Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/241

Rh "Oceanic, or occasional visitants." "The first of these divisions corresponds with the 'Arctic' and 'Boreal' types of Forbes and Hanley; and the second to their 'Atlantic' and 'Lusitanian' types. Their 'South-British,' 'European,' 'Celtic,' and 'British' types indicate mixed or neutral ground, and partake both of northern and southern characters." The high authority of Mr. Gwyn Jeffreys would induce me to adopt this broad division; but for geological purposes, such as tracing the old land-margins, the old sea-areas, and other questions connected with the physical geography of former periods, I think it desirable to look at the subject more in relation to existing continents and sea-margins. I have therefore retained the term "Arctic" for the species living on the Spitzbergen or Greenland coasts, "Scandinavian" for the species frequenting the coasts of Norway, Sweden, and Denmark, "British" for those of the seas immediately surrounding Great Britain, "West European" for the species frequenting the coast of Europe from France to the Straits of Gibraltar. Although Mr. Jeffreys has shown that the Mediterranean molluscan fauna cannot be considered distinct from that of the East Atlantic, I have retained the Mediterranean area as a separate province, in consequence, not so much of its existing fauna, as of the relation of that fauna with the fauna of the later or recent Tertiaries of Italy, France, and England—a relation of the most marked character. For the species which have a more southern range and are found on the shores of Madeira, the Canary Isles, and the Azores I use the term "Mid-Atlantic." To this another region is now added, embracing the great depths of the Atlantic generally—depths from 1200 to 15,000 feet.

Mr. Searles Wood described 322 species of Coralline-Crag Mollusca, which, with the 5 species of Brachiopoda described by Mr. Davidson, gives a total of 327 species. The late Dr. Woodward, basing his calculations on these lists, was of opinion that the number of extinct species was 159, and of recent species 168, which gave a percentage of 51 of recent species. Of the latter he considered that 139 were still to be found in British seas, whilst 27 were now confined to southern and 2 to northern seas*. The great extension of the field of research by means of deep-sea dredging, however, has brought to light facts which render a review of the relation of the fossils of the Crag to living species desirable. Several species which were then supposed to be extinct have since been found living; and other links have been found which tend to show that some of the species supposed to be distinct may be considered merely varieties of others; and I am glad to have

Elements of Geology,' p. 178, just published (1871), Sir Charles Lyell has revised these lists as under:—
 * Sir Charles Lyell's 'Antiquity of Man,' 1863, p. 209. In his 'Student's

Total number.

Bivalves 161 Univalves 184 Brachiopods 5

Not known as living.

47 60 3

Percentage of shells not known as living.

31-5.