PART CHAZYAN AND RELATED BRACHIOPODS—COOPER 897 
entiated, the larger ones setting off groups of several smaller ones, all beautifully 
cancellated by strong fila; prominent oblique wrinkles marking posterior margins. 
Pedicle valve fairly evenly and moderately convex in lateral profile and with 
the maximum convexity at the middle; anterior profile fairly evenly and broadly 
convex ; umbonal region gently swollen ; median region swollen and full; anterior 
slope steeper than the lateral slopes because of a fairly abrupt bending of the 
anterior third toward the brachial valve. Pseudodeltidium a remnant. 
Brachial valve flat to gently convex in the posteromedian region ; anterior third 
gently deflected toward the pedicle valve. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness 
TIpigtupe acces yacls siete sae, « 37.9 36.9 45.2 48.4 5.0 
Pararype, ClI77O4 sce sss suse 35.9 ? 44.4 ? cy 
2 RITZ ZO5O parece cess 29.0 P 34.3 42.6 ? 
Types.—Holotype: 117787; figured paratypes: 117784, 117785c; unfigured 
paratypes: 117785a,b, 
Horizon and locality.—Yellow-weathering limestone in Roberts Mountains 
(1°) Quadrangle, Nev.: Above 25-foot sandstone at base of Eureka group on 
the crest of the Antelope Range, 3 miles south of Nine Mile Canyon; in the 
saddle just north of hill 8167, Martins Ridge, Monitor Range; 2 and 3 miles 
north of Martin Ranch; 1.9 miles N. 31° E. of Blair (=Segura) Ranch. 
Discussion.—This species is distinguished by its moderately large size, wide 
hinge, flattish brachial valve, and generally low or moderate convexity. It is 
suggestive of M. duplistriata but does not attain the large size or fairly strong 
convexity of that species. In size it is similar to M. bella, but it is less convex 
and with a flatter brachial valve. 
MACROCOELIA ORNATA Cooper, new species 
Plate 233, A, figures 1-3; plate 236, A, figures 1-7 
Shell of moderate size for the genus, attaining a width of nearly 14 inches; 
hinge forming the widest part ; cardinal extremities alate; sides gently rounded, 
oblique; anterior margin broadly rounded; surface marked by costellae formed 
into groups of as many as 8 fine ones bounded by stronger costellae. 
Pedicle valve moderately convex in lateral profile and with the maximum 
convexity slightly anterior to the middle; anterior profile moderately domed; 
umbonal region gently swollen ; median region moderately swollen; lateral slopes 
long and moderately gentle; anterior slope short and steep; interarea moder- 
ately long; pseudodeltidium small. Interior with long, slender median ridge; 
diductors with prominent thickenings along their inner edge. 
Brachial valve with posterior flat to gently concave in lateral profile; maxi- 
mum concavity anterior to the middle; sides and anterior margins deflected 
gently in the direction of the brachial valve; cardinal extremities deflected 
slightly toward the pedicle valve and forming a small concavity. 
