LAMELLIBRANCHIA TA. 
331 
Beaks between the anterior third and fourth of the length of the shell, 
prominent, rising above the hinge-line. Umbonal ridge distinctly defined, 
sharply angular above, becoming truncate below in its extension to the 
posterior extremity. 
Surface marked by fine, regular, equal, sharp concentric striae, which con¬ 
verge upon the posterior end of the shell, cross the umbonal angle, and are 
obsolescent on the post-cardinal slope. 
Hinge crenulated with minute teeth which extend half the distance from 
the beak to the posterior end. 
Three specimens measure respectively 16, 13 and 10 mm. in length, and 
6.5, 6, and 4.5 mm. in height. 
This species differs from L. diversa in its more elongate form, in the more re¬ 
curved and falcate posterior extremity, proportionally more anterior beaks, finer 
and more regular striae, which do not become confluent on the umbonal ridge. 
Some of the specimens are marked by extremely fine striae, which are scarcely 
visible except under a magnifier. This character, and their somewhat shorter 
form, led to their separation under the name of L. perstriata, but the distinction 
is found not to be tenable, as in some specimens the striae are extremely fine in 
the upper part of the shell, and have the characteristic appearance of typical 
specimens of L. rostellata in the lower part. The older individuals are more 
extremely attenuate behind than the younger specimens. 
Formation a,nd localities. In the shales of the Hamilton group, on the shores 
of Skaneateles, 0wasco and Seneca lakes, and at Pratt’s falls, Onondaga 
county, N. Y. 
Leda obscura, n. sp. 
PLATE XLVII, FIG. 48. 
Leda ( Nuculana) curta, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 47, fig. 48. 1883. 
Not Leda curta, Meek. Proc. Acad. Nat. Sci. Phila. 1861. 
Shell small, ovate-triangular, acute at the posterior extremity ; length one-third 
greater than the height. Gibbous in the umbonal region, and regularly con¬ 
vex below, with a slight depression at the base toward the posterior end. 
Beak between the middle and anterior third. Umbonal ridge not defined. 
