21 
many authors, but the hinge differs essentially, and has more 
the character of Luzina , which also has frequently the fosset 
under the apex. Orbiculus , Megerle, Lentillaria , Schumacher, 
Exoleta , Brown, are synonymes of the present genus which 
is very different from Jlrtemis of Oken, an example of which is 
Venus pectinata of Chemnitz. 1 adopt the name given by Poli, 
on the authority of Blainville, as I have not seen the work in 
which it was originally described. 
LUCINA ACCLINIS. Tab. 6, fig. 2. 
Suborbicular, or lentiform, a little oblique, with strong line3 
of growth; hinge with 2 diverging teeth in each valve; posterior 
tooth of the right valve bifid; anterior muscular impression not 
profoundly elongated. 
Locality. York-town, Ya. Upper Tertiary. 
This species I obtained only in a very circumscribed spot, 
at a considerable elevation, in sand composed chiefly of com- 
minuted shells. This calcarious sand prevails more or less in 
every part of the high bank at York-town, and as it is formed 
of shells not partially decomposed but comminuted by attrition, 
the fact is obvious that it has been subjected to a violent action 
of the waters at a period anterior to the deposition of the perfect 
shells it encloses, which could only have been effected in a 
tranquil sea. 
CRASSATELLA ALTA. Tab. 7. 
Suboval, thick and ponderous, compressed; anterior margin 
obtusely rounded; posterior margin broad and slightly angular; 
beaks with regular concentric grooves, and somewhat angulated 
behind; inner margin crenulated. 
Locality . Claiborne, Alab. Middle Tertiary. 
This fine species is allied to C. tumida , Lam. but is propor- 
tionably shorter, and the beaks more central. The cartilage 
still remains in the valve here represented, and the shell is in 
the finest state of preservation. 
B 
