450 
PALAEONTOLOGY OF NEW YORK. 
The name S. Cayuga was given to a specimen sloping more abruptly along 
the cardinal line, with the basal margin a little emarginate just anterior to the 
post-inferior angle, which is distinctly nasute. These features are only a 
greater development of characters belonging to typical forms of S. appressus. 
Formation and localities. In the Hamilton group, on the shores of Seneca 
and Cayuga lakes ; at Pratt’s falls, Onondaga county; and Summit, Schoharie 
county, N. Y. 
ScHIZODUS ELLIPTICUS. 
PLATE LXXV, FIGS. 13-15. 
Schizodus ellipticus, Hall. Prelim. Notice Lamellibranchiata, 2, p. 96. 1870. 
Cytherodon ( Schizodus) ellipticus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 75, 
figs. 13-15. 1883. 
Shell small, sub-elliptical; length one-fourth greater than the height; basal 
margin regularly curving. Posterior extremity obliquely or sometimes 
almost vertically truncate. Cardinal line short. Anterior end broadly 
rounded. 
Valves depressed-convex below, convex in the middle and above. 
Beaks behind the anterior third, small, appressed, rising very little above 
the hinge-line. Umbonal slope obtusely angular, extending to the post¬ 
inferior extremity. 
Surface marked by line, somewhat regular concentric striae. Interior 
unknown. 
Two specimens measure respectively 15 and 24 mm. in length, and 12 and 
16.5 mm. in height. 
This species differs from S. appressus in its more elliptical form, longer ante¬ 
rior end, and the post-inferior extremity is less produced. 
Formation and locality. In the soft shales of the Hamilton group, on the shore 
of Canandaigua lake, N. Y. 
