CYPRINA. 



Europe. The fossil species are only found in the tertiary 

 bed, contemporaneous with the Londo7i Clay and Calcaire 

 grassier. 



Shell equivalve, inequilateral, obliquely cordate, 

 umbones obliquely curved anteriorly, Avith three cardi- 

 nal teeth in each valve, approximated at their bases, but 

 somewhat diverging at their upper parts ; and a posterior 

 lateral tooth at a distance from the hinge teeth. Two 

 lateral, distant muscular impressions in each valve. 



Muscular impression of the mantle entire. 



Ligament external, partly buried in a deep, marginal, 

 posterior, dorsal sinus. Epidermis horny, thick, rough, 

 and of a dark olive colour in full grown individuals, though 

 in young specimens it is frequently very thin and pale. 



In several characters the Cyprinae approach Lamarck's 

 ConchcB fluviatilesy a circumstance which he has observed, 

 and it is remarkable that the two species peculiar to 

 Iceland and Newfoundland are generally eroded at and 

 near the umbones; it must however be stated that this 

 peculiarity appears to be common to such shells as belong 

 to very northern, frozen regions, and to such as are found 

 in fresh water and at the mouths of rivers. 



