224 
PALAEONTOLOGY OF NEW YORK. 
wing of the right valve is scarcely defined from the body and less deeply 
concave on the margin. 
Test marked by fine, irregular, concentric striae which are strongly fascicu¬ 
late and lamellosS on the ventral side and anterior end, and are shown on 
the wing as sharp, elevated, regular striae. Some specimens preserve fine 
regular striae on the body of the valve, but they are usually somewhat irreg¬ 
ular and lamellose. In an exfoliated and macerated condition they x show 
fine radiating lines which probably belong to the intimate structure of the 
shell. 
Ligamental area (as preserved in an imperfect right valve) 1.5 mm. wide, 
and marked by very fine, minutely undulating longitudinal striae. The 
hinge also shows an obscure oblique lateral tooth. 
A left valve, of medium size, has a greatest length of 56 mm., height 
31 mm., and hinge-line about 51 mm. 
This species somewhat resembles L. aviforme, but is distinguished by its more 
oblique form, and wider anterior end. Specimens are quite abundant in an 
argillo-calcareous sandstone of the Upper Chemung group, associated with 
Spirifera Verneuili. 
Formation and locality. In the Upper Chemung group, Auburn township, 
Susquehanna county, Pa. 
Leptodesma aviforme, n. sp. 
PLATE XCI, FIG. S. 
Shell large, sub-rhomboidal; body elongate-ovate, broad behind, and rapidly 
narrowing toward the beak, oblique at an angle of a little less than 45° to 
the hinge-line; height more than one-half the length; ante-byssal margin 
very oblique, continued in a straight line into the shallow sinus, thence 
curving to the posterior extremity, which is broadly rounded. 
Left valve gently convex below, very convex above, and moderately 
gibbous on the umbo. Right valve unknown. 
