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Show 358 ON THE DISTRIBUTION OF MARINE MAMMALS. [Mar. 16, In conclusion, I will call attention to some of the more remarkable points in the general distribution of the marine Mammals and to their apparent significance. In the first place it is evident that the Pacific has much more in common with the Notopelagian region than the Atlantic. Otaria and Macrorhinus, quite unknown in the Atlantic, extend themselves to the northern extremity of the Pacific, the former pervading that ocean up to Bering's Straits, and the latter reaching to the Californian coast. It follows that in former ages there must have been some barrier in the Atlantic which did not exist in the Pacific to stop their progress northwards. The only barrier I can imagine that would have effected this must have been a land uniting S. America and Africa, across which they could not travel. Adopting this hypothesis, we have at the same time an explanation of the presence of the Manatee on both the American and African coasts. The Manatee could hardly live to cross the Atlantic. It is only found close to the coast, where it browses on sea-wTeeds and other vegetable food in shallow water. H o w did it travel from America to Africa (or vice versa), unless there were a continuous shore-line between them ? The same may be said of the Monk- Seal (Monachus), of which one species lives in the Mediterranean and on the African coast and islands and another in the West Indies. W e can hardly believe that these creatures could easily traverse the whole Atlantic. Tbe hypothesis of a former barrier of land between Africa and America, which we know is supported by other facts of distribution \ would alone explain the difficulty. O n the other hand, in the Pacific w e find no such break between the north and south. The aquatic Mammals of Notopelagia have evidently had free access to the whole of the Pacific for a long period and have well availed themselves of this facility. Again, while the great Southern Ocean exhibits a considerable uniformity of marine Mammalian life, w e see the Northern waters divided into two distinctly recognizable Regions by the interposed masses of land. All these facts, with the one exception of the supposed Atlantic Barrier, would tend in favour of the now generally accepted doctrine that the principal masses of land aud water are not of modern origin, but have existed mainly in their present shapes throughout all ages. TOPOMORPHS OF THE SlX SEA-REGIONS. I. ARCTATLANTIS. IV. ARCTIRENIA. Halichcerus. Otaria. Cystophora. Rhytlna. Hyperoodon. Rhachianectes. 1 Cf. Wallace, Geogr. Distrib. vol. i. p. 156. |