1892.] MR. O. THOMAS ON MAMMALS FROM NYASSALAND. 551 



16. ISOMYS DORSALIS, A. Soi. 



a. Ad. al. 2 . 

 . It appears on the whole more convenient to recognize Isomys as 

 a genus distinct from JSIus, as it unquestionably is a natural group, 

 and no species really intermediate between the two are known. 

 Troue5sart'sie;»«J5co?«ys I include, of course, with Isomys, as, apart 

 from the small value of striation as a generic character, certain of 

 the species (e. g. I. abyssinicus and I. variegatiis) are quite inter- 

 mediate even iu this character. 



17. IsoMYS PUMiLio, Sparrm. 



a-e. 5 ad. sk. Milanji Plateau, 6000 ft. 27l\Ql-2IUl9\. 



" The common Rat of the Milanji Plateau, 6000 feet ; has a 

 metallic chirp very similar to the Warblers or Tailor-birds of Ceylon, 

 and I was sure at first that tlie noise came from a bird," — A. Whyte. 



These specimens, although rather smaller and more brightly 

 and definitely marked, may be fairly assigned to the typical Cape 

 I. pumilio ; but the same cannot be said of some other specimens 

 hitherto referred to that form, which these beautiful specimens have 

 enabled me more carefully to examine and compare, and which I 

 now consider to represent two distinct subspecies, and may take this 

 opportunity of describing. 



The first is a northern form, based on two specimens taken much 

 further north than the species was otherwise known to occur, 

 namely in Masailand, near Lake Naivasha. It may be called — 



Isomys pumilio dimimitus, subsp. n. 



Size decidedly smaller, and tail shorter, than in typical Cape 

 examples. Ground-colour of body strongly suffused with yellowish 

 orange, especially on the rump. Inner surface of ear rich fulvous, 

 and a tuft of similarly-coloured hairs at the anterior base ; anterior 

 margin of outer surface shining black, as usual. Dorsal lines fairly 

 distinct, the lighter ones pale greyish white, the median and the 

 lateral of much the same tone. Tail, as usual, blackish brown above, 

 yellowish white on the sides and below. 



Dimensions of the typical skin. — Head and body 94 mm. ; tail 62 ; 

 hind foot 20-2. 



Hah. Mianzini, just east of Lake Naivasha, Masailand. 



Coll. F. J. Jackson. August, 1889. 



The second subspecies is an inhabitant of Bechuanaland, Central 

 South Africa, and its colour peculiarities are those characteristic 

 of the desert representatives of striped forms in all parts of the 

 world : — 



Isomys p. hechuancB, subsp. n. 



Size large ; feet and tail much elongated ; the latter nearly twice 

 as long as iu I. p. diminutus. General colour sandy or fawn-grey. 



