C HAS S AT ELLA, Lamarck . 
Gen. Char. Shell equalValved, inequilateral, 
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. 
CkassatI'LLa: 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. R. Sower by. 
