46 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 72 



The descendants of the primitive Squalodonts are the members of 

 the family Platanistidae M^hich appeared early in the Tertiary and 

 was soon widely distributed. Most of the genera have died out 

 again ; only four, Pontoporia [Stenodelphis] , Lipotes, Inia and Pla- 

 tanista, have come down to the present time. These have doubtless 

 avoided being crowded out by higher cetaceans purely because they 

 have chosen a peculiar habitat, rivers and estuaries, which they have 

 been almost alone in utilizing. 



Early in the Tertiary the family Delphinidae branched off from 

 primitive Platanistids. Extinct genera, especially in the Miocene, 

 are known from localities that were even then far apart ; at present 

 the family is universally distributed, many of the genera and species 

 being nearly cosmopolitan. The family seems to be having its 

 flourishing period now. Only a few of the recent genera have 

 ranges that are somewhat restricted, as Dclphinapterus and Monodon 

 in the Arctic Ocean, Tursio [Lissodelphis'] in the Pacific, Orcclla in 

 the rivers of Southeast Asia and in the neighboring sea, Ncoineris 

 [Neophoccuna] on the eastern and southern coast of Asia and the east 

 coast of Africa. 



Early in the Tertiary the family Physeteridae originated from the 

 most primitive Delphinids. It had already reached its climax in the 

 Pliocene, widely distributed. Only rather few genera, but these very 

 highly developed, have come down to the present day. They are 

 widely distributed, essentially cosmopolitan. 



