180 



LYMNiEANA.— Three Genera. 



Shell spirivalve, the external surface mostly smooth; the right margin of the 

 aperture always sharp, and not reflected. 



Planorbis. Shell discoidal, spire depressed, the whole of the whorls 

 shown above and beneath; aperture oblong, lunate, very distant from the 

 axis of the shell; the margin never reflected. No operculum. 



P. cornu-arietis, 

 ' corneus, 

 ' carinatus, 

 ' lutescens, 



P. orientalis, 

 ' spirorbis, 

 1 vortex, 



P. deformis, 

 ' contortus, 

 ' hispidus, 



P. nitidus, 

 ' imbricatus, 

 ' ansrulatus. 



Physa. Shell convolute, oval or oblong; the spire prominent; aperture 

 longitudinal, contracted at the upper part; columella twisted; right lip very 

 thin, sharp, partly projecting above the plane of the aperture. No operculum. 



P. castanea, P. fontinalis, P. hypnorum, P. subopaca. 



LymNjEa. Shell oblong, sometimes turreted; the spire prominent; aper- 

 ture entire, longitudinal; outer lip sharp, the lower part ascending over the 

 columella, forms a very oblique plait, re-entering the aperture. No oper- 

 culum. 



L. columnaris, 

 ' stagnalis, 

 ' palustris, 

 1 Virginiana, 



L. luteola, 

 ' acuminata, 

 ' auricularia, 

 ' ovata, 



L. peregra, 

 ' intermedia, 

 ' leucostoma, 



L. minuta, 

 ' rubiginosus,(n.s. 

 ' lessoni, (n. s.) 



MELANIANA.— Three Genera. 



Margins of the aperture of the shell disunited, the right alio ays sharp. 



Melania. Shell turreted, aperture entire, oval or oblong, effuse at the 

 base; columella smooth, incurved. Operculum horny. 



M. inquinata, M. laevigata, 



1 asperata, ' clavis, 



' truncata, ' decollata, 



' coarctata, ' amarula, 



' punctata, ' thiarella, 



' corrugata, ' spinulosa, 

 ' subulata, 



M. subularis, (n. s.) Lea, vol. 4, pi. xv. 

 fig. 30. 

 ' tuberculata, (n. s.) do. pi. xv. f. 31. 



M. gronifera, 

 ' carinifcra, 

 ' truncatula, 

 ' fasciolata, 

 ' lasvissima, 

 ' aurita, 



M. lineolata, 

 ' Byronensis, 

 ' Sayii, 

 ' lineata, 

 ' sulculata, 

 ' helvetica, 



M. acuta, (n. s.) Lea, Trans. Am. Phil. Soc. 

 vol. 4, pi. xv. fig. 32. 

 ' elongata, (n. s.) Lea, hab. W. Tennes. 



