Key to the Families of Fluviatile Mollusca 
inhabiting the United States. 
Order PULMONIFERA. 
Section A.—Adelopneumona (inoperculata). 
Includes both fluviatile and terrestrial species. 
Shell without operculum. 
Sub-order Limnophila. 
Amphibious and fluviatile species. Head 
furnished with too tentacule, with eyes at 
their bases. 
A few of these shells are considered terres- 
trial, because they inhabit land within reach 
of the tides. 
Family Puysap. 
Shell spiral, elongated or discoidal, or coni- 
cal and nen-spiral. Covered with a green 
epidermis. Outer lip of aperture simple. 
Species belonging to this familv inhahit the 
