MANUAL OF NATUEAL HISTORY. 145 



3. AchatinincB. Aperture of shell longer than 



wide ; columella truncate ; spire more or 

 less elevated. 



4. Vitrinince. Animal not completely retrac- 



tile within the shell ; shell thin, trans- 

 parent. 



II. SU-0I)E. FRESH-WATER PULMONIFERS 

 (Limnophila). 



Eyes sessile ; tentacles sub-cylindrical or flat- 

 tened, simply contractile ; operculum none. 



6. FAMILY. Pond-Snails (Limnseidse). Tentacles 



contractile, flattened ; eyes sessile on their 

 inner bases ; shell horn-ooloured ; aperture 

 without plaits. Fluviatile. 



7. FAMILY. Marsh - Volutes (Auriculidse). Ten- 



tacles contractile; eyes sessile on nape at 

 inner sides of bases of tentacles ; shell with 

 the aperture plaited. Terrestrial, or living in 

 marshes. 



III. SUB-ORDER. MARINE-PULMONIFERS 



(Thalassophila). 



Eyes sessile on front part of frontal disk formed 

 by the expanded tentacles. Living on the shores or 

 in salt marshes. 



8. FAMILY. Siphon-Shells (Siphonariidse). Ten- 



tacles forming a large bilobed frontal disk ; 

 mantle with a fleshy lobe on right side co- 

 vering the respiratory aperture ; shell coni- 



