162 
PALAEONTOLOGY OF NEW YORK. 
sions: length 39, 34, and 25 mm., height 41, 38, and 26 mm., hinge-line 37, 
39, and 26 mm. The right valve, mentioned above, is 23 mm. in length, 25 
mm. in height, and 23 mm. along the hinge-line. 
This species resembles the two preceding, but the form of body is more 
narrowly ovate, the obliquity appears to be intermediate between the two; 
the ear is less strongly defined; the wing is .comparatively narrower, and less 
extended at the extremity. 
Formation and localities. In the shales o'f the Hamilton group, on the shores 
at Skaneateles lake; at Bellona, Yates county, and Leonardsville, Madison 
county, N. Y. ; a single specimen from the Corniferous limestone of Delaware, 
Ohio, has been referred to this species. 
Leiopteria Sayi, n. sp. 
PLATE LXXXVUI, FIGS. 15-20. 
Shell above the medium size, sub-orbicular ; body very broadly ovate, scarcely 
oblique; height greater than the length; margin nearly straight in front, 
thence regularly rounded. 
Left valve very convex, gibbous in the umbonal region. Bight valve 
smaller and less convex. 
Hinge-line straight, longer than the length of the shell. 
Beaks acute, situated near the anterior extremity of the hinge, prominent, 
inclined forward, arching over the hinge-line. Umbonal region ample, sub¬ 
tending a right angle. 
Ear small, bending downward, defined by a broad, shallow sulcus. Byssal 
sinus narrow. Wing large, triangular, greatly extended along the hinge-line, 
defined by the retral bending of the striae ; margin concave ; extremity acute. 
The wing of the right valve is very broad, flat, and much extended; not dis¬ 
tinctly defined. 
Surface marked by fine, closely arranged striae of growth, with distant, 
elevated lamellae, which are extensions of strong fascicles of striae. These 
leave angular concentric folds and undulations in the casts. The striae are 
