«!• PALAEONTOLOGY OF NEW-YORK. 



DoBSAL valve moderately and evenly convex with a well-defined low 

 rounded mesial fold ; beak, and margin of the valve in the middle, 

 slightly arched. Area narrow at the sides, but having the width of a 

 line in the middle. 



SoKFACE marked by from sixteen to twenty plications on each side of the 

 mesial fold and sinus : these plications are rounded and well defined ; 

 about eight of them reach the apex on the ventral valve, and the re- 

 mainder coalesce with the angular border of the area. In perfect spe- 

 cimens the entire surface has been covered by fine concentric undula- 

 ting striae, which are crossed by fine radiating striae. The remains of 

 these, upon some of the silicified specimens, give a granulose surface. 

 The length of full grown individuals is a little more than three-fourths 



of an inch, with a width of about an inch and three-eighths : the height 



varies from three-fourths of an inch to a little less. 



I have before me more than a dozen specimens from near the Falls of the 

 Ohio or from Charleston landing, among which there is very little variation in the 

 general features. The smallest individual of these has a length of a little more 

 than half an inch. 



Dr. Owen first noticed this species in his Report in 1839. In 1841, I re- 

 ceived specimens from him with this name attached ; and during many years, so 

 far as I know, the specimens from the Falls of the Ohio and from Charleston 

 landing were the only ones distributed under this name. In his Catalogue of Spe- 

 cies, appended to the Geological Report of Wisconsin, Iowa and Minnesota, page 

 628, Dr. Owen cites as localities " Pine creek ; Davenport ; below Rockingham ; 

 New-Bufliilo ; Rapid creek ; Wapsinonox ;" and " elsewhere in the United States, 

 Columbus, Ohio ; Charleston landing, Indiana ; Falls of the Ohio." 



The figures 6 a, b (ut cit.) appear to me to be of the typical form, and may have 

 been made from Indiana or Ohio specimens ; but certainly figures 2 and 2 a are 

 not of the same species. I have not seen specimens from Pine creek er elsewhere 

 in Iowa, which I regard as identical with those of Charleston landing, although 

 such may occur. I can only suppose that the similarity of form may have misled 

 Dr. Owen, and induced this reference ; l)ut I believe it will be more just and 

 more satisfactory to retain the name 8. euruteines for the species to which it was 

 originally applied by Dr. Owen himself. 



