In the brain the whole of the cerebellum and the olfactory lobes are covered by the cerebrum. In general form the latter resembles that of the species of _Cebus_. The frontal and occipital regions of the skull approximate in form to those in Man; the angle of the mandible is expanded, but less so than among the Howlers (_Mycetes_). The ribs are relatively broader in this genus than in any other of the American Monkeys. I. THE HAIRY SAKI. PITHECIA MONACHUS. _Simia monachus_, Humb. and Bonpl., Obs. Zool., p. 359 (1811). {183}_Pithecia monachus_, Geoffr., Ann. Mus., xix., p. 116 (1812); Flower, P. Z. S., 1862, p. 326, pl. xxxvii.; Gray, Cat. Monkeys Brit. Mus., p. 59 (1870). _Pithecia hirsuta_, Spix, Sim. et Vespert. Bras., p. 14, pl. 9 (1823). _Pithecia inusta_, Spix, t. c. p. 15, pl. x. (1823). _Pithecia irrorata_, Gray, Voy. Sulphur, Zool., p. 14, pl. 3 (1844). _Pithecia albicans_, Gray, P. Z. S., 1860, p. 231, pl. lxxxi. _Pithecia monacha_, Schl., Mus. Pays Bas, vii., p. 220 (1876). CHARACTERS.--Fur harsh, long and loose, with a hood of forwardly-directed hairs on the upper part of the head, neck, and shoulders. Face bare, long, and narrow; nose large and full; nostrils widely separated and lateral. Face dark purplish-brown, and black on the nose, paler round the eyes, and sparingly covered with short coarse whitish hairs; a yellowish-white patch on the cheeks, terminating in front in a distinct line from the inner corner of the eye to below the angle of the mouth; margin of upper lips white; ears large, round, naked, and of the same colour as the face; upper part and back of head, neck, shoulders, back, arms, thighs, and tail, black, washed with yellowish-white, becoming yellowish-brown on the hinder part of the body. Throat, breast, under side of body, and inside of thighs, pale yellowish-brown, sparingly haired. Tail 18 inches long, cylindrical, and bushy at the end; the hair long, coarse, curled, black, washed with pale yellowish-brown. Legs black; fore-arm black, washed with white; upper surface of hands, feet, and digits, white. Hands small, thumbs short, parallel to the other fingers; nails black, somewhat compressed, pointed, that of the thumb flatter; great-toe well developed, standing apart from the other toes, its nail flat {184}and pointed; nails of the other toes long, curved, and compressed. DISTRIBUTION.--Mr. Bates states that the "Parauacú," as this Monkey is called by the natives of its own country, is found on the "terra firma" lands of the north shore of the Solimoens, or Upper Amazon, from Tunantins to Peru. It exists also on the south side of the river on the banks of the Teffé, but there under a changed form, which differs from its type in colours, as much as the red differs from the white Uakarí. This variety is Dr. Gray's _Pithecia albicans_.