214 
PALEONTOLOGY 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 beds, on Seely creek, Tioga county, Pa. 
Leptodesma Pelops, n. sp. 
PLATE XC, FIGS. 28, .29. 
Shell larger than the medium size, sub-rhomboidal; body ovate, oblique at an 
angle of about 40° with the.hinge-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 concavity 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 body 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 striae. 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 ligamental area, and, apparently, a 
slender lateral tooth. 
A large left valve has a length of 44 mm., height 28 mm., and hinge-line 
42 mm. 
This form is more oblique, and the wing is longer and narrower than in 
L. Orodes. 
