[10] 



§§ Shell ohlong or oval. 



Family Orthalicid^. 



Tropical, a few species inhabiting the Gulf States. 



§§§ Shell cylindrical or pupeeform. 



Family Pupad^. 



Distribution universal. 



tt Shell internal, rudimentary, contained heneath the 

 jnantle. 



§ Shell small, flattened, not spiral. Respiratory orifice 

 in the posterior right margin of the mantle. 



Family LiMAClDiE. 



Distributed throughout the States east of the Kooky 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 hya few agglomerated calcareous 

 granules. Respiratory orifice in the anterior of the 

 right margin of the mantle. 



Family Arioxid^. 



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

 ern States. 



fft Shell entirely absent. Mantle covering the entire 

 upper surface of the body of the animal. 



Family PhilomyoenidtE. 



There are two species known, which inhabit the Northern 

 'and Middle States. 



** Tentacles (and head) conteactile beneatit 

 the mantle, which completely covers the bodv 

 of the animal. 



§ Mantle smooth, coriaceous. 



Family VERONiCELLlDiE. 



Tropical. One species only occurs in Florida. 



§§ Mantle tuberculate. 



Family Onghidiid^. 



A single species is found in Lower California. 



