78 EINAR LONNBEEG, MAMMALS COLLECTED IN CENTRAL AFRICA. 



upper incisors than the other skull, the combined breadth of both at the lower edge being 

 in the former 5,4 mm., in the latter 4,5 mm. The antero -posterior diameter of an upper 

 incisor above the worn surface is in the former case 4 mm., in the latter only 3,2 mm. 

 This proves that the difference in size is not confined to one dimension only. The differ- 

 ence is, however, probably not fundamental, but due to the more intensive wearing of the 

 larger teeth caused by gnawing on some hard material. The incisors of these animals 

 appear during their continuous growth to become larger with age as in the series of G. g. 

 hivuensis the younger animals have narrower incisors than the older. But if this is the 

 case, a very intensive wearing of the incisors by gnawing on hard material may in one 

 individual at an earlier age produce broader and stouter incisors than in average indivi- 

 duals, which have not subjected their incisors to the same degree of wearing. Consequent- 

 ly two individuals of the same age may have incisors of different size due to difference in 

 wearing. 



The frontal processes of the premaxHlary extend rather far backwards, almost as 

 far as the nasals. The raised lines on the frontals are well developed, vertical and not 

 converging at their anterior ends. The interparietal is rather small, measuring about 

 9 mm. transversally, and about 5 mm. longitudinally. Bullae rather small. 



The great variability of these Giant Rats makes it rather risky to create new forms, 

 but in this case it appears evident that a rather well defined species has been found. It 

 is easily recognized on its comparatively very small and rounded ears, its general colour- 

 ation etc. The dark-bellied G. ansorgei Thomas from Angola has much larger ears (47 

 mm. ), and larger molars (length of upper molars 12, i mm. ), and it appears also to be much 

 paler (»drab brown »). Cricetomys gamhianus elgonis Thomas has also much longer ears 

 (42 mm.) and fingers and toes white and »tail dark for about one third its length*. 



Thryonomys rutshuricus n. sp. 



Two specimens from Rutshuru (one i, the other unsexed*, skin somewhat muti- 

 lated), 18th of June 1914. 



This new species is very easily recognized on its big skull and on its very short tail 

 which latter measures only about 75 mm. from anus to tip. Its length is thus contained 

 more than six, or practically seven times in the length of the head and body, which is 

 about 520 mm., and the tail is shorter than the greatest length of the skull, which is 99,5 

 mm. (with a basal length of 85,5 mm.). 



For comparison may be mentioned that in Th. swinderianus Tbmminck, or perhaps 

 more correctly, in the specimens recorded in the literature under this probably collective 

 name, the length of the tail is stated to be contained from hardly more than two, to at 

 most four times in the length of the head and body. 



In VON Heuglin's ))Aulacod)US semij^lmatus )> the tail is about half the length of 

 the body (= head and body), »von halber Korperlange ».i 



1 Verh. d. K. Leop. Akad. d. Naturf. 1864, p. 7. 



