Like Harvey’s Duiker of Eastern Africa, the Black-fronted Duiker, which is its representative and close ally in the great western wood-region, carries a coat of a nearly uniform chestnut. Like _C. harveyi_, also, it has a distinct black blaze down the centre of the face, whence the appropriate name _C. nigrifrons_ has been bestowed on it. Its distinctions from Harvey’s Duiker, as pointed out by Thomas, are that it is of a much more uniform colour all over and hardly paler below, while in the last-named species the cheeks, sides of the neck, and throat are of a pale bay, and the chin is white as in _C. natalensis_. Its most striking characteristic is, however, the fact that its hoofs are very much longer than is usual in the genus, an elongation which is probably due to its inhabiting marshy and boggy regions, where its long hoofs would prevent its sinking so deeply as it otherwise would into the muddy soil. The typical specimens of this Duiker formed part of the collection made by Mr. DuChaillu during his celebrated visit to the Gaboon in 1856 and the following years, the greater part of which were ultimately acquired by the British Museum. On reference to the ‘Explorations and Adventures in Equatorial Africa’ of DuChaillu we can find no reference to it, unless, as is probable, it is alluded to as one of the “four species of Gazelle not yet determined,” which are enumerated in the appendix. When, however, DuChaillu’s specimens came under the experienced eye of the late Dr. Gray, on the occasion of his preparing a monograph of the genus _Cephalophus_ (subsequently published in the Zoological Society’s ‘Proceedings’ for 1871), it was quickly discovered that amongst them was a representative of a new and distinct species of the present genus, which was described and figured as _C. nigrifrons_. In a subsequent communication to the ‘Annals of Natural History’ in 1871, Dr. Gray described a specimen of what he believed to be another new species of _Cephalophus_ under the name of _C. aureus_. On this occasion he tells us that the specimens, both of his _C. nigrifrons_ and of his _C. aureus_, “had been sent home from Africa by Mr. DuChaillu as materials for stuffing out the skin of a specimen” of a larger Antelope (_Tragelaphus euryceros_). We believe it to be the fact that, as Sclater was assured by the late Dr. Gray, he described four new species of Antelopes from skins found in the interior of this _Tragelaphus_ when it was unstuffed for the purpose of being remounted for the collection of the British Museum. As regards the so-called _C. aureus_, however, a close examination of the typical specimen, made by Thomas in 1892, convinced him that it was a very young animal and was probably only an immature individual of the present species. We may observe, however, that its body is far brighter and more fulvous than that of the adult, that the withers and shoulders are browner, and that the caudal tuft is more abundantly mixed with white.