2V2 PALEONTOLOGY OF NEW YORK. 



Leptodesma Corydon, n. sp. 



PLATE XC, FIG. 2i. 



Shell above the medium size, sub-rhom]>oi(I;il ; body narrowing very rapidly 

 toward the beak, oblique to the liiii^e-liae at an angle of about 30°; length 

 less than twice the height; ante-byssal margin oblique, nearly straight, 

 slightly impressed at the sinus, broadly curved at the base and rounded on 

 the posterior extremity. 



Left valve depressed-convex below and slightly gibbous on the umbo 

 (as preserved in thinh' laminated shale). Right valve unknown. 



Hinge-line straight, about equal to the greatest length of the shell. 



Beak sub-anterior, directed forward, little elevated above the cardinal line. 

 Umbonal region moderately gibbous, subtending an acute angle. 



Anterior end narrow, rostrate, acute, extended, defined by a distinct, 

 shallow, byssal depression wliicli produces a long, gentle curvature in the 

 margin of tlie valve. Wing narrow, joining the body at nearly the posterior 

 e.vtremity ; margin abruptly recurved l)elow and somewhat deeply concave a 

 little below the cardinal line ; extremity forming a spiniform extension. 



Test thin, marked by fine concentric stria>, which are fasciculate on the 

 ])ody at unequal distances, and shai-ply elevated and more distinct on the 

 wing. 



Interior unknown. 



A left valve of medium size has a length of 42 mm., height 25 mm., 

 hinge-line about 4(1 nun. 



Compared with L. Clitus, the body of the shell is more elongate-ovate or 

 sub-spatulate, narrowing more rapidly toward the post-extremity ; the wing is 

 wider and the sinuosity less deep, its greatest depth being near the cardinal 

 line. 



Formation and locality. In the Chemung group, Kelly's creek, Tioga county, 

 Pa. 



