154 INTRODUCTION. 
possibly be clue the passage of some of the, smaller 
species, of universal diffusion in the United States, to 
the Island of Cuba. Among these are Helix mirvmcula, 
Pupa contractu, and P. rwpieola, 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 
limits, only in the States of New York and Vermont on 
the boundary of Canada, and in the north-eastern States 
fi'om Massachusetts to the British pi-ovinces along the 
borders of the sea. In the first-named localities, its 
presence is accounted for, by its extension under usual 
circumstances from Canada, where it is said to be com- 
mon. On the searcoast, 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 cast, it 
is lost until it again appears on a small islam! 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 mainland, 
although the islands referred to are in close proximity 
to it. In New Brunswick it begins to occur in the inte- 
