178 
PALAEONTOLOGY OF NEW YORK. 
margin truncate at the extremity, curving below into the sinus; basal 
margin rounded, somewhat abruptly recurved posteriorly. 
Left valve regularly convex below, gibbous above the middle. Right 
valve depressed-convex below and abruptly gibbous above. 
Hinge-line straight, (and including the spine) equal to or greater than the 
length of the shell. 
Beaks sub-anterior, prominent. Umbonal region abruptly gibbous, sub¬ 
tending an acute angle. 
Anterior end short, defined by the oblique byssal depression which extends 
to more than one-third the length of the valve below the beak; extremity 
obtusely angular. Wing not large, joining the body nearly at the posterior 
third; margin oblique below, acutely recurved above, the greatest concavity 
being just below the cardinal extension; extremity produced into a long 
spiniform process. 
Test thin, marked at irregular intervals by strong concentric lamellae, with 
intermediate fine striae. The lamellae are stronger on the anterior side and 
obscure on the wing. The casts are often nearly smooth. 
Interior unknown. 
A specimen of medium size has a length of 29 mm., height 20 mm., hinge¬ 
line to base of spine, 12 mm. A smaller specimen has a length of 20 mm., 
height 14 mm., hinge-line, to base of spine, 12 mm. 
This species closely resembles L. Rogersi, but is distinguished by the oblique 
and more extended byssal depression, shorter wing, and more rounded basal 
margin. 
Formation and localities. In shales of the Chemung group, on the Chemung 
river above Elmira, and along the Blossburg railroad near Painted Post, N. Y. 
