[9] 



Key to the Families of Terrestrial Mollusca inhahiting the 

 United States. 



Order PULMONIFERA. 



Section A.— ADELOPNEUMONA (Inoperculata). 



Includes botli terrestrial and fluviatile species. 

 Shell without operculum^ 



Sub- order GeophilI. 



Terrestrial shells. Head furnished with four teutaculee, 

 either retractile by inversion or contractile, the superior pair 

 with the eyes at their summits. Eespiratory orifice closed by 

 a valve. 



* Tentacles reteactile by inversion. 



f Shell external, 



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



§ Shell ohlong-oval or fusiform. 



Family Oleacinid^. 



The species of Oleacinidse inhabit the vicinity of sea-shores 

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

 Paciiic 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. 



§1 Shell obliquely oval, ivhorls very few, rapidly increas- 

 ing in size, the la^ one constituting nearly the entire 

 shell. 



Family Succinid^. 



Distribution universal. 



§§i§ Shell discoidal, suhorbicular, turbinate or trochiform. 



Family IIelicellid.e. 



Inhabit throughout the United States, but mostly in the 

 Northern States east of the Rociiy Mountains. 



XX 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 IIelicid^. « ♦ 



istribulion universal. 



