126 . 
INTRODUCTION. 
diate territory, the most peculiar species of the two are 
the same. This is an instance of the tendency of similar 
causes to reproduce the same forms in localities -widely 
separated, though upon the same continent. In it the 
influences are unfavorable, and the species gradually run 
out towards the north-east, until, in Nova Scotia, the 
only one of our larger species common to the more south- 
ern sections, known to prevail, is Helix altemata, pro- 
bably the most universally diffused species of our whoTe 
catalogue. The number of individuals is also greatly 
diminished, and they never attain the same size and 
beauty which they reach in more favorable situations. 
In many parts of this section, land shells are never seen, 
and throughout the whole of it they are more or less rare. 
But, while such is the operation of climate and soil on 
our native species, Helix hortmsis, a species undoubtedly 
introduced from Europe, has made a successful lodgment, 
and is the most abundant species throughout the greater 
part of Nova Scotia, the islands north and east of it, 
parts of Lower Canada, New Brunswick, and on several 
small islands on the coast of Maine and Massachusetts, 
but does not extend to more southern and temperate 
parts. The genus Vdrina also belongs to this section, 
as does also Bulimus harpa. 
The distribution of the genera and species in each of 
the preceding sections is exhibited in the synopsis on 
pages 128, 129 ; the species supposed to be introduced 
from foreign countries being printed in italics. The 
catalogues are, of course, imperfect, and additions and 
alterations will be made from time to time. 
