MARINE MAMMALS 207 



a connecting link between the two preceding genera and 

 the marine Dolphins. 



The third family of Toothed Whales, containing the 

 Dolphins, Delphinidte, is very numerous in species and 

 embraces at least fifteen or sixteen genera, of which the 

 Common Dolphin (Fig. 49) is a good example. But in 

 spite of the efforts of Mr. True, who has recently given 

 us an excellent summary of our present knowledge of 

 them, 1 both the genera and species of Delphinidss are still 

 so imperfectly understood that not much can be said 

 about their geographical distribution. Most of the forms 



Fig 49. — The Common Dolphin. 



( Delphinus delphis.) 



[Flower and Lyd. Mamm., p. 271.] 



appear to be very widely distributed, but it may be said 

 generally that Dolphins are most abundant in the inter- 

 tropical seas and less plentiful both to the north and 

 south of them. 



There are, however, two forms that are exclusively 

 inhabitants of the Northern Oceans. These are the very 

 remarkable Narwhal (Monodon), in which the male is 

 furnished with a single enormous horn-like tusk, and the 

 Beluga, or White Whale (Delphinapterus), closely allied 



i See "A Review of the Family Delphinidse," by Frederick W. True. 

 Bull. U.S. Nat. Mus., No. 36 (Washington, U.S., 1889). 



