TheCJutons. Ill 



MULTIYALVES. 



We liave insensibly passed from tlie Bivalve sliells 

 to tliose composed of several pieces^ and therefore 

 called Multivalves ; probably, perliaps_, tlie Eock- 

 borerSj last described^ come into tliis division^ for 

 altlLOugb 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 

 TerecUna and TeredOj included by Lamarck in the 

 family which he calls Tululidcs, 



The first group of multivalves we shall have to 

 notice^ are 



THE CHITONS, 



forming the family Chitonidce. 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 wliich re- 



