The atlas vertebra transverse, nearly twice as broad as high; the central canal subtrigonal, narrow below. Skull nearly one-third the entire length of the body. Lachrymal bone wanting. The zygomatic process is formed of the malar bone. Vertebral column rough and rather spongy. Vertebræ 50: 7 cervical, 11 dorsal, 8 lumbar, 24 caudal. The atlas separate; the other 6 cervical united by their bodies and spines into one consolidated mass, and sometimes united to the first dorsal vertebra. The atlas subquadrangular, broader than long. The transverse process truncated. Upper edge nearly straight, lower slightly curved. Neural canal triangular, one of the angles directed downwards. The thyro-hyal triangular, thick in front, thinner behind; the basihyal broad and flat. The basihyal and thyro-hyal united. The ribs long, all but the first slender and light. The first rib is short, broad, and very thick near the lower end. Sternum large, triangular, the apex turned backwards. The broad front end nearly straight, composed of two large anterior and a small posterior piece. Pectoral limb small. Scapula higher than broad; outer surface concave, inner convex. Acromion very large, dilated at the end. Coracoid large, narrow, and about half the length of the acromion. Humerus compressed. Radius and ulna not quite so long as the humerus, often united at the ends and separate in the middle. The carpus wide and short. The carpal bones six, nearly in a single row. The fingers five, all well developed, the second, third, and fourth not differing greatly in length, the fourth the shortest; the first consisting of two, the second and third of six, the fourth of five, and the fifth of four joints; the second finger two-thirds the length of the arm-bones. The skull of the young animal is much shorter and broader than in the adult (Flower, Trans. Zool. Soc. vol. vi. tab. 57). 1. Catodon macrocephalus. B.M. Catodon macrocephalus, _Gray_, _l. c._ pp. 196 (f. 54), 202, 387; _Synops. Whales & Dolph._ p. 4. Physeter macrocephalus, _Flower_, _Trans. Zool. Soc._ vol. vi. p. 309, tab. 55 to 61, and woodcuts. Inhab. Tropical seas, accidentally in the temperate ones. Mr. Flower (Trans. Zool. Soc. vol. vi.) considers _C. australis_, Gray, _l. c._ p. 206, fig. 55, the same species; and certainly there does not appear to be any character in the skeleton to divide them. Maury remarks:—“The Sperm-Whale, according to the result of this chart, appears never to double the Cape of Good Hope. It doubles Cape Horn. Since this fish delights in warm water, shall we not expect to find off Cape Horn an under-current of warm water heavier with its salt?”—_Maury_, _Whale-Charts_, p. 267.