134 MANUAL OF NATURAL HISTORY. 



bilobate, lobes subulate ; operculum annu- 

 lar, regular ; shell turbinate, thin ; aperture 

 entire in front. Fluviatile. 



41. Family. — River -Snails (Viviparidse). Eyes 



sessile on outer bases of tentacles ; rostrum 

 entire ; mantle simple in front ; operculum 

 annular, regular; shell turbinate, covered 

 with an epidermis ; aperture entire in front. 

 Fluviatile. (Paludinacea, Phil.) 



42. Family. — Valve-Shells (Valvatidse). Eyes ses- 



sile on outer sides of tentacles ; siphon none ; 

 gills plumose, exposed, protected by a long, 

 slender lobe ; operculum spiral, many-whorl- 

 ed ; shell spiral, turbinate or discoidal ; aper- 

 ture entire. Fluviatile. 



43. Family. — Periwinkles (Littorinidse). Eyes ses- 



sile on outer side of tentacles ; mantle-margin 

 with a slight siphonal fold ; operculum sub- 

 spiral ; shell turbinate ; aperture simple in 

 front. Marine. 



44. Family. — Rissoas (Rissoidse). Eyes on outer 



bases of tentacles ; rostrum adnate to fore 

 part of foot ; mantle simple in front ; oper- 

 culigerous lobe with tentacular appendages ; 

 shell spiral, white, more or less turreted ; 

 aperture entire in front. Marine. 



45. Family. — Quoyias (Planaxidse). Eyes sessile 



on outer bases of tentacles ; mantle with a 

 siphon in front ; foot with the sides simple ; 

 operculum sub-spiral ; shell turreted, with 

 a notch at fore part of aperture. Marine. 



