199 PALEONTOLOGY OF NEW- YORK. 



Dorsal valve concave, the concavity less than the convexity of the 

 opposite valve. The area is narrow, that of the dorsal valve* being a 

 bare line : the ventral area is tAvice as wide in the middle as near the 

 extremities. Cardinal spines small, and usually but slightly oblique to 

 the hinge-line, rarely more than two or three visible on each side of 

 the beak. 

 Surface marked by numerous slightly elevated rounded striae, a few 

 of which are more prominent near the beak, and increase by bifurca- 

 tion and intercalation till the number on the margin becomes from 

 fifty-four to sixty or more. The striae towards the cardinal angles are 

 less conspicuous, and sometimes from exfoliation are not at all visible. 

 The entire surface in well preserved specimens is marked by extremely 

 fine concentric striae. 



The cast is a little constricted within a line about two-thirds the 

 length from the beak, the middle being more gibbous, while it is a little 

 expanded beyond this line. The surfacg of the cast is punctate, moderately 

 marked by striae, becoming more strongly marked at the constrictiou 

 and from thence to the margin. The interior of the valve preserves 

 similar markings, the surface being papillose or pustulose. The muscular 

 impressions of the ventral valve are sometimes defined, and there is a 

 median longitudinal ridge. The interior of the dorsal valve is pustulose 

 in lines corresponding to the striae. The muscular impressions and base 

 of cardinal process are not defined in any specimens observed. 



After an examination of a large number of individuals, I find the variation in 

 number of stria3 too great to offer any reliable character for specific distinction. 



The species is doubtless the one figured by Mr. Vanuxem (loo. cit.); and I am 

 disposed to believe that the Strophomena crehristriata* and S. lineata of Conrad 

 (loc. cit.) may be the same species. It is most nearly allied to C. yandellana, and 

 may perhaps be regarded as identical with that species. There are, however, cer- 

 tain differences which are constant in all the specimens examined. The C. lineata 

 is always more gibbous ( See figs. 3/ and 4 d, Plate 20) : in C. yandellana the cavity 

 of the ventral valve is more regularly concave, and loss distinctly constricted 



• I have already referred with doubt a species from the Sclioharie grit to S. crehristriata of Conrab i 

 bat since that description has been printed, I have had reason to question the correctness of my refe- 

 rence. It is impossible to determine positively the species to which some of these descriptions refer. 



