OF CONCHOLOGY. 223 



§§ Shell oblong or oval. 



Family Orthalicid^e. 



Tropical, a few species inhabiting the Gulf States. 



§§§ Shell cylindrical or pupeeform. 



Family Pupad^e. 



Distribution universal. 



ft Shell internal, rudimentary, contained beneath the 

 mantle. 



§ Shell small, flattened, not spiral. Respiratory orifice 

 in the posterior right margin of the mantle. 



Family Limacid^e. 



Distributed throughout the States east of the Rocky Moun- 

 tains, and one species in Oregon. Most of the species are 

 European in origin, and only occur near the coast, especially 

 in the vicinity of the large commercial cities. 



§§ Shell represented only by a few agglomerated calcareous 

 granules. Respiratory orifice in the anterior of the 

 right margin of the mantle. 



Family Arionid^e. 



A single European species is found in seaports of the North- 

 ern States. 



ttt Shell entirely absent. Mantle covering the entire 

 upper surface of the body of the animal. 



Family Philomycenid^e. 



There are two species known, which inhabit the Northern 

 and Middle States. 



** Tentacles (and head) contractile beneath 

 the mantle, which completely covers the body 

 of the animal. 



§ Mantle smooth, coriaceous. 



Family Veronicellidjs. 



Tropical. One species only occurs in Florida. 



§§ Mantle tuberculate. 



Family OnchidiiDuE. 



A single species is found in Lower California. 



