Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/403

390 from Greenland to the Scottish Seas, and not known south of Britain. The Nucula nuclea and the Lima range from Greenland to the Mediterranean, but the variety of the former taken is confined to northern seas, and the latter is very rare, and only found at great depths in seas south of Britain. The dead mollusks taken were Abra Boysii, a species of similar range with Nucula nuclea, Cardium Lövenii a Scandinavian species, and Pecten danicus, a Norwegian species, found only in the British Seas in the lochs of the Clyde, and there rarely alive, though dead valves are abundant, as if the species thus isolated were now dying out. The echinoderms were Ophiocoma filiformis, and Brissus lyrifer, the former a Norwegian species; the latter ranging to the Arctic Seas, but southwards not known beyond the Clyde region. The Crustacean was new, both as to genus and species. It will be observed, that the assemblage of animals thus taken at this great depth, was essentially Arctic, Subsequently we added to the list three species of Neæra, N. costellata, N. rostrata, and N. abbreviata. Of these the second ranges throughout the European Seas. All three are known inhabitants of the Mediterranean, where they are found associated only at very great depths. All three are inhabitants of the coasts of Norway, where they have been observed by Professor Löven.

Deep dredgings elsewhere on the British coasts yielded similar results, the assemblages of deep-sea species presenting a decidedly boreal character, and maintaining the representation of the faunas of northern latitudes, mainly through identical species.

In the deepest of the regions of depth in the Ægean, this representation of a northern fauna is maintained, partly by identical and partly by representative forms. The three species of Neæra, already mentioned, the Pandora obtusa, the Arca pectunculoides, the Saxicava rugosa, Pecten similis, Trochus millegranus, Fusus echinatus, Rissoa reticulata, and Terebratula cranium, are instances of the former, whilst Crania ringens, Abra profundissima, Astarte pusilla, Cardium minimum, Nucula sulcata and ægeensis, Leda commutata, Lottia unicolor, and Pleurotoma abyssicola are examples of the latter. The presence of the latter is essentially due to the law [of representation of parallels of latitude by zones of depth], whilst that of the former species depended on their transmission from their parent seas during a former epoch, and subsequent isolation. That epoch was doubtless the Newer Pliocene, or Glacial Æra, when the Mya truncata, and other northern forms, now extinct in the Mediterranean, and found fossil in the Sicilian tertiaries, ranged into that sea. The changes which there destroyed the shallow-water glacial forms, did not affect those living in the depths, and which still survive.