LAMELLIBRANCHIATA. 439 



LUNULICARDIUM TRANSVERSUM, n. Sp. 

 PLATE XCIV, FIGS. 24, 25. 



Shell above the medium size, sub-cylindrical ; length more than twice the 

 height; basal margin gently curving. Posterior extremity narrowly 

 rounded. Cardinal line essentially straight, declining posteriorly. Hiatus 

 elongate, more than half the length of the shell ; margin defined, but with no 

 exterior expansion preserved. Anterior end short, narrowly rounded. 



Valves very convex in the middle and above ; the convexity declining 

 gradually toward the posterior end and abruptly toward the base and ante- 

 rior. 



Beaks sub-anterior, small, acute and directed forward. Umbonal slope 

 convex, not strongly defined, extending to the posterior extremity above the 

 middle of its height. 



Surface marked by about forty narrow rays, which are flattened or rounded 

 on the middle of the shell, and sub-angular on the anterior and posterior ends. 

 Entire surface also marked by closely arranged, lamellose concentric striae, 

 which are often aggregated and at intervals produce sub-imbricating lamellae. 



The specimen described has a length of 45 mm. and a height of 20 mm. 



This species is distinguished by its elongate and sub-cylindrical form. The 

 specimen described is somewhat vertically compressed so that the height given 

 is less than that of the shell in its natural condition. 



Formation and locality. In the Chemung group, at Elmira, N. Y. 



