Arvicanthis Lesson, 1842 . Nouv. Tabi. Regn. Anim. Mammalifères, p. 147.

TYPE SPECIES: Lemmus niloticus Desmarest, 1822 .

SYNONYMS: Isomys .

COMMENTS: Opinions on the number of species in the genus have varied from one (Misonne, 1974) to several (Allen, 1939; Corbet and Hill, 1991; Dollman, 1911; Ellerman, 1941; Rousseau, 1983). The first, and in many ways still most useful, review of Arvicanthis was made by Dollman (1911). Several recent attempts to assess variability in the genus using breeding studies (Petter et al., 1969), morphometric analyses (Rousseau, 1983), chromosomal evidence (Capanna and Civitelli, 1988; Orlov et al., 1992; Volobouev et al., 1987; and references therein), and electrophoretic patterns of blood proteins (Kaminski et al., 1984) have provided partial insights into species-diversity within Arvicanthis, as have results obtained based on examination of museum specimens (focusing on qualitative traits as well as external and craniodental measurements), and study of the discussions by Dollman (1911), Hollister (1919), Osgood (1936), and Corbet and Yalden (1972). Of the five species we list, three ( abyssinicus, blicki, and somalicus) are easily diagnosed and recognizable, but two ( niloticus and nairobae) are not and the geographic ranges and synonyms we provide for each of them are provisional until a sound systematic revision becomes available.