L68 PALEONTOLOGY 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, liner, 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 line, crowded, concentric stria?; 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 l.WWIll. FIUS. 24, 25 



SHELL small, sub-rhomboidal ; body broadly ovate, very moderately oblique; 

 heighl 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. 



