STR0PH0D0NTJ3 OF THE UPPER HELDERBERG GROUP. 
87 
Figure 12 represents a young individual, and figure 13 is twice enlarged. 
The figures 18 & 19 are ventral and profile views of a large individual, and the fasciculate 
striae upon the inner surface of the shell are shown in figure 20. 
The specimen figure 21 is a larger individual, with similar crowded striae and rounded 
cardinal angles. 
In the well-marked specimens of this form, I have not been able to learn the 
character of the muscular impressions; and in one small specimen only I have 
seen a short bifurcating cardinal process. 
Among some obscure specimens from the same localities are some casts of dorsal 
valves which are much elevated, or obtusely subcarinate along the centre, with 
duplicating striae. One of these shows a cardinal process and muscular impression, 
as illustrated in figure 23 of Plate xi. This may be identical with the preceding 
form. 
Geological formation and locality. In the Schoharie grit at Clarksville and Knox 
in Albany county, and at Schoharie. 
8tropiiodonta inequiradiata. 
PLATES XI, XII & XIII. 
Strophodonta inequiradiata : Hall, Tenth Report on the State Cabinet, p. 113. 1857. 
Shell semielliptical or semicircular, more or less gibbous, approaching a 
hemispheric form : cardinal extremities sometimes salient, but often 
rounded, and the cardinal line less than the width of the shell below. 
The ventral valve varies from moderately convex to gibbous, often 
forming a somewhat regular arch from beak to front, usually with the 
greatest convexity above the middle, depressed and often concave be¬ 
tween the umbo and the cardinal extremities, which (in perfect shells) 
are somewhat salient : beak a little elevated above tlie hinge-line, and 
incurved; area very narrow, linear and finely crenulate. The dorsal 
valve is concave, often in a less degree than the convexity of the 
ventral valve; the disc sometimes very slightly concave, and abruptly 
deflected or almost geniculate towards the front. 
The surface presents much variety of character and aspect, both’ in the 
original shell and in its partial or entire exfoliation. The strise on the 
ventral valve are often coarse and uneven, somewhat fasciculate, and 
