1N90.] 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 Antelope brought home by Capt. Spekeand 

 given to the Museum in 1863 evidently belongs to the same species ^ ; 

 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 urundhiacea. 



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 " Ohoor ; " 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 Geograpliical Distribution. 

 By P. Chalmers Mitchell, B.A., Senior Demonstrator 

 in the Morphological Laboratory, Oxford. (Communi- 

 cated by F. E. BeddarDj M, A., Prosector to the Society.) 



[Received September 26, 1800.] 



In lecturing on the Geographical Distribution of Animals, I have 

 found pictorial representation of the facts a considerable difficulty. 

 The construction of a sufficient number of coloured maps is trouble- 

 some 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 Selater's list of the animals observed by Speke 

 and Grant (Proc. Zool. Soc. 1864, p. 103) as no. 23, Kohus 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, f(jr it is evident that the " Helcufrugiis 

 redimcua" {no. 20 of the same list),of wjiich Grant shot an example in Usagar.'i,, 

 was a male of Cervk-aj^ra bvhur. 



41* 



