196 
PALEONTOLOGY OF NEW YORK. 
Interior unknown. 
A left valve of medium size has a length of 41 mm., height 22 mm., length 
of cardinal line about 35 mm. 
This species differs from L. Hector in its greater obliquity, broader body 
below, more produced and abruptly recurved post-basal extremity, deeper and 
broader byssal depression, more produced anterior end, and narrower and 
more deeply sinuate wing, with a more extended extremity. 
Formation and localities. In the central portion of the Chemung group at 
Philipsburg, Alleghany county, N. Y., and below the conglomerate (same 
position) in Sullivan township, Tioga county, Pa. 
Leptodesma curvatum. 
PLATE XXY, FIG. 5. 
Leptodesma curvatum, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI 25, fig. 5. Jan., 1888. 
Shell above the medium size, rhomboidal; body ovate, sub-arcuate above, 
oblique at an angle of nearly 30° with the hinge-line ; length and height as 7 
to 4; ante-byssal margin oblique above, curving into a long, shallow sinus; 
basal and posterior margins forming a broad, continuous curve, and abruptly 
recurving at the post-basal extremity. 
Left valve regularly convex below, gibbous above the middle. Right 
valve unknown. 
Hinge-line straight; length about equal to the length of the valve, but not 
fully seen, as the spiniform termination is imperfect. 
Beak sub-anterior, prominent, directed forward. Umbonal region gibbous, 
subtending an acute angle. 
Anterior end large, abruptly acute at the extremity, limited by a distinct, 
nearly vertical byssal depression. Wing narrow-triangular, joining the body 
at the posterior extremity; margin very oblique below, concave above, 
abruptly recurved just below the cardinal line and extended into a spiniform 
process. In a cast of the left valve the wing is distinctly separated from 
the body by a marked furrow. 
