be considered as restricted within the borders of the 

 United States.* 



Swainson formed the following curious generic 

 system for the shells under consideration :t 



Family TURBID^. 



(Subfamilies Ampullarince, Melaniance^ Turbince, Janthince.) 



Subfamily MELANIAN^. 



Genus Paludomus, Swainson. 

 Subgenus Anculosa, Say. 



Genus Melania, Lam. 

 Subgenus Hebiisinus, Swainson. 



Genus Melanopsis, Lam. 



Subgenus Melafusus, Swainson. 



Subfusiform, the base contracted, and the aperture and spire 

 nearly equal. 1 species. America. (^ lo.) 



Subgenus Melatoma, Swainson. 



Fusiform, longitudinally ribbed ; a deep sinus at the 

 top of the outer lip ; base contracted, channel 

 wide. M. costata. (This species, mistaken by 

 some for our genus Schizostoma, is actually an 

 exotic inarine shell =: genus Clionella. A copy 

 of Swainson's figure is subjoined (fig. 1). 



Genus Cerithidea, Swainson. 



Clavate, cerithiform ; aperture subemarginate. 



Subgenus Cerithidea, Swainson. 



Shell light, decollated ; outer lip semicircular, dilated by a 

 flattened border ; aperture emarginate. C. lineolata, Griff. 

 Cuv., t. U, f. 4. Cfragilis, Ibid , t. 32, f. 12. {— Pota- 



MIDES.) 



♦Three or four are extra-limital, inhabiting Cuba and Mexico ; but 

 these do not constitute one per cent, of the whole number of species, 

 t Manual of Malacology, 18iO. 



