346 AMPULLARIID^. 



support to the thick, shelly operculum. The species 

 appear to be most numerous in the rivers of Africa and 

 India. Their eggs are large, and are contained in cap- 

 sules, usually of a greenish colour, disposed in masses, 

 and attached to plants under the water. 



Species of Ampullaria. 



ampullacea, Linn. orbata, Perry. 



aperta, Phil. orientalis, Phil. 

 Aulameri, Bev. and Hupp. . Orocconensis, Ziegl. 



carinata, Swains. ovata, Oliv. 



crassa, Sivaiiis. oviformis, Desh. 



corrugata, Sivains, pallens, Phil. 



dubia, Guild. polita, Desh. 



eximia, Dkr. puncticulata, Swains. 



fasciata, Gray. pygmaea, Becluz. 



Gevesensis, Desh. Sinamarina, Brug. 



lineata, Wagn. speciosa, Phil. 



obloiiga, Swains. sulcata, Moms. 



Genus rOMUS, Humphrey. 



Siphon elongate. 



Operculum horny, dextral. 



Shell dextral, globose, widely umbilicated, last whorl 

 very large, ventricose ; spire short ; aperture entire, ob- 

 long, large, expanded, peritreme simple, always thin, 

 sometimes subreflexed. 



Syn. Ampullaria, Guild., not Lam. 



Ex. P. scalaris, D''Orhigtiy, pi. 37, fig. 2. Operculum, 

 P. urceus, Mailer, fig. 2, «, 2, b. Shell, P. urceus, 

 fig. 2, c. 



The genus Pomus differs from Ampullaria in the ab- 

 sence of the thickened ledge within the peritreme for the 



