452 PROCEEDINGS OF THE NATIONAL MUSEUM vor,. loe 



Provo Pluvial until the present. It is thought to be approximately 



12,000 years in duration." Thus, in this period of about 12,000 

 years, differentiation has occurred in tlie pocket gophers to form the 

 complex distributional pattern of subspecies known today. During 

 a similar interval of time, the mountain forests of central Africa, 

 together with their mammalian faunas, have been isolated by the en- 

 croachment of arid savannas. The distinction between the Salt 

 Lake Valley and the isolated mountains of the wSudan is that the 

 former was invaded, then isolated, whereas the latter is a relict of a 

 former widespread habitat now isolated. In both cases, however, 

 differentiation has progressed to the point where pronounced distinc- 

 tions are evident. 



The present report recognizes 91 genera and 224 species and sub- 

 species of mammals other than bats. Of the 224 kinds known from 

 the Sudan, 39.5 percent have been described from localities outside 

 its present geographic boundaries. Of the remaining 60.5 percent, 

 described from within the boundaries of the Sudan, 11 percent have 

 been described from the Imatong Mountains and envuons, 8.6 per- 

 cent from the Jebel Marra and environs, 4.5 percent from the Nuba 

 Mountains area, and the remaining 36.4 percent from many other 

 localities. 



It is apparent that the Sudan has been populated by a mammal 

 fauna coming from several duections. The period wliich apparently 

 has had the most eft'ect on the distribution of present-day mammals 

 is the time immediately after the last Pleistocene Pluvial and up to 

 the present. Most of the mammals occurring in the Sudan today 

 apparently have invaded from the south. Characteristic genera 

 which may be noted in this category are: aard vaark (O/^ycteropus) , 

 swamp rats (Otomys), tree mice (Dendromus) , giant rats {Cricetoinys) , 

 multimammate mice (Mastomys), mole rats {Cryptomys), cane rats 

 {Thryono7nys) , and elephant (Loxodonta). 



Mammals Avhich apparently have derived from a northern palae- 

 arctic stock and which reach the southernmost limits of their distribu- 

 tion are: gerbils (subgenus Dipodillus), sand rats (Psammomys) , 

 jerboas (Jaculus), and the ibex (Capra). 



Two West African genera which reach an eastern limit of distribu- 

 tion in the Sudan are African striped squirrels (Tamiscus) and red- 

 legged ground squirrel (Euxerus). 



The grass hare (Poelagus) appears to be found only in the southern 

 Sudan and extreme northern Uganda. This is apparently the only 

 genus endemic to the region. Another genus (Desmodilliscus) is found 

 only in northern Nigeria and the central Sudan; its origin is not de- 

 terminable at this time. 



