104 ANIMALIA MOLLUSCA. 



various forms, and upon which depends the division of these 

 animals into eight orders. We give the three principal. 



ORDER I. PULMONEA. 



Respiration effected in a cavity the narrow orifice of which 

 they open and shut at pleasure ; no branchiae ; a net-work of 

 pulmonary vessels creeps over the parietes of the respiratory 

 cavity. Some inhabit the earth; others the water; the latter 

 are obliged to rise occasionally to the surface, and open the 

 orifice of their pectoral cavity to breathe. Two remarkable 

 genera. 



GENUS I. LIMAX, Lin. Slug. 



Naked semi-cylindrical Mollusca; the skin forming a shield 

 upon the back containing often the rudiments of a shell ; pul- 

 monary orifice at the right side of this buckler. Three re- 

 markable subgenera. 



SUBGENUS I. LIMAX PROPER, Lara. 



Body generally elongated, and provided, in some cases, 

 with a small oblong and flat shell, or with a calcareous con- 

 cretion ; orifice of the respiratory cavity at the right side of 

 this species of buckler ; four tentacula susceptible of protru- 

 sion and retraction by evolving like the fingers of a glove; in 

 the mouth a single jaw in form of a dentelated crescent. 



SUBGENUS II. VAGINULU?, Ferus. 



Mantle dense, without shell, and extending over the whole 

 length of the body ; four tentacula. [East and West Indies.] 



SUBGENUS III. TESTACELLA, Lam. 



Mantle very small, placed upon the posterior extremity, 

 containing a small oval shell with a very wide aperture, and 

 a very small spire; this shell is not the tenth part of the body 

 in length. 



GENUS II. IlEiiix, Lin. Snail. 



Shell complete, apparent and globular; the opening a little 

 encroached upon by the projection of the penultimate turn of 

 the spire, and circumscribed in the form of a crescent. The 



