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CLASS III. GASTEROPODA, 



ORDERS. 



1. NUDIBRANCHI. (1) 



No shell. PL 15, fig. 7, 

 8, 9. 



sal. 



Branchiae naked, dor- 



Her iiti aphrodite, 



2. Inferobranchi. 



Ditto. PI. 15, fig. 10, 

 11, 12. 



Branchiae naked, un- 

 der the edges of the 

 mantle. 



3. Tectibranchi. 



Shell more or less de- Branchise covered by • • • • 



veloped, within the man- the mantle, 

 tie. PI. 16, fig. 1,2,3. ' 



4. PULMOBRANCHI. 



A great number with A cavity for respira- .... 

 turbinated shells, always tion, opened and shut 

 without opercula. at will. 



5. Pectinibranchi. 



Shells completely tur- Branchiae hidden in a Sexes separate, 

 binated, and generally dorsal cavity open above 

 more or less closed by jthe head. PI. 13, fig. 18. 

 an operculum attached to 

 the posterior part of the 

 foot. 



6. SCUTIBRANCHI. (2) 



Shells very open, often Ditto. Hermaphrodite, 

 in the form of a shield, 

 without opercula. PI. 14, 



(1) The greater number swim reversed, the foot (concave like a boat) on the surface, 

 aiding themselves with the edges of their mantle and using their tentacula as oars. 



(2) The heart is traversed by the rectum, and receives the blood by two auricles, 

 as in the greater number of Bivalves. 



fig. 20. 



7. Cyclobranchi. 



Shells of one or several 

 pieces, never turbinated, 

 without opercula. 



Branchiae around the 

 foot, under the edges of 

 the mantle. PI. 14, fig. 

 5,6. 



