Lamellibranchiata. 359 



Formation and localities. In the Upper Chemung group at Olean, 

 Portville, Oassadaga lake, and in loose specimens collected near 

 Panama, N. Y. 



Leptodesma potens, var. juvens. 



Leptodesma potens, var. juvens, Hall. Pal. N. Y., vol. v, pt. 1. Plates and 

 Explanations : PI. 22, fig. 16. Jan., 1883. 



Shell small, rhomboidal ; body ovate, oblique ; the greatest length 

 more than once and a half the height; anterior margin oblique, 

 very broadly curving below ; post-basal extremity rounded and ab- 

 ruptly recurved. Left valve convex below, very gibbous and ventri- 

 cose in the middle and above. Eight valve unknown. Hinge-line 

 straight, less than the length of the shell. Beak obtuse, situated at 

 the anterior third of the hinge-line, prominent, arching over the 

 hinge-line and inclined slightly forward. Umbonal region ventri- 

 cose, obscurely limited anteriorly by an undefined depression, and 

 on the posterior side by the abrupt and almost vertical post-umbonal 

 slope. Umbonal angle acute. Anterior end short, triangular; 

 extremity acute. Wing broad, triangular, joining the body of the 

 shell near the posterior end ; margin regularly concave ; extremity 

 acute. 



Test thin, marked by extremely fine, regular concentric striae, 

 which are crowded into fascicles on the anterior end. 



The specimen described has a greatest length of 25 mm., height 

 15 mm., hinge- line 22 mm. 



This shell resembles L. potens, but it is apparently more extended 

 and acute in front, sub-truncate on the posterior end; the wing joins 

 the body near the posterior extremity, and its margin is less deeply 

 sinuate than L. potens. These variations appear in comparison with 

 the older individuals of that species, and cannot be taken as positive 

 evidence of specific difference, while at the same time their common 

 characters may be insufficient to unite them. 



Formation and locality. In the Chemung group at East Eandolph, 

 Cattaraugus county, IS". Y. 



Leptodesma Moktoni. 



Leptodesma Mortoni, Hall. Pal. N. Y., vol. v, pt. 1 . Plates and Explana- 

 tions : PI. 21, figs. 29, 31, 32 (pi. 22, fig. 20 in error). Jan., 1883. 



Shell above the medium size, sub-rhomboidal ; body elongate sub- 

 ovate, very oblique ; length more than one-half greater than . the 

 height; ventral margin broadly curving to the base ; the posterior 



