450 PALMONTOLOGY OF NEW YORK. 



The n.aine S. Cai/uga 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. appressns. 



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 ELLIPTICU8. 



I'LATE LXXV, FIGS. 13-15. 



Schizodus elliplieics. Hall. Prelim. Notice Lamellibranchiata, 2, p. 96. 1870. 



Cytherodon (Schizudtis) elliptietis, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 75, 



figs. IS-LI. 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 fine, somewhat regular concentric striae. Interior 

 unknown. 



Two specimens measure I'espectively 15 and 24 mm. in length, and 12 and 

 16.5 mm. in height. 



This species diifers from S. appressvs 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. 



