CLASSIFICATION 93 



CLASS II. 

 GASTEROPODA. 



Animal. Body free, without Umhs to aid progres- 

 sion; hut with an abdominal expansion or foot 

 suitable for craivling, and in a small number for 

 swimming ; head distinct, bearing commonly one 

 or more pairs of tentacles, and almost always eyes 

 variously situated upon or near the tentacles ; res- 

 piratory organs branchial, very variable in their 

 form and position. 



Shell. External, internal, or wanting, almost al- 

 ways a single piece, conical or spiral when exter- 

 nal, and more or less rudimentary when internal, 

 sometimes operculated. Inhabiting the sea, fresh 

 water, and land. 



The subdivisions of tHs class, or the Orders, have, 

 in nearly all the methods, been founded upon differ- 

 ences in the structure of the respiratory apparatus, and 

 the genera are grouped into them, according to their 

 supposed relations ia this particular, and without ref- 

 erence to their other characters. But, the arrange- 

 ment of the genera is not the same in any two of 

 them, and the same terms being used by different au- 



