Pvn H,i I'UitlS

58 PECTINID.E.
P. Islandicus, Miiller, once lived within the area which
now constitutes the more northern part of the British
seas and nearly the whole of Scotland. It is, however,
no longer an inhabitant of our coasts. Dead shells in a
semifossil state, but occasionally retaining their beau-
tiful pink colour, are not unfrequently dredged upon
both sides of Scotland and off the coasts of Shetland,
close to land and also at various distances from it, at
of from 30 to 80 fathoms. It is not uncommon
depths
in pleistocene beds on the west of Scotland and in the
Moray Firth. The best explanation
I can offer for its
never having been found alive in any part of our seas is
by suggesting
that the ancient sea-bed which it in-
habited during some part, if not the whole, of the glacial
above the level of the
epoch was afterwards upheaved
sea, so as to cause the extinction of this and other arctic
species, and that at a subsequent period a great part of
this district was slowly submerged and is now again
covered by the sea. We know that this process of eleva-
tion in some and depression in other parts of the Atlantic
sea-bed is still going on. Sweden and Greenland are
instances of the former phenomenon ;
and to the latter
may be referred the discovery by Dr. Wallich of starfishes
belonging to a species which usually inhabits
shallow water, living at a depth of 1260 fathoms, as
well as the occurrence of Nassa incrassata and other
littoral kinds of Mollusca in nearly 80 fathoms off the
coast of Shetland. P. Islandicus survives and is abun-
dant in every part of the Arctic Ocean at depths varying
from 15 to 150 fathoms. It has not been recorded as
living south of Drontheim ;
and Malm says that it does
not now exist anywhere on the Swedish coast, although
it is common there in a fossil state. This species is not
unlike the variety nivea of P. varius in shape and the