320 
PALAEONTOLOGY OF NEW YORK. 
abruptly rounded at the posterior extremity. Cardinal line declining from 
the beaks in both directions. Anterior end sloping rapidly from the beaks 
and rounded below; posterior end longer and more pointed. 
Valves convex, gibbous in the nmbonal region. 
Beaks usually at about the anterior third, sometimes sub-central, short, 
moderately elevated, broad and slightly incurved. Umbonal slope not dis¬ 
tinctly defined, rounded, direct, extending to the post-basal extremity. 
Surface marked by very fine concentric striae, and by irregular varices of 
growth, which sometimes produce strong undulations in the surface of the 
shell. 
The post-cardinal teeth are large and strong, contrasting with the preced¬ 
ing species, N. varicosa. 
Three specimens measure respectively 17, 16 and 14 mm. in length, and 
12.5, 12 and 9 mm. in height. 
This species is distinguished by its sub-equilateral triangular form. 
Formations and localities. In the shales of the Hamilton group, on the shores 
of Cayuga, Seneca and Canandaigua lakes ; and a single doubtful specimen from 
the Chemung group, of Ithaca, N. Y. 
Nucula lamellata. 
PLATE LI, FIGS. 18-21 ; PLATE XLV, FIG. 13 ; and PLATE XCIII, FIG. 7. 
Nucula lamellata, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : PI. 51, fig's. 1S-21. 1883. 
Shell small, elongate-ovate, truncate behind; length twice the height; basal 
margin broadly curving, straight, or slightly arcuate in the middle; poste¬ 
rior margin short, obliquely truncate. Cardinal line straight, directed some¬ 
what upward toward the anterior. Anterior end large and regularly 
rounded. 
Valves gibbous, with a broad flattened depression extending from the beaks 
to the base and sometimes slightly constricting the margin. 
Beaks sub-central or posterior to the middle of the shell, incurved, rising 
a little above the hinge-line. Umbo gibbous. Umbonal slope obtusely sub- 
