Page:The Zoologist, 4th series, vol 1 (1897).djvu/249

Rh knowledge of them, both the genera and species of Delphinidæ are still so imperfectly understood that I cannot say much about 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, and 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 tusk, and the Beluga or White Whale, Delphinapterus, 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.

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 which I proposed to separate the terrestrial portion of the globe in 1874, and which were subsequently adopted by Mr. Wallace in his standard work on the Geographical Distribution of Animals. I propose to call these sea-regions:—

(1) The or  (ἄρκτος and ἀτλαντίς=the daughter of Atlas), consisting of the northern portion of the Atlantic down to about 40° N. lat.

(2) The or  (μέσος and ἀτλαντίς), consisting of the middle portion of the Atlantic down to about the Tropic of Capricorn.

(3) The or  (ίνδὀς and πέλαγος), 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 or  (ἄρκτος Zool. 4th ser. vol. I., May, 1897.