period than would have been
imagined, had we merely taken into account its present range in our own
continent. Professor Boettger, who is the highest authority on
_Clausilia_, tells us that the genus is known from the earliest deposits
of the Tertiary Era. About 700 species are now known, and these have
been sub-divided by Professor Boettger and others into a number of
sub-genera. Some of these are extinct, but the great majority are still
living. The sub-genus _Phaedusa_ occurs in the eocene and oligocene of
Southern Europe, but it is extinct as far as our continent is concerned.
Close upon a hundred species, however, still inhabit India, the Malayan
Islands, China, Ceylon, and Japan. Then again, the sub-genus
_Laminifera_ occurs in the oligocene and miocene of Central Europe, and
survives in a single species, _Cl. Pauli_, in South-western France. The
groups _Garnieria_ of China, _Macroptychia_ of East Africa, _Boettgeria_
of Madeira, and _Nenia_ of South America, have no fossil
representatives. We have here some very remarkable cases of
discontinuous distribution which testify to the antiquity of the genus,
and this is certainly confirmed by the fossil evidence. However, it is
hardly likely that the headquarters, as it were, of _Clausilia_ have
always been in South-eastern Europe. Most of that part of the Continent
has been submerged since eocene times more than once. The peculiar
distribution of the genus might be explained, I think, if we supposed
the original home of _Clausilia_ to have been in Southern Asia, that
from this centre Southern Europe was colonised, where a new centre
developed in oligocene and miocene times, sending colonies off to
Madeira and across the old land-connection which united Northern Africa
and South America about that time. The most active centre of development
then gradually shifted eastward again, while the older centres were
perhaps submerged during the physical changes in the distribution of
land and water.

I should have mentioned that the species wandering westward and
northward from this South-European centre of distribution, would
naturally have joined the migrants which came from beyond the borders of
our continent. They might thus appear to be true Oriental migrants, and
on a previous occasion I grouped all these together under the term of
"Southern Fauna," as I assumed the observer to be stationed in the
British Islands. All new-comers from the south-east, south, or
south-west