ITS PALAEONTOLOGY OF NEW YORK. 



margin truncate al 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, suit- 

 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; extremilv 

 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 stria?. 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 20 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. Rogcrsi. 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, X. Y. 



