Subgenus Acomys. Formerly included in A. cahirinus (Setzer, 1975) or A. cineraceus (Musser and Carleton, 1993). Recently, Sicard and Tranier (1996) provided a detailed report on the geographic distribution of three pelage color phenotypes of Acomys occurring in Burkina Faso (all with 2n = 66 or 68; also see Gautun et al., 1986), assigned them to A. johannis, and contrasted their external, cranial, and dental morphology with A. chudeaui (2n = 42), A. airensis (2n = 40 to 46) and the Algerian A. seurati (2n = 38). Using mtDNA cytochrome b sequences, Barome et al. (2000) identified the specimens from Burkina Faso as Acomys sp. and specimens from Niger, Benin, Cameroon, and Niger as A. johannis. This species is a member of the A. cahirinus-A. dimidiatus group (Barome et al., 2000) and different from either A. cahirinus or A. cineraceus, but it needs to be more clearly diagnosed and its geographic range delineated.
Sicard and Tranier (1996) were impressed with the close similarity in cranial and dental traits between A. johannis from Burkina Faso and A. mullah from Ethiopia and Somalia. This observation may be significant because Sokolov et al. (1992, 1993) karyotyped specimens of Acomys from the Ethiopian Rift Valley. Several samples characterized as 2n = 36 were determined to be A. cahirinus, and another sample with 2n = 68 was identified only as Acomys sp. If the latter is A. mullah, which occurs in Ethiopia, it would corroborate the morphological alliance suggested by Sicard and Tranier. In addition to A. cahirinus and A. mullah, only A. cineraceus (2n = 48 or 50; Kunze et al., 1999a, b), A. wilsoni (2n = 50; Matthey, 1968), and A. percivali (karyotype unknown) have been recorded from Ethiopia.