296 
GEOGKAPHICAL DISTRIBUTION. 
12. Melania Matonii. Gray^ Linn, Trans, vii. 150. t. 4. f. 6. 
An African river shell. 
Thus have I felt myself called on to exclude from our Fauna 
no fewer than 54 species. 
IV. 
GEOGRAPHICAL DISTRIBUTION. 
In considering the geographical distribution of the British land 
and fresh-water Mollusca, we must look at them at least 
in two points of view : first, as regards their bearing on the 
general distribution of Mollusca in the rest of Europe ; and 
secondly, the extent to which the various species are diffused 
over the different parts of the island, which is influenced by 
the climate, the elevation, and the nature of the subsoil, or of 
the rock of which the country is chiefly formed. 
All the species which appear to be really native, and are 
therefore noticed in this work, are found in France, or in 
different parts of Germany, except the following : — 
1. Assiminia Gray ana. — 2. Vertigo angustior. — S. Amphipe’^ 
plea involuta,—^. Cyclas pallida. — 5. C. pisidioides. 
These are newly described species, and may have been over- 
looked, or only considered as varieties of other well-known 
species, by the zoologists of the Continent. It is to be re- 
marked that, in general, the British species, although they vary 
among themselves, attain a moderate and nearly uniform size, 
compared with those of the rest of Europe. Thus I have never 
seen Lymneus stagnalis, Paludina achatina or crystallina^ so 
large as those found in the south-eastern part of Germany ; or 
Helix nemoralis^ and other more common Helices^ as those found 
in Portugal, or the Helix aspersa from Algiers ; nor, on the 
other hand, have I seen any English specimens of Helices so 
stunted in growth as the Alpine varieties of H. nemoralis and 
H. arhustorum^ which I have received from the Swiss Alps. 
Ferussac has observed (Journ, de Phys, 1820) that it is re- 
