28 



branchiae, but a mere net- work of pulmonary vessels which creep 

 over the parietes of the respiratory cavity and chiefly on its ceiling. 



Some of them are terrestrial; others are aquatic, but are com- 

 pelled to visit the surface from time to time for the purpose of open- 



Genus Aplysia 

 . . , . Dolabella 



;:::;} 



r Respiratory organs situated as 

 Sixth Family. I in the BuU^ens, and also 



Les Aplysiens. S covered by a shield ; but this 



L family possesses tentaculae. 



Second Section. — Les Pneumobranchiee. 



Genus Onchidium 



.... Parmacella 



.... Liraax . . 



.... Testacellus 



.... Vitrina . . 



Seventh Family. 

 Les Limaciens. 



Genus Helix 



CarocoUa . 

 Anostoma . 

 Helicina . . . 



Pupa 



Clausilia. . . 

 Bulimus . . . 

 Achatina. . . 

 Succinea. . . 



Auricula . . . 

 Cyclostoma, 



r Branchiae, or respiratory organs 

 < rampant, in the form of vas- 

 I cular net, on the thickness of 

 a particular cavity, the aper- 

 ture of which the animal con- 

 tracts or dilates at will. 

 L They only breathe fresh air. 



Third Order. — Les Trachelipodes. 

 The bodies of the animals spirally contorted at their posterior part, which is sepa- 

 rated from the foot, and always enveloped in a shell ; the foot free, flattened, 

 attached to the lower base of the neck or at the anterior part of the body, and useful 

 to assist the animal in crawling : a spiral shell covering the body. 

 First Section. — Les Phytiphages. 

 Animals feeding on vegetable substances. 



"Trachelipodes without a pro- 

 jecting syphon, breathing 

 generally by a hole. The 

 greater number feed on vege- 

 table substances, and are 

 furnished with jaws : aper- 

 ture of the shells entire, not 

 having at the base any dorsal 

 notch, or canal; they only 

 breathe air. Shell spirivalve, 

 smooth or with striae, the 

 right margin often reflected 

 £ outwardly ; smooth and not 



[2 distinctly nacreous. This 



family is terrestrial ; they 

 have cylindrical tentaculae, 

 with eyes at their summits 

 with or without an opercu- 

 lum. They all live out of the 

 water, 

 r Amphibious Trach«'lipodes, with 

 two tentaculae without eyes 

 at their summit ; generally 

 no operculum, their tentacula; 

 flattened ; they inhabit fresh 

 J water, and rise to breathe the 

 air on its surface. — Shell spi- 

 rivalve, most frequently 

 smooth on its external sur- 

 face, and having the right 

 margin of its aperture always 

 sharp, and not reflected. 



With four tenta- 

 s. culfe. 



With two tenta- 

 culae. 



Planorbis 



Physa 



Lvmnaja . 



;;;:} 



Second Family. 

 Les Lymneens. 



