89 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 Tjardinal 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 xi, 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, 

 arc 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. 



Stropliodonta callosa. 



PLATE XI & XX. 



Strophodonta callota : Hau, Sixteenth Report on the State Cabinet, p. 36. 1868. 



Casts of the ventral valve are semi-elliptical, longer than wide or with 

 nearly equal length and breadth, very convex or gibbous ; across the 



