524 
GEOGRAPHICAL ZOOLOGY. 
[part IV. 
absence of genera confined to, and characteristic of Africa and 
India. One small sub-genus of Helix , ( Pachis ), and one of Acha- 
tina, ( Homorus ), appear to have this distribution, — a fact of but 
little significance when we find another sub-genus of Helix , 
( Hapalus ), common and confined to Guinea and the Philippine 
Islands ; and when we consider the many other cases of scattered 
distribution which cannot be held to indicate any real connection 
between the countries implicated. No genus is confined to the 
Paleearctic and Nearctic regions as a whole. A large number 
of sub-genera, many of them of considerable extent, are peculiar 
to one or other of these regions, but only 3 sub-genera of Helix 
and 2 of Pupa are common and peculiar to the two combined, 
and these are always such as have an Arctic range and whose 
distribution therefore offers no difficulty. 
We find, then, that each of our six regions and almost all of 
our sub-regions are distinctly confirmed by the distribution of the 
terrestrial mollusca ; while the different combinations of them 
which have at various times been suggested, receive little or no 
support whatever. Even those remarkably isolated sub-regions, 
New Zealand and Madagascar, have no strictly peculiar genera of 
land-shells, although they both possess several peculiar sub- 
genera; being thus inferior in isolation to some single West 
Indian Islands, to the Sandwich Islands, and even to the North 
Atlantic Islands (Canaries, Madeira, and Azores), each of which 
have peculiar genera. This of course, only indicates that the 
means by which land mollusca have been dispersed are some- 
what special and peculiar. To determine in what this speciality 
consists we must consider some of the features of the specific 
distribution of this group. 
The range of genera, and even of sub-genera is, as we have 
seen, often wide and erratic, but as a general rule the species 
have a very restricted area. 
Hardly a small island on the globe but has some land-shells 
peculiar to it. Juan Fernandez has 20 species, all peculiar. 
Madeira and Porto Santo have 109 peculiar species out of a total 
of 134. Every little valley, plain, or hill-top, in the Sandwich 
Islands, though only a few square miles in extent, has its 
