 

cardinal process characteristic of the genus even at this 

early stage and can be readily distinguished from similarly small specimens of Austinella (pl. 55, figs. 2, 7). 

Holotype: USNM 133227 

Paratypes: USNM 133228-133237 

Localities: D203 CO, D234 CO, D235 CO, D236 

CO, D237 CO, D238 CO, D240 CO, D304 CO, D306 

CO, D308 CO, D309 CO, D311 CO, D312 CO, D313 

CO, D316 CO. 

Disoussion.-Whittard and Barker (1950, p. 564-565, 

pl. VI, figs. 8, 9) described H esperorthis onniensis from 

the Upper Valentian of Shropshire. A latex cast of 

the type and only known specimen is illustrated here 

(pl. 54, fig. 26). This Lower Silurian species closely 

resembles the present one in outline and convexity of 

the bracial valve. The brachiophores are not quite 

so long, however. Because the exterior of the British 

valve is unknown, no further comparison can be made. 

Williams (1951, p. 89) has criticized Whittard and 

Barker for assigning specimens of this type to Hesperorthis rather than to Dolerorthis and has redescribed 

and illustrated Dolerorthis plioata Sowerby (Williams, 

1951, p. 88-89, pl. 3, figs. 1-3) from the Llandovery; 

this species differs from the Saturday Mountain specimens in its lack of deltidial plate, character of its ribbing, and bluntness of brachiophores. 

Cooper (1956, p. 298-299, pl. 36E, figs. 32-39) has 

described Orthambonites braohiophorus from the Effna-Rich Valley and Boutetort formations in Virginia 

(Porterfield Stage of Cooper, 1956, p. 8, chart 1). This 

species is strikingly similar to L. variabilis in several 

respects : the type of cardinal process and brachiophores, fine concentric ornamentation, convex brachial 

valve with a shallow sulcus disappearing toward the 

anterior margin, pedicle muscle pattern and pallial 

markings. 

Cooper ( 1956, p. 294, 299) notes that his species does 

not conform to the strict concept of 0 thambonites and 

that it does resemble H esperorthis in cardinalia and 

outline. However, he states that no evidence for a 

pseudodeltidium has been found, a fact which militates 

against assignment of 0. braohiophont.S to H esperorthis. 

As more information is gathered on forms similar 

both to 0. braohiophorus and to Lordorthis variabilis 

a closer relationship than is now indicated may become 

evident. This possibility suggests that species of 

Lordorthis may be discovered in Middle as well as in 

Upper Ordovician strata. 

Subfamily GLY:PTORTHINAE Schuchert and Cooper, 1931 

Genus Glyptorthis Foerste, 1914 

Glyptorthis cf. G. pulchra Wang 

Plate 54, figures 39, 40; Plate 56, figures 18-20, 25, 26 

Glyptorthis pulcllra Wang, 1949, Geol. Soc. America Mem. 42, 

p. 4, pl.1E, figs.1-10 

This species is represented by seven specimens. The 

material is too poor to make accurate comparisons with 

other species but good enough to be sure that it does 

not belong to any of the species described by Cooper 

(1956, p. 361-383) from Middle Ordovician rocks. It 

most closely resembles G. pulohra Wang. 

It is a fairly large species, two pedicle valves being 

20 mm ·wide and 15 mm long. The anterior outline is 

bilobed, particularly in pedicle valves. Convexity of 

both brachial and pedicle valves is about equal. The 

brachial one possesses an angular sulcus of al~ost uni-
BRACHIOPOD FAUNA OF SATURDAY MOUNTAIN FORMATION 449 

form depth; at the front this contains 6 costellae on 

one specimen and 9 on another. The surface is covered 

by 51-55 costellae; in 5 mm at the front there are 

6-7. Concentric lamellae are spaced 10 in 5 mm. A 

single strong costella forms the crest of the pedicle 

fold. 

In the pedicle valve the muscle field extends forward about hal£ the length of the valve and has a 

raised front edge. · 

Figured specimens: USNM 133244, 133264, 133265, 

.133266. 

Localities: D237 CO, D238 CO, D240 CO, D306 CO. 

Discu8sion .. -A complete individual was obtained 

from locality D238 CO which is obviously more mature 

than the other specimens (pl. 56, figs. 18, 25, 26). Unfortunately lateral compression has deformed the two 

valves, accentuating the brachial sulcus at the anterior 

margin and creating a false sulcus at the front of the 

pedicle valve. Another equally large specimen from 

locality D240 CO shows that the pedicle fold extends 

to the margin. 

Family DINORTHIDAE Schuchert and Cooper, 1931 

Genus. Plaesiomys Hall and Clarke, 1892 

Plaesiomys subquadratus <Hall) 

Plate 55, figures 1, 6, 12, 14, 15, 18, 19, 23 

Orthis subquadrata Hall, 1847, Paleontology of New York, v. I, 

p. 126, pl. 32A, figs. la-d. 

I-Iall's (1847) original type specimens were never 

well illustrated. Three of them are here shown in 

stereoscopic view so that comparisons may be made 

more accurately. 

Figured specimens: AMNH 913/6. 

Locality: "Hudson River Group," Cincinnati, Ohio. 

Plaesiomys subquadratus subspecies idahoensis Ross, 

n. subsp. 

Plate 54, figures 29, 30, 33, 34, 37, 38, 41, 42; plate 55, :figures 

22, 26, 27, 30, 31 

Shell outline is subrectangular to subelliptical ~nd 

about three-fourths as long as wide. The brachial valve 

is moderately convex with a shallow sulcus. The pedicle 

valve is almost flat with a very low_ narrow fold, that 

is carinate near the umbo. The hinge line is straight, 

the width at hinge being about three-fourths the greatest width of the shell. Cardinal angles are rounded 

and/or obtuse. Ornamentation is multicostate, averaging 14 costae in a space of 10 mm at a distance of 15 

mm from the beak. The costae may bifurcate 2 to 3 

times and are rounded with narrow interspaces. 

The pedicle interarea is short and apsacline; the 

brachial interarea is short, and orthocline to slightly 

apsacline. The cardinal process with its crenulated 

myophore projects beyond the plane of the interarea. 

Type specimen : USNM 133239 

Figured specimens: USNM 133240-133243 

Localities: D203 CO, D235 CO, D236 CO, D237 CO, 

D238 CO, D240 CO, D306 CO, D309 CO, D314 CO, 

D316 CO. 

Discussion.-Features which have been used to distinguish the species of Plaesiomys in the past are relative length and width of valves, width at the hinge line 

relative to the total width, definition of sulci and folds, 

and character of the ribbing. For instance, P. iphigenia_ 

(Billings) and P. meedsi Winchell and Schuchert are 

distinguished from other species on the basis of their 

possession of a pedicle rather than a brachial sulcus. 

P. subquadratus as described by previous authors is 

highly variable in relative length, width, and hinge· 

width, as well as in the spacing of costellae. Of the 

previously described species of Plaesiomys the majority 

of the specimens from the Saturday Mountain formation compare most closely with P. subquadratus. The 

original type specimens of that species are here figured 

photographically for the first time (pl. 55, figs. 1, 6, 12, 

14, 15, 18, 19, 23). On the average, the Idaho specimens ar~ smaller. in size but this might be the result of 

environment. Outline and convexity of the valves are 

proportionately very nearly the same. There are significant differences between the two; however, these 

may not be evident when comparing single specimens. 

A statistical analysis of P. subquadratus was based 

on the three type specimens illustrated here plus 20 

specimens for which Shaler (1876, Table IX) tabulated 

measurements. The necessary initial assumption was 

made that Shaler's sample represented a single species. 

Scatter diagrams of several ratios were made for P. 

subq'ltadratus and for the Saturday Mountain specimens (figs. 146-154). Raw data for these diagrams 

are given in. table 2. Invariably these diagrams show 

much wider limits of variation for P. subquadTafJus 

than for the Idaho material, and the latter when plotted 

on the same diagram will fall within the limits of variation of P. subquadratus (as an example, see fig. 146). 

However, when the regression lines, computed separately for the type and for the materials from the 

Saturday Mountain are plotted they do not coincide 

and several differences indicated are thought to be 

significant. 

·, As an indicator of outline the length and width were 

plotted (figs. 147-150) and the resulting graphs compared for brachial and pedicle valves. Figures 147 

and 148 show that the slope of the regression line for 

both samples of brachial valves is essentially the same 

but that these differ in position of the y intercept. By 

. itself this might mean little if the same were not the 

case in a comparison of the pedicle valves (figs.· 149 

and 150). 
450 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

J 

30 

i4 

\.~0 

·o~ c:,"' 0c:, :(,. 

~eOJ 

1_3 20 19 

. 18 CJ) 25 

a:: "15 

"12 

. 

4 

11 

lJ.I 

1-

w 

~ 17. 

16 

_J 2"• 9 24 

2"2 ;/ t"o 23 

_J 

2 

21 31 

20 /3 + 0 X o35 38 X 30 

z 

.. \ 26>< • 0 37 

I 0 / 8 

• 32 /34 • o40 

6 0. 0 33 7 

~1 0 

8 39 

36 

1-

(.!) 

z 

w 

_J 

X 0 "5 

/27x 29 

10 

20 30 

WIDTH, IN MILLIMETERS 

40 

FIGURE 146. Plaesiomys subquadratus and comparable species. Scatter diagram of length: width, making no separation of brachial and pedicle valves. 

Regression line computed on 3 qf Hall's type spe~imens (1847) and 20 of Shaler's (1876, Table IX) specimens. See table 2. 

'There is good correlation in both these cases between 

length and width. This is wholly expected, for· one 

observes empirically that the shells become wider .as 

they grow longer. For P. subquddratus the brachial 

valves tend to follow the following formula : Length= 

0.82 Width -0.76. For the Idaho sample the formula 

is: Length= 0.83 Width -1.33. The difference between the two is in the constant, which indicates that 

for any given width brachial valves from Idaho will be 

0.56 mm (1.33-0.76} shorter than those of typical P. 

subquadratus. This difference could never be detected 

on 1 or 2 specimens and is so small that it may not be 

reliable when large samples are measured. 

The comparison of pedicle valves (figs. 149 and 150} 

indicates that the two lots tend to differ by 0.71 mm 

in length, the Idaho specimens being th~ shorter for any 

given width. Again, this difference cannot be ascertained with 1 or 2 specimens. and would require large 

· samples for comparison. 

The width at the hinge line has been used to differentiate the variety occidentalis by Ladd ( 1929, p. 402-

403, pl. 5, figs. 7-9). This variety is supposed to. be 

much narrower at the hinge than other forms of 

Plaesiomys. Ladd (1929, p. 403) states that the hinge 

is little more than half as wide as the shell's total width. 

Figure 151 is a plot of the hinge width against the total 

width of valve. Computations of regression line and 

standard error were limited to P. subquadratus (points 

1-24}. Here we find that variety occidentalis (point 

26} ·is well within limits of variation for the species and 

has no more narrow a hinge than one of Hall's original 

type specimens (pl. 55, figs. 12, 14} (point 3}. , The 
BRACillOPOD FAUNA OF SATURDAY MOUNTAIN FORMATION 451 

en 30 a: 

w 

1-

w 

:::iE 

:::i 

....1 

i 

~ 

~ 

1- 20 C!l 

z 

w 

....1 

lOL---~~----~------------~----------~ 10 20 30 40 

WIDTH,IN MILLIMETERS 

FIGURE 147. Scatter diagram oflength: width in brachial valves of Plaesiomys subquadratus. Regression llne (Y=0.82X-0.76) based on 2 of Hall's types and 14 of 

Shaler's specimens (see table 2). Standard error (Sy)=l.2. 

~0 ------------------~----------------. 

(f) / a:: 

~ /» w 

1-

w 

~ 20 ...J o/ . / ...J 

~ / 7:'/ / z / 33o / 

::r: / "39/ 

1- /~ / l!) 

z / ,,~ / w 

_I ~ c;~/.o~ /. / ~' £:.. 10 ~~ ~ 

<(-~a; / 

. ~/ 

~? 

5 

10 20 30 

WIDTH~ IN MILL I M E.T.ERS 

FIGURE 148. Scatter diagram of length: width in brachial valves of Plaesiomys subquadratus subsp. idahoensis. Regression line: Y=0.83X-1.33. Standard error 

(Sy)=0.68. For list of points see table 2. Computation excludes point 38. 

graph (fig. 151) also shows that tJ::te specimen identified 

by Wang (1949, p. 5-6, pl. 2D) as var. oooidentalis (fig. 

151, point 30) has a wider hinge than is average for 

the species and therefore cannot belong to Ladd's variety. P. bellilamellosus Wang (point 31) is so close 

to variety oooidentalis in all respects that I suspect that 

they ar.e one and the same. 

(f) 

a:: 

w 

1-

w 

:2: 

...J 

...J 

:2: 

z 

::r: 

1-

l!) 

z 

w 

...J 

/ 

30~--------------~----- ~ ~ 

~ 

~Si/· 

~ 

~ 

~ 

~ 

~ 

~ 

~ 

/ ~ 

~ 

~ 

~ 

~ 

24 ~ 

/ 

~ 

/ ~ 

lOL---------------~----------------~ ro ~ ~ 

WIDTH,IN MILLIME_TERS 

FIGURE 149. Scatter diagram of length: width in pedicle valves of Plaesiomys subquadratus. Regression llne: Y=0.72X+1.6. Standard error (Sy)=1.12. Computation based on 1 of Hall's types and 6 of Shaler's specimens (see table 2). 

30 

(f) 

a:: 

w 

1-

w 20 ~ 

...J 

...J 

~ 

z 

::r: 

1-

l!). 

z 

w 

...J 

10 

5 L-----------------L---------------~ 10 • 20 30 

WIDTH, IN MILLIMETERS 

FIGURE 150. Scatter diagram of length: width in pedicle valves of P. subguadratus 

subsp. idahoemis. Regression llne: Y=0.71X+0.89. Standard error (Sy)=0.57. 

See table 2 for specimens. Computation excludes number 38. 

The graph for the same proportion in the Idaho specimens (fig. 152) shows a different slope for the regression line. For specimens with widths under 30 mm the 

Saturday Mountain specimens will be·wider at the hinge 
452 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

40.-------------.------------,,------------. 

/ 9~ . y 3/ 

31 ·12/ 

/ 

/ 

./ 

/ 

'Y / ------1 

XX// 

26/ lQL-------~~--2-0--~--------~3~0----------~~ 

TOTAL WIDTH, IN MILLIMETERS 

FIGURE 151. Scatter diagram of hinge width: total width in Plaesiomys subquadratus. 

Regression line: Y=0.898X-4.99. Standard error (Sy)=l.83. Computation 

based on three of Hall's types and 20 of Shaler's specimens (see table 2). 

If) 

a:: 

LIJ 

tLIJ 

~ 20 

..J 

..J 

::E 

:= 

-I 

t0 

3: 

10 

10 20 30. 40 

\OTAL WIDTH, IN MILLIMETERS 

FIGURE 152. Scatter diagram of hinge width: total width in P. subquadratus subsp. 

idahoensis. Regression line: Y=0.77~-0.93. Standard error (Sy)=l.S. (See 

table 2 for specimens.) 

than will those of P. su'Qquadratus. Again, this is not 

a difference that min be told from individual specimens, 

unless they are so narrow at the hinge as to fall below 

the expectable limits of variation of the Saturday 

Mountain forms. 

Finally there are plotted in figures 153 and 154, the 

number of costellae in a space of 10 mm at the front 

~ 

zz 

;:;~ <tc:r 

j::E 

~ ~ 20J------------+~2..-3 ________ -4-------------I 

If) !f) 

0 a::· Ow 

u.toW ::E 

~:::i 

CD~ 

::E::E 

::> 

z 101-------

20 30 40 

LENGTH OF VALVE, IN MILLIMETERS 

FIGURE 153. Scatter diagram of number of costellae in 10 mm at front of valve: length 

of valve in mm for Plaesiomys subquadratus. Regression line: Y =11.68-0.02X. 

Computation based on three of Hall's types and nineteen of Shaler's specimens 

(specimen 23 excluded from computation) (see table 2 for list of specimens). 

of the valve against the length of the valve. These 

graphs show at once that there is practically no correlation between the size of the valve and the spacing 

of costellae. I have obtained similar results by taking 

the number of costellae in 10 mm at a set distance of 15 

mm from the beak. The two populations can obviously 

be differentiated on the basis of rib spacing. In P. subquadratus there is an average of 11-12 costellae in 10 

mm at the front of the shell, while in the Saturday 

Mountain forms the average is 14-15. There is obvious 

overlapping between the two tendencies. 

The specimens· of Plaesiomys frmn the Saturday 

Mountain formation are very similar to P. subquadratus. They differ in being smaller in size, in 

having finer costellation, in being very slightly shorter, 

and in being a little wider at the hinge than P. subquadratus. The differences do not seem to be great 

enough to warrant placing the Idaho specimens ~n a 

0 

z~ -<.9 

wo: 20 

<!<{ 

....1~ 

....ItW<! 

t-(J) (J)o: 

ow 15 

ot36 

LLw 

0~ 

o:-

w-' 

CD~ lei ~~ 

:::> 

z 

34 

33 

41 3s 

'35 .. 

39 32 

40 37 

20 

LENGTH OF VALVE 

30 

FIGURE 154. Scatter diagram of number of costallae in 10 mm at front of valve: length 

of valve in mm for P. subquadratus subsp. idahoensis. Regression line: Y=14.57-

0.01X. (See table 2 for list of specimens.) 
No. on Kind of 

graph specimen 

1 c 

2 B· 

3 p 

4 c 

5 B 

6 B 

7 B 

8 B 

9 B 

10 B 

11 B 

12 B 

13 B 

14 B 

15 B 

16 B 

17 p 

18" p 

19 p 

20 p 

21 B 

22 B 

23 p 

24 p 

25 -------- 26 c 

30 c 

31 c 

27 p 

28 p 

29 B 

32 p 

33 c 

3·i B 

35 B 

36 p 

37 p 

39 B 

40 p 

41 p 

c 

BRACmOPOD FAUNA OF SATURDAY MOUNTAIN FORMATION 453 

TABLE 2.-Measurements of specimens of Plaesiomys subquadratus and related forms 

[Numbers correspond to points on graphs (figs. 146-154). Specimens are designated brachial (B), pedicle (P), or complete (0)) 

Dimensions, millimeters Number of 

Remarks 

Length 

15. 5 

22:0 

21. 0 

24.4 

13 

16 

16 

18 

22 

21 

24 

25 

28 

32 

26 

23 

23 

27 

29 

29 

19 

21 

21 

22 

------------ 18 

18. 4 

19. 0 

13 

14. 7 

12. 3 

15. 7 

15. 1 (P) 

15. 6 (B) 

17. 3 

19.0 

12. 9 

17. 9 

15. 0 

16. 3 

16.2 

19. 2 (P) 

19. 5 (B) 

costellae in 

I Greatest width I 10 mm at Hinge width front 

Plaesiomys subquadra tus Hall 

19.5 12 12 One of Hall's original type specimens (pl. 55, figs. 15, 18, 19, 

22), Hall, 1847, pl. 5A, fig. 1 a, f, d. 

28. 5 18. 5 11 One of Hall's original type specimens (pl. 55, figs. 1, 6), 

Hall, 1847, pl. 5A, fig. 1 o. 26. 1 14.5 10 One of Hall's original type specimens (pl. 55, figs. 12, 14), 

Hall, 1847, pl. 5A, fig. 1, I, m. 33. 0 ------------ -------- Specimen figured by Meek, 1873, pl. 9, figs. 2 a-g. 

18 14 14 Specimen measured by Shaler, 1876, Table IX, No. I. 

19 12 11 Specimen measured by Shaler, 1876, Table IX, No. II. 

22 17 9 Specimen measured by Shaler, 1876, Table IX, 1~0. III. 

23 17 12 Specimen measured by Shaler, 1876, Table IX, No. IV. 

28 15 14 Specimen measured by Shaler, 1876, Table IX, No. V. / 

28 22 11 Specimen measured by Shaler, 1876, Table IX, No. VI. 

31 25 12 Specimen measured by Shaler, 1876, Table IX, No. VII. 

33 26 11 Specimen measured by Shaler, 1876, Table IX, No. VIII. 

32 26 12 Specimen measured by Shaler, 1876, Table IX, No. IX. 

38 30 13 Specimen measured by Shaler, 1876, Table IX, No. X. 

34 21 11 Specimen measured by Shaler, 1876, Table IX, No. XI. 

30 21 12 Specimen measured by Shaler, 1876, Table IX, No. XII. 

29 24 11 Specimen measured by Shaler, 1876, Table IX, No. XIII. 

35 27 11 Specimen measured by Shaler, 1876, Table IX, No. XIV. 

38 30 8 Specimen measured by Shaler, 1876, Table IX, No. XV. 

36 30'? -------- Specimen measured by Shaler, 1876, Table IX, No. XVI. 

22 14 9 Specimen measured by Shaler, 1876, Table IX, No. XVII. 

25 13 11 Specimen measured by Shaler, 1876, Table 12§c No. XVIII. 

29 25 20 Specimen measured by Shaler, 1876, Table I , No. XIX. 

31 22 11 ~ecimen measured by Shaler, 1876, Table IX, No. XX. 

------------ ------------ -------- all and Clarke, 1892, pl. 5A, fig. 18 (not a photo). 

23. 5 11. 7 -------- P. subquadratus occidentalis Ladd, 1929, pl. V, figs. 7-9. Type. 

24.4 18. 1 -------- P. subquadratus occidentalis Ladd (Wang, 1949, p. 5, SUI 

1807). 

23. 4 12. 1 -------- P. bellilame!losus Wang (1949, p. 6; SUI 1804). Type. 

P. proavlta Winchell and Schuchart 

16 ------------ -------- Wang, 1949, p. 5, SUI 1808. 

17. 3 ------------ -------- Wang, 1949, p. 5, SUI 1809. 

16. 5 ------------ -------- Wang, 1949, p. 5, SUI 1810. 

Plaesiomus subquadratus subspecies idahoensis Ross n. sp. 

19. 6 

20. 3 

20. 5 

21. 1 

24. 6 

17.4 

23. 4 

20. 6 

22.6 

------------

21. 2 (P) 

21. 8 (B) 

13. 6 13 Specimen from Saturday Mountain formation. 

14.4 16 Specimen from Saturday Mountain formation (pl. 54, figs. 29, 

30, 33, 34). 

13. 0 18 Specimen from Saturday Mountain formation (pl. 55, figs. 

30, 31). 

17. 2 14 Specimen from Saturday Mountain formation. 

13. 2 16 Specimen from Saturday Mountain formation. 

19. 6 12 Specimen from Saturday Mountain formation. 

16. 2 13 Specimen from Saturday Mountain formation (pl. 54, figs. 

41, 42). 

16. 1 12 Specimen from Saturday Mountain formation (pl. 54, figs. 

37, 38). 

------------ 15 Specimen from Saturday Mountain formation. 

Plaesiomus cf. P. bellilamellosu·s Wang 

Specimen from Saturday Mountain formation (pl. 55, figs. 

34, 35, 38~ 39). 
454 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

separate species, but I do ·believe they should be considered a subspecies. 

Whether this is a geographic or a stratigraphic subspecies is open to question. There is ample reason to 

~lieve that it could be geographic, since the Lemhi 

Range is about 2,000 miles west of Cincinnati, Ohio. 

- Throughout the statistical computations on subspecies 

idahoensis one specimen (point 38 on the graphs; pl. 55, 

figs. 34, 35, 38, 39) was omitted. The belief that it belongs to a separ~te species seems justified by most of 

the statistical data. A second specimen (pl. 55, figs. 30, 

31, and point 34 on the graphs) conforms very nicely 

with the rest except· in regard to fineness of costellae in 

the central part of the shell. Conformation of the margin suggests that this may be a pathologic specimen. 

Plaesiomys a:fl'. P. bellilamellosus Wang 

Plate 55, figures 34, 35, 38, 39 

Plaesiomys bellilameZZosus Wang, 1949, p. 6, pl. 2C, figs. 1-7. 

The outline is subcircular. There is a shallow, narrow sulcus on the brachial valve. The postero-lateral 

flanks are slightly concave in posterior profile. The 

pedicle valve lacks a pronounced fold and is flattened 

anteriorly. The surface is multicostate, there being 17 

costae in 10 mm at 10 mm from umbo but 15 costae at 

15 mm from umbo. 

The brachial interarea is short, narrow, and orthocline to slightly apsacline. The cardinal process with 

its crenulated myophore projects· beyond the plane of 

the interarea. The notothyrium is wide, and the median 

septum short and weak. The pedicle interarea is short, 

apsacline, and slightly curved. 

Length 

Figured specimen (complete)------- 19.5 

Brachial valve--------------------- 17.1 

Figured specimen: USMN 133245 

Localities : D236 CO, D312 CO. 

Width 

21.2 

18.1 

Hinge 

width 

12.0 

11.7 

Discussion.-This species is represe~ted by 1 complete specimen and 1 brachial valve in tlie present collections, an inadequate sample on which to base com" 

parisons. These are readily differentiated from all 

other specimens of Plaesiomys by the subcircular out-· 

line and narrow hinge .. The closest relative seems to 

be P. bellilamello8U8 Wang. The range of outline or of 

hinge width is not determinable from Wang's description. Compared with the holotype the present specimens are not quite as wide relative to length and the 

hinges are slightly wider relative to the total width 

of the shell. Convexity is about equal, but ribbing is a 

little finer than that of P. bellilamellosus at a distance 

of 15 mm from the umbo. On figures 146-154 the 

single complete specimen is plotted as point 38. Wang's 

. type of P. bellilamellosus is point 31. 

P. bellilamellosus may prove synonymous with P. subq_uadratus var. occidentalis. Wang states that it differs 

in its subcircular to subquadrate outline, but this is 

precisely the outline required by the narrow hinge of 

variety occidentalis. The specimen identified by Wang 

as· variety occidentalis (Wang, 1949, pl. 2D, figs. 1-5) 

compares very closely in outline and relative hinge 

width with P. subquadratus, but not with variety 

occidental is. 

Genus Austinella Foerste, 1909 

This genus was originally given rather informal 

designation as a subgenus of Plectorthis by Foerste 

(1909, p. 224). He gave no clear description, merely 

stating that it was typified by Orthis kankrikensis McChesney and included 0. whitfieldi Winchell. Although this statement established A. kanlcrikensis as the 

nominal type species, later Foerste ( 1912, p. 130) 

erroneously designated A. scovillei Miller as genotype. 

According to Cooper (1944, p. 298) the genus possesses undivided costae, actually too stringent a restriction and one not borne out by Cooper's figures ( 1944, 

pl. 112, figs. 1, 2). Wang's illustrations (1949, pl. 2, 

A, B) show that both A. kankakensis and .A. whitfieldi have bifurcating and {or) intercalated costae. 

Foerste (1912, pl. 8, fig~ 8) shows that A. scovillei has 

few costae with almost no tendency to bifurcate or intercalate except close to the margin. 

Foerste (1912, p. 131) differentiated .A. scovillei from 

A. kankakensis and A. 'lohitfieldi (which he believed 

synonymous) because it had approximately 40 rather 

than 60-70 costae. Winchell and Schuchart ( 1895, p. 

438) used precisely the same criterion to differentiate 

A. whitfieldi from A. kankakensis. But they placed 

equal weight on the supposed fact that the former had 

a much shorter hinge line than the latter. This interpretation is supported by Hall and Clarke (1892, pl. 5, 

figs. 24, 26) and their illustrations may have been the 

basis for Winchell's and Schuchert's differentiation. 

Schuchert and Cooper ( 1932, pl. 9, figs. 16, 19) il-

. lustrated a specimen as .A. 'whitfieldi that has the proportions and ribbing of A. kankakensis. Wang (1949, 

p. 8, pl. 2 A, B, figs. 1-5) illustrated the more transverse of two species as A. whitfieldi, but stated (p. 9) 

that A. kankakensis has more numerous third generation costae. He expressed the opinion that outline is 

not diagnostic between the two species. 

The great variation in ribbing and in outline of the 

specimens from the Saturday Mountain formation 

suggests that neither of these can be relied on 

indiscriminately. 
BRACffiOPOD FAUNA OF SATURDAY MOUNTAIN FORMATION 455 

Austtnella a1f. A. Whttfield,i Winchell ~d Schuchert 

Plate 55, figures 2-5, 7-11, 13, 16, 17, 20, 21, 24, 25, 28, 29, 82, 

83, 36, 37 

Outline subelliptical, hinge narrower than greatest 

width. Pedicle more convex than brachial valve. Some . 

specimens markedly wider than long (pl. 55, fig. 20), 

others longer than wide (pl. 55, fig. 28) with all gradations between. 

Costation yaries between two extremes. One is simple 

with bifurcations limited to the area near the cardinal 

extremities (pl. 55, fig. 20); the other has many bifurcations and intercalations (pl. 55, figs. 11, 24). Between 

these are integrading specimens in which most bifurcation is at the sides. Many specimens have a very fine 

raised line in the interspace between each pair of 

costae (pl. 55, figs. 4, 9, 11, 36). Growth lines are 

strong and numerous on some specimens and lacking on 

others. A few have regularly spaced pits on the costae 

(p1. 55, figs. 11, 17, 36). These are similar to those 

of Plectorthis punctata Cooper ( 1956, pl. 84F). 

The pedicle interior possesses the usual muscle scar 

for the genus with a straight raised front edge.· Adjustor scars are well developed on the sides of stout receding dental plates and extend in front of the plates 

on the floor of the valve. The diductor scars may have 

sharp angles at the antero-lateral corners from each 

of which a double pallial trunk runs antero-laterally 

(pl. 55, figs. 21, 25). A few well-preserved specimens 

show a diamond pattern on the floor of the valve outside the muscle scars (pl. 55, figs. 21, 25). 

The brachial valves show great variation in the 

shape of the cardinal process; some are thin with hardly 

any myophore (pl. 55, fig. 16) but others have a knoblike myophore, crenulated posteriorly (pl. 55, fig. 3). 

All gradations exist between these extremes. The quadripartite adductor scars are variously developed; in 

some specimens there are strong radiating ridges in the 

posterior pair but in others the ridges are faint or lacking. 

Figured specimens: USNM 133246-133256 

Localities: D203 CO, D234 CO, D235 CO, D236 CO, 

D237 CO, D238 CO, D240 CO, D304 CO, D306 CO, 

D308 CO, D309 CO, D311 CO, D312 CO, D313 CO, 

D314 CO. 

Discu.ssion.-The largest collection of this species 

co~es from locality D240 CO. Unfortunateli these 

specimens cannot make up in quantity what they lack 

in quality. All are rather coarsely silicified and almost all have a thin coating of clay like material pressed 

upon them. This may account for the fact that fewer 

of the specimens from this locality show the fine raised 

line between costae than do those from some of the 

other localities. It may also explain why few of the 

figured specimens from locality D240 CO seem to have 

pits on the costae. Actually they do, but the pits are 

barely discernable. 

Locality D240 CO may be at. a differe~t stratigraphic 

level from the others. This cannot be ascertained until 

more detailed mapping of the area is undertaken, but 

a different level is not indicated by the rest of the 

fauna. 

Like the collections .of other species from this formation those of Austinella suggest that some of the common criteria for distinguishing species are of little 

practical value. 

These features may be of interspecies significance: 

1. Simple vs. bifurcating or intercalated ribbing. 

2. Presence vs. absence of pits on ribs. 

3. Strong myophore vs. thin myophore. 

4. Transverse vs. elongate outline. 

5. Absence vs. presence of a fine costella between 

each pair of costae. 

These are the most striking differences among specimens in the Saturday Mountain collections. Using them 

I have attempted to sort specimens into groups. Examination of the few specimens figured here will give 

some idea of the nearly chaotic results. Separations 

made on one basis fail when others are taken into consideration. The specimens at hand probably represent 

a single variable population. 

One example seems to illustrate the point. Three of 

the figured specimens, here called A, B, and C, have 

a fine costella between costae ; these are. specimens in 

plate 55, figures 9, 11, 17. Of these, A (fig. 9) is a 

brachial valve of the elongate variety, B and 0 (figs. 

11, 17) belong to a transverse variety. All three have 

comparable adductor scars. A and B (figs. 8, 10) have 

small myophores, 0 (fig. 16) has almost none. (Another specimen, not figured, from the same locality as 

0 has the same ribbing and outline but has a large 

myophore like that in plate 55, figure 3.) A and B 

(figs. 9, 11) have bifurcating costae, 0 (fig. 17) does 

not. A (fig. 9) has no evident pits on costae, 0 (fig. 

17) definitely does, and ·they can be made out on the 

imperfectly preserved surface of B (fig. 11). 

. From this small fraction of the entire sample it is 

clear that the size of the myophore is not significant in 

distinguishing species in this case. Outline of the 

shells is not consistent with the type of ribbing. This 

last agrees with Wang's ( 1949, p. 8-9) conclusion that 

A. whitfieldi and A. kankakensis cannot be differentiated on the basis of shape. Sixteen specimens from 

the type locality of A. whitfieldi, 1 mile east of Spring 

Valley, Minn., were furnished by Professor Robert E. 

Sloan of the University of Minnesota. In that sample 

there is no correlation whatsoever between width at 
456 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

the hinge and the number of costae; 1 specimen is wide 

hinged with 60 costae, fitting Winchell's and Schuchert's (1895, p. 438) concept of A. kankakensi:J. 

About seven could be classed as .A. whitfieldi and the 

rest are intermediate. The specimen illustrated by 

Wang (1949, pl. 2.A, figs.l-5) as .A. whitfieldi probably 

should be considered in the intermediate category. 

Like the Saturday Mountain specimens those from 

Minnesota show regularly spaced pits on the costae 

wherever preservation permits. 

Wang (1949, p. 8) states that the costae of A. whitfieldi are "strong, subrounded, separated by narrow and 

deep interspaces." The topotype material shows that 

this is. true only if one is observing a pedicle valve; 

the brachial valves have narrower costae with .wider 

interspaces. In specimens of the A. kankakensis type 

the costae are narrowly rounded on both valves' and 

· the interspaces are of the same width as the costae. 

A few of the specimens from Spring Valley show 

a trace of a fine costellae between costae; it is definitely not present in all specimens, but seems to be more 

common in the paucicostate individuals. 

Ignorance of the full range of features of other 

species renders difficult, if not impossible, a comparison 

between them and the Saturday Mountain specimens. 

In outline, profile, and ·size the average Saturday 

Mountain specimens are very similar to A ustinella 

cooperi Roy from Frobisher Bay. However, specimens of that species in the United States National 

Museum have simple costae without bifurcation or intercalation. 

All of the Saturday Mountain specimens are too 

coarsely ribbed for A. kankakensis as illustrated by 

other authors. Ribbing is too coarse for A. whitfieldi 

as illustrated by "\Vang (1949, pl. 2.A) but on many 

specimens it compares favorably with illustrations by 

Winchell and Schuchert ( 1895, pl. 33, figs. 10, 13). 

Shape of the shells conforms more closely to that of A. 

whitfieldi as figured by Winchell arid Schuchert than 

with those of specimens illustrated by Schuchert and 

Cooper (1932, pl. 9, figs. 16, 19) or by Wang (1949, pl. 

2A). Some specimens are very Closely comparable to 

A. scovillei as illustrated by Foerste (1912, pl. 8, figs. 

Sa-c). The more elongate, more narrowly hinged specimens bear a striking resemblance to the original figures of A. scovillei (Miller, 1882, pl. 1, figs. 5, 5a, 5b). 

According to Miller (1882, p. 40) the costae of that 

species increase by bifurcation, not by intercalation, 

and its pedicle valve is nearly flat. 'These t\VO considerations seem to distinguish it from most of the 

Saturday Mountain forms. 

It is obvious that some selected specimens from the 

present collections could be identified as .A. whitfieldi 

and others as A. scovillei. The evident variation between specimens suggests that these two may be varieties or subspecies of one species. When compared with 

material in the U.S. National Museum specimens from 

Idaho are in general closer to those labelled A. scovillei than to A. whitfieldi or A. kankaken-sis. 

The specimen illustrated in figures 16 and 17 

of plate 55 can be distinguished from A. delicata Wang 

(1949, pl. 1F) only by the pits on the costae. It possesses the same crowding of costae in the postero-lateral 

corners that Wang used as a criterion to distinguish 

his species from A. scovillei. It also has a thin cardinal 

process. This last is by no means a specific criterion; 

I believe the crowding of costae has been overweighted 

by Wang. 

The pits on costae are true punctae in the youthful 

stages of growth. The small perforations are arranged 

in roughly concentric rows paialleling the margin. The 

row closest to the margin still opens into the inside of 

the shell but those closer to the umbo are sealed internally by shell material. Most of the older, thicker 

shells show no pits at all, the inner ends having been 

sealed and the outsides of the shells abraded. 

Superfamily RHYNCHONELLACEA 

Undetermined rhynchonellid ( 1) species 

Plate 56, figures 29, 30 

Two immature specimens of a rhynchonellid ( ~) 

brachiopod are present in the collections. These are 

very neat little shells, moderately convex for a rhynchonellid. The brachial valve is nearly circular in outline. T~e greatest width of the pedicle valve is well 

forward, giving the shell a "tear~drop" form. There 

are 4 costae of equal size on the low brachial fold and 

4 on each flank. The pair of costae adjacent to the fold 

are the largest. The surface is smooth, not lamellose. 

It is not possible to tell from the two specimens 

whether· small size is a constant feature or merely a 

sign of immaturity. Because no adult specimens were 

fou~d no attempt is made to identify or name the 

species. 

Figured specimens: USNM 133271 

Localities: D237b CO, D240 CO. 

Superfamily SPIRIFERACEA 

Genus ZYGOSPIRA Hall, 1862 

Zygospi'na is represented by numerous specimens in 

the present collections. All specimens are small, only 

three out of 80 exceeding 5 mm in length. The variety 

of form is somewhat surprising. A few can be assigned 

to Z. recurvirostris, a Middle Ordovician species, a few 

to Z. putilla, a Silurian species. If they were larger 

most of the specimens might pass for Z. a.equivalvis 
BRACHIOPOD FAUNA OF SA'l'URDAY MOUNTAIN FORMATION- 457 

Twenhofel or Z. kentuckiemis Nettleroth, supposedly 

late Ordovician species. A somewhat similar assemblage was found in a collection made by E. 0. IDrich 

from· "IGmmswick, Pratt's quarry, % mile south of Elsb~rry, Mo." (loc. 258g), but it lacks the true Z. putilla 

and the Z. cf. Z. circularis of the Idaho collections. 

If material in the U. S. National Museum is typical 

one may observe. from it that most Late Ordovician 

Zygospiras are large and coarse-ribbed, whereas Middle Ordovician species are.· small· and fine-ribbed. In 

these respects, the Idaho specimens resemble most 

closely Middle Ordovician species. 

Zygospira cf. Z. recurvirostris Hall 

Plate 54, figures 3, 7, 12, 18 

Three of about 80 specimens of Zygospira from Locality D240 CO can be assigned to this species; examples are present in other collections of the Saturday 

Mountain formation. 

Because the type specimen of Hall's species (Hall, 

1847, p.140, pl. 33, figs. 5a-d) has never been adequately 

figured, photographs of it are included here (pl. 56, 

figs. 3, 4, 9, 10). This and two topotype specimens from 

the New York State Museum show that the median 

, costa of the brachial valve and the median interspace 

of the pedicle valve are wider than the others, a fact 

not mentioned in any previous description I have been 

able to find and illustrated only by Cooper ( 1956, pl. 

142H). In this species the flanks of the pedicle valve 

ar.e flat or very slightly convex. In all the other forms 

found in the strata of the Saturday Mountain formation the pedicle flanks are concave. In the past, specimens from the so-called Trenton of Kentucky and states 

other than New York have been identified as Z. recurvirostris despite concavity of pedicle flanks and possession of bifurcating costae; several of these have been 

reexamined by Cooper ( 1956, p. 669-67 4). 

Figured specimens: USNM 133238 

Localities: D237b CO, D240 CO. 

Zygospira putilla Hall and Clarke 

Plate 56, figures 11, 12 

Zygospira putiZZa Hall and Clarke, 1895, Nat. History N. Y., 

Paleontology, v. 8, pt. 2, p. 365--366, pl. 83, figs. 29, 30. 

Only two specimens have·been found and both are 

in poor condition. They closely resemble Hall's and 

Clarke's figures. Z. jupiterensis Twenhofel (1927, p. 

215, pl. 19, figs. 13-15) probably belongs to this ~pecies 

or is very closely related. 

Figured specimen: USNM 133262 

Localities: D203 CO, D313 co~ 

Discussion.-Savage (1917, p. 130) reassigned this 

species to .A. trypa on the basis of specimens from the 

. Silurian Edgewood limestone, but gave no reason and 

I find no evidence in the present collections that excludes it from Zygospira. 

Comparison with specimens in the U. S. National 

Museum from the Edgewood limestone shows that the 

present material very closely resembles it in all but 

size. The two Idaho specimens are very much smaller. 

Zygospira aff. Z. putilla Hall and Clarke 

Plate 56, figures 16, 17 

About eight percent of the specimens o'f Zygospira 

in the Saturday Mountain collections resemble Z. putilla in outline and profile, but none have the bifurcating or implanted costae which characterize that species. 

These specimens have about 15 costae of which 5 are 

within a very shallow brachial sulcus; the median rib 

is larger than the others, but not as large as the same 

rib in z. putilla. 

Savage (1917, p. 130) noted that many specimens of 

Z. putilla in the Edgewood limestone of Silurian age 

have simple rather than bifurcating costae. In a collection made by Ulrich (Loc. 258g), labelled "Kimmswick * * * one-half mile south of Elsberry, Mo.", 

. there are five specimens of Zygospira. Two of these 

are almost indistinguishable from the Saturday Mountain specimens of this type. 

Figured specimens: USNM 133263. 

Localities: D237 CO, D240 CO. 

Discussion.-These specimens are not to be confused 

with specimens identified as Z. putilla (pl. 56, figs. 11, 

12) from Locality D203 CO. 

Zygospira cf. Z. circularis Cooper 

Plate 56, figures 21-24, 27, 28 

Zygospira circularis Cooper, 1956, Smithsonian Misc. Coli., v. 

127, p. 670, pl. 1410, figs. 18-21; pl. 142B, figs. 6-10; pl. 142D, 

fig. 16. 

Sixteen percent of the specimens of Zygospira from 

locality D240 CO are of a type similar to this species. 

In outline the Idaho specimens agree almost perfectly, 

but in profile they are a little more compressed, with 

more distinctly concave pedicle flanks. There are an 

average of 24 costae on the Saturday Mountain forms 

and only 22 (Cooper, 1956, p. 670) on those from Tennessee. The western specimens seem to be slightly 

.smaller than those from the east. 

Figured specimens : USNM 133267-133268. 

Localities: D235 CO, D237 CO, D240 CO, D304 CO, 

D308 CO. 

Discussion.-The specimens from Idaho also bear a 

resemblance to Z. resupinata Wang, from which they 

differ in possession of rounded rather than angular 

costae and much weaker sulcus and fold. 
458 SHORTER' CONTRIBUTIONS TO GENERAL GEOLOGY 

This species contributes a Middle rather than Late 

Ordovician element to the fauna. Z. ciTcula:ria is described from the Carters limestone of Tennessee, which 

Cooper ( 1956, Chart 1) considers older than the 

Trenton. 

Zygospira cf. Z. lebanonensis Cooper 

Plate 56, figures 31, 32, 35, 36, 37, 38, 41,42 

Zygospira Zebanonensis Cooper, 1956, Smithsonian Misc. Coil., 

v. 127, p. 671-672, pl.142C, figs. 11-15. 

Most of the specimens of ZygospiTa fall into this 

category. The outline is subcircular to subpentagonal. 

The profile is compressed. The brachial sulcus is broad, 

ill-defined, and seems to include 5 costae, of which the 

center 1 is the largest. The flanks of the pedicle valve 

are concave. Ribbing is fairly coarse. The average 

number of ribs is 18, but the number may range from 

14 to 22. The ribbing is simple, there being only 1 

aberrant specimen on which 1 rib bifurcates. 

Figured specimens: USNM 133269, 133270 

Localities: D235 CO, D237 CO, D240 CO, D308 CO, 

D311 CO. 

Discussion.-These specimens differ from typical Z. 

lebanonensis only in possessing a median rib a little 

larger than the others and. having 14.--22 costae instead 

of 18-23. The close resemblance suggests correlation 

with the Lebanon limestone of Tennessee, the Camp 

Nelson limestone of Kentucky, arid the Barnhart formation of Cooper (1956, p. 116) of Missouri. 

Specimens similar to this, but much larger, have been 

collected from the Reedsville shale in western Virginia 

and from the so-called Trenton ( ~) near Harrogate, 

Tennessee. They resemble Z. kentuckiensis Nettleroth 

(as figured by HaH and Clarke, 1895, pl. 54, fig. 15) except in size and similarly compare closely with Z. 

aequivalvis Twenhofel, of which a topotype is figured 

here (pl. 56, figs.13, 14, 15). 

Superfamily STROPHOMENACEA 

Genus Thaerodonta 

~late 55, figures 4o-43 

One and possibly two species of this genus are present in the Saturday Mountain formation. · The second 

of these is known from a dozen specimens only one of 

which shows the critical hinge. The first is represented 

by three poorly preserved valves. The specimens are 

figured as a matter of record, but with such inadequate 

material no attempt is made to identify them to species. 

Figured specimens: USNM 133257, 133258. 

Localities: D203 CO, D237 CO, D238 CO, D240 CO, 

D308 CO, D311 CO, D312 CO. 

Superfamily DALMANELLACEA 

Genus· Diceromyonia Wang 1949 

Diceromyonia cf. D. tersa ( Sardeson) 

Plate 56, figures 33, 34, 39, 40, 43, 44 

Orthis tersa Sardeson, 1892, Bull. Minn. A.cad. Nat. Sci., v. 3, 

p. 331-332, pl. 5, figs. 11-13. 

Resserella tersa (Sardeson), Cooper, 1944, in Shimer and 

Shrock, Index fossils of North America, p. 353, pl. 138, figs. 

19, 20. 

· Diceromyonia tersa ( Sardeson), Wang, 1949, Geol. Soc. America 

Mem. 42, p. 36, pl. 12B. 

The present specimens are all poorly silicified. They 

have the transversely elliptical outline and narrow 

hinge which characterizes the species, but the brachial 

valve is a little more convex than might be expected. 

Growth lines are lacking on almost all specimens. 

Figured specimens: USNM 133272, 133273, 133376 

Localities: D234 CO, D235 CO, D236 CO, D238 CO, 

D240 CO, D308 CO, D311 CO, D312 CO, D314 CO. 

REFERENCES CITED 

Barnes, V. E., Cloud, P. E., Jr., and Duncan, H., 1953, Upper 

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Bassler, R. S., 1911, The early Paleozoic Bryozoa of the Baltic 

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Clark, T. H., 1952, Montreal area, Laval and Lachine map areas: 

Quebec Dept. Mines, Geol. Rept. 46, 159 p. 

Cloud, P. E., Jr., 1948, Assemblages of diminutive brachiopods 

and their paleoecological significance: Jour. Sedimentary 

Petrology, v. 18, pp. 56-60. 

Cooper, G. A.., 1944, Brachiopoda in Shimer and Shrock, Index 

fossils of North America, p. 277-365, pls. 105--143. 

--1956, Chazyan ru:td related brachiopods, parts I and II : 

Smithsonian Misc. Coli., v.127, 1024 p., 269 pls. · 

Flower, R. H., 1952, New Ordovician, cephalopods from eastern 

North America: Jour. Paleontology, v. 26, pl. 24-59, pis. 

5-10. 

-- 1956, Montoya-Bighorn-Richmond correlations: (Abstract) Geol. Soc .. America Bull., v. 67, p. 1793-1794. 

Foerste, A. F., 1909, Preliminary notes on Cincinnatian fossils: Denison Univ., Sci. Lab., Bull., v. 14, p. 209-228, pl. 4. 

-- 1912, Strophomena and other fossils from Cinciilllatian 

and Mohawkian horizons, chie1ly in Ohio, Indiana, and 

Kentucky: Denison Univ., Sci. Lab., Bull., v. 17, p. 17-139, 

pis. 1-18. 

Hall, James, 1847, Palreontology of New York, v. 1, 338 p., 33 

pls. 

Hall, Jam·es, and Clarke, J. M., 1892, Paleontology of New York, 

v. 8, pt.l, 367 p., 20 pis. 

Jaanusson, V., 1944, Ubersicht der stratigraphie der· Lyckholmkomplexstufe : Comm. geol. Finlande Bull., no. 132, p. 

92-100. 

Ladd, H; S., 1929, The stratigraphy and paleontology of the 

Maquoketa shale of Iowa: Iowa Geol. Survey, v. 34, p. 

305--417, pis. 4-12. 

McEwan, E. D., 1920, A. study of the bra.chiopod genus Platyatrophia: U. S. Natl. Mus. Proc., v. 56, p. 383--449, pls. 42-52. 
BRACHIOPOD FAUNA OF SATURDAY ' MOUNTAIN FORMATION 459 

Meek, F. B., 1873, Descriptions of fossils of the Silurian and 

Devonian system: Ohio Geol. Survey, v. I, pt. II (Paleontology), p. 1-242, pis. 1-23. 

Merriam, C. W., ailld Anderson, C. A., 1942, Reconnaissance survey of the Roberts Mountains, Nevada: Geol. Soc. America 

Bull., v. 53, p. 1675-1727, 4 pls. 

Miller, S. A., 1882, Description of two new genera and eight 

new species of fossils from the Hudson River group, with 

remarks upon others: Cincinnati Soc. Nat. History Jour., 

v. 5, p. 34-44, pl. 1, 2. 

Nolan, T. B., Merriam, C. '\V., and Williams, J. S., 1956, The 

stratigraphic section in the vicinity of Eureka, Nevada: 

U.S. Geol. Survey, Prof. Paper 276, 77 p. 

{)pik, A.~ 1934, tiber klitamboniten : Tartu Ulikooli. GeoloogiaLnstituudi Toimetused, no. 39, 190 p., 48 pis. 

6pik, A., and Laasi, A., 1937, Geologie von Liilinemaa : Tartu 

Ulikooli Geoloogia·Instituudi Toimetused, no. 51, p. 20-29. 

Raymond, P. E., 1916, Expedition to the Baltic provinces of 

Russia and Scandinavia; Part I, the correlation of the 

Ordovician strata of the Baltic basin with those of eastern 

North America: Harvard Coil. Mus. Comp. Zoology Bull. 

56, p. 179-286. 

Ross, C. P., 1934, Correlation and interpretation of Paleozoic 

stratigraphy . Ln south·central Idaho: Geol. Soc. America 

Bull., v. 45, p. 937-1000. 

--- 1937, Geology and ore deposits of the Bayhorse region, 

Custer County, Idaho: U. S. Geol. Survey Bull. 877, 161 p. 

--- 1947, Geology of the Borah Peak quadrangle, Idaho: 

Geol. Soc. America Bull., v. 58, p.1085-1160. 

Ruedemann, R., 1947, Graptolites of North America: Geol. Soc. 

America, Mem. 19, 527 p., 92 pis. 

Savage, T. E., 1917, Stratigraphy and Paleontology of the Alexandrian Series in Illinois and Missouri : Illinois Geol. Survey Bull. 23, p. 67-160, pis. 1-9. 

Schuchert, C., and Cooper, G. A., 1932, Brachiopod genera of 

the suborders Orthoidea and Pentameroidea: Yale Peabody Mus. Nat. History Mem., v. 4, pt. 1, 270 p., 29 pis. 

Shaler, N. S., 1876, On the fossil Brachiopoda of the Ohio Valley: Kentucky Geol. Survey Mem., v. I, pt. 3, 44 p., 7 pls. 

Sinclf!ir, G. W., 1956, Review of A. K. Miller, Ordovician cephalopod fauna of Baffin Island, Geol. Soc. America Mem. 62: 

Am. Jour. Sci., v. 254, p.126-128. 

Teichert, C., 1930, Die cephalopoden-fauna der Lyckholm-stufe 

des Ostbaltikums: Palaeont. Zeitschr., v. 12, p. 264-312. 

Treece, W. A., 1955, Estimation of vertical exaggeration in 

stereoscopic viewing of aerial photographs : Photogrammetric Engineering, v. 21, no. 4, p. 518-527. 

Twenhofel, W. H., 1916, Expedition to the Baltic provinces 

of Russia and Scandinavia, 1914--Part 2, The Silurian and 

high Ordovician strata of Esthonia, Russia, and their 

faunas ; Part 3, An interpretation of the Silurian section 

of Gotland: Harvard Coli. Mus. Comp. Zoology Bull. 56, 

p. 289-354. 

--- 1927, Geology of Anticosti Island : Canada Geol. Survey 

Mem. 154, 351 pp., 60 pls. 

Ulrich, E. 0., and Cooper, G. A., 1938, Ozarkian and Canadian 

Brachiopoda: Geol. Soc. America, Spec. Paper 13, 323 p., 

57 pis. 

Umpleby, J. B., Westgate, L. G., and Ross, C. P., 1930, Geology 

and ore deposits of the Wood River Region, Idaho: U. S. 

Geol. Survey Bull. 814, 250 p. 

Wang, Y., 1949, Maquoketa Brachiopoda of Iowa: Geol. Soc. 

. America Mem. 42, 55 p., 12 pis. 

Whittard, W. F., an~ Barker, G. H., 1950, The Upper Valentian brachiopod fauna of Shropshire, Part I, Inarticulata, 

Protremata, and Orthoidea: Ann. and Mag. Nat. History, 

12th ser., v. 3, no. 31, p. 553-589, pis. V-VIII. 

Williams, A., 1951, Llandovery brachiopods from Wales with 

special reference to the Llandovery District: Quart. Jour. 

Geol. Soc., v. 107, p. 85-136, pls. III-VIII. 

Winchell, N. H., and Schuchert, C., 1895, The lower Silurian 

Brachiopoda of Minnesota : Geology of Minnesota, v. 3, p. 

333-4 7 4, pl. 29-34. 

Page 

Abstract ___________ ----------------------------_ 441 Acknowledgments ____________________ --------_. 441 

aequivalvis, Zygospira _______________ 441,456,458, pl. 56 

amoena, Platystrophia., _________________ -------- 446 

annieanna, Platystrophia _________________ ._______ 446 

Atrypa ___ -------------------------------------- 457 

Austinella __ -------------------------------444, 448, 454 

cooperi •• _________ -- ______ -- _ -------- _ -- _- --- 456 

delicata. ______ ----- ____________ ------ _- ___ -- 456 

kankakensiB----------------------------454, 455, 456 scovillei. ___________________ --_________ -____ 454, 456 

whitjieldL _____________ -441, 444,454, 455-456; pl. 55 

Bayhorse quadrangle.-------------------------- 443 

bellilamellosus, Plaesiomys ___ ------------------445, 464 

Bighorn dolomite ________ ----------------------- 443 

Borah Peak quadrangle .•• --------------------- 443 

Boreadorthis. ___ -------------------------------- 447 

brachiophorus, OrthamboniteB-------------------- 448 

Brachiopod fauna, composition and significance 444 

capax, Lepidocyclus. ---------------------------- 446 

circularis, Zygospira _____________ 444, 445, 457-458; pl. 56 

clarksvillensis, Platystrophia •. __ -- _ _ _ _ _ _ _ _ _ _ _ _ __ _ 446 

colbiensis, Platystrophia_ -.----------------------- 446 

Collecting localities, fossils---------------------441-443 

cooperi, Austinella. _ ---------------------------- 456 

delicata, Austinella ____ -------------------------- 456 

Diceromyonia tersa _____________________ 445, 458; pl. 56 

Dolerorthis .•• --- _ --- __ -- _______ ------- __ --- __ • 444, 447 

plicata. ________ ------- __ -------------------- 448 

rustica osiliensis .. --------------------------- 448 

eleoantula, Platy atrophia._---------------------- 446 

equiconvexa, Platysirophia _____________________ 445,446 

extensa, Platystrophia •• _ ------------------------ 446 

facula, Sceptropora ____________________________ 441, 445 

Fauna, age.---------------------------------- 444-445 

composition and significance________________ 444 

ecologic significance •••••••••••••••••••.••• 445-446 

Fern vale formation •• --------------------------- 445 

Fish Haven dolomite--------------------------- 443 

Formic acid, useonsmallrock samples__________ 441 

Fossils, collecting localities. __ ---------------- 441-443 

INDEX 

[Italic numbers Indicate descriptions] 

Page 

Glyptorthis pulchra _________________ 445, 448-449: pl. 54 

Graptolites.---------------------------------- 443, 444 

Hanson Creek formation._------------------- 443,444 

HesperorthiB.------------------------- 444,446-447,448 

onniensis ___ -------------------------------- 448 Hypsiptycha. ___________ ------ ____ -- ______ ---- __ 445 

Introduction. __ -------------------------------- 441 

iphigenia, Plaesiomus. __ ------------------------ 449 

jupiterensis, Zygospira. _ ------------------------ 441 

kankakensis, Atutinella.-. ---------------- 454; 455, 456 

Orthis __ ------------------------------------ 454 

kentuckiensis, Zuoospira .••.. -------------------- 458 

Kinnlkinic quartzite.--------------------------- 443 

lebanonensis, Zyoospira _____________ 444, 445, 458; pl. 56 

Lepidocyclus .• -------------- __ ------------------ 444 

capax __ ------------------------------------- 446 

rectanoularis ••. ---------.--- __ ---------- __ ___ 445 

Lordorthis variabilis n. SP---------- 444,445,446,441,448 

Maclurites ____ ----- _______ ------------ ______ -- _ _ 443 

meedsi, PlaesiomyB.----------------------------- 449 Mount Hamilton, Nevada______________________ 443 

Occidentalis ... ---- ____ ---- __ ---------------- _ _ _ _ 454 

onniensis, HesperorthiB-------------------------- 448 

Orthambonites brachiophorus_____________________ 448 

Orthis kankakensis. _ ---------------------------- 454 

subquadratus ____ ---------------- ____ -------- 449 

tersa ...• ------------------------------------ 458 

whitjieldi. _______________________ ------ __ ---- 454 

osiliensis, Dolerorthis rustica •• ~------------------ 448 

Phi Kappa formation •••• _______________________ 444 

Plaesiomys bellilamellosus _____________________ 445,454 

iphioenia ______________________ ------------- _ 449 

meedsL---------------------------------- __ • 449 

subquadratus __________________________ 441, 449-454 

idahoensis n. subsp_____________________ 449 

Platystrophia amoena. __ ------------------------ 446 

annieanna. ____ ------------------- ______ ---- 446 

clark811iUensis ____ ------------- ___ _ __ __ __ _ _ __ 446 

colbiensis. _ --------------------------------- 446 

eleoantula·------------ ____ : ___ ____ ------ __ --. 446 

equiconvexa •• ----------------------------- 445,446 

extensa. _- ---------------------------------- 446 

Page 

Plectorthis. _ ------------------ _____ ------ _ _____ _ 454 

punctata .• ____________ --- ___ -------- ____ ---- 455 

plicata, Dolerorthis. ----------------------------- 448 

pulchra, Glyptorthis ________________ 445,448-449: pl. 54 

punctata, Plectorthis. ___ ------------------------ 455 

putilla, Zyoospira .. ------------ 444,445,456, 451; pl. 56 

Ratinesquinar SP----------------- __ ------------- 445 

Ramsborn slate--------------------------------- 444 Receptaculites _______________________ -- ________ -- 443 

rectangular is, Lepidocyclus __________ -_- _______ -_ 445 

recurvirostris, Zygospira ___________________ 441,445,457 

References cited. _____________________________ 458-459 

Reaser ella tersa ______________________ ------------ 458 

resupinata, Zygospira. ----------- ~--------- --·--- 457 

Rbyncbonellacea. __ ----------------------- 456; pl. 56 

robustum, (Grewinkia) Streptelasma. ------------ 445 

rustica osiliensis, Dolerorthis.-------------------- 448 

Sceptropora facula. ___ -------------------- ____ 441, 445 

Scope of Investigation ••.•••• ___________________ 441 

scovillei, Austinella ____________________________ 454, 456 

Stereopbotograpby, of specimens. __ ------------ 441 

Streptelasma (Grewinkia) robustum______________ 445 

Strophomena SP--------------------------------- 445 Stropbomenacea ___________________________ 458; pl. 55 

subquadratus, Orthis. ___ ------------------------ 449 

Plaesiomys _ ---------------~---------- 441, 449-464 

tersa, Diceromyonia _____________________ 445, 468,· pl. 56 

Orthis __ ------------------------------------ 458 

Resserella ___ ----- ___ ------------------------ 458 

Thaerodonta sp ___ --------------------'---------- 445 

variabilis, LordorthiB--------------- 444,445,446,441,448 

whitjieldi, AustineUa ________ 441,444, 454, 455-456; pl. 55 

Orthis __ ------------------------------------ 454 

Zvoospira ______________ ___ ------------- _ -------- 456 

aequivaliJiB.------------------------------- 441,458 

circulariB--.---------------- 444, 445, 457-468; pl. 56 

jupiterensis. ----------------------------- •• 441 

kentuckiensis. ___ --------- ___ --- _------------ 458 

lebanonensis ____________________ 444,445, 458; pl. 56 

putilla _____________________ 444,445,456,457: pl. .';6 

recurvirostriB-------------------------- 441,445,457 

resupinata _____________________ ------------. 457 

461 
PLATES 54-56 

[All specimens have been photographed stereoscopically. Details on several specimen$ cannot be seen with the unaided eye but can be made 

out with a pocket stereoscope.] · 
/ 

PLATE 54 

[All figures natural size except as indicated] 

FIGURES 1, 2, 4-6, 8-11, 13-17, 19-25, 27, 28, 31, 32, 35, 36. Lordorthis variabilis Ross n. sp. (p. 447). 

1, 2, 5, 9. Holotype, dorsal, lateral, posterior, and ventral views, loc. D240 CO, USNM 133227. 

4, 8. Pedicle valve of transverse, finely ribbed variety, paratype, loc. D238 CO, USNM 133228. 

6, 10. Immature brachial valve, X 3, para type, loc. D240 CO, USNM 133229. 

11, 15, 17, 20. Immature complete specimen, showing Hesperorthis-like form, paratype, loc. D306 CO, USNM 133230. 

13, 19. Pedicle valve of elongate, poorly ribbed variety, paratype, loc. D240 CO, USNM 133230. 

14, 16. Pedicle valve with arched deltidial plate, paratype, loc. D240 CO, 133232. 

21. Brachial valve, showing simple cardinal process and Hesperorthis-like brachiophores, paratype, loc., D240 CO 

USNM 133233. 

22, 25, 28, 32. Immature specimen, complete, X 2, paratype, loc. D240 CO, USNM 133234. 

23, 24. Pedicle valve, showing deltidial plate isolated exteriorly by shell material added to sides of delthyrium. Plate 

growing forward beneath this material. Paratype, loc. D240 CO, USNM 133235. 

27, 31, 36. Very sn;1all, immature specimen, X3, showing lamelose surface. Paratype, locality D240 CO, USNM 

133236. 

35. Small brachial valve showing arched chilidium, paratype, locality D240 CO, USNM 133237. 

3, 7, 12, 18. Zygospira cf. Z. recurvirostris (Hall), X 3 (p. 457). Locality D237b CO,· USNM 133238. 

26. Hesperorthis onniensis Whittard and Barker (p. 448). Latex cast of the holotype, GSM 82515. See Whittard and 

Barker, 1950, pl. 6, fig. 9. From Upper Valentian Purple Shales· of the Onny River section, Shropshire. 

29, 30, 33, 34, 37, 38, 41, 42. Plaesiomys subquadratus subsp. idahoensis Ross n. subsp. (p. 249). 

29, 30, 33, 34. Holotype, locality D237b CO, USNM 133239. 

37, 38. Pedicle valve, paratype, more coarsely ribbed than holotype~ locality D240 CO, USNM 133240. 

41, 42. Brachial valve, paratype, more coarsely ribbed than holotype, locality D240 CO, USNM 133241. 

39, 40. Glyptorthis cf. G. pulchra Wang. (p. 448). · Brachia~ valve, locality D240 CO, USNM 13324·4. 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 294 PLATE 54 

' ImACHIOPOD FAVNA Ol S.\TUHDAY l\IOUJ:\TAI}; FORMATION 
GEOLOGICAL SURVEY PROFESSIONAL PAPER 294 PLATE 55 

BRACHIOPOD FAUNA OF SATURDAY MOUNTAIN FORMATION 
PLATE 55 

[.All figures natural size except as indicated] 

FIGU.RES 1, 6, 12, 14, 15, 18, 19, 23. Plaesiomys s:ubquadratus (Hall) (p. 449). Three specimens from Hall's (1847) type lot. AMNH 

913/6. "Hudson River group", Cincinnati, Ohio. 

1, 6. Brachial valve (Hall, 1847, pl. 32A, fig. 1o). 

12, 14. Pedicle valve (Hall, 1847, pl. 32A, fig. 11, m) 

15, 18, 19, 23. Complete specimen (Hall, 1847, pl. 32A, figs. 1a, f. d). 

22, 26, 27, 30, 31. Plaesiomys subquadratus subspecies idahoensis Ross, n. subsp. (p. 449). 

22, 26, 27. Immature specimen, locality D237b CO, USNM 133242. 

30, 31. Brachial valve, finely ribbed in median section, possibly pathologic, paratype, locality D240 CO, USNM 133243. 

34, 35, 38, 39. Plaesiomys cf. P. bellilamellosus Wang, complete specimen, locality D312 CO, USNM 133245 (p. 454). 

2-5,7-11, 13, 16, 17, 20, 21, 24, 25, 28, 29, 32, 33, 36, 37. Austinellaaff. A. whitfieldi Winchell and Schuchert (p. 455). 

2, 7. Smallest brachial valve obtained, X3. Part of same specimen as figures 5, 13, locality D240 CO, USNM 133246. 

3, 4. Brachial valve of transverse variety, with large myophore and relatively simple ribbing, locality D240 CO, 

USNM 133248. 

5, 13. Smallest pedicle valve obtained, X3. Same specimen as figures 2, 7, locality D240 00, USNM 133247. 

8, 9. Brachial valve of elongate variety, with small myophore, bifurcating costae, and a fine costella between costae, 

locality D240 CO, USNM 133249. 

10, 11. Brachial valve of transverse variety, with small myophore, bifurcating costae, and a fine costella between 

costae, locality D306 CO, USNM 133250. 

l6, 17. Brachial valve of transverse variety, with virtually no myophore, intercalated costae, and a fine costella between 

costae, locality D203 CO, USNM 133251. 

20, 21. Pedicle valve of transverse variety, with relatively simple costae, locality D240 CO, USNM 133252. 

24, 25. Pedicle valve with bifurcating costae, locality D240 CO, USNM 133253. 

28, 29. Pedicle valve of elongate variety, with bifurcating costae, locality D240 CO, USNM 133254. 

32, 33, 37. Immature specimen, X2, locality D237 CO, USNM 133255. 

36. Brachial valve with simple costae, fine costella between costae, and pits on costae, locality D237b CO, USNM 

133256. 

40, 42. Thaerodonta sp. or Sowerbyella sp., X2, locality D240 CO, USNM 133257 (p. 458). 

41, 43. Thaerodonta sp., brachial valve, X2, locality D240 CO, USNM 133258 (p. 458). 
PLATE 56 

· All figUres natural size except as indicated 

FIGURES 1, 2, 5, 6, 7, 8. Platystrophia cf. P. equiconvexa Wang (p. 446). 

1. Brachial valve, X 1, with front margin broken, locality D238 CO, USNM 133259. 

2, 5, 6. Brachial valve, not full grown, X 1, locality D313 CO, USNM 133260. 

7, 8. Pedicle valve, immature, X 1, locality D316 CO, USNM 133261. 

3, 4, 9, 10. Zygospira recurvirostris (Hall) (p. 457). 

Type specimen, X3, from Trenton limestone, Martinsburg, N. Y., AMNH 705/3. (Hall, 1847, pl. 33, figs. 5 a-c.) 

11, 12. Zygospira putilla Hall and Clarke (p. 457). 

·x3, locality D203 CO, USNM 133262. 

13, 14, 15. Zygospira aequivalvis Twenhofel. 

X3, English Head formation, east bank of the Capelin River, Anticosti Island, YPM 20194. 

16, 17. Zygospira aff. Z. putilla Hall and Clarke (p. 457). 

X 3, locality D240 CO, USNM 133263. 

18, 19, 20, 25, 26. Glyptorthis cf. G. pulchra Wang, X 1 (p. 448). 

18, 25. Brachial valve of an old specimen, from same individual as figure 26. Note tectonic deformation near margin. 

Locality D238 CO, USNM 133264. 

19, 20. Pedicle valve, locality D240 CO, USNM 133266. 

26. Pedicle valve of an old specimen, slightly deformed by lateral compression which seems to have caused a false 

sulcus at anterior margin. Same individual as figures 18, 25. Locality D238 CO, USNM 133265. 

21, 22, 23, 24, 27, 28. Zygospira cf. Z. circularis Cooper, X3 (p. 457). 

21-23. Subelliptical specimen, locality D237b CO, USNM 133267. 

24, ~7, 28. Subcircular specimen, locality D240 CO, USNM 133268. 

29, 30. Unidentified rhynchonellid, immature, X3, locality D240 CO, USNM 133271 (p. 456) 

31, 32, 35, 36, 37, 38, 41, 42. Zygospira cf. Z. lebanonensis Cooper (Compare with pl. 56, figs. 13, 14, 17) (p. 458). 

31, 32, 35, 36. Small specimen, X 3, locality D240 CO, USNM 133269. 

37, 38, 41, 42. Specimen with "median" rib off-center, X 3, locality D240 CO, USNM 133270. 

33, 34, 39, 40, 43, 44. Diceromyonia cf. D. tersa (Sardeson), X2, locality :0240. CO ·(p. 458). 

33, 34, 39, 40. Complete specimen, USNM 133272. · 

43. Brachial valve, USNM 133273. 

44. Pedicle valve, USNM 133376. 
GE OLOGICAL SURVEY PROFESSIONAL PAPER 294 PLATE 56 

BRACHIOPOD FAUNA OF SATURDAY MOUNTAIN FORMATION