Like many other characteristic animals of North-eastern Africa, the present Antelope was one of the discoveries of the great explorer and naturalist Rüppell, who first described it in his volume upon new Mammals from Abyssinia which contained the results of his long investigations in that country. Rüppell called this species “_decula_,” from the Latin transliteration of its Amharic native name, remarking at the same time that this word must not be confounded with “_thecula_,” which is the Abyssinian name for the Hunting-dog (_Lycaon pictus_). He remarks that the species belongs to the subgenus _Tragelaphus_ of Blainville, and is closely allied to _T. sylvaticus_ of the Cape, from which it is distinguishable by its smaller size and different colouring. Rüppell obtained a good series of this Antelope, and gives excellent descriptions of the adult male, the adult female, the two-year-old male, and the newly-born calf. He met with it in the bushy valleys of Central Abyssinia, round the lake of Dembea or Tana, where it feeds principally on small leaves of trees, and is said to be specially fond of the ripe fallen fruits of the sycamore fig-tree. The Deculas pair in the month of May in this district, and produce their young ones in October. They are very quick and shy, but are occasionally hunted by the natives with dogs. Their flesh, according to Rüppell, is not particularly palatable. The only other African explorer that appears to have come across this Antelope in its native wilds is Heuglin, who, however, does not favour us with a very distinct account of his experiences of it. In his memoir on the Antelopes and Buffaloes of North-east Africa, published in 1863, Heuglin states that the range of this species extends over the districts of Upper Nubia bordering on Abyssinia, Galabat, the River Settite, and Takeh. He also gives a figure of the skull of a specimen obtained by him, which he points out differs slightly in the shape of the horns from that figured by Rüppell and in some other particulars. In a subsequent work (‘Reise in Nordost-Afrika’) Heuglin has described what he considered to be possibly a different animal (although closely allied to the Abyssinian _T. decula_) from the banks of the White Nile, where it is called by the Djengs “_Bor_,” in Bonga “_Towa_,” and by the Dgurs “_Burah_.” This Antelope he met with in pairs amongst the high grass and thick bushes of _Bauhinia_ and _Acacia_-trees in the above-named districts. In case of its proving different from _T. decula_ he proposed to designate it _Tragelaphus bor_. As will be seen by our subsequent remarks, it is not quite certain which of the species of this group of _Tragelaphus_ occurs on the White Nile. It may be either the present _T. decula_ or one of the forms of _T. scriptus_.