MOLLUSC A OR UNIVALVES. 261 



with a mouth terminating in two strong man- 

 dibles, similar to the beak of a parrot; it likewise 

 possesses a perceptible organ of hearing, and two 

 large eyes, immoveable, and without eyelids. 



The animals may be separated into three 

 divisions, — Polythalama, in which the shell is 

 chambered or divided into numerous cells ; Mo- 

 nothalama, in which the shell has only one 

 chamber, destitute of partitions ; and a third, 

 in which there is no shell whatever. 



The mantle of the Cephalopoda is in the 

 form of a bag, and covers the lower part of the 

 body. Most of the recent species live at great 

 depths in the sea, and are found nearly all over 

 the world. Some swim, and attach themselves 

 to marine bodies ; others creep on the sand, by 

 the aid of their tentacula, and often retire into 

 holes in the rocks. They are all zoophagous, 

 living on crabs and other animals, which they 

 seize and devour. 



The following is a list of the genera which 

 Lamarck has introduced into this order : — 



1. Belemnites. 



2. Orthoceras. 



*3. Nodosaria. 

 4. Hippurites. 



s 3 



