CRASSATELLA MARYLANDICA. Tab. 
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 Easton, Md. Upper Ter. 
This species is very common and perfect, the vaives 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 Cytherea 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 Crassatellci , all of which are abundant, yet 
this appears to be the only genus of that formation, with the 
exception of a Pholadomya , 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 which 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, fig. 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 I inch and 3 tenths in height. 
