MARINE MAMMALS 215 



The Sirenians are absent from Notopelagia, but 

 Cetaceans of every kind are abundant. Besides one or 

 more representatives of the true Whalebone Whale 

 {Balarna), Notopelagia has a smaller representative of the 

 group (Neobal&na) entirely restricted to its area. It has 

 also representatives of Megaptera and Balienoptera, though 

 it is doubtful how far they are even specifically distinct 

 from some of their northern representatives. 



Among the Toothed Whales (Odontoceti) we find a 

 large Ziphioid form, Berardius, restricted to the Pacific 

 area, while Ziphius and Mesoplodon also occur there. 

 The Dolphins {DelphinidiB) are likewise numerous, and 

 present some distinct species, but not, so far as our 

 present knowledge extends, any generic forms that do 

 not occur elsewhere. 



But Notopelagia is sufficiently distinguished from all 

 the five more northern Sea-regions by possessing four 

 genera of Seals and two of Cetaceans entirely restricted to 

 its area. 



Section XII. — Conclusions 



It has therefore been shown that, for the geography 

 of marine mammals, the ocean may be conveniently 

 divided into six Sea-regions (Plate VIII., p. 216), which 

 are as follows : — 



I. Regio Arctatlantica, characterized by its Seals 

 (Phocinie), of which two genera, Halichcerus and Cysto- 

 phora, are peculiar, whilst Phoca is common to it and 

 Arctirenia ; by the absence of Sirenians ; and by the 

 possession of a peculiar genus of Cetaceans {Hyperoodon). 



II. Regio Mesatilantica, sole possessor of the Monk- 



