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Show 350 MR. P. L. SCLATER ON THE [Mar. 1 6\ principal facts connected with the distribution over the world's surface of the marine or aquatic members of the Class of Mammals. Aquatic mammals which pass their lives entirely, or for the greater part, in the w?ater are, of course, subject to very different laws of distribution from those of the terrestrial forms. As regards aquatic mammals, land is of course an impassable barrier to their extension, and, subject to restrictions in certain cases, wrater offers them a free passage. Just the opposite is the case with the terrestrial mammals, to which in most cases land offers a free passage, while seas and rivers restrain the extension of their ranges. The groups of aquatic mammals that are represented on the earth's surface at tbe present time are three in number, viz.:- (1) the suborder of the Carnivora, containing the Seals and their allies, generally called the Pinnipedia, which are semi-aquatic; (2) the Sirenia, which are mainly aquatic ; and (3) the Cetacea, which never leave the water, and are wholly aquatic. W e will consider briefly the principal representatives of these three groups, following nearly the arrangement of them employed in Flower and Lydekker's ' Mammals, living and extinct.' II. Distribution of Pinnipeds. The Pinnipeds, wdiich I will take first, comprise three distinct families-the OTARIIDCE, the TRICHECHICE, and the PHOCID.E. Beginning with the Olariiclce or Eared Seals, commonly known as Sea-lions and Sea-bears, we find the greater number of the species confined to the South Polar Ocean, where they pass most of their time at sea, but, as is well known, resort to the land at certain seasons for breeding purposes. In the Atlantic Ocean, so far as I know, the Eared Seals have never been ascertained to occur further north than the estuary of the La Plata on the American coast, and the vicinity of the Cape on the African coast. But in the Pacific, on the contrary, three distinct species of Otaria are found all over the Arctic portion of that ocean, and there is good evidence of Eared Seals having been met with in the Galapagos, while they still occur on the coasts of Peru and Chili. I think therefore we may assume that Otaria was originally an Antarctic form, but has travelled northwards along the West- American coast and is now firmly established in the North Pacific. In a parallel way in the class of birds, the Albatrosses (Dlomedea), which are essentially a group of the Antarctic Seas, are represented by three distinct species in the North Pacific. The second family of the marine Carnivora, on the other hand, the Walruses (Trichechidce), are entirely Arctic in their distribution- one species (Trlchechus rosmarus) being peculiar to the North Atlantic, while a second nearly allied species (T. obesus) takes its place in the Northern Pacific. The third family of Pinnipeds is more numerous and varied, both in genera and species, than the two preceding and bas a more |