236 BERMUDA. 



1. Genus Patella, — The Patella (or Limpets) have 

 the body entirely covered with a conical shell. We 

 have an example of the genus in the species Patella 

 pellucida, 



2. Genus Chiton. — The Chitons crawl upon their 

 feet or fleshy disks, and are attached to rocks and 

 stones, like the limpets. They are found along our 

 shores at no great depth. They have power of 

 rolling themseves up into a ball, like the woodlouse 

 or hedgehog. Chiton marginatus is an example of 

 the genus. 



To the fourth class of Mollusca belong \heAcephala. 

 The animals of this class are divided by Cuvier into 

 two sections ; the first, which is most numerous, con- 

 tains all the bivalve and some of the multivalve 

 shells. The other, Acephala nuda, comprises those 

 in which the shell is replaced by a cartilaginous 

 membrane. 



I. First Order of Acephala: Testacea (or Ace- 

 phales with four branchial leaflets). — The shells of 

 this class are more or less inequivalve, and open by 

 a hinge. A considerable number of bivalves possess 

 Tvhat is called^ a byssus, that is, a bundle of more or 

 less delicate filaments issuing from the base of the 

 foot, and by means of which the animal fixes itself to 

 foreign bodies. It employs the foot to guide the 



