LAMELLIBRANCHIATA. 451 



SCHIZODUS CONTRACTUS, n. sp. 



PLATE LXXV, riGS. 27, 28. 



In part Cytherodon (Schizodus) cuneus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 75, 



figs. 27-.30. 1883. 



Shell small, ovate-cuneate ; length one-third greater than the height ; basal 

 margin regularly curving. Posterior extremity pointed, nasute below, 

 obliquely truncate above. Cardinal line more than half the length of the 

 shell. Anterior end short, regularly rounded. 



Valves regularly convex below, gibbous in the middle and above. 



Beaks at about the anterior third, prominent, incurved, flattened. Umbo- 

 nal slope distinctly angular, extending to the post-inferior extremity. Post- 

 cardinal slope concave, marked by a narrow depression near the cardinal 

 line. 



Surface marked by fine, elevated, sharp, filiform concentric striae, which 

 become fasciculate toward the margin ; also sometimes marked by very fine 

 radiating striae. 



Anterior muscular impression strongly limited posteriorly. 



Two specimens measure respectively 14 and 15 mm. in length, and 9 and 

 10 mm. in height. 



This species resembles S. cuneus, of the Waverly sandstone, but is propor- 

 tionally longer, the umbonal angle is sharper, the cardinal slope is broader and 

 the basal margin is more broadly rounded. 



This shell hfis the general aspect of a Nucula, but the contraction of the pos- 

 terior end and the umbonal angle, indicate its relations with Schizodus. 



Formation and locality. In the Hamilton group, near the top of the formation, 

 on the shore of Cayuga lake, N. Y. 



