220 PALEONTOLOGY OF NEW YORK. 



Two left valves have respectively these dimensions: length 48, and 42 mm., 

 heiffht 32, and 30 mm., hintie-line 40, and 35 mm. 



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

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

 sinuosity in the margin of the win<: being nearer to the cardinal line, and the 

 extremity of tlic wing more acuminate. 



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

 county. N. Y. 



Leptodes.ma aliforme, 



I'l.ATK .\XII, KIU is; AMI I'LATK XCI, FIG. 2. 

 Liplnr!,.\mn aliforme, IlAr.i.. Pal. N. Y., vol. v. pt. 1. Plate.'; and Explanations: PI. 22. tig. 28. Jan., 1SS3. 



SiiEM, large (right valve), elongate, triangular : body narrow, spatulate, oblique 

 at an angle of about 30° witli tlie 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 po.'^terior 

 extremity, whicli is abruptly rounded. 



Right valve nearly flat below, depressed-convex in tbe middle, .-^lightly 

 gitjbous in the unilionul region. Left val\e luiknown. 



Hinge-line straight ; length equal to the greatest length of tlie >liell. 



Beak sub-anterior, depressed, directed forward. 



Anterior cml narrow-triangular; extremity attenuate, very acute. Wing 

 narrow, elongate, triangular, extending to tlie 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 strias. 



Muscular impression large, situated at about the middle of the k-ngtli of 

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

 slight interruptions, nearly to the lieak. The hinge is furnished with a slen- 

 der, oblique lateral tooth. 



