L96 PALEONTOLOGY OF NEW YORK. 



Interior miknuwii. 



A left valve of medium size has a length of 41 mm., height 22 nun., length 

 of cardinal line aboui 35 mm. 



This species differs from L. Hector in its greater obliquity, broader body 

 below, more produced and abruptly recurved post-basal extremity, deeper and 

 broader byssal depression, more produced anterior end, and narrower and 

 more deeply sinuate wing, with a more extended extremity. 



Formation and localities. In the central portion of the Chemung group at 

 Philipsburg, Alleghany county, N. Y., and below the conglomerate (same 

 position) in Sullivan township, Tioga county. Pa. 



Leptodesma curvatum. 



PLATE XXV, FIG. 5. 

 Leptodesma cnrvatum, Hall. Pal. N. T., vol. v, pt. 1. Plates and Explanations : l'l 25, fig. 5. Jan., 1883 



Shell above the medium size, rhomboidal; body ovate, sub-arcuate above, 

 oblique at an angle of nearly 30° with the hinge-line ; length and height as 7 

 to 1; ante-byssal margin oblique above, curving into a long, shallow sinus; 

 basal and posterior margins forming a broad, continuous curve, and abruptly 

 recurving at the post-basal extremity. 



Left valve regularly convex below, gibbous above the middle. Right 

 valve unknown. 



Hinge-line straight; length about equal to the length of the valve, but not 

 fully seen, as the spiniform termination is imperfect. 



Beak sub-anterior, prominent, directed forward. Umbonal region gibbous, 



Subtending an acute angle. 



Anterior end large, abruptly acute at the extremity, limited by a distinct. 

 ncarl\ vertical lyssal depression. Wing narrow-triangular, joining the bod} 

 at the posterior extremity; margin very oblique below, concave above, 

 abruptly recurved just below the cardinal line and extended into a spiniform 



process. In a cast of the left valve the wing is distinctly separated from 

 tin- body by a marked furrow . 



