LAMELLIB RANCHI A TA . 
229 
Wing large, undefined; margin very oblique in the lower part, slightly 
concave above, the greatest concavity being a little below the hinge-margin ; 
extremity produced into an angular extension. The right valve shows less 
distinction between the body of the valve and the wing. 
Test thin, marked by distant lamellose lines of growth with intermediate 
finer striae. These lines are more regular upon the wing and very much 
crowded and fasciculate upon the anterior side of the body. 
Interior unknown. 
Hinge, posterior to the beak, furnished with a slender lateral tooth 
A left valve of this species has a length of 55 mm., height 35 mm., hinge¬ 
line 37 mm., and the body, at the posterior end, having a width of 25 mm. 
A right valve has a length of 45 mm., height 30 mm., and hinge-line about 
28 mm. 
The specimens of this species observed are casts of the interior in coarse 
sandstone, or impressions of the exterior in the same rock. The species is 
distinguished by its straight ventral side and the nearly parallel direction of 
the sides of the body in the left valve. 
Formation and localities. In a coarse sandstone of the Upper Chemung group, 
on the road from Olean, N. Y., to Smethport, Pa., and at Bradford, Pa. 
Leptodesma akciforme, n. sp. 
PLATE XCI, FIG. 12. 
Shell large, narrow, sub-rhomboidal; body sub-cylindrical, oblique at an angle 
of about 30° to the hinge-line; length nearly one-half greater than the 
height; anterior margin oblique, merging into the broad, low curvature of 
the ventral margin ; posterior margin abruptly rounded and curving into the 
undefined wing. 
Yalves very convex, strongly gibbous, obtusely sub-angular along the 
middle; the greatest convexity distant from the beak one-third the height 
of the valve. The right valve is less gibbous, but otherwise similar to the 
left. 
