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Show 1892.] MR. O. THOMAS ON MAMMALS FROM NYASSALAND, 551 16. ISOMYS DORSALIS, A. Sm. a. Ad. al. $ . It appears on the whole more convenient to recognize Isomys as a genus distinct from Mus, as it unquestionably is a natural group, and no species really intermediate between the two are known. Tra^iSM-Vs Lemniscomys 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. variegatus) are quite intermediate even in this character. 17. ISOMYS PUMILIO, Sparrm. a-e. 5 ad. sk. Milanji Plateau, 6000 ft. 27/10/-2/11/91. " 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 the 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 diminutus, 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. Hab. 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. bechuanee, subsp. n. Size large ; feet and tail much elongated; the latter nearly twice as long as in I". p> diminutus. General colour sandy or fawn-grey, |
