2] I PALAEONTOLOGY OF NEW YORK. 



much stronger. In all these characters it also differs more extremely from 

 L. extenuatum. 



Formation and locality. In compact sandstone of the Upper Chemung group, 

 alternating with some red heds. on Seely creek. Tioga county, Pa. 



Leptodesma Pelops, n. sp. 



PL VI' K M FIGS 28, '-".' 



Shell larger than the medium size, sub-rhomboidal ; body ovate, oblique at an 

 angle of about 10° with the binge-line : height two-thirds the greatest length : 

 ante-byssal and ventral margins very oblique and continuing in nearly a 

 straight line for two-thirds the length, with a slight concavit}- for the byssal 



sinus; posterior margin very broadly curving. 



Left valve depressed-convex below, gradually becoming more convex above 

 the middle, and somewhat gibbous on the umbo. Right valve unknown. 



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



Beak sub-anterior, inclined forward, obtuse, scarcely elevated above the 

 hinge-line. Umbonal angle acute. 



Anterior end triangular, prolonged, acute. Wing joining the bod\ of the 

 shell at the posterior extremity ; margin symmetrically concave ; extremity 

 produced and acutely angular. 



Test marked by distant, sub-equal, lamellose elevated striae, with finer 

 intermediate stria'. The stronger striae are regular on the wing and posterior 

 slope of the body, and become irregular and fasciculate on the anterior side 

 and lower half. 



Interior unknown. 



The hinge shows a narrow striated liganiental area, ami, apparently, a' 

 slender lateral tooth. 



A large left valve has a length of 44 mm., height 28 mm., and hinge-line 

 12 mm. 



This form is more oblique, ami the wing is longer and narrower than in 

 L. Orodes. 



