350 ilR. p. I" SCLATER OX THE [MsiV. 1 ft, 



principal facts conuected with the clistributiou over the world's 

 surface of the umriue or aquatic members of the Class of Mammals. 



Aquatic mammals which pass their lives entirely, or for the 

 greater part, in the water are. of course, subject to verj' 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, water 

 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 the present time are three in number, viz. : — 



(1) the suborder of the Carnivora, containing the Seals and their 

 allies, generally called the Pinnipedia, m hich are semi-aquatic ; 



(2) the Sirenia, which are mainly aquatic : and (3) the Cetacea, 

 which never leave the water, and are wholly aquatic. We will 

 consider briefly the principal representatives of these three groups, 

 following nearly the arrangement of them employed in Flower and 

 Lydekker's 'Alamraals, living and extinct.' 



II. Distribution of Pinnipeds. 



The Pinnipeds, which I will take first, comprise three distinct 

 families — the Otabiid.e, the Tkichechid.e, and the PHOCid. 

 Beginning with the Otariida' or Eared Seals, commonly kno^vn 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 Oiaria 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 AVest- 

 Amei'ican coast and is now firmly established in the North Pacific. 

 In a parallel way in the class of birds, the Albatrosses (Diomedea), 

 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 AYalruses {Trichechida), are entirely Arctic in their distri- 

 bution — one species {Trichechus rosmarus) being ])ecidiar to the 

 North Atlantic, while a second nearly allied species {T. ohesvs) 

 takes its place in the Northern Pacific. 



The third family of Pinnipeds is more numerous and vai'ied, 

 both in genera and species, than the t\\ o preceding and has a more 



