2n = 62, FNa = 76 (Volobouev et al., 2002a). This is the species separated from A. niloticus and identified as chromosomal type ANI-4, and the subject of studies incorporating data from chromosomes, allozymes, mtDNA cytochrome b sequences, and morphometrics (Capanna et al., 1996b; Capula et al., 1997; Civitelli et al., 1995; Corti et al., 1996b; Ducroz et al., 1998; Fadda and Corti, 2001; Garagna et al., 1999; Volobouev et al., 2002a). This species and A. blicki are the largest in body size among the species of Arvicanthis (Fadda and Corti, 2001). Phylogenetic analysis of mtDNA cytochrome b sequences by Ducroz et al. (1998) indicated that A. rufinus is most closely related to samples from the Central African Republic (2n = 58, FNa = 70), an affinity also supported by chromosomal data even though the karyotypes seem very different (Volobouev et al., 1987, 2002a), but contradicted by three-dimensional geometric morphometric analysis (Fadda and Corti, 2001). All available data, including morphometrics (Fadda and Corti, 2001) point to the Central African Republic sample as representing a distinct species, but additional and larger samples from Central Africa must be analyzed before a name can be applied to it (Volobouev et al., 2002a).

Only the holotype of mordax was included in the morphometric study by Fadda and Corti (2001) and shown to match specimens with the cytotype ANI-4; the other scientific names associated with this species are based on holotypes collected from places within the known range of ANI-4 and were not employed in any of the analyses cited above. No other species of Arvicanthis is known to be sympatric with A. rufinus so the assignment of these names seems reasonable.