GASTEROPODA PULMONEA. 27 



their branchiae are attached under the margin of their mantle, as in 

 the Inferobranchiata(a). 



ORDER I. 

 PULMONEA* 



The Pulmonia are distinguished from the other Mollusca by respiring 

 elastic air through a hole opening under the margin of the mantle, 

 and which they dilate and contract at will ; and accordingly have no 



* M. de Blainville prefers the term Pulmonobninchiuta. 



{C^* OO The Gasteropodes form, in Lamarck's classification, the Second Order 

 of his 



t\\t<:lfth class. 



Mollusca. 



Order II. — Les Gasteropodes. 



Animals with the body straight, never in a spiral form, nor enveloped in a shell 



capable of containing the whole of it ; they have beneath the belly a foot or muscular 



disk, united nearly to the whole length of the body, and serving them to crawl with. 



Some are naked, others are screened by a dorsal shell, not sheathed in the body ; 



and others again, have a shell more or less concealed in their mantle. 



First Section. — Les Hydrobranchitn. 



AxiMALS only breathing water. 



rThe respiratory organs, in what- 

 I ever part they are situated, 

 ', are always elevated, either 

 I in filets, laminae, tufts, or 

 \ like a comb ; they are placed 

 I above the mantle, either ou 

 the back or on the sides, and 

 L not in any particular cavity. 

 TRespiratory organs placed be- 

 neath the border or edge 

 of the mantle, and disposed 

 in a longitudinal series round 

 the body, or on one side, not 

 being placed in any particular 

 L cavity. 



r Gills as above, but placed on 

 I the right side of the body 

 L only. 



r Respiratory organs placed in a 

 ■ cavity appropriated to them 

 I on the back of the animal, 

 I near the neck, projecting 

 ', either within the cavity or 

 j above it. Shell always exter- 

 nal and covering the animal, 

 L w-hich is without tentaculae. 

 /-Gills placed in a particular ca- 

 I vity near the posterior part 

 of the back, and covered by 

 I the mantle or by an opercu- 

 1 lary shield. — No tentaculsc. 



