21 



many athors, but the hinge differs essentially, and has more 

 the character of Lucina, 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 Artemis of Oken, an example of which is 

 Venus pectinata of Chemnitz. I 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 lines 

 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, Va. 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 sliells 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. 



