78 REPORT—1863. 
Crab (Pagurus Prideauxii) kept possession of the body or last whorl; and a 
Sea-anemone (Adamsia palliata) enveloped the whole surface of the shell 
with its slimy mass, This group of various animals formed “a happy 
family,” and did not seem to interfere in the least with one another. 
There is good reason to believe that the sea-bed in this district has sunk 
considerably since the close of the glacial epoch. Single valves of Rhyn- 
chonella psittacea, Pecten Islandicus, Astarte borealis (or arctica), Tellina cal- 
carea (or prowima), and Mya truncata, var. Uddevallensis, as well as dead 
shells of Trophon clathratus (or scalariformis), are occasionally brought up 
by the dredge from depths of between 75 and 85 fathoms, and in various 
parts of our northern sea, All the specimens have an unmistakeably fossilized 
or dull appearance, compared with that which distinguishes dead shells of 
other species still existing in the same locality. They are very different in 
that respect from the shells of Columbella Holbéllii, and other species dredged 
off the coast of Antrim but not alive. These last are quite fresh-looking, 
and may never have been exposed to the air or parted with the animal matter 
which permeates the shell. None of the species first enumerated have ever 
been found in a living or recent state in the British seas. All are essentially 
Arctic forms. Their usual habitat is in rather shallow water ; and the variety 
of Mya truncata lives between tide-marks. Other species of Mollusca, which 
are common in our seas, and inhabit the sublittoral or laminarian zone on 
the southern coasts, are found only in deep water off the Shetland Isles. 
Such are Lamellaria perspicua, Nassa inerassata, and Cyprea Europea. 
Not one of these last is an Arctic form. I have already noticed the pecu- 
larity of their occurrence at the above-mentioned depths, in the Report 
which I had the honour to present to the Association in 1861, and I ven- 
tured to express an opinion that it was owing to this part of our northern 
sea-bed having sunk within a comparatively recent period. Dr. Wallich 
has since confirmed this impression on my part by his history of the “ sunken 
land of Buss,” in the North Atlantic, not far from which supposed tract he 
found several specimens of Ophiocoma granulata living at the enormous depth 
of 1260 fathoms, the same species inhabiting on the opposite coast of Iceland 
from 10 to 20 fathoms only. Now, inasmuch as Pecten Islandicus and the 
other Arctic species above named are large and conspicuous forms, as well as 
gregarious in the places where they are now found, the question naturally 
arises, ““ Why has not a single living individual ever been discovered in that 
part of the British sea where the dead shells are not uncommon, although 
it has been sufficiently explored?” It cannot be said that they have died 
out, or become extinct, in consequence of the water having become of a 
higher temperature than it was during the period when they formerly in- 
habited the same part of the sea, or because some other conditions, unfa- 
vourable to their existence, have supervened. We have no proof or reason 
to believe that the temperature of the sea at a depth exceeding 75 fathoms 
has been at any time since that period different from what it is at present. 
Very many species of Mollusca, which are natives of the Polar sea, are also 
inhabitants of our coasts, where they apparently have not suffered the least 
diminution in number or vigour, although they may have dwindled in size. 
Several of the peculiarly Arctic forms above referred to, and which no longer 
live in the British seas, continue to exist in a parallel latitude on the 
coast of Norway; and two of them (Astarte borealis and Tellina calearea) 
survive in Kiel Bay, more than 5° south of Unst, at a depth not exceeding 
25 fathoms. I therefore can only account for this apparent extermina- 
tion in our seas of the six species in question by suggesting that the 
