8S 
PALAEONTOLOGY OF NEW YORK. 
hinge-line is sometimes a little longer and sometimes a little less than the 
width of the shell. 
The occlusor muscular imprints are small and deeply marked, and the 
impressions of the divaricator muscles form together an elongate-ovate scar, 
with the sides nearly straight, and each division showing two or three lobes. 
Near the exterior margin of the valve there is a depression reaching from 
the hinge-line entirely around the front of the shell, indicating a callosity 
upon the interior of the valve, which is marked by striae and by vascular 
impressions in well preserved specimens. 
The cast of a dorsal valve, of the same form, and associated with the 
ventral valves, shows the imprint of the submarginal callosity, with vascu¬ 
lar markings and a crenulated hinge-line: the cardinal process is bifurcate, 
and directed outwards as in other species of the genus. 
The length of the shell is from one-half to three-fourths of an inch, with 
a somewhat greater breadth. 
Figure 3, Plate si, is a young individual in which the ventral valve has a slight convexity, and the 
muscular impression, is but faintly defined in the lower part; while in fig. 2, an older specimen, it is a 
little concave, with a strongly defined muscular impression. 
The characters of the species, as represented in the figures of the ventral valve, 
are constant in as many as nine or ten individuals under examination, and they 
show no near approach to any other species in the collection. Fig. 1 is the inte¬ 
rior of a dorsal valve, which has been referred to this species from its association 
and similarity of form, while the vascular impressions also correspond in the 
two valves. 
Geological formation and localities. In the Schoharie grit at Clarksville, and at 
Knox, Albany county, N. Y. 
Stropliorionta callosa. 
PLATE XI & XX. 
Strophodonta callosa: Hall, Sixteenth Report on the State Cabinet, p. 36. 1863. 
Casts of the ventral valve are semi-elliptical, longer than wide or with 
nearly equal length and breadth, very convex or gibbous; across the 
