ORDER TESTACEA. 105 
food, but is dangerous if eaten to excess. Add mytilus bar- 
batus, L., &c. 
Some of them are found fossil, and have been formed into a 
sub-genus by M. Brongniart, under the name of MYTILOIDA. 
In the 
Mopiouus, Lam., 
Separated from the mytili by Lamarck, the summit is lower 
and nearer the third of the hinge. This summit is also more 
salient and rounded, approximating the modioli more closely 
to the ordinary form of the bivalves. We may also separate 
from the mytili, 
LITHODOMUS, Cuwwv., 
In which the shell is oblong and almost equally rounded at 
the two ends, the summit being close to the anterior ex- 
tremity. The species of this sub-genus at first simply attach 
themselves to stones, like the common mytili; subsequently, 
however, they perforate and excavate them in order to form 
cells, into which they enter, and which they never quit after- 
wards. Once entered, their byssus ceases to grow. 
One of them, the mytilus lithophagus, Lin., is very com- 
mon in the Mediterranean, where, from its peppery taste, it is 
esteemed as food. 
A second (modiola caudigera, Encyc. pl. xxcci. f. 8.) has a 
very hard small appendage at the posterior extremity of each 
valve, which perhaps enables it to excavate its habitation. 
ANODONTES, Brug., 
The anterior angle rounded like the posterior, and that next 
to the anus obtuse and almost rectilinear. The shell thin, 
and moderately convex, has no appearance whatever of a 
tooth at the hinge, being merely furnished with a ligament 
