382 Thirty-fifth Report on the State Museum. 



Test thin, marked by sharp, elevated, concentric striae with finer 

 intermediate ones. The stronger striae are regular on the wing and 

 posterior side; irregular and fasciculate on the anterior. 



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, Pa. 



Leptodesma aliforme. 



Leptodesma aliforme, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: 

 PI. 22, fig. 28. Jan., 1883. 



Shell large (right valve), elongate, triangular ; body narrow, spatu- 

 late, 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, show- 

 ing 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 

 slender, oblique lateral tooth. 



The specimen described is 60 mm. in length, with a height of 29 

 mm., and hinge-line 61 mm. 



This species bears considerable resemblance to L. extenuation in the 

 characters of the right valve ; but it is proportionally narrower, the 

 posterior extremity more abruptly recurved and the hinge-line less 

 extended behind, k. single right valve is the only specimen at present 



