LAMELLIBRANCHIATA. 399 



mens similar markings appear, in a subdued degree, over the anterior portion 

 of the shell. Interior unknown. Ligamental area narrow. 



Four specimens measure respectively 28, 33, 38 and 42 mm. in length, 

 and 12, 14, 16 and 16.5 in height. The largest specimen observed has a 

 length of 72 mm. and a height of 28 mm. 



This species is distinguished by its long anterior end and peculiar ornamen- 

 tation on the posterior half of the shell. 



Formation and localities. In the shales of the Hamilton group, Sherburne 

 creek near Sherburne, Hamilton, Bellona and on the shores of Canandaigua and 

 Cayuga lakes, N. Y. 



Sphenotus contractus. 



PLATE LXVI, FIGS. 1, 3-9, U-13, 15 (10, IB, 17, 19?); AND PLATE XCIV, FIG. 2. 



Cypricardia eontravia. Hall. Geol. Sui-v. N. Y., Rep. Fourth Dist., p. 292, t. 139, fig. 4. 1S43. 



In part Sanyuiiwlites rU/Uliis (White and Whitfield), Hall. Prelim. Notice Lamellibranchiata, 2, p. 44. 



1870. 

 " " " " " Pal. N. Y., vol. V, pt. 1. Plates and Ex- 



planations: PI. 66, figs. 1-19. 18S3. 



Shell ranging from small to large size; trapezoidal, wider behind; length 

 more than twice the height; basal margin nearly straight, scarcely con- 

 stricted in the middle and gently curving to either extremity. Posterior 

 extremity oblique, somewhat doubly truncate. Cardinal line straight, long, 

 nearly parallel to the basal margin. Anterior end short, abruptly declining 

 from the beak and narrowly rounded below. 



Valves of moderate convexity, except in the upper portion and umbonal 

 region, where they are gibbous. 



Beaks sub-anterior, small, appressed and closely incurved over the hinge- 

 line. Umbonal slope distinctly angular, extending to the post-inferior 

 extremity. Post-cardinal slope flat, marked along its centre by a distinct 

 fold, which reaches to the posterior end, producing an extension of the mar- 

 gin, leaving a more oblique truncation above than below. Cincture without 

 distinct limitation, producing a flattening above and a slight depression 

 below the middle of the valve. 



