with a revision of the Limn<eidee of Authors. 351 



Sub-genus Taphivs. H. & A. Ad. 1855. 



Shell excavated beneath. Whorls rounded, columella recti- 

 linear. 



T}-pe Tap/tins andecola. H. & A. Adams. 



Sub-genus Helisoma. Swains. 18-40. 



Shell ventricose, whorls angulated. Spire sunk below the 

 body whorl. 



Type Helisoma bicarinata = Planorbis bicarinatus. Sby. 



Sub-genus Planorbis. (Guett.) 1 756. 



Central tooth bilobed. 



Spire depressed, whorls rounded, last whorl ventricose, aper- 

 ture crescentic. 



Type Planorbis eorneus. Linn. 



Sub-genus Planorbella. Ilald. 1844. 



Shell few whorled, aperture campanulate. 

 Type Planorbella campanulata = Planorbis campanula- 

 tus. Say. 



Sub-genus Adula. H. Ad. 1861. 



Whorls rounded and numerous. Deeply umbilicate on 

 the upper and convex on the under side, aperture campanu- 

 late. 



Type Adula multivolvis = Planorbis multivolvis. Case. 



Sub-genus Menetus. H. & A. Ad. 1855. 



Shell depressed, whorls rapidly increasing. Periphery angu- 

 lated. 



Type Menetus opercularis = Planorbis opercular/ s. < rid. 



Sub-genus (lijrauhix. Agassi/;. 1*37. 



Shell rounded above, flat beneath, whorls few, rapidly in- 

 creasing. 



Tvpe Gyraulus albus = Planorbis alius. Mull. 



