LAMELLIBRANCHIA TA. 
169 
Hinge-line straight, less than the length of the shell. 
Beak anterior, acute, rounded, inclined forward, prominent. Umbonal 
region gibbous, subtending an acute angle. 
Ear short, directed downward, limited by an undefined sulcus, with 
scarcely any evidence of a byssal sinus. Wing comparatively small, flat, 
not strongly defined, joining the body of the shell above the middle of its 
height; margin concave; extremity abruptly acute. 
Test marked by fine concentric striae, which, at intervals, are crowded into 
fascicles upon the body of the shell, giving an undulating surface. On the 
wings they are closely and evenly arranged. 
Interior unknown. 
One specimen has a length of 20 mm., height 25 mm., and hinge-line about 
17 mm. A small specimen has a length of 13 mm., height 15 mm., and 
hinge-line 12 mm. 
This species is more prominent on the umbo and more convex below than 
any of the forms described in this group; the wing is shorter and smaller, 
with less extension along the posterior slope. A young shell referred to this 
species and in the same association has a body less abruptly defined on the 
posterior side. 
Formation and locality. In the coarser grits of the Hamilton group, in the 
southern part of Schoharie county, N. Y. 
Leiopteria Gabbi, n. sp. 
PLATE LXXXVIII, FIG. 14. 
Shell small; body ovate, very slightly oblique; height considerably greater 
than the length; anterior margin nearly erect for half the height of the 
valve, and regularly curving to the post-basal margin, which is scarcely 
produced. 
Valves sub-equally convex; the greatest convexity being a little above the 
middle in the left valve, and on the umbo of the right valve. 
Hinge-line not extended, less than the length of the shell. 
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