206 
PALAEONTOLOGY OF NEW YORK. 
Wing joining the body near the post-extremity of the shell, defined by a 
shallow groove; margin oblique, straight, apparently slightly concave just 
below the cardinal line. 
Test thin, leaving upon the cast the marks of the striae of growth which 
have been somewhat fascicled upon the body, giving it an obscurely undulated 
appearance. 
Interior unknown. 
A specimen of this species has a length of 35 mm., height 24 mm., and 
hinge-line nearly 24 mm. 
This species resembles L. Orodes, but differs in its greater obliquity; the 
body is more attenuate toward the anterior, and the wing is distinctly limited. 
This one, and several other species, have shown the presence of an alar 
furrow and obscure fold, similar to Ptychopteria. 
Formation and locality. In a coarse sandstone of the Upper Chemung group, 
south of Smethport, McKean county, Pa. 
Leptodesma Orodes. 
PLATE XXV, FIGS. 6, 9, (10?); AND PLATE XC, FIG. 8. 
Leptodesma Orodes, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 25, figs. 6, 9(10?). 
Jan., 1883. 
Shell of medium size, sub-rhomboidal; body ovate, oblique to the hinge-line 
at an angle of about 55°; length one-fifth greater than the height; ante- 
byssal margin a little oblique, nearly vertical above, curving into a long, 
undefined sinus; ventral margin rounded into the broad posterior curve. 
Left valve moderately convex in the lower part, increasing in convexity 
to the middle of the length, where it becomes gibbous. Right valve 
unknown. 
Hinge-line straight, a little less than the height of the valve. 
Beak sub-anterior, directed forward, moderately prominent, scarcely rising 
above the cardinal line. Umbonal region abruptly gibbous, subtending an 
angle of about 30°. 
