376 Thirty-fifth Report on the State Museum 



eptodesma corydon. 



Leptodesma Gory don, Hall. Pal. N. Y., vol. v, pt. 1. Unpublished. 



Shell above the medium size, sub-rhomboidal ; body narrowing very 

 rapidly toward the beak, oblique to the hinge-line 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 thinly 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, denned by a distinct, 

 shallow, byssal depression which produces a long, gentle curvature 

 in the margin of the valve. Wing narrow, joining the body at 

 nearly the posterior extremity; margin abruptly recurved below and 

 somewhat deeply concave a little below the cardinal line ; extremity 

 forming a spiniform extension. 



Test thin, marked by fine concentric striae, which are fasciculate 

 on the body at unequal distances, and sharply elevated and more 

 distinct on the wing. 



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

 hinge-line about 40 mm. 



Compared with L. Glitus, the body of the shell is more elongate- 

 ovate or sub-spatulate, narrowing more rapidly toward the post- 

 extremity ; the wing is wider and sinuosity less deep, its greatest depth 

 being near the cardinal line. 



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

 Tioga county, Pa. 



Leptodesma Jason. 



Leptodesma Jason, Hall. Pal. N. Y., vol. v, pt. 1. Unpublished. 



Shell above the medium size, sub-triangular ; body elongate-ovate 

 or subspatulate, attenuate toward the anterior end, oblique at an 

 angle of about 40° with the hinge-line ; length once and a half the 

 height; margin on the anterior gently curving into the undefined 

 byssal sinus ; thence nearly straight to within one-fourth the length 

 of the valve from the posterior extremity, which is regularly and 



