234 
PALAEONTOLOGY OF NEW YORK. 
Anterior end convex, limited by a shallow, oblique, byssal depression which 
is nearly as long as the height of the valve; length one-half the height; 
extremity slightly produced. Wing triangular, scarcely defined, joining the 
body at the posterior extremity; margin oblique, straight or slightly convex; 
extremity obtuse-angular. An imperfect right valve presents about the same 
characters of wing. 
Test marked by fine striae of growth which are strongly fasciculate on the 
anterior end. 
Interior unknown. 
A left valve has a greatest length of 31 mm., height 20 mm., and hinge¬ 
line 21 mm. 
This species is distinguished by its short, broad, sub-quadrate form. It has 
very much the aspect of Modiomorpha, but clearly belongs with L. Pham and 
L. Lichas, which are among the extreme variations of the species of Lepto- 
DESMA. 
Formation and locality. In the Upper Chemung group, Lindley township, 
Steuben county, N. Y. 
Section /, mytiloidea. 
Leptodesma acutirostrum, n. sp. 
PLATE XCI, FIG. 21. 
Shell of medium size, rhomboid-ovate; body narrowly ovate and rapidly 
attenuate toward the beak, oblique, making an angle of a little less than 
45° with the hinge-line; length nearly one-third greater than the height; 
ante-byssal margin oblique, sloping into the shallow sinus; broadly rounded 
below, the curvature continued into the posterior extremity. 
Left valve depressed-convex in the lower part, moderately convex in the 
middle, and slightly gibbous above. Right valve unknown. 
Hinge-line straight, less than the height of the valve. 
Beak anterior, acute, directed forward, scarcely rising above the hinge- 
