The Chitons. 111 
MULTIVAY ks. 
We have insensibly passed from the Bivalve shells 
to those composed of several pieces, and therefore 
called Multivalves ; probably, perhaps, the Rock- 
borers, last described, come into this division, for 
although their covering consists mainly of two 
principal portions or valves, yet there are often 
additional parts; in some a calcareous tube enve- 
lops the whole mollusk, leaving only an opening 
behind. This is more especially the case with those 
which most resemble worms, such as the genera 
Teredina and Teredo, included by Lamarck in the 
family which he calls Tubulide. 
The first group of multivalves we shall have to 
notice, are 
THE CHITONS, 
forming the family Chitonide. The term has a 
Greek derivation, and means a coat of mail. These 
mollusks are covered by a shell formed of eight 
distinct portions, arranged along the back in a 
single row, and attached to a mantle which re- 
