LAMELLIBRANCHIA TA. 
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intervals, have been elevated into fascicles, and on the external shell, were 
probably sharp lamellose striae. 
Interior unknown. 
The specimen described has a length of 50 mm., height 31 mm., and 
hinge-line 35 mm. 
This species resembles L. Orodes, and may be distinguished by the more 
extended and acute anterior extremity, and the larger wing which is distinctly 
concave on the margin and recurved just below the cardinal line. It differs 
from L. Maclurii in its more produced anterior extremity, and broader wing 
which is less abruptly recurved at the extremity. 
Formation and locality. In a coarse sandstone of the Upper Chemung group, 
south of Smethport, McKean county, Pa. 
Leptodesma Lesleyi, n. sp. 
PLATE XCI, FIG. 7. 
Shell large, sub-rhomboidal; body narrow, elongate-ovate, making an angle of 
30° with the cardinal line; length more than one-third greater than the 
height; ante-byssal margin oblique, nearly straight above, curving into the 
broad sinus; ventral margin broadly curved; posterior extremity abruptly 
rounded. 
Left valve convex below, narrowly gibbous in the middle and on the 
umbo. Right valve less convex, depressed below. 
Hinge-line straight, nearly equal to the greatest length of the shell. 
Beaks sub-anterior, directed forward, acute and arching over the hinge in 
the left valve, depressed in the right valve. Umbonal region of the left 
valve narrowly gibbous, and subtending a very acute angle. 
Anterior end large, limited by a broad, distinct, oblique byssal depression; 
extremity flattened and acuminate. Wing large, triangular, joining the 
body near the post-basal extremity, limited by the abrupt forward bending of 
the striae; margin deeply concave ; extremity produced and acute. The 
