190 PALEONTOLOGY OF NEW YORK. 



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 binge-line and inclined slightly forward. Umbonal region 

 ventricose, 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 line, regular concentric stria', which are 

 crowded into fascicles on the anterior end. 



Interior unknown. 



'The specimen described has a greatest length of 2"i mm., height 15 mm., 

 hinge-line '2'2 nun. 



This shell resembles L. potens. hut 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 he taken as positive evidence of specific difference, while at the 

 same time their common characters may lie insufficient to unite them. 



Formation and locality. In the Chemung group at East Randolph, Cattaraugus 

 county. N. V 



Leptodesma Mortoni. 



PLATE \X1. FIGS. 20, SI, 32 IND PLATE I. XXXIX, FIGS. 9-11. 



Leptodesma Mortoni, II mi.. Pal. X. V.. vol. v, \A. 1. Plates and Explanations: PI. 21, figs. 29, 31,32 



(pl. 22, fig. 20 in error). -Ian., L883 



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 margin extended and abruptly 

 recurved. 



