KEY TO FAMILIES. 9 
Family VALVATIDA. 
Tentacles elongated, with eyes at their outer 
bases. Foot bilobed 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 StrePpoMatip#&. 
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 Melanide, or oriental species from which this. 
family is separated, have a fringed mantle-margian, 
