1891. J MAMMALS FROM EASTERN AFRICA. 185 



Colour a coarsely grizzled brownish yellow mixed with black, the 

 grizzling appearing all the coarser from the great length of the fur. 

 Longer hairs on centre of back black-tipped, those on sides yellow- 

 tipped. Bases of hairs all over, above and below, pale slaty grey for 

 seven-eighths of their length ; tips of belly-hairs dirty yellow. Ears, 

 as usual, large and rounded. Tail short, bicolor, black along the top, 

 shining greyish white along the sides and under surface. 



Skull very much as in O. irroratus, but the bones rather lighter 

 and more delicate. 



Teeth. Upper incisors narrower and flatter in front than in 

 O. irroratus ; their anterior faces each with one deep groove in the 

 position of that of O. irroratus, a faint internal one also as in that 

 species, and between the two a third very faint and indistinct one, 

 just flattening the part of the tooth that is most convex in the allied 

 species. Lower incisors each with two deep and distinct grooves, 

 the outer one clearly corresponding to the single groove in O. ir- 

 roratus, the inner one running along the part that is so prominently 

 convex in that species. Lamina formula of molars ^^j as in all the 

 present set of O. irroratus. 



Dimensions : — Head and body approximately 120 millim. ; tail (of 

 b, that of a being broken) 4/ ; hind foot 25'5. 



Skull. Basal length .31-4, greatest breadth 18" 1 ; nasals, length 

 16, breadth 6'2; interorbital breadth 4 ; interparietal, length 4'9, 

 breadth 9"5; anterior palatine foramen &b; diastema 7'7 ; length 

 of upper molar series (crowns only) 7'8 ; combined breadth of upper 

 incisors 3"6 ; lower jaw, condyle to incisor tip 23'8. 



As already shown, the more numerously grooved incisors separate 

 this new species at once from O. irroratus, while O. brantsii, Smith, 

 and O. unisulcatus, F. Cuv., the only other species recognized, have 

 incisors even less grooved than in the form to which I have com- 

 pared it. It represents therefore a most interesting step towards 

 Oreomys typus, Heugl,^, a native of the high mountains of Abyssinia, 

 which has no less than three deep grooves on each of its incisors 

 and a lamina formula of ^^ ; in fact its discovery may necessitate 

 the union of " Oreomys " with Otomys, the number of incisor grooves 

 being in this group evidently not a generic, but only a specific 

 character. Without having examined a specimen of Heuglin's 

 animal, however, and only from his description, I do not care for the 

 present definitely to abolish the genus. 



This striking new species is one of the many important zoological 

 discoveries made by Mr. Jackson during his ascent of Mount Elgon 

 in January 1890, and it is with much pleasure that I connect with 

 it the name of so distinguished an explorer and naturalist as he has 

 proved himself to be. 



<■ Eeise N.O.-Afr. ii. p. 76 (1877). 



^ Heuglin, in his description, stated that there were 4 upper molars present 

 in Oreomys, with a lamina formula of 3-2-3-5 ; but he had evidently mistaken 

 the long posterior tooth for two, and I have therefore corrected his formula into 

 that above given. 



