168 
PALAEONTOLOGY OF NEW YORK. 
Beak anterior, acute, prominent, inclined forward, rising above the hinge. 
Umbonal region gibbous, abruptly limited on the anterior side by the sulcus, 
and on the posterior side sloping rapidly to the wing. 
Wing large, flat, triangular, joining the body of the valve below the 
middle of the height, limited by the gently retral curve of the striae ; margin 
moderately concave ; extremity acute or mucronate. 
Surface marked by regular, equidistant, undulating, lamelliform, concentric 
expansions, which become crowded, finer, and to some extent less undulated 
on the wing, stronger and very much crowded on the anterior of the shell. 
The undulations extend forward in an abrupt curve, bending gently back¬ 
ward, and being thus opposite and slightly imbricating, they give an 
appearance of radiation. 
Interior unknown. 
The specimen described has a length of 35 mm., height 37 mm., and hinge¬ 
line about 29 mm. 
In general aspect, this species resembles Adinopteria Boydi, but the body is 
much less oblique and wider below; the surface is without proper rays; the 
wing has only fine, crowded, concentric striae; while in that species the wing is 
marked with strong radii and a few lines of growth. 
These comparisons are made from similar casts of the interior of both species. 
Formation and locality. In the coarse grits of the upper part of the Hamilton 
group, in the northern part of Schoharie county, N. Y. 
Leiopteria Leai, n. sp. 
PLATE LXXXVI1I, FIGS. 24, 25. 
Shell small, sub-rhomboidal; body broadly ovate, very moderately oblique; 
height much greater than the length; margin regularly rounded from above 
the middle on the anterior side, to a similar point on the opposite side, of the 
valve ; post-basal margin slightly produced. 
Left valve very convex; gibbous from below the middle to the umbo. 
Right valve unknown. 
