Reithrodontomyini. Genus viewed as closely related to Peromyscus, whether defined broadly (Hooper and Musser, 1964b) or narrowly (Carleton, 1980). Cladistic interpretations of banded chromosomes have not corroborated so close an affinity (Rogers et al., 1984; Stangl and Baker, 1984b), but those of mitochondrial and nuclear gene sequences continue to support near kinship (Allard and Honeycutt, 1991; D’Elía, 2003; Engel et al., 1998; Smith and Patton, 1999), although the sampling of critical exemplars in the latter studies can be much improved.

Alpha taxonomy revised by Allen (1895), Howell (1914), and Hooper (1952), the last of whom framed the currently-used subgeneric division (Aporodon and Reithrodontomys) and species groups (megalotis, fulvescens, mexicanus, and tenuirostris). For comparative studies of morphology, see Arata (1964), Carleton (1973, 1980), and Hooper (1952, 1959); of karyology, see Carleton and Myers (1979), Engstrom et al. (1981), Hood et al. (1984), and Robbins and Baker (1980); of allozymic variation, see Arellano et al. (2003), Arnold et al. (1983), and Nelson et al. (1984); of gene-sequence data, see Bell et al. (2001). In general, the aforementioned studies and information sources lack the taxonomic breadth or data structure appropriate to critically test the phyletic validity of the subgeneric dichotomy and all four species groups proposed by Hooper (1952). We repeat his intrageneric classification as the last synoptic treatment, bearing that caveat in mind: e.g., Carleton and Myers (1979) recommended research emphasis upon species-group associations and their interrelationships instead of the two subgenera. Distributions and species limits of all species groups in Middle America require renewed systematic attention. A key to the species is found in Spencer and Cameron (1982); ecogeographic distributions of Mexican species reviewed by Sánchez (1993).