63 



M U L T I y A L y E s . 



We have insensibly passed from the Bivalve shells to those 

 composed of several pieces, and therefore called Multivalves; 

 properly, perhaps, the Hock-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 calcarious tube envelopes the whole mollusk, 

 leaving only an opening behind; this is more especially the 

 case with those which most resemble worms, such as the 

 genera Teredma and Teredo, included by Lamarck in the family 

 which he calls Tuhulidce. \ 



The first group of multivalves we shall have to notice, are 



THE CHITONS, 



forming the family Chitonidce. The term has a Greek deriva- 

 tion, 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 

 resembles leather, being very tough and wrinkled; the edges 

 of this mantle extend beyond the borders of the plates, which 

 overlap each other, so as to constitute a kind of armour, very 

 different from the conical shell of the Limpit, or the turbinated, 

 that is twisted, case of some of the Borers. The coverings 

 of the Chitons are variously marked, so that each distinct 

 species is known by its peculiar pattern, as a knight of old 

 by the quarterings of his shield. All the mantles, however, 

 have scaly, haiiy, or spiny margins. In this coat of mail, the 

 animal can roll itself up like an armadillo, and so be tolerably 

 secure from its enemies; it has an oval foot, the sides of 

 which are covered with small leaflets, and by means of this 

 it can attach itself to rocks, like the Limpit, or travel about 

 in search of adventures. It has no distinct head, therefore it 

 is acephalous; nor any perceptible eyes. The mouth is fur- 

 nished with a long tongue, curled up spirally, like a watch- 

 spring, and armed with horny teeth. 



The members of the Cliiton fnmih' arc numerous, being 



