190 PALEONTOLOGY OF NEW YORK. 



HiiiiiC-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-lint' and iii( liiifd slii:litly forward. Umbonal region 

 ventricose, ob.scurely limited anteriorly by au undefined depression, and on 

 the posterior side by the abrupt and almost vertical post-umbonal slope. 

 Umbonal angle acute. 



Anterior end sliort, triangular; cxticiiiity acute. Wing broad-triangular, 

 joining tbe Ixxly of the shell near the posterior end : margin regularly 

 concave ; extremity acute. 



Test thin, marked by extrenudy fine, regular concentric striae, which are 

 crowded into fascicles on the anterior end. 



Interior unknown. 



The specimen described has a greatest leiigtli of "J") mm.. heiLLht I "i mm., 

 hinge-line 22 mm. 



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

 in front, sub-trnncati' 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 specifie diiTerence, while at the 

 same time their common characters may 1)6 insnflicient to unite them. 



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

 county, N. Y. 



Leptouesma Moktom. 



I'LATE XXI, KIUS. 2!l, :il, M; AND ri.ATK LXXXIX, FIGS. !)-Il. 



I^ptodesma Muftinii. Hall. PjiI. N. Y., vol. v, ))t. 1. Plates and Explanjitioii." : PI. •l^. fiir^. 2il. HI, :W 



(pi. 22, tiir. 20 in en-or). Jan., ]88:^. 



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

 oblique; length more than one-half greater than the height ; ventral margin 

 broadly curving to tlie Ijase; the posterior margin extendeil ami abruptly 

 recurved. 



