DISTRIBUTION.--North-east Africa: Kordofan and Darfur, to a height of 3,000 feet above the sea. A specimen living in the Zoological Gardens in 1882 was stated to have come from Somali-land. Allied to the Patas and the Nisnas is Peters' Guenon (_Cercopithecus ochraceus_, Peters, Reis. Mossamb. Säugeth., p. 2, pl. 1a), from Querimba, Mozambique, which has the upper side yellowish, and is probably but a variety of _C. pyrrhonotus_. XXI. THE REDDISH-GREEN GUENON. CERCOPITHECUS RUFO-VIRIDIS. _Cercopithecus rufo-viridis_, Geoffr., C. R., xv., p. 1038 (1842); id. Dict. Hist. Nat., iii., p. 307 (1849); Schl., Mus. Pays-Bas, vii., p. 78 (1876); Scl., P. Z. S., 1893, p. 258. _Chlorocebus rufo-viridis_, Gray, Cat. Monkeys Brit. Mus., p. 25 (1870). _? Cercopithecus flavidus_, Peters, Reis. Mossamb., p. 3, pl. i.b. CHARACTERS.--Face black; a large frontal band white; head above olive-green; back green washed with rufous, gradually becoming bright rufous, slightly speckled with black on the sides {66}of the body between the fore- and hind-limbs; shoulders and thighs grey, washed with green; the rest of the external aspect of the limbs grey; under side of body and inner side of limbs white; hands speckled black; the feet greyish; tail, dark grey above, pale grey below. DISTRIBUTION AND HABITS.--Unknown. The form described by Peters as _C. flavidus_ comes from Mozambique. IV. CERCOPITHECI MELANOCHIRI. The species which we now proceed to describe belong to Prof. Schlegel's Section v., and Dr. Sclater's _Cercopitheci melanochiri_, of which the members have the arms and legs either black or dark grey, and have a black band from the outer corner of the eyes to the ears. XXII. THE MONA GUENON. CERCOPITHECUS MONA. _Simia mona_, Schreber, Säugeth., i., p. 97, pl. xv. (1775). _Cercopithecus mona_, Erxleb. Syst. Regne An., p. 32 (1777); Geoffr., Dict. Hist. Nat., p. 304 (1849); Martin, Mammif. An., p. 527 (1841); Wagner, in Schreb. Säugeth. Suppl., v., p. 47 (1855); Gray, Cat. Monkeys Brit. Mus., p. 22 (1870); Schleg., Mus. Pays-Bas, vii., p. 80 (1876); Sclater, P. Z. S., 1893, p. 250. _La mone_, F. Cuvier, Hist. Nat. Mamm., i., livr. ix. (Août, 1819).