61 



CRAS8ATELLA. Lamarck. 



Gen. Char. Shell equalvah ed, inaequilateral, 

 transverse ; hinge with two strong teeth in 

 one valve, receiving one tooth from the other 

 valve, ligament internal, inserted into a pit 

 in each valve ; lateral teeth none or obso- 

 lete ; sides closed ; attachment of the man- 

 tle entire. 



C/KASSATELL.^: are commonly strong shells, although 

 some of the fossil species are not remarkably so, whilst 

 others are extremely thick and weighty : the valves are 

 depressed, often ovate, and sometimes approaching or- 

 bicular : the pits for the attachment of the hinge liga- 

 ment are placed on the anterior side of the teeth ; there 

 does not appear to be any true lateral tooth, but in the 

 right valve there is often a pit, bounded by a short 

 process, that receives the edge of the other valve : since 

 this may be considered as the rudiment of lateral teeth, 

 the strongest character to distinguish this genus from 

 Mactra by, will be the entire marginal line of attachment 

 for the mantle, which in Mactra is deeply sinuated ante- 

 riorly, this character is more valuable because it must 

 be immediately connected with the structure and habits 

 of the animal, and also with the open or closed sides of 

 the valves. 



For further particulars of this genus see Genera of 

 recent and fossil Shells, by G. B. Sowerby. 



