KEY TO FAMILIES. 



Family Valvatid^. 



Tentacles elongated, with eyes at their outer 

 bases. Foot bilohed in front. Operculum 

 multispiral, corneous. Shell globular or de- 

 pressed, spiral, aperture rounded, lip entire. 



Inhabit fresh waters of temperate and sub- 

 tropical countries. 



Family Strepomatid^. 



Rostrum entire or slightly notched in, front, 

 tentacles tapering, with eyes on tubercles at 

 their outer bases. Mantle simple in front, the 

 margin plain.* Operculum ovate, sub-spiral. 

 Shell generally elongate, spiral, smooth, striate 

 or tuberculate. Aperture more or less pro- 

 duced or notched in front. - 



Distribution. — The United States, but very 

 few species extra-limital. Entirely confined 

 to North America. 



*The MelanidsE, or oriental species from which this 

 family is separated, have a fringed mantle-margin. 



