PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 583 
Measurements in mm.—Holotype, length 8.1, brachial length 8.0, width 8.7, 
hinge width 2.6, thickness 6.4. 
Type.—Holotype: 117147. 
Horizon and locality—vYellow limestone on 25-foot sandstone at base of 
Eureka group in Nevada: 34 miles N. 17° E. of Martin Ranch, Roberts Moun- 
tains (1°) Quadrangle. 
Discussion.—This species is somewhat like C. tennesseensis in having a 
strongly swollen brachial valve. It has 3 costae in the sulcus which is unusually 
wide. The species has the form of Perimecocoelia or Parastrophina, but the 
cruralium as seen when the shell is wet seems to be short and small like that of 
Camerella. This species is most like C. virginiensis but differs in having a more 
tumid brachial valve, a more prominent fold, and a deeper sulcus. 
CAMERELLA UNICOSTATA Cooper, new species 
Plate 113, B, figures 6-9 
Shell small, suboval in outline with the length slightly greater than the width. 
Greatest width at about the middle. Beak angle about 100° formed by slightly con- 
vex posterolateral margins. Lateral and anterior margins fairly strongly convex. 
Posterior half smooth, anterior half costate with a single costa occupying the 
sulcus, 2 costae on the fold, and 2 and an incipient third marking the flanks. 
Pedicle valve with lateral profile gently convex; broadly convex in anterior 
profile. Posterior half gently convex; sulcus originating about 4 mm. anterior 
to the beak, abrupt, shallow, occupying less than half the width at the front 
margin. Costa bounding sulcus elevated above the others, narrowly rounded. 
Flanks narrowly rounded with steep lateral slopes. 
Brachial valve more strongly convex than the pedicle one in lateral profile ; 
strongly arched in anterior profile. Fold low and narrow, defined only at the 
front where it makes a small anteriorly projecting lobe. Flanks narrowly rounded 
with steep lateral slopes. 
Measurements in mm.—Holotype, length 5.4, brachial length 4.9, width 5.0, 
thickness 4.0. 
Type.—Holotype: 111161. 
Horizon and locality.—Ward Cove formation in Tennessee: 2 miles south of 
Hall Crossroad, south of Hickey place, Fountain City (T.V.A. 146-SW) 
Quadrangle. 
Discussion——This species is of about the size and shape of C. minuta but 
differs in the possession of a single costa in the sulcus, a more oval outline, and 
less costate flanks. 
CAMERELLA VARIANS Billings 
Plate 110, B, figures 6, 7; plate 110, D, figures 12-15; plate 110, E, figures 16-21; 
plate 118, F, figures 50-54 
Camarella varians Brtuincs, Canadian Nat. Geol., vol. 4, p. 445, fig. 24, 1859; Geol. Canada, 
p. 127, fig. 52, 1863—Raymonp, Ann. Carnegie Mus., vol. 7, No. 2, pp. 250-253, pl. 36, 
figs. 25, 26, IQIT. 
