FOSSILS OF THE DEVONIAN. 181 
point, which is above the transverse center of the shell, the outline curves 
down into the broadly-rounded basal margin; posterior extremity a little 
below the transverse center and broadly angular, the line above rounding 
upward into the cardinal line and to the beaks with a uniform curvature; 
beaks elevated above the hinge-line, rather small, and situated on the ante- 
rior third of the shell. 
Surface of cast with an obscure anterior muscular scar and obscure 
concentric lines of growth. 
In the absence of the structure of the hinge the generic reference is ac- 
companied with more or less uncertainty, but in the light that the present 
specimens afford the species is referred to the genus Anodontopsis. 
Formation and localities —Lower Devonian horizon of Lone Mountain, 
18 miles northwest of Eureka; and Gray’s Canon, Kureka District, Nevada. 
Genus SCHIZODUS King. 
CYTHERODON Hall. 
Schizodus (Cytherodon) orbicularis, n. sp. 
Plate v, figs. 8, 8a. 
Shell of medium size; suborbicular, or subrhomboidal in outline. Gen- 
eral surface strongly convex, with the umbonal ridge rounded. Beaks smail 
and but little elevated above the cardinal line. 
Surface smooth or marked by slightly impressed concentric lines of 
growth. Interior characters unknown. 
Dimensions: height, 3°"; breadth, 3.5°™; convexity of right valve, .75™. 
A small shell (fig. 8a) still more quadrate in outline occurs in the Lower 
Devonian of Atrypa Peak. It is probable that it is a young shell of the 
species under consideration. 
In Cytherodon (Schizodus) quadrangularis Hall (Pal. N. Y., vol. v, pt. 1, 
Plates and Explanations, p. 18, pl. xxv, figs. 31-36), from the Chemung and 
Waverly Groups, we have the nearest form to S. (C.) orbicularis. 
The beaks in the former are more subcentral and the outline less sub- 
orbicular. They are, however, very closely allied species. 
Formation and locality—lLower Devonian of Lone Mountain, 18 miles 
northwest of Eureka, Nevada. 
