220 THE ZOOLOGIST. 



IV. Distribution of Cetaceans. 



Adopting the recognized division of the Cetaceans into two 

 Suborders (Mystacoceti and Odontoceti) according as to whether 

 their mouths are furnished with baleen ("whalebone") or teeth, 

 we will first consider the True or Whalebone Whales, which 

 consist of a single family Balcenidce, usually divided into five 

 genera — Balcena, Neobalcena, Rhachianectes, Megaptera, and Bales- 

 noptera. Of these, Balcena, Megaptera, and Balcenoptera are 

 almost cosmopolitan — species of them, whether distinct or not is 

 at present more or less uncertain, being met with in nearly every 

 part of the ocean. But Rhachianectes has as yet been ascertained 

 to occur only in the Northern Pacific, and Neobalcena in the South 

 Polar Ocean ; so that we have in these cases two well-marked 

 local types to deal with. 



The Toothed Whales (Odontoceti) are more diversified than the 

 preceding group, and are usually held to embrace at least four 

 existing families besides several extinct forms. The first family, 

 containing the Physeteridce, or Sperm Whales, consists of at least 

 six genera — Physeter, 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, however, so far as we know at present, 

 is restricted to the South Polar Ocean. 



The third family of Toothed Whales contains only the Plata- 

 nistidce, or Freshwater Dolphins, which although, in some cases, 

 at the present day entirely fluviatile, must 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 Amazons, and Pontoporia of the river La Plata; the last 

 form making a connecting link between the two preceding genera 

 and the marine Dolphins. 



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 



