More fortunate than the smooth-back, the rorquals, or fin-whales (_Balænoptera boops_, _musculus_, _physalis_, and _rostratus_), still remain in their ancient seats, from which they are not likely to be dislodged, as the agility of their movements makes their capture more difficult and dangerous; while at the same time the small quantity of their fat and the shortness of their baleen render it far less remunerative. They are of a more slender form of body, and with a more pointed muzzle than the Greenland whale; and while the latter attains a length of only sixty feet, the _Balænoptera boops_ grows to the vast length of 100 feet and more. There is also a difference in their food, for the Greenland whale chiefly feeds upon the minute animals that crowd the olive-colored waters above described, or on the hosts of little pteropods that are found in many parts of the Arctic seas, while the rorquals frequently accompany the herring-shoals, and carry death and destruction into their ranks. The seas of Novaja Zemlya, Spitzbergen, and Greenland are the domain of the narwhal, or sea-unicorn, a cetacean quite as strange, but not so fabulous as the terrestrial animal which figures in the arms of England. The use of the enormous spirally wound tusk projecting from its upper jaw, and from which it derives its popular name, has not yet been clearly ascertained, some holding it to be an instrument of defense, while others suppose it to be only an ornament or mark of the superior dignity of the sex to which it has been awarded. [Illustration: 35. THE NARWHAL.] Among the numerous dolphins which people the Arctic and Subarctic seas, the beluga (_Delphinus 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 with a broad truncated snout. Beyond 56° of latitude it is frequently seen in large shoals, particularly 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 a magnificent spectacle. Their white color appears dazzling, from the contrast of the sombre background, as they dart about with arrow-like velocity. The black dolphin (_Globicephalus globiceps_) is likewise very common in the Arctic seas, both beyond Bering’s Straits and between Greenland and Spitzbergen, 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 blubber is three or four inches thick.