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Show IS'90.] ON A FORMULA FOR GEOGRAPHICAL DISTRIBUTION. 607 The horns are much stronger and larger than in our specimens of Cervicapra redunca ; their basal portion is somewhat flattened from the front backwards, but similarly corrugated; they diverge very slightly, and have their points strongly curved forwards. The skull of a female x\ntelope brought home by Capt. Spekeand given to the Museum in 1863 evidently belongs to the same species l; it has the basal portion of the nasal bones raised into a slight convexity, whilst this part is flat in the male. A similar sexual difference exists in the skulls of Cervicapra arundinacea. Sir Samuel Baker seems to have met with the same species, to judge from the sketch which he has kindly given me of a skull in his possession. In the notes added to this sketch he states that the Antelope is of the size of a Fallow-deer, and that its native name among the Madi tribe is "Oboor; " that it is never seen in herds, but generally in pairs, excepting when a young calf is with the parents. He found it between 4° and 2° 30' N. lat. 5. A Graphic Formula to express Geographical Distribution. B y P. C H A L M E R S M I T C H E L L , B.A., Senior Demonstrator in the Morphological Laboratory, Oxford. (Communicated by F. E . B E D D A R D , M . A V Prosector to the Society.) [Eeceived September 26, 1890.] In lecturing on the Geographical Distribution of x\nimals, I have found pictorial representation of the facts a considerable difficulty. The construction of a sufficient number of coloured maps is troublesome and tedious, and it is impossible for students to copy them. I have designed a graphic formula to supply their place. The formula can be drawn, copied, or printed with great ease. Take a map of the world on Mercator's projection and draw across it an equatorial line. Through the middle of this let a vertical line be drawn at right angles to the equatorial line. Next let the lower right-hand space be bisected by a vertical line, and let the space to the right of this new line be bisected by a horizontal line. These lines map out the world into the zoogeographical regions. As the relative positions of the spaces correspond to the relative positions of the regions, it is unnecessary in the formula to inscribe in them the names of the regions represented. A set of lines which can 1 This skull is referred to in Sclater's list of the animals observed by and Grant (Proc. Zool. Soc. 1864, p. 103) as no. 23, Kobus sp. ?, with a note by Speke "that its native name is Ndjezza, and that it is found among the grasses near water in Uganda." Speke, however, was mistaken in thinking that he met with females only of this Antelope, for it is evident that the " Heleotragus rcduncus " (no. 20 of the same list), of which Grant shot an example in Usagarn,, was a male of Cervicapra bohor. |