390 Mr. O. Thomas on the 
the others by characters of such value that I now think they 
should be distinguished generically. The new genus might 
be called Chwromys, with genotype C. gregorianus (I. grego- 
rianus, Thos.). 
Its skull differs in several important respects from that of 
Thryonomys, the chief being the almost complete absence of 
the large frontal sinuses present in the latier, and so developed 
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 Cha@romys, 
broad below and narrow above in Thryonomys, where its 
upper corners have been compressed by the large frontal 
sinuses. Owing to this absence of sinuses the 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 of gregorianus, and now found to be constant in all 
the specimens referable to Cheromys. 
A further character seems to be that in Charomys there 
are only two pairs of mammee instead of three, but I cannot 
say how far this difference is likely to be constant, as only 
one female Ch@romys is available. Finally, all the known 
species of Chwromys have quite a short tail, barely or not 
exceeding the outstretched hind foot, while in Zhryonomys 
the tail is twice this length or more. 
In Cheromys the following subspecies seems to need 
description :— 
Cheromys harrisoni congicus, subsp. n. 
Like true harrisont 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 harrisont 
and rutschuricus, which appear to be rather doubtfully 
distinct from each other. But the colour is far paler, about 
as in sclatert, the anterior part of the body brown, the hairs 
tipped with buff, not the grizzled blackish of harrisoni. 
Posteriorly the buffy, which there covers most of the surface, 
becomes only “ pinkish buff,” and not the deep ochreous buff 
of harrisoni and rutschuricus. Below buffy whitish, the 
hairs of the inguinal region mostly whitish to the roots. 
Skull of the general shape of that of harrisond. 
Dimensions of the type :— 
Head and body 380 mm.; tail 90; hind foot 59. 
Skull: greatest length 82; condylo-incisive length 72:5; 
