86 PALEONTOLOGY OF NEW-YORK. 



The form .and proportions are not materially unlike those of S. callosa; but the 

 ■tria) are much stronger, the muscular impression of different form, and the surface 

 of the casts much more distinctly marked by the impressions of striae. 



Figure 5 of Plate xi is from the impression of a dorsal valve ; and figure 11 of the same 

 plate b a cast of the ventral valvo enlarged two diameters, showing the muscular impression 

 and marks of the striae. Farther illustrations are given on Plate xv. 



Geological formation and locality. In the Schoharie grit, at several localities in 

 Albany and Schoharie counties. 



Strophodonta crebristriata. 



• PLATE XL 



t Strophomena crtbrittriata : Cohrad, Jour. Acad. Nat. Sciences, Vol.viii, pa. 254, pi. 14, f. 3. 



SfiELL semielliptical ; length and greatest width nearly as two to three. 

 Ventral valve convex or moderately gibbous, more elevated in the 

 centre : hinge-line straight, with the extremities usually a little sa- 

 lient ; area linear and finely crenulated ; the beak slightly prominent, 

 and a little incurved. Dorsal valve concave, following the form of the 

 ventral valve. 



SoRFACE marked by £ne crowded striae which regularly bifurcate from 

 their origin, or sometimes in fascicles of threes which again subdivide. 



Mr. Conbad's description of S. crebristriata is as follows : 

 " Semi-orbicular, with fine crowded bifurcating radii ; inferior valve ventricose, 

 " slightly depressed or flattened in the middle ; sides depressed or concave to- 

 " wards the hinge margin, the extremities of which are slightly salient and not 

 " very acute ; summit of the umbo elevated above the hinge-line." This species 

 is cited as occurring both in the Schoharie grit and in the limestone above. 



The specimens described are all from the Schoharie grit. The smaller ones are 

 about half an inch in length, and the larger ones of the same character are an 

 inch in length by one inch and a half in width. In the younger specimens, and 

 those of medium size, the cardinal extremities are a little salient, and this charac- 

 ter prevails in nearly all the specimens. 



I had referred the smaller specimens, with some hesitation, to the Strophomena 

 crebristriata of Cornad ; but the gradations to those of larger size are quite im- 

 perceptible, and all must be included under one designation. 



