MOLLUSC A OR UNIVALVES. 163 



guished from young specimens of the Helix by 

 their never being umbilicated or perforated; 

 they greatly resemble them in other particulars.* 



Order III. 



TRACHELIPODA. f 



The mollusca constituting this order differ 

 from those which are comprehended in the 

 last by having the foot attached to the neck, 

 and the hinder part of the body coiled up and 

 covered by a shell, which is always spiral, and 

 to which the animal is fixed : this part of the 

 body never leaves the shell, but the head and 

 foot can also be drawn in at pleasure. The 

 Trachelipoda are much more diversified in 

 form than the last order, and are divided into 

 a far greater number of genera, some of which 

 inhabit the sea, others are found in fresh water, 

 whilst others again are met with on land. 

 Many of these are herbivorous, and many car- 

 nivorous ; it will therefore, from the great 



* Draparnaud. 



f Les Trachelipodes, Lamarck. 

 M 2 



