LAMELLIBRANCHIA TA. 
165 
line 31, 21, and 23 mm. A smaller specimen has length of 17 min., height 
16 mm., hinge-line 15 mm. 
This species resembles in form L. Conradi and L. Rafinesquii, but there are 
some differences in shape and obliquity, and more decidedly 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 narrowing more rapidly from the base, and the striae are 
equal and uniform. 
Formation and localities. In the soft shales of the Hamilton group; at Skane- 
ateles 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. 
PLATE XX, FIGS. 3, 11, 13-15; AND PLATE LXXXVIII, FIG. 23. 
Leiopteria Bigsbyi, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PL 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 towards the base. Right 
valve gibbous on the umbo, depressed-convex below, shorter than the left 
valve. 
Hinge-line straight, equalling or less than the length of the shell. 
Beaks anterior, acute, prominent, rising above the hinge-line, inclined for¬ 
ward. 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 
