Key to the Families of Fluviatile MoUusca 

 i^ihahiting the United States. 



Order PULMONIFERA. 



Section A. — Adelopueumona (inoperculata) . 

 Includes both fluviatile and terrestrial species. 

 Shell without ojDcrculum. 



Sub-order Limnophila. 



Amphibious and fluviatile species. Head 

 furnished with tico tentaculaB," with eyes at 

 their bases. 



A few of these shells are considered terres- 

 trial, because they inhabit land within reach 

 of the tides. 



Family Physad^. 



Shell spiral, elongated or discoidal, or coni- 

 cal and non-spiral. Covered with a green 

 epidermis. Outer lip of aperture simple. 



Species belonging to this family inhabit the 



