Other species are similar to those of the Antarctic seas, but not nearly so numerous, and besides these there are two worthy of special mention, namely, the White whale (Delphinapterus leucas) and the Narwhal (Monodon monoceros). The white whale is found skirting the shores of almost every Arctic land, and is very easily distinguished by its cream-coloured skin; so regular are its movements along a coast that skilful hunters seldom fail to secure the greater part of a school of them by knowing that they will travel along a certain coast by a certain route. They are driven ashore by means of boats and nets. They yield a considerable amount of oil, and their skins are manufactured into "porpoise" boot-laces. The narwhal is nearly allied to the white whale, but is easily distinguished by the male's single long spiral ivory tusk, often 7 or 8 feet long, which has earned for it the name of "unicorn," or "uni," by whalers. It is hunted by whalers for the value of the ivory of the tusk and for its oil; the tusk is usually developed on the left side, but occasionally two are developed. It has a circumpolar range. (For a fuller account of Arctic whales and seals than is possible here, see papers by Dr. R. Brown on "Seals of Greenland and Spitsbergen Seas" (Proceedings Zoological Society, London, 1868, pp. 405–438), and on "Cetacea of Davis
