and L. jmlustris at Beverley. Indeed it may be doubted 
whether any species of plants or animals do not occasionally 
present white varieties, though some kinds have a much greater 
tendency to white varieties than others. The common Hare¬ 
bell, the Foxglove, the Fritillary are instances of plants where 
the white variety is very common—possibly it is in these oases 
a return to an earlier form. However in the genus Limnsea, 
the white variety is very rare, and I do not in Yorkshire 
know of any but casual instances of individuals. It is clear, 
however, that among land-snails the white variety is trans¬ 
mitted from parent to child, for year after year I have observed 
a colony of white garden-snails on a hedge bank at Brid¬ 
lington, though there are plenty of the common coloured ones 
on each side of them, so that there is evidently nothing 
peculiar in the soil or vegetation affecting the individual. As 
these white snails must be very conspicuous to thrushes it is 
a wonder they have survived. Besides the white varieties, I 
believe a striped form (which is exceedingly rare) is the only 
exception to the uniform horn-colour of the Limnaeas. 
As to varieties of form, they are much more numerous, and 
naturally the more numerous according to the variety of 
localities which a species affects. Some kinds are very much 
restricted in distribution, and only occur under special cir¬ 
cumstances ; others are found over a wide area, and under a 
great variety of conditions. The restricted kinds generally 
show but little variation in form, texture, or colour, while the 
widely diffused often exhibit great diversity in these particulars. 
This is what we should expect. Similar surroundings produce 
similar forms ; varied surroundings evoke corresponding modi¬ 
fications. Most of our Limnaeas affect still grassy pools or 
very slow ditches, but the commonest kind of all —Lmincea 
peregra —seems to have almost as astonishing powers of 
adaptation to circumstances as man himself. A puddle, a 
ditch, a deep river, a mountain lake, a rapid pebbly stream, 
our common pond-snail will make itself at home in any of them. 
One of the commonest modifications shells suffer is decol¬ 
lation, f.e., loss of the end of the spire. This may be due to 
either of two causes. Some snails secrete the material of their 
