142 [ Senate 



form and large size of the shell are sufficient to distinguish it from these 

 species. 



Geological position and locality. In the Hamilton group : Eighteen- 

 mile creek, Seneca and Canandaigua lakes, etc. 



Strophomena ( Strophodonta) INEQUISTRIATA. 



Strophomena inequistriata [?] Conrad: Jour. Acad. N'at. Sci. P]iil. 1842, Vol. 



viii, pa. 254, pi. 14, f. 2. 

 Strophomena inequistriata, Hall : Geol. Rep. 4th Dist. 1843, pa. 200, f. 4. 

 Compare Orthis inter strialis, Phillips : Pal. Fossils. 1839, pa. 61, pi. 25, 



f. 103, a, b, c, d. 



Shell semicircular or semioval in outline ; hinge-line extended 

 beyond the width of the shell, acute, sometimes auriculate : 

 dorsal valve moderately concave : ventral valve more or less 

 gibbous in the middle, abruptly arched towards the hinge-line, 

 and often depressed-convex at the summit or umbo, more gra- 

 dually sloping towards the base and abruptly contracted at the 

 cardinal extremities ; beak small, scarcely prominent on the 

 hinge-line; area narrow, linear, extending to the extremities of 

 the hinge-line, striated vertically with the inner margins crenu- 

 late; foramen none, a slight linear elevation extending across 

 the area ; area of dorsal valve scarcely more than half as wide 

 as the other, and having, in very perfect specimens, a narrow 

 elevated ridge crossing it in continuation of that of the opposite 

 valve. Surface of the entire shell marked by slender distant 

 elevated strise. which are increased by interstitial addition, and 

 the spaces occupied by much finer closely arranged stria:^, which 

 are scarcely visible to the naked eye ; transversely marked by 

 fine concentric striae. 



This species bears such close resemblance to the figures of Professor 

 Phillips cited above, that in my Report on the Fourth Geological District 

 of New-York, I regarded the two as identical. I have, however, some 

 doubts of the propriety of this reference. It is indeed somewhat uncertain 

 whether the identification with Mr. Conrad's species is correct. His de- 

 scription mentions " sharp radii alternating in size ; " and the figure re- 

 presents the striae as alternately larger and smaller, but without any in- 

 dication of fascicles of finer striae between the stronger ones. I am there- 



