190 
PALEONTOLOGY OF NEW YORK. 
Hinge-line straight, less than the length of the shell. 
Beak obtuse, situated at the anterior third of the hinge-line, prominent, 
arching over the hinge-line and inclined slightly forward. Umbonal region 
ventricose, obscurely limited anteriorly by an undefined depression, and on 
the posterior side by the abrupt and almost vertical post-umbonal slope. 
Umbonal angle acute. 
Anterior end short, triangular; extremity acute. Wing broad-triangular, 
joining the body of the shell near the posterior end; margin regularly 
concave; extremity acute. 
Test thin, marked by extremely fine, regular concentric striae, which are 
crowded into fascicles on the anterior end. 
Interior unknown. 
The specimen described has a greatest length of 25 mm., height 15 mm., 
hinge-line 22 mm. 
This shell resembles L. potens, but it is apparently more extended and acute 
in front, sub-truncate on the posterior end; the wing joins the body near 
the posterior extremity, and its margin is less deeply sinuate than L. potens. 
These variations appear in comparison with the older individuals of that species 
and cannot be taken as positive evidence of specific difference, while at the 
same time their common characters may be insufficient to unite them. 
Formation and locality. In the Chemung group at East Randolph, Cattaraugus 
county, N. Y. 
Leptodesma Mortoni. 
PLATE XXI, FIGS. 29, 31, 32; and PLATE LXXXIX, FIGS. 9-11. 
Leptodesma Mortoni , Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 21, figs. 29, 31, 32 
(pi. 22, fig. 20 in error). Jan., 1883. 
Shell above the medium size, sub-rhomboidal; body elongate sub-ovate, very 
oblique ; length more than one-half greater than the height; ventral margin 
broadly curving to the base; the posterior margin extended and abruptly 
recurved. 
