The representative of the Black-rumped Duiker in Uganda has recently been separated by Herr Matschie from _C. melanorheus_ under the name of _C. æguatorialis_ on account of its darker belly, which is stated to be of a bright isabella-brown colour, “nearly of the tint which Mr. Ridgway, in his ‘Nomenclature of Colours’ (tab. iii. no. 21), calls écru drab, and scarcely lighter in colour than the back.” The species was based upon five specimens obtained by Stuhlmann in Chagwè, Uganda, in the month of December. Dr. Stuhlmann’s note is that this Antelope lives in the forests of Uganda, and that its skins are brought in numbers to the market at Mengo. A living example of this species, we are informed by Herr Matschie, was in 1892 in the Zoological Garden of Berlin. On examining two skins of adult females of what we suppose to be the same Antelope, obtained by Capt. W. H. Williams in Uganda, and presented to the British Museum in April 1893, we do not find the character, assumed by Herr Matschie as distinctive of the species, to be quite constant. The bellies of the two specimens just referred to are scarcely darker than in West-African specimens of _C. melanorheus_. Moreover, two examples of the latter species from Cameroons, collected together, differ markedly in the coloration of their bellies. We should therefore not have been inclined to admit _C. æquatorialis_ as a distinct species were it not for the fact that the perfect skull of one of the specimens in the British Museum shows no traces of horns. This is also stated to be the case in two female specimens in the Berlin Museum upon which Herr Matschie established the species. In _C. melanorheus_, as already stated, the horns are always present in both sexes. Under these circumstances it is better to keep _C. æquatorialis_, provisionally at least, as distinct, until further information is obtained. Mr. Scott Elliot during his recent adventurous journey to Mount Ruwenzori obtained a single specimen (now in the British Museum) of this Duiker in Uganda, and has favoured us with the following note upon it:-- “The _Cephalophus_ of which I brought home the skin was obtained from some natives at Kampala, Uganda, in February 1894. It was a female. I believe it was found on the highlands bordering Lake Victoria Nyanza, at an elevation of from 3900 to 4100 feet.” _August, 1895._ 35. THE BLUE DUIKER. CEPHALOPHUS MONTICOLA (THUNB.). [PLATE XXI. FIG. 1.] _Capra monticola_, =Thunb.= Resa, ii. p. 66 (1789); =id.= Engl. Transl. ii. p. 58 (1793). _Antilope monticola_, =Thunb.= Mém. Ac. Pétersb. iii. p. 314 (1811); =Afz.= N. Act. Ups. vii. p. 220 (1815).