LAMELLIBRANCHIATA. 239 



Interior unknown. 



The specimen described has a length of 29 mm., height 1G mm., and hinge- 

 line 31 mm. 



This species is much smaller than P. profundus, less elongate and less gibbous 

 in its proportions. The beak is apparently more elevated and angular, but 

 the angularity of the umbonal region is not continued along the body as in the 

 preceding form. 



Formation and locality. In the shales of the Chemung group at Rockville, 

 Alleghany county, N. Y. 



Pteronites inoptatus, n. sp. 



PLATE LXXXVII, FIG. 5. 



Shell of medium size, broadly semi-ovate ; body ovate, oblicpie, making an 

 angle of about 25° with the cardinal line ; ventral and basal margins broadly 

 rounded ; post-basal extremity abruptly recurved. 



Left valve regularly convex, slightly gibbous above. Right valve unknown. 



* 



Hinge-line straight, less than the greatest length of the shell. 



Beak sub-anterior, directed forward, prominent and incurved over the 

 cardinal line. Umbonal angle acute. 



Anterior end short, nasute ; extremity acute. Wing very narrow-trian- 

 gular, scarcely defined, joining the body at the posterior extremity ; margin 

 oblique, in direct continuation with the posterior extremity and curving 

 backward just beneath the cardinal line ; extremit}^ acute. 



Test marked by concentric striae of growth which are strongly fasciculate 

 on the anterior end and ventral margin. 



Interior unknown. 



The left valve described has a length of 38 mm., height 21 mm., and 

 hinge-line 33 mm. 



This species is distinguished from the other forms of this genus by its narrow 

 wing and shorter hinge-line. It has the characteristic aspect of Pteronites 

 although approaching, in several particulars, to some species of Leptodesma. 



Formation and locality. In the Chemung group, Mansfield, Tioga county, Pa. 



