206 THE GEOGRAPHY OF MAMMALS 



The first family, containing the Physeteridae or Sperm- 

 Whales, consists of at least six genera, Physeter (Fig. 47, 

 p. 205), Cogia, Hyperoodon, Ziphius, Mesoplodon, and 

 Berardius). Physeter and Cogia are inhabitants of the 

 whole oceanic area between the tropics, extending in certain 

 localities some way beyond them. Hyperoodon is confined 

 to the North Atlantic. Ziphius has an extensive range, 

 and has been found in nearly every part of the ocean. 

 Mesoplodon is also widely distributed, but is apparently 

 more abundant in the Southern Hemisphere. Berardius, 



Fig. 48.— The See-see. 



(Platanista gangetica.) 



[Flower and Lyd. Mamm., p. 25S.] 



however, so far as we know at present, is restricted to the 

 Pacific Ocean. 



The second (existing) family of Toothed Whales con- 

 tains only the Platanistidm, or Freshwater Dolphins, which 

 although, in some cases, at the present day entirely fluvia- 

 tile, must probably have descended from oceanic forms. 1 

 The three known genera are Platanista of the Ganges 

 and Indus (Fig. 48), Inia of the river Amazon, and 

 Pontoporia of the river La Plata; the last form making 



1 Sir William Flower ("Whales, Past and Present," Proc. Roy. Inst, 

 x., p. 360, 1883) rather favours the idea of a freshwater origin of the 

 Cetaceans. 



