How far the Black-rumped Duiker extends over the forests of the Congo basin is, as yet, quite uncertain. The authorities of the Congo Free State have, up to the present time, persistently neglected to obtain any accurate information of the zoology of the great region which they have occupied. The little we know of the animals of this wide area is based upon fragmentary specimens obtained by passing explorers. It is very probable, however, that _C. melanorheus_ may range over nearly the whole of the great woody basin of the Congo and its tributaries. But when we come to the eastern slope of Africa, from various parts of which specimens referred to this species have been received, we meet, as Sundevall has pointed out, with a slightly different form, which for the present it is proposed to regard as a subspecies (following Fitzinger) as _Cephalophus melanorheus sundevalli_. The fact is that, as regards these small Duikers, a far better series from the various points of their range must be rendered accessible before we can come to any accurate determination as to their systematic arrangement and distribution. Herr Matschie informs us that some specimens received in Berlin from Dar-es-Salaam, in German East Africa, rather more resemble _C. monticola_ than _C. melanorheus_; so here is another riddle yet unsolved. _August, 1895._ 34. THE UGANDA DUIKER. CEPHALOPHUS ÆQUATORIALIS, MATSCH. _Antilope grimmia_, =Schweinf.= Herz. v. Afrika, i. p. 267 (fig. of head), ii. p. 535 (1874). _Cephalolophus æquatorialis_, =Matsch.= SB. Ges. nat. Freund. 1892, p. 112 (Chagwè); =Scott-Elliot=, P. Z. S. 1895, p. 341. _Cephalophus æquinoctialis_, =Lyd.= Horns and Hoofs, p. 209 (1893). VERNACULAR NAME:--“_Mtelaganya_” in Uganda (_O. Neumann_). Similar to _C. melanorheus_ in almost all respects, but the under surface only little lighter than the upper, and the female, at least in all the three specimens known, entirely without horns. Dimensions (from Matschie):--“Height at shoulder 10–12 inches, height on rump 12–13.” Skull (♀): basal length 4·14 inches, greatest breadth 2·16, muzzle to orbit 2·34. Horns of a male 1¼ inch long, half an inch thick at the base (_Matschie_). _Hab._ Uganda.