342 Thirty-fifth Report on the State Museum. 



Leiopteria Troosti. 



Leiopteria Troosti, Hall. Pal. N. Y., vol. v, pt. 1. Unpublished. 



Shell above the medium size, sub-rhomboidal; body broadly ovate, 

 moderately oblique ; height somewhat greater than the length ; 

 anterior margin, from the wing to about half the height, nearly 

 vertical, curving broadly around the base, and more abruptly 

 rounded behind. Left valve moderately convex, gibbous on the 

 umbo. Right valve unknown. Hinge-line straight, somewhat less 

 than the length of the shell. Beak anterior, acute, prominent, in- 

 clined forward, rising above the hinge. Umbonal region gibbous, 

 abruptly limited on the anterior side by the sulcus, and on the pos- 

 terior 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 striaB ; 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 backward, and being thus opposite 

 and slightly imbricating, they give an appearance of radiation. 



The specimen described has a length of 35 mm., height 37 mm., 

 and hinge-line about 29 mm. 



In general aspect, this species resembles Actmopteria 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. 

 Leiopteria Leai, Hall. Pal. N. Y., vol. v, pt. 1 Unpublished. 



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 



