28 



MOLLUSC A. 



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 Onchidium .... 

 .... Parmacella. . . . 



.... Limax 



.... Testacellus . . . 

 Yitrina 



Seventh Family. 

 Les Limaciens. 



f Respiratory organs situated as 



Genus Aplysia 1 Sixth Family. I in the Bullccns, and also 



.... Dolabella . . . . J Les Aplysiens. S covered by a shield ; but this 



L family possesses tentaculce. 



Second Section. Les Pneumobranchiee. 



r Branchiae, or respiratory organs 

 rampant, in the form of vas- 

 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 

 distinctly nacreous. This 

 family is terrestrial ; they 

 have cylindrical tentaculse, 

 with eyes at their summits 



Genus Helix 



.... Carocolla . 



.... Anostoma . 



.... Helicina . . . 



.... Pupa 



Clausilia. . . 



.... Bulimus . . . 



.... Achatina. . . 



.... Succinea. . . 



.... Auricula . . . 



.... Cyclostoma. 



With four tenta- 

 culse. 



... I With two tenta- 

 ... j culse. 



Planorbis 



Physa 



Lyranaea . . 



Second Family. 

 Les Lymncens. 



with or without an opercu- 

 lum . They all live out of the 



L water. 



f Amphibious Trachelipodes, with 

 two tentaculse without eyes 

 at their summit; generally 

 no operculum, their tentaculac 

 flattened ; they inhabit fresh 

 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. 



