348 FIEl.D-XOTKS ON MAMMALS IN TIJE SOUTHERN SUDAN. 



but no further. With the first rains tliey dipappenr to the south, 

 and thougli a few may be found lingeiing well on into the 

 summer in the low country east of Mongalla (lat. 4° 30'), I am 

 of the opinion that the great majority migrate very long distances 

 towards the higher and, drier country lying in the extreme S.E. 

 of the Sudan near the East African border, Sind that somewhere 

 among these plateaux lie their summer quarters. Here they 

 come not very far from the northern range of the true thomsoni, 

 and are not separated from this animal by any natural boundary 

 so formidable as that formed by the Sobat River and its swamps, 

 which cut the species off from G. rnfifrons in the north. More- 

 over, the Mongalla Gazelle never ranges within 100 miles of the 

 Sobat River, the intermediate country being, in fact, unsuited to 

 the habits of Gazelles to a considerable degree. Probably the form 

 is almost exactly intermediate between thomsoni and ruffrons, 

 with tendencies towards the former. 



It is not found west of the Bahr-el-Gebel. 



White Rhinoceros {Rhinoceros simus). 



This animal exists all along the west bank of the Nile in the diy 

 season, but is always very rare in the area under considera,tion. 

 The natives say they drink at the river at night, and retire great 

 distances into the forest during the day. 



The above notes, which only deal with quite a small area of 

 coinitry (approximately 200 miles by 150) and have no preten- 

 sions to discuss the distribution of the animals mentioned outside 

 thereof, tend to show how peculiarly patchy even Avithin the same 

 small area the distribution of any given species tends to be, and 

 is an example on a small scale of what we often find and with as 

 little apparent reason throughout the whole continent of Africa. 



I 



