220 
PALAEONTOLOGY OF NEW YORK. 
Two left valves have respectively these dimensions: length 48, and 42 mm., 
height 32, and 30 mm., hinge-line 40, and 35 mm. 
This species resembles L. Pelops, but 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. N. Y. 
Leptodesma aliforme. 
PLATE XXII, FIG. 28; and PLATE XCI, FIG. 2. 
L<ptorlcsma aliforme, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PL 22, fig. 28. Jan., 1883. 
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 flat 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, very 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 hinge is furnished with a slen¬ 
der, oblique lateral tooth. 
