744 



SCIENCE. 



[N. S. Vol. V. No. 124. 



necessarily have all descended from what 

 were originally oceanic forms. The three 

 known genera are Platanista of the Ganges 

 and Indus, Inia of the river Amazon, and 

 Pontoporia of the river La Plata]; the last 

 form making a connecting link between the 

 two preceding genera and the marine Dol- 

 phins. 



The fourth family of Toothed "Whales, 

 containing the Dolphins, Delphinidce, is very 

 numerous in species and embraces at least 

 fifteen or sixteen genera. But in spite of the 

 efforts of Mr. True, who has recently given 

 us an excellent summary of our present 

 knowledge of them,* both the genera and 

 species of Delphiniclce are still so imperfectly 

 understood that I cannot say much about 

 their geographical distribution. Most of 

 the forms appear to be very widely distrib- 

 uted, 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 ITorth At- 

 lantic. These are the very remarkable Nar- 

 whal (Monodon), in which the male is fur- 

 nished with a single enormous horn-like 

 tusk, and the Beluga, or White Whale {Del- 

 phinaptenis') , 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 MAEINE AREA OF THE 

 GLOBE INTO SEA-EEGIONS. 



From what has been already said, it will 

 be evident that although many of the Ma- 

 rine 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 



*See 'A Eeview of the family Delphinidse,' by 

 Frederick W. True : Bull. U. S. Nat. Mus. No. 36; 

 Washington, U. S., 1889. 



into six Sea-regions, corresponding to a cer- 

 tain 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 North- Atlantic Sea-region or Arc- 

 tatlantis (^apxroi and arXavrti = the daughter 

 of Atlas), consisting of the northern portion 

 of the Atlantic down to about 40° N. lat. 



(2) The Mid- Atlantic Sea-region or Mesat- 

 lantis (/aio-o? and arAavri'y), consisting of the 

 middle portion of the Atlantic down to 

 about the Tropic of Capricorn. 



(3) The Indian Sea-region or Indopelagia 

 (ivSo? and iriXayo?), containing the Indian 

 Ocean down to about the same degree of 

 S. lat., and extending from the coast of Af- 

 rica on the west to Australia and the great 

 Oriental islands on the east. 



(4) The North Pacific Sea-region or Arcti- 

 renia (apxroi and ei'/'i;'i";=pax), containing 

 the northern portion of the Pacific Ocean 

 down to about the Tropic of Cancer. 



(5) The Mid-Pacific Sea-region or Mesirenia 

 (fii(7o<; and eipri'^ri') containing the inter-trop- 

 ical portion of the Pacific Ocean; and finally 



(6) The Southern Sea-regio7i or Notopelagia 

 (voToi and 7r^/la;-of), containing the whole of 

 the South Polar Ocean all around the globe 

 south of the above mentioned limits. 



We will now proceed to consider shortly 

 the characteristic Mammals of these six 

 Sea-regions. 



VI. THE NORTH ATLANTIC SEA-REGION, OE 

 ARCTATLANTIS. 



Amongst the Pinnipeds, two well-marked 

 generic forms, the Gray Seal {Halichwrus) 

 and the Bladder-Seal (Cystoj^hora) are ex- 

 clusively confined to Arctatiantis. The True 

 Seals (Phoca) and the Walrus {Tricheehus) 

 are found in this region and in Arctirenia ; 

 and of the former genus three species (P. 



