ITS PALEONTOLOGY OF NEW YORK. 



mar<::in truncate at the extremitv, curving below into tlie sinus: ))asal 

 margin rounded, somewhat abruptly recurved posteriorly. 



Left valve regularly convex below, gibbous al)Ove 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, dcdncd by tlie oblique byssal depression wliicli extends 

 to more than oiic-tliinl thi' length of the valve below the Ijeak ; 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 l)elow the cardinal extension : extremity pro(hiced into a long 

 spiniform process. 



Test tliin, marked at irregular intervals by strong concentric lanieike, with 

 intermediate fine striae. The lamellne 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 nun., height 'Jn mm., liinge- 

 Hne to base of spine, \'l mm. A smaller specimen has a length of 'JO mm., 

 height 14 mm., hinge-line, to base of sjjine, VI mm. 



Tliis specii's (;losely resembles L. Rogers/, but is distinguished l)v the obli(pie 

 and more extended byssal depression, sliorter wing, and more rounded basal 

 margin. 



Formation and localities. In sliales of tlie Chemung group, on the Chemung 

 river above Elmira, and along the Blossburg railroad near Painted Post, N. Y. 



