ely related to the arctic marine _Mysis oculata_. According to
Professor Sars, the genus _Mysis_ as a whole may be regarded as arctic
in character. The occurrence of these two species, therefore, in his
opinion, points to a recent connection of the Caspian with the Glacial
Sea.

A large number of other crustaceans have been described by the same
author from the Caspian. Of the order Cumacea, which is exclusively
marine, ten species are mentioned, but none of these seems to range
beyond the Caspian. Among the smaller species of crustaceans, a minute
pelagic copepod (_Limnocalanus grimaldii_) also inhabits the Baltic and
the Arctic Ocean. The marine isopod _Idotea entomon_, related to the
common wood-louse, has a similar distribution.

Genuine Arctic species of Fishes do not seem to occur in the Caspian,
though some, viz., _Clupea caspia_, _Atherina pontica_, _Clupionella
Grimmi_, and _Syngnathus bucculentus_, are almost certainly the
descendants of marine forms.

The Seal of the Caspian (_Phoca caspica_) is closely allied to the
Arctic Seal, and its presence alone in that sea indicates that at no
very distant date--at any rate since pliocene times--a closer connection
with the Arctic Ocean existed than at present.

I am sure it will be readily granted that there is zoological evidence
for the belief of such a connection or union between the two great seas.
However, it may be urged that owing to the presence of an ice-sheet in
Northern Europe during the Glacial period, such a connection must either
have been pre-glacial or have existed after that period. But the
connection must have occurred at a time when the Caspian extended far to
the north--when indeed the so-called post-tertiary Caspian deposits were
laid down (Fig. 17). Since the boulder-clay which covers the plain of
Northern Russia is assumed to be the ground-moraine of the great
northern ice-sheet, we might expect to find that the Caspian deposits
were not contemporaneous with it. Curiously enough, it has been shown by
Mr. Sjoegren that all observations have pointed to the fact that these
two deposits do not overlie one another, but occur side by side, and are
therefore contemporaneous. This seems to warrant our belief, that while
the boulder-clay was being laid down in Northern Europe, the
Aralo-Caspian Sea had some communication with the White Sea.

[Illustration: Fig. 17.--Map of European Russia (after Karpinski). The
faintly dotted parts indicate the are