340 Thirty-fifth Report ok the State Museum. 



in surface characters. The wing is not so much extended as in L. 

 Conradi, the striae are more abruptly recurved, and the post-cardinal 

 slope is more strongly defined. There is a general resemblance with 

 L. Bigsbyi, but the body and hinge-line are longer, the body narrow- 

 ing more rapidly from the base, and the striae are equal and uniform. 

 Formation and localities. In the soft shales of the Hamilton group, 

 at Skaneateles and Cayuga lakes ; and in the upper coarse beds and 

 lower shales at Pratt's falls, Onondaga county ; also at Schoharie, 

 N. Y. It is widely distributed from the eastern to the central portion 

 of the State. 



Leiopteria Bigsbyi. 



Leiopteria Bigsbyi, Hall. Pal. N. Y., yol. v, pt. 1. Plates and Explanations : 

 PI. 20, figs. 3, 11, 13-15. Jan., 1883. 



Shell larger than medium size, sub-rhomboidal; body ovate, oblique; 

 height greater than the length; anterior margin nearly vertical for 

 about half the height of the shell, thence regularly rounded along 

 the base ; posterior side moderately extended. Left valve gibbous 

 upon the umbo, less convex toward the base. Right valve gibbous 

 on the umbo, depressed-convex below, shorter than the left valve. 

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

 Beaks anterior, acute, prominent, rising above the hinge-line, in- 

 clined forward. Umbonal region prominent, subtending an angle 

 of about 55°. Ear short, bending moderately downward, with a 

 strong fold at the upper side, limited by a broad, undefined sulcus. 

 Byssal sinus shallow. Wing triangular, wide, nearly flat ; margin 

 concave; extremity acute. The wing of the right valve is less de- 

 fined than the left, and the byssal sinus is a little deeper. 



Test thin; specimens partially exfoliated, or occurring in the con- 

 dition of casts, show sharply elevated, lamellose, concentric strias, 

 which are very distinct on the wings, and crowded and somewhat 

 fasciculate on the anterior side and ear. No intermediate finer 

 striae have been observed. In well-preserved specimens the sharp 

 lamellae have undulating margins. Interior unknown. Ligamental 

 area marked by a single groove. 



A large specimen has a length of 43 mm., height 50 mm., hinge- 

 line 37 mm. Another example has a length of 32 mm., height 33 

 mm., hinge-line 30 mm. In the younger shells the height is pro- 

 portionally somewhat less than in the older ones. 



This species, compared with the preceding, has a greater height of 

 body and shorter hinge-line, and differs in the conspicuous, sharp, 



