394 PALEONTOLOGY OF NEW YORK. 



SPHENOTUS, N. G. 

 Sphenotus truncatcs. 



PLATK LXF, FIGS. 1, *-6. 



Oyprieardites truneatux, Conrad. Jour. Acad. Nat. Sci., Phila., vol. viii, pi. 12, fig. 17, p. 244. 1842. 

 Sanffuiiwlites truncatus (Conbad), Hall. Prelim. Notice Lamellibranchiata, 2, p. 42. 1870. 



" " " " Pal. N. Y., vol. V, pt. 1. Plates and Explanations : PI. 65, figs. 



1-6. 1883. 



Shell small, trapezoidal ; length twice the height; basal margin nearly straight, 

 slightly constricted anterior to the middle. Posterior extremity obliquely 

 truncate. Cardinal line straight. Anterior end narrow, rounded. 



Valves depressed-convex at the posterior end, moderately convex below, 

 becoming gibbous above the middle. 



Beaks at about the anterior fourth or fifth, small, oppressed, incurved, 

 rising but little above the hinge-line. Umbonal slope angular, extending to 

 the post-inferior extremity. Post-cardinal slope flat, or concave, with an 

 obscure fold along the middle. A shallow cincture extends from the beak 

 obliquely to the base of the shell. 



Surface marked by fine concentric striae, which are fasciculate on the 

 anterior portion and umbonal region, producing low undulations ; also marked 

 by very fine radiating striae. Interior unknown. 



Three specimens measure respectively 10, 15 and 18 mm. in length, and 5, 

 7 and 9 mm. in height. 



This species differs from S. arcmformis in its straighter basal margin, less 

 pointed and less obliquely truncate posterior end and in its smaller size. 



Formation and localities. In the shales of the Hamilton gi'oup, at Summit and 

 Bear's gulf, Schoharie county, and on the shore of Skaneateles lake, N. Y. 



