Arvicanthis nairobae J. A. Allen, 1909 . Bull. Am. Mus. Nat. Hist., 26:168.

TYPE LOCALITY: Kenya, Nairobi .

DISTRIBUTION: Recorded in and east of the Rift Valley from Mount Lololokwi ("an isolated mountain east of the Mathews Range, about midway between Mount Kenia and Mount Marsabit," Hollister, 1919) in C Kenya south to the Dodoma region in EC Tanzania; N and S limits unknown.

SYNONYMS: chanleri, pallescens, praeceps, virescens.

COMMENTS: The name nairobae is the oldest applicable to samples from east of the Rift Valley in Kenya and Tanzania containing animals smaller in body size and gererally brighter and buffier in pelage than those larger and darker specimens we have identified as A. niloticus from west of the Rift. Some specimens of A. nairobae closely resemble those of A. somalicus in pelage coloration, and might be mistaken for it, but are larger in body size. Corbet and Yalden (1972) even suggested that chanleri might represent somalicus, but the holotype is larger and fits within the range of variation seen among samples of nairobae . Records of sympatry between nairobae and somalicus are documented by series from Mount Lololokwi (specimens in the National Museum of Natural History), and the Dodoma region of Tanzania (samples in the American Museum of Natural History), and the two are probably broadly sympatric throughout their ranges in Kenya and Tanzania.

The morphological and geographic relationships between A. nairobae and A. niloticus require resolution, which could be accomplished by systematic review of the niloticus-nairobae complex. For example, nairobae is found with A. somalicus in the Dodoma region and they are the only species of Arvicanthis represented by specimens from E Tanzania. In contrast, samples from the Tabora area, to the west of Dodoma, contain A. somalicus and a species significantly larger in body size with darker pelage than samples of A. nairobae from Dodoma. It is this larger species that ranges south into Zambia and north through W Tanzania, W Kenya, and Uganda. Studying the distribution of characters from samples collected along a transect between the Dodoma and Tabora regions would elucidate character and geographic relationships between the two kinds.