MARINE MAMMALS 209 



(3) The Indian Sea-region, or Indopelagia ("IvSos 

 and TreXayos), 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 North Pacific Sea-region, or Arctirenia 

 (apKTos and elptjwq = pax), containing the northern portion 

 of the Pacific Ocean down to about the Tropic of Cancer. 



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

 and elprjvrj), containing the inter-tropical portion of the 

 Pacific Ocean ; and finally, 



(6) The Southern Sea-region, or Notopdagia (voto? 

 and 7re\a<yo<;), containing the whole of the South Polar 

 Ocean all round the globe south of the above-mentioned 

 limits. 



We will now proceed to consider shortly the char- 

 acteristic mammals of these six Sea-regions. 



Section VI. — The North Atlantic Sea-region, 

 or Arctatlantis 



Amongst the Pinnipeds two well-marked generic forms, 

 the Grey Seal (Halichoerus) and the Bladder-Seal (Cysto- 

 phora), are exclusively confined to Arctatlantis. The 

 True Seals (Phoca) and the Walrus (Trichechus) are found 

 in this region and in Arctirenia ; and of the former genus 

 three species (P. vitulina, P. grcenlandica, and P. barbata) 

 are actually common to both these Sea-regions, while the 

 Walruses (Trichechus rosmarus and T. obesus) of the two 

 Sea-regions are perhaps somewhat doubtfully distinguish- 

 able. It may be easily understood how this has come to pass, 



