GENERA OF SHELLS. 69 



upon the columella, forming a very oblique fold 

 as it enters the aperture. No operculum. 



The very oblique fold on the columella, distinguishes 

 it from bulimus, and the regular, uninterrupted plane of 

 the aperture from the physa. 



L. columnaris, stagnaUs, palustris, Virginiana, luteola, 

 acuminata, auricularia, ovata, peregra, intermedia, leucosto- 

 ma, minuta, — columella, elongata, catascopium, reflexa, ap- 

 pressa, elodes, desidiosa, macrostoma, emarginata, humilis, 

 modicella, obrussa, pinguis, galbana. 



MELANIANA. 



Margins of the aperture of the shell disunited, the right al- 

 zcays sharp. 



Melania. Shell turreted. Aperture entire, 

 ovate or oblong, effuse at base. Columella 

 smooth, incurved. A horny operculum. 



M. asperata, truncata, coarctata, punctata, corrugata, subu- 

 lata, laevigata, clavus, decollata, amarula, thiarella, spinulosa, 

 granifera, carinifera, truncatula, fasciolata, — nupera, depygis, 

 Virginica, semicarinata, laqueata, canaliculata, elevata, 

 conica, catenaria, multilineata, simplex, proxima. 



Melanopsis. Shell turreted. Aperture en- 

 tire, ovate oblong. Columella callous superi* 

 orly, truncated at base, separated from the lip 

 by a sinus. Operculum. 



The callus on the upper part of the columella dis- 

 tinguishes melanopsis from melania, as well as its 

 being truncated at base, like the achatina, which is 

 never the case in melania. 



M. costata, laevigata. 



