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GRASSATELLA MARYLANDICA. Tab. 8, /. 1. 



Ovate oblong, thick and ponderous; posterior side narrowed 

 and produced, with the extremity slightly angular or obtusely 

 rounded; umbonial slope subangular; inner margin entire. 



Locality. Choptank river, near East on, Md. Upper Ter. 



This species is very common and perfect, the valves being 

 generally in their natural connexion. It is distinguished from 

 other American Crassatellae by its smooth and entire surface. 



The bank of the Choptank river, where this species is found, 

 is twenty-five or thirty feet high and perpendicular from the 

 water when the tide is in.- A stratum at the base, about twelve 

 feet thick, is composed almost entirely of bivalve' shells, the 

 most abundant of which are a large species of Cythereci and 

 the shell above described, neither of which have I yet seen in 

 any other deposit. 



It is remarkable that although our Upper Marine contains 

 several species of Crasfiatelhi, all of which are abundant, yet 

 this appears to be the only genus of- that formation, with the 

 exception of a Pholadoiuya, without a living representative 

 on the coast of North America. 



Blainville observes, that this genus is remarkable from the 

 circumstance, that all the recent species w.hich it contains, 

 eleven in number, exist only in the seas of Australasia, although 

 there are seven in the fossil state in France. De France, with 

 some doubt, enumerates twenty in the inferior Chalk. . 



CRASSATELLA PROTEXTA. Tab. 8, Jig. 2. 



Elongated; umbonial slope angular or obscurely plicated; 

 the posterior side produced, or rostrated with age, and the 

 extremity obliquely truncated ; beaks with concentric grooves ; 

 inner margin crenulated. 



Locality. Claiborne, Alab. Middle Tertiary. 



This fine shell, though variable in outline, is distinguished 

 by a length, in proportion to the height, unusual in the genus, 

 it is abundant, and a single valve measures 2 inches in length 

 and 1 inch and 3 tenths in height. 



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