260 POPULAR CONCHOLOGY. 



during the thickness of these internal walls by 

 absorption, either for the purpose of giving 

 itself more room, or in order to diminish the 

 weight of the shell. 



They are found abundantly in all tropical 

 countries, particularly in Asia, but become 

 more rare as they approach the northern hemi- 

 sphere ; a few species only are found in the 

 Mediterranean. 



Order IV. 



CEPHALOPODA.* 



There is much difficulty attending the classi- 

 fication of this order, which derives its name 

 from the position of the animal's apparatus 

 for moving; it possesses for that purpose a 

 circle of eight, ten, or more fleshy processes, 

 which may be indifferently called arms, legs, or 

 tentacula. These appendages are attached to 

 the head of the animal, which is also furnished 



* Les Cephalopodes, Lamarck. 



