300 Mr. O. Thomas on the 



the others hy cliaracters of sucli value tliat I now tliiiik tlioy 

 shouM be distinguished generically. The new genus might 

 be called ChceromySy with genotype C. gregoriamis {T. grego- 

 rianus, Thos.). 



Its skull differs in several important respects from that of 

 ThryonomySy the chief being the almost complete absence of 

 the large frontal sinuses present in the latter, and so develo[)ed 

 as to produce a totally different shape of the opening that 

 leads from the cerebral to the olfactory fossa of the skull. 

 This opening is narrow below and broad above in C/iceromi/s, 

 broad below and narrow above in Thryonoim/s, where ils 

 upper corners have been compressed by the large frontal 

 sinuses. Owing to this absence of sinuses tike frontal area 

 is flat instead of convex, while there is also the difference in 

 the position of the incisive grooves mentioned in the original 

 description oi gregoriamts, and now found to be constant iu all 

 the specimens referable to Choeromys. 



A further character seems to be that in Chceromys there 

 are only two pairs of mammas instead of three, but I cainiot 

 say how far this difference is likely to be constant, as only 

 one female Chmromys is available. Finally,. all the known 

 species of Chceromys have quite a short tail, barely or not 

 exceeding tiie outstretched hind foot, while in Thryonomys 

 the tail is twice this length or more. 



In Charomys the foUowitig subspecies seems to need 

 description : — 



Chceromys harrisoni congicusj subsp. n. 



Like true harrisoni of the Upper Nile and Lake region, 

 but colour much paler. 



General characters, so far as can be judged by the com- 

 parison of a female with males, very much as in harrisoiu 

 and rutschuricus, which appear to be rather doubtlully 

 distinct from each other. But the colour is far paler, about 

 as in sclateri, the anterior part of the body brown, the hairs 

 tipped with buff, not the grizzled blackish of harrisoni. 

 I'oateriorly the buffy, which there covers most of the surface, 

 becomes only "pinkish buff," and not the deep ochieous butt" 

 of harrisoni and rntschuricus. ]5clow buffy wiiitisli, the 

 hairs of the inguinal rt-gion mostly whitish to the roots. 



JSkull of the general shape of that of harrisoni. 



Dimensions of ihe type : — 



Head and body 380 mm.; tail 90 ; hind foot 59. 



tikuU : greatest length b2; condylo-ineisivc kngth 72'5; 



