The Narwhal is essentially an Arctic animal, frequenting the icy circumpolar seas, and but rarely seen south of 65° N. lat. Three instances have, however, been recorded of its occurrence on the British coasts, one in the Firth of Forth in 1648, one near Boston in Lincolnshire in 1800, while a third, which entangled itself among the rocks in the Sound of Weesdale, Shetland, in September 1808, is described by Fleming in the _Memoirs of the Wernerian Society_, vol. i. Like most other Cetaceans, it is gregarious in its habits, being usually met with in “schools” or herds of fifteen or twenty individuals. Its food appears to be various species of cephalopods, small fishes, and crustaceans. The purpose served in the animal’s economy by the wonderfully developed asymmetrical tusk—or “horn,” as it is commonly but erroneously called—is not known. As it is present only in the male sex, no function essential to the well-being of the individual, such as the procuring of sustenance, can be assigned to it, but it must be looked upon as belonging to the same category of organs as the antlers of deer, and perhaps may be applied to similar purposes. Very little is, however, known of the habits of Narwhals. Scoresby describes them as “extremely playful, frequently elevating their horns and crossing them with each other as in fencing.” They have never been known to charge and pierce the bottom of ships with their weapons, as the sword-fish often does. The name “Sea Unicorn,” sometimes applied to the Narwhal, refers to the resemblance of its tusk to the horn represented as projecting from the forehead of the fabled unicorn. The ivory of which the tusk is composed is of very good quality, but, owing to the central cavity, which extends the greater part of its length, is only fitted for the manufacture of objects of small size. The entire tusks are sometimes used for decorative purposes, and are of considerable, though very fluctuating, commercial value. _Delphinapterus._[156]—This genus is closely allied to the last in external form, as well as anatomical structure, differing mainly in the very distinct character of the dentition. Teeth from ⁸⁄₈ to ¹⁰⁄₁₀, occupying the anterior three-fourths of the rostrum and corresponding portion of the mandible, rather small, conical, and pointed when unworn, but usually becoming obliquely truncated, separated by intervals considerably wider than the diameter of the tooth, and implanted obliquely, the crowns inclining forwards, especially in the upper jaw. Skull rather narrow and elongated, depressed. Premaxillæ convex in front of the nares. Rostrum about equal in length to the cranial portion of the skull, triangular, broad at the base, and gradually contracting towards the apex, where it is somewhat curved downwards. Vertebræ: C 7, D 11, L 9, C 23; total 50. Cervical vertebræ free. Manus broad, short, and rounded, all the digits being tolerably well developed, except the first. No dorsal fin, but a low ridge in its place.