lOG PALjEONTOLOGY OF NEW YORK. 



Interior unknown. 



A left valve of medium size has ji length of 41 mm., hcii:lit '22 mm., leiiiitli 

 of cardinal line about o") mm. 



'riii.-i .species diflfers from />. Ihctor \\\ its greater <>lili(|nity, 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 th(> central portion of the Chemung group at 

 Philipsburg, Alleghany county, N. Y., and below the conglomerate (.-<anie 

 position) in Snllivan township, Tioga county, Pa. 



LeI'TODESMA CUUV.\TU.M. 



I'L.VTE XXV, FIG. 5. 



Ltjil'>dfxiii.:i i-amttMin. M\\.\.. l';il. N. Y., vol. v. jit. 1. Plates and Exiilauatioiis ; PI 2S, tij'-. .'). Jan., 1883. 



Shell above the nn-diuin size, rhomboidal; bodv ovate, sub-arcuate above, 

 oblique at an angle of nearly ^^0° with the hinge-line ; length and height as 7 

 to 4; ante-l)yssal margin oldique above, curving into a long, .shallow sinus; 

 l)asal and posterior margins forming a broad, continuous curve, and abrujjtly 

 recurving at the post-basal extremity. 



Left valve regularly convex Ijelow, gibbous above tlu' middle. Right 

 valve luikiiown. 



Hinge-line straight; length about equal to the lengtii of the valvt-. but not 

 fidly .seen, as the spiniform termination is imperfect. 



Beak sul)-antt'rior. proiniinMit, ilii-cctcil linwai'il. riiilioual region gibbous, 

 subtending an acute angle. 



Anterior end large, abruptly acute at the extremity, limited liy a distinc't, 

 nearly vertical l)yssal depression. Wing narrow-triangular, joining the bod\ 

 at the posterior extremity; margin very oblique l)elow, concave above, 

 abruptly recurved just l)elow the cardinal line and extended into a .spiniform 

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

 the body by a marked liu row. 



