ARCTIC MARINE ANDIALS. 61 



enormous spirally wound tusk projecting from its upper jaw, and from which 

 it derives its popular name, has 4iot yet been clearly ascertained, some holding 

 it to be an instrument of defense, w hile others suppose it to be only an orna- 

 ment or mark of the superior dignity of the sex to which it has been awarded. 

 Among the numerous dolphins which people the Arctic and Subarctic seas, 

 the beluga {Delphlnas leucas), improperly called the white whale, is one of the 

 most interesting. When young it has a brown color, which gradually changes 

 into a perfect white. It attains a length of from twelve to twenty feet, has no 

 dorsal fin, a strong tail three feet broad, and a round head Avith a broad trun- 

 cated snout. Beyond 56° of latitude it is frequently seen in large shoals, par- 

 ticularly near the estuaries of the large Siberian and North American rivers, 

 which it often ascends to a considerable distance in pursuit of the salmon. A 

 troop of belugas diving out of the dark waves of the Arctic Sea is said to afford 





THE NARWHAL. 



a magnificent spectacle. Their white color appears dazzling, from the con- 

 trast of the sombre background, as they dart about with arrow-like velocity. 



The black dolphin ( Globiceplialus globiceps) is likewise veiy common in 

 the Arctic seas, both beyond Bering's Straits and between Greenland and Spitz- 

 bergen, whence it frequently makes excursions to the south. It grows to the 

 length of twenty-four feet, and is about ten feet in circumference. The skin, 

 like that of the dolphin tribe in general, is smooth, resembling oiled silk ; the 

 color a bluish-black on the back, and generally whitish on the belly ; the blub- 

 ber is three or four inches thick. 



The full-grown have generally twenty-two or twenty-four teeth in each jaAv; 

 and when the mouth is shut, the teeth lock between one another, like the teeth 

 of a trap. The dorsal fin is about fifteen inches high, the tail five feet broad ; 

 the pectoral fins are as riiany, long and comparatively narrow ; so that, armed 

 with such excellent paddles, the black dolphin is inferior to none of his relatives 

 in swiftness. Of an eminently social disposition, these dolphins sometimes con- 

 gregate in herds of many hundreds, under the guidance of several old expcri- 



