PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 587 
with 2 costae in the sulcus, 3 on the fold, and 1 on the flanks. Pedicle valve 
flatly convex in both profiles; sulcus originating two-thirds the length from the 
beak, broad and shallow ; brachial valve deeper than the pedicle one and probably 
more convex ; fold weathered away but apparently fairly wide and low as indi- 
cated by the pedicle tongue. 
Figured specimen.—117151. 
Horizon and locality.—Yellow beds above the 25-foot sandstone in Nevada: 
On the saddle just north of hill 8167, Martins Ridge, Monitor Range, Roberts 
Mountains (1°) Quadrangle. 
CAMERELLA sp. 4 
Plate 121, FE, figure 14 
A single brachial valve indicates a species of Camerella different from others 
described herein. The specimen is 6.2 mm. long and 6.6 mm. wide. It is mod- 
erately convex in both profiles. The fold is low and margined by 2 costae 
that extend to about the middle. Between these costae the fold is gently de- 
pressed. The flanks are marked by 2 costae. The obscure costae appear in the 
depression bounded by the costae of the fold. 
Figured specimen.—123294. 
Horizon and locality—Whitesburg formation in Tennessee: 14 miles west of 
Bulls Gap, Bulls Gap (T.V.A. 171-SE) Quadrangle. 
Genus IDIOSTROPHIA Ulrich and Cooper, 1936 
Idiostrophia UtricH and Cooper, Journ. Paleont., vol. 10, No. 7, p. 631, 1936; Geol. Soc. 
Amer. Special Pap. 13, p. 249, 1938. 
This genus is most readily recognized by its triangular form. It is not com- 
mon in any of its known occurrences. Previous to the present writing it was 
known only from boulders of the Mystic conglomerate which correspond in age 
to part of the Table Head series of Newfoundland. Several new species are 
added here which extend the geographic range to Nevada and Newfoundland. 
The triangular form is not the only peculiar external character of the genus. It 
has a peculiar type of folding which may be characterized as broadly uniplicate. 
In Camerella a well-marked fold is generally present, and the flanks bounding 
fold and sulcus are fairly wide and prominent. In Idiostrophia the flanks bound- 
ing the sulcus are narrow folds, generally with an angular ridge facing outward 
and connecting with the beak. At its anterior extremity this fold generally ter- 
minates in a narrow lobe. The lateral lobes correspond to the flanks of the 
camerellid which bound the sulcus. Thus the broad and often somewhat swollen 
area between the lateral folds corresponds to the sulcus of the camerellid. 
In the brachial valve the steeply sloping side is usually more or less deeply 
concave and forms a broad fold facing outward. At the anterior end of the fold 
a projection of considerable size, such as that in J. nuda, extends toward the 
pedicle valve and unites with it at the anterior point where the pedicle lateral 
plication dies out and the pedicle tongue is given off. At this point the pedicle 
valve is very shallow. The space between the brachial lateral ridges is thus the 
