CONTRIBUTIONS TO PALEONTOLOGY. 37 



crenulated. Muscular impression strong, deeply bilobed, with a 

 wide groove between the divisions. The margin of the valve (in 

 the cast) is elevated ; and within this is a depression, while the 

 space between this and the muscular impression is marked by 

 punctate vascular impressions. 

 The casts are rarely more than half an inch in length, and are 

 readily recognized by the convexity, the narrow elevated bor- 

 der, and the comparative shortness of the hinge-line. 



Geological formation and locality. In the Schoharie grit : at Clarksville 

 and Knox, Albany county. 



STROPHODONTA CREBRISTRIATA. 



Strophomena crebristriatall] Conrad, Journal Acad. Nat. Sciences, Yol. viii. p. 254; 



PI. 14, f. 3. 



There is a small species of Strophodonta in the Schoharie grit, 

 having a width of about half an inch, which I have referred with 

 some hesitation to the above cited species. The casts are well 

 marked ; that of the ventral valve somewhat gibbous, with a bi- 

 lobed but not strongly defined muscular impression ; while the 

 lower part of the surface is marked by vascular imprints, without 

 marginal callosity. 



The partially preserved shell is marked by numerous fine bi- 

 furcating stride. 



Geological formation and locality. In the Schoharie grit : at Clarksville 

 and Knox, Albany county. 



STROPHODONTA PARVA ( n. s.). 



Shell small, subhemispheric, a little wider than long. Ventral 

 valve gibbous : hinge-line usually a little shorter than the 

 greatest width of the shell ; area linear. 



Surface marked by few, strong, rounded or subangular striae or 

 costsBj which are bifurcated or increase by bifurcation towards 

 the margin, and are covered by minute or almost microscopic 

 undulating striae. The larger striae are sometimes marked by a 

 sharp elevation along the middle. 



In exfoliated specimens, the surface has the aspect of those with 

 fascicles of fine striae, with single sharp elevated striae between. 

 The form and proportions of the species is very constant, rare- 

 ly exceeding and usually less than half an inch in width. 



Geological formation and locality. In the Schoharie grit of Albany and 

 Schoharie counties. 



