Arvicanthis niloticus (Desmarest, 1822) . Mammalogie in Encyclop. Méth., 2:281.

TYPE LOCALITY: Egypt .

DISTRIBUTION: Specimens we examined were from S Mauritania, Senegal, and Gambia east through Sierra Leone, Ivory Coast, Ghana, Burkina Faso, Togo, Benin, Nigeria, S Niger, S Chad, Sudan, and Egypt to the western half of Ethiopia (to and in the Rift Valley); south through NE Zaire, Uganda, S Burundi, Kenya and Tanzania west of the Rift Valley, into E Zamibia, where the population is isolated from the nearest one, which is in SW Tanzania (Ansell, 1978); there is a record from N Malawi (1 skull only, living animals never found; Ansell and Dowsett, 1988); and the species occurs in SW Arabia.

SYNONYMS: ansorgei, centralis, centrosus, dembeensis, discolor, jebelae, kordofanensis, luctosus, variegatus var. major, mearnsi, variegatus var. minor, mordax, muansae, naso, nubilans, occidentalis, ochropus, pelliceus, raffertyi, reichardi, rhodesiae, rossii, rubescens, rufinus, setosus, solatus, tenebrosus, testicularis, variegatus, zaphiri .

COMMENTS: We include dembeensis, which has been recognized as a distinct species occurring in Ethiopia and nearby regions (Yalden et al., 1976; Demeter, 1983). Thomas (1910b) had once associated dembeensis with Desmomys, noting that it had already been referred to Mus, Arvicanthis, Golunda, Pelomys, and Oenomys . Later, however, Thomas (1928a) referred dembeensis to Arvicanthis, a view confirmed by Osgood (1936) and reinforced by Dieterlen (1974). The name lacernatus was once used in place of dembeensis for the Ethiopian samples of Arvicanthis (Allen, 1939; Corbet and Yalden, 1972; Osgood, 1936) but cranium of the holotype is an example of Meriones (Yalden et al., 1976) . Arvicanthis dembeensis was thought to be a separate species because Ethiopian samples were originally contrasted by Corbet and Yalden (1972, under the name lacernatus) with abyssinicus, which they treated as a subspecies of A. niloticus. However, abyssinicus is a distinctive species related to A. blicki and not to A. niloticus. We observed that the diagnostic features attributed to dembeensis also described samples of Arvicanthis from throughout Africa west and south of Ethiopia. Sympatry with other species of Arvicanthis has been recorded at several places in Uganda (Delany, 1975; Dollman, 1911; Hollister, 1919), but we cannot distinguish two kinds at the localities. The only verifiable sympatry is between the large-bodied A. niloticus and the small-bodied A. somalicus in the Rift Valley of Ethiopia (niloticus was recorded as either dembeensis or lacernatus; Corbet and Yalden, 1972; Demeter, 1983) and in the Mawele region (Mwanasomano's, 30 mi S Tabora) In C Tanzania (documented by specimens in the Museum of Comparative Zoology, Harvard). Allopatry or parapatry, however, is usual. In Ethiopia, A. niloticus occurs up to about 2000 ft and is replaced at higher elevations by A. abyssiniens and A. blicki (Rupp, 1980; Yalden et al., 1976); in Kenya and Tanzania, A. niloticus ranges west of the E Rift Valley and is allopatric with A. nairobae, found in and east of the Rift.

Our definition of A. niloticus is unsatisfactory. There is appreciable intra- and interpopulational variation in body size, pelage coloration, and cytological and biochemical traits, and the significance of this variation should be assessed by a critical systematic revision; more than one species may be present in the complex, as suggested by morphometric (Rousseau, 1983), chromosomal (Viegas-Pequignot et al., 1983; Volobouev et al., 1987) and electrophoretic (Kaminski et al., 1984) analyses. Furthermore, Corbet (1984) questioned including the Arabian naso with A. niloticus. Capanna and Civitelli (1988) recorded a karyotype with 2N=44 from a sample they identified as A. niloticus from Somalia; this contrasts with the range of 56-62 usually reported among samples of the species.