DESCRIPTION.--Allied to _C. petaurista_. Fur tolerably long and but loosely applied to the body. Face naked; whiskers bushy; beard short; tail very long; callosities small. Length of body (type specimen), 22 inches; tail, 26. Length of a female, 19 inches; tail, 24. General colour of head, back, and upper side of the basal part of the tail olive-green, distinctly annulated, the hairs being grey at their base, ringed above with several bars of yellowish-green and black. Face blue; nose-spot, commencing in the middle of the ridge, and extending over its sides and the upper and lower lips, yellowish-white; a black line extending up the ridge of the nose from the end of the white spot to the brow and encircling the eyes; {48}a black bar crossing the forehead from ear to ear; whiskers green; beard white; throat, chest, under side of body, inside of limbs and under side of three-fourths of the tail, greyish-white; fore-arms black; legs black; the arms and thighs of the same colour as the back; upper side of the tail beyond the basal region, and its terminal portion, black; hands and feet black. As Dr. Sclater has pointed out (_loc. cit._): "It is at once distinguishable from _C. petaurista_ by the black fore-limbs and feet, by the greenish colour on the tail above; the greenish cheeks, without any white stripe beneath the ears, and the bluish skin of the face." DISTRIBUTION.--Martin's Guenon is generally brought to Europe from the island of Fernando Po, where it is probably indigenous. It may also inhabit the neighbouring coast of Western Africa. VI. THE LUDIO GUENON. CERCOPITHECUS LUDIO. _Cercopithecus ludio_, Gray, P. Z. S., 1849, p. 8, pl. ix., fig. 1; id., P. Z. S., 1868, p. 182; id., Cat. Monkeys Brit. Mus., p. 21 (1870), Wagner, in Schreb., Säugeth. Suppl., v., p. 51 (1855); Sclater, P. Z. S., 1893, p. 245. _Cercopithecus ascanias_, Schl., Mus. Pays-Bas, vii., p. 87 (1876). CHARACTERS.--Spot on lower half of nose large, oblong, higher than broad. General colour of fur black or dark greenish-olive, minutely speckled with greyish-yellow. Face and lips blackish-blue, the nose-spot white; ridge of nose above the white spot, superciliary band, crown of head, shoulders and fore-limbs, black; outer and inner aspects of hind-limbs and extremity of tail black; chin, chest, inner side of the upper part of the arms, and under side of body, whitish; {49}whiskers black; rump and under side of the base of the tail rufous. Distinguished from _C. petaurista_ by its black limbs, reddish rump and base of tail. DISTRIBUTION.--West Africa: Cameroons and the Delta of the Niger. VII. THE BLACK-CHEEKED GUENON. CERCOPITHECUS MELANOGENYS.