GEOGRAPHICAL DISTRIBUTION. J 37 
observations. Ten years since, we observed great num- 
bers of Helix hortensis on a small uninhabited island 
comprising less than an acre of surface, near the shore 
of Cape Ann, in Massachusetts. Dr. Mighels has 
observed the same species very abundant on an island , 
of only a few rods in extent, in Casco Bay. Helix sep- 
temvolva and Helicina orbiculata occur in such quan- 
tities as almost to cover the ground upon small islands 
on the coast of Florida. The diminutive islands called 
the Brothers, in Lake Champlain, near Burlington, fur- 
nish the shells of that district in abundance. Oak 
Island, 1 a little wooded islet a few miles eastward of 
Boston, surrounded by extensive salt marshes and at 
high water by the sea, was, a few years since, covered 
by myriads of Bulimus lubrieus, and Vertigo ovata. 
And very recently, on throwing a bridge from Goat 
Island, at Niagara Falls, to an islet near it, the surface 
of which measures but a few hundred square feet, and 
which had been previously inaccessible, it was found to 
contain the Helices and Succinece of the neighborhood 
so plentifully, that hundreds might have been taken in a 
few moments. In all these cases, the fact that individ- 
uals were greatly multiplied above their numbers on 
the adjacent main land, was striking and beyond doubt. 
The locality, in each instance, being situated within the 
1 The railroad from Boston to Salem now passes through this island, and 
connects it, in two directions, with the main land. This will probably eflect 
an entire change in its peculiar molluscous~fauna, or rather cause the ex- 
tinction of tiiese animals. 
vol. i. 36 
