LAND AND FRESH WATER SHELLS. 
315 
Lists of the Fresh-water Fishes and of the Land 
and Fresh-water Shells of the county appear in 
another place, and it is here only needful to observe 
in regard of the molluscs, that there are two chief 
peculiarities in the physical character of our South 
Hams, namely vast abundance of wood, and great 
number of rivers and streams. The land and 
fluviatile shells certainly correspond in great mea¬ 
sure to these circumstances, but I believe no instance 
can be adduced where the Fauna of a locality 
accords so precisely with its physical conditions, 
as to include all those creatures generally found in 
such spots, and to exclude those generally absent 
from the same. Perhaps indeed our w 7 oods being 
particularly damp and shaded, a number of Land 
Shells may on that account be denied us, such as 
Carocolla lapicida and Clausilia biplicata, and 
again,our deficiency in large ponds, pools, and other 
standing or slow r running water, may cause us to 
be deprived of the genera Anodon and Mysca, but 
then Succinea amphibia is denied us, while the 
Succinea oblonga is granted us, and yet they are 
in some counties found in the same marsh. Paludina 
stagnorum occurs here, but its congeners do not. 
It is to be remarked how singularly w^ell defined 
are the limits of some species of these tribes, so 
much so as to induce the belief that these limits in 
some cases correspond with the boundaries of soils, 
or with the geographical distribution of certain 
vegetable and other productions on wdiich they feed, 
though possibly the facts of these cases may after 
all be quite as inexplicable as the limits of dis¬ 
persion observed by the Nightingale, and some 
other birds. At the least however, it will be allowed 
that comparisons between the geographical limits 
of the various productions, mineral, vegetable, and 
animal, of a given district, would in all probability 
lend considerable assistance in the determination 
