222 AMERICAN JOURNAL 



Key to the Families of Terrestrial Mollusca inhabiting the 

 United States. 



Order PULMONIFERA. 



Section A.— ADELOPNEUMONA (Inoperculata). 



Includes both terrestrial and fluviatile species, 

 Shell without operculum. 



Sub-order Geophila. 



Terrestrial shells. Head furnished with four tentaculas, 

 either retractile by inversion or contractile, the superior pair 

 with the eyes at their summits. Kespiratory orifice closed by 

 a valve. 



* Tentacles retractile by inversion. 



f Shell external. 



X Shell thin, polished, translucent, lip sharp -edged. 



§ Shell oblong-oval or fusiform. 



Family Oleacinid^e. 



The species of Oleacinidse inhabit the vicinity of sea-shores 

 of the Southern States from South Carolina to Texas ; also the 

 Pacific coast, but not extending so far northwards as Califor- 

 nia. They are all large in size, and are stragglers from the 

 Mexican and "West Indian faunas. 



§§ Shell obliquely oval, whorls very few, rapidly increas- 

 ing in size, the last one constituting nearly the entire 

 shell. 



Family Succinic. 

 Distribution universal. 



§§§ Shell discoidal, suborbicular, turbinate or trochiform. 

 Family Helicellid^e. 



Inhabit throughout the United States, but mostly in the 

 Northern States east of the Kocky Mountains. 



\% Shell thicker, striate, frequently banded with colors, 

 lip thick-edged, or generally either with an interior 

 thickening caused by a marginal deposit of callus, or 

 else reflected outwards and appressly flattened. 



§ Shell discoidal, orbicular, turbinate or trochiform. 



Family Helicice. 



Distribution universal. 



