396 
PALAEONTOLOGY OF NEW YORK. 
Sphenotus cuneatus. 
PLATE LXV, FIGS. 12-17. 
Pterinea cuneata, Conrad. Geol. Surv. N. Y., Ann. Rep., p. 110. 1838. 
Sanguinolites cuneatus (Conrad). Hall. Prelim. Notice Lamellibranchiata, 2, p. 39. 1S70. 
“ “ “ “ Pal. N. Y., vol. v, pt. I. Plates and Explanations: PI. 65, fiurs. 
12-17. 1883. 
Shell large, trapezoidal; length more than twice the height; basal margin con¬ 
stricted anterior to the middle and gently curving to both extremities. Pos¬ 
terior extremity oblicpiely sub-truncate, sinuate. Cardinal line straight. 
Anterior end short, rapidly declining from the beak and narrowly rounded 
below. 
Valves depressed-convex posteriorly, moderately convex below the middle 
and becoming somewhat gibbous in the umbonal region. 
Beaks sub-anterior, small, battened and closely appressed. Umbonal slope 
marked by an obtusely angular fold or ridge, extending to the post-inferior 
extremity. Post-cardinal slope concave, marked along its centre by a low 
fold, which is a little nearer the cardinal line than to the umbonal ridge, 
extending to the posterior extremity. Cincture oblique, extending from the 
beak to the base of the shell, producing a depression of the surface and a 
sinuosity in the margin. 
Surface marked by hne concentric striae, which become fasciculate and 
often form low undulations anterior to the umbonal ridge; also by hne radi¬ 
ating striae on the body of the shell, which have not been observed on the 
post-cardinal slope. 
Four specimens measure respectively 33, 42, 42 and 48 mm. in length, and 
14, 17, 18 and 19 mm. in height. 
This species differs from S. arc&formis in its proportional^ greater length, 
with a greater height at the posterior end; in its sinuate posterior margin, 
constricted basal margin and more regular concentric striae. 
In certain conditions of preservation, the radiating striae are obscure or 
obsolete, and sometimes worn by weathering, and are therefore not to be relied 
upon as characterizing the species in all cases. 
