Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/374

Rh Echinoderms, Ophiocoma granulata and bellis, Goniaster pulvillus (Templetoni), Echinus Flemingii? Brissus lyrifer, Psolus phantapus, Cucumaria frondosa, Thyone raphanus, and other Holothuriadæ, are good examples; as are the species of Beroë and Alcinoë, among the Acalephæ. Of zoophytes Virgularia mirabilis, and other species frequent only in the northern coasts of Britain, belong to this type, as also do several sponges.

The sub-Arctic type is well marked in the Zetland Seas by the presence of several Radiata which do not range farther south; such as, Echinus neglectus, Cidaris papillata, Echinarachneus placenta? Lucernaria fascicularis, ,,Actinea intestinalis, Oculina prolifera, Primnoa lepadifera, Astrophyton scutatum, Priapulus caudatus, Corymorpha nutans, Flustra setacea, and Tethya cranium.

I have dwelt thus fully on the distribution, horizontally, of British marine animals, because a knowledge of it is of the greatest importance to the geologist who directs his attention to the phenomena presented by tertiary strata, not only within our own area, but throughout the northern hemisphere, and because the subject is one of which there is no connected view presented in any published work, whilst even the details of many parts are either not in print or scattered through many books, journals, and memoirs. In the first section of this essay, it was not necessary to do so when our flora and terrestrial fauna were concerned, as (especially of the former) the details are fully collected and combined in accessible and well-executed works. This is also the case with the marine vertebrata, but not as yet with the greater part of the invertebrate animals of our seas, whose remains, as will be seen hereafter, furnish an invaluable clue to the history of conditions, climatal changes, and changes in the distribution of submarine life, which preceded the historical epoch, and organized, as it were, the present state of things.

The ancient history of this fauna—so far as the area under discussion is concerned—may be clearly made out. The most ancient traces of existing species still inhabiting the British Seas are probably to be found as far back as the cretaceous epoch, when Terebratula caput serpentis, certain existing foraminifera identified by Ehrenberg), and possibly some deep-sea corals lived under similar conditions of depth with those which now determine their distribution. About these, however, there may still be doubts, and even about most or all of the forms identified with existing British species, found in strata of the eocene period, when the assemblage of inorganic and organic phenomena within our area was such as cannot be compared with that presented by it at present, though closely approximating the state of things in certain regions nearer the equator. The close of the eocene period was probably marked by such a change in the disposition of land and water in the