Lamellibranchiata. 351 



Test thin, marked by fine, irregular, concentric striae of growth, 

 which are abruptly recurved on the post-cardinal slope, and extend 

 along the margin for nearly half the length of the body before 

 recurving into the wing. The striae are more elevated and crowded 

 on the anterior side. 



The original specimen of this species has a greatest length from 

 beak to base of 42 mm., height 24 mm., hinge-line about 38 mm. 

 A small right valve has a length of 22 mm., height 12 mm., hinge- 

 line 24 mm. 



This species resembles L. Roger si, but the shell attains a larger 

 size; the body is more oblique to the hinge-line, and the posterior 

 extremity more abruptly recurved ; the wing is smaller and not ex- 

 tending so far down the body of the valve ; the sinus is narrower with 

 the deepest portion just beneath the hinge; the spine is stronger and 

 more distinctly defined ; the right and left valves are the same in form; 

 the sinus in the wing of the right valve is not so deep as in the left 

 valve, but much deeper than in the right valve of that species . 



This form is associated with Avicula spinigera of Conrad, which 

 is a smaller shell, less oblique, narrower, and with a more angular 

 anterior extremity. 



Formation and localities. In the Chemung group, at Painted Post, 

 Steuben county, between Corning and Elmira, and at Chemung 

 Narrows, N. Y. 



Leptodesma Shttmardi. 

 Leptodesma Shumardi, Hall. Pal. N. T., vol. v, pt. 1. Unpublished. 



Shell of medium size, sub-rhomboidal ; body narrow, very obliquely- 

 ovate ; length somewhat less than twice the height ; margin very 

 broadly curving from the anterior extremity to the base; basal 

 margin rounded and abruptly recurved at the post-basal extremity. 

 Left valve quite convex ; the greatest convexity about one-third the 

 length of the valve below the apex^ Right valve unknown. Hinge- 

 line straight ; length about equal to the height of the shell. Beak 

 sub-anterior, obtuse, prominent and arching over the hinge-line. 

 TJmbonal region gibbous, subtending an acute angle. Anterior 

 extremity short, acute, straight above, oblique below. Wing small, 

 narrow-triangular, extending to a point below the middle of the 

 length of the shell ; margin concave ; extremity acute, probably 

 spiniform. 



Test thin, marked by lamellose, often fasciculate striae, which are 



