154 INTRODUCTION. 



possibly be due the passage of some of the smaller 

 species, of universal diflPusion in the United States, to 

 the Island of Cuba. Among these are Helix minuscula, 

 Piqja contracta, and P. rupicola, which from their gen- 

 eral distribution on the continent, may be supposed to 

 have originated there rather than upon the island. 



We cannot help thinking, too, that such currents have 

 had some agency in introducing Helix hortensis on our 

 north-eastern coast, at some former period, although we 

 are not aware of the existence of one, capable of produ- 

 cing such an effect. This species is found, within our 

 hmits, only in the States of New York and Vermont on 

 the boundary of Canada, and in the north-eastern States 

 from Massachusetts to the British provinces along the 

 borders of the sea. In the first-named localities, its 

 presence is accoimted for, by its extension under usual 

 circumstances from Canada, where it is said to be com- 

 mon. On the sea-coast, some other explanation is neces- 

 sary. Commencing at what appears to be its southern 

 limit, it occurs on the sandy soil at the extreme end of 

 Cape Cod ; it then disappears in the intermediate country, 

 and is next found on a small, rocky, uninhabited island, 

 on the shore of Cape Ann ; proceeding further east, it 

 is lost until it again appears on a small island of a sim- 

 ilar character in Casco Bay, Maine. Along this exten- 

 sive line, it is nowhere found inland, and, with the excep- 

 tion of the locality on Cape Cod, never on the main land, 

 although the islands referred to are in close proximity 

 to it. In New Brunswick it begins to occur in the mte- 



