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Show 1897.] DISTRIBUTION O F M A R I N E M A M M A L S . 353 their geographical distribution. Most of the forms appear to be very widely distributed, but it may be said generally that Dolphins are most abundant in the inter-tropical seas aud less plentiful both to the north and south of them. There are, however, two forms that are exclusively inhabitants of the North Atlantic. These are the very remarkable Narwhal (Monodon), in which the male is furnished with a single enormous horn-like tu.sk, and the Beluga or White Whale (Delphinaptcrus), closely allied to the Narwhal in many points of its general structure. These may be looked upon as quite isolated forms characteristic of the Arctic portion of the Atlantic but not known in the Pacific \ V. Division of the Marine Area of the Globe into Sea-regions. From what has been already said, it will be evident that although many of the Marine Mammals have a wide distribution, others are very definitely localized ; and a study of the latter will, I think, enable us to divide the oceanic portion of the globe into six Sea-regions, corresponding to a certain extent with the six Land-regions into wdiich I proposed to separate the terrestrial portion of the globe in 1874, and which were subsequently adopted by Mr. "Wallace in bis standard work on the Geographical Distribution of Animals. I propose to call these Sea-regions :- (1) The N O R T H - A T L A N T I C SEA-REGION, or A B C T A T L A N T I S (HOKTOS and 'ArAay-is = thc daughter of Atlas), consisting of the northern portion of the Atlantic clown to about 40° N . lat. (2) The M I D - A T L A N T I C SEA-REGION, or M E S A T L A N T I S (pectus and 'ArXai'Tts), consisting of the middle portion of the Atlantic down to about the Tropic of Capricorn. (3) The I N D I A N SEA-REGION, or INDOPELAGIA("II'COS and neXayos), containing the Indian Ocean down to about the same degree of S. lat., and extending from the coast of Africa on the west to Australia and the great Oriental islands on the east. (4) The N O R T H PACIFIC SEA-REGION, or A R C T I R E N I A (upicros and e((o»yy»j = pax), containing the northern portion of the Pacific Ocean down to about the Tropic of Cancer. (5) The MID-PACIFIC SEA-REGION, or M E S I R E K I A (peaos and eipnn), containing the inter-tropical portion of the Pacific Ocean ; and finally (6) The S O U T H E R N SEA-REGION, or N O T O P E L A G I A (VOTOS and neXayos), containing the whole of the South Polar Ocean all round the globe south of the above-mentioned limits. W e will now proceed to consider shortly the characteristic Mammals of these six Sea-regions. VI. The North Atlantic Sea-region, or Arctatlantls. Amongst the Pinnipeds two well-marked generic forms, the Grey Seal (Halichcerus) and the Bladder-Seal (Cystophora), are exclusively 1 In a recent letter to ' Science' (1897, p. 843) Dr. Dall has pointed out that this is an error. Both Monodon and Delphinaptcrus occur in tbe North Pacific-P.L.S., 4. vi. 97. |