220 PALEONTOLOGY OF NEW YORK. 



Two l«l't valves have respectively these dimensions: length 48, and 42 nun.. 

 height 32, and 30 mm., hinge-line 40, and 35 mm. 



This species resembles L. Pelops, lint the body is broader and less oblique, 

 the anterior portion not so attenuate, the wing somewhat wider, the greatest 

 sinuosity in the margin of the wing being nearer to the cardinal line, and the 

 extremity of the wing more acuminate. 



Formation and locality. In shales of the Chemung group, Mansfield, Tioga 

 county. X. Y. 



Leptodesma aliformk. 



PLATE XXII, PIG 28; i\n PLATE XXI. PIG 2 

 Lfptndcxma aliforme, Ball. Pal. N. V.. vol. v. pt. 1. Plates ami Explanations: PI. 22, fig. 38. -Ian.. IS83. 



Shell large (right valve), elongate, triangular; body narrow, spatulate, oblique 



at an angle of about 30° with the cardinal line: length twice the height; 

 margin of shell oblique anteriorly, continued along the base in nearly a 

 straight line for two-thirds its length, thence curving to the posterior 

 extremity, which is abruptly rounded. 



Right valve nearly Hat below, depressed-convex in the middle, slightly 

 gibbous in the umbonal region. Left valve unknown. 



Hinge-line straight ; length equal to the greatest length of the shell. 



Beak sub-anterior, depressed, directed forward. 



Anterior end narrow-triangular: extremity attenuate, ver}' acute. Wing- 

 narrow, elongate, triangular, extending to the posterior extremity of the 

 valve, not defined ; margin concave, the greatest concavity below the middle : 

 extremity slightly produced, angular. 



Test not preserved. The specimen is a cast of the interior, showing some 

 faint indications of concentric striae. 



Muscular impression large, situated at about the middle of the length of 

 the posterior slope. Pallial line continued parallel to the anterior side, with 

 slight interruptions, nearly to the beak. The binge is furnished with a .^len- 

 der, oblique lateral tooth. 



