Akodontini. Type species of this neglected genus, based on a fossil form, incorrectly synonymized under the phyllotine Calomys callosus by Hershkovitz (1962), an allocation followed by McKenna and Bell (1997), but identification as akodontine and generic priority over Bolomys earlier reestablished by Massoia (1985). Diagnostic dental traits, lectotype selection, nomenclatural history, and allocation of fossil and living species provided by Massoia and Pardiñas (1993). Those authors referred to conifer as a nomen dubium, a misleading choice of words because the meaning clearly intended in their discussion is that the fossil is not certainly identifiable with a living species, namely N. benefactus which today occurs in the same region as conifer.

Allocation of amoenus to Necromys, and by extension the junior synonymy of Bolomys, is weakened by certain phylogenetic iterations of cytochrome b sequence data (Smith and Patton, 1993) but not others (D’Elía, 2003; D’Elía et al., 2003; Smith and Patton, 1999). Whether species in high Andean grasslands (Bolomys) and those in the S lowland savannas (Necromys) form monophyletic, diagnosable clades with respect to one another and to Akodon proper will require broader sampling of critical taxa. The issue parallels the evolutionary and systematic questions involving Andean Thomasomys and those ‘thomasomyine’ forms isolated in SE South America (see remarks under Delomys). Sister genus to the clade Akodon Thaptomys (Smith and Patton, 1993, 1999), to Thaptomys (D’Elía et al., 2003), or to Thalpomys (D’Elía, 2003) according to gene sequence studies.

Contains species conventionally known in the recent literature under Bolomys, a taxon recognized either as a subgenus of Akodon (Cabrera, 1961; Ellerman, 1941) or as an akodontine genus (Gyldenstolpe, 1932; Musser and Carleton, 1993; Reig, 1987; Thomas, 1916). Emendation of diagnostic traits, synonymy of Cabreramys, and provisional list of species presented by Reig (1987). Complex taxonomic history and diagnosis further refined based on Bolivian species by Anderson and Olds (1989) and on Argentinian and Uruguayan forms by Galliari and Pardiñas (2000). Chromosomal traits and invalid karyotypic references reviewed by Maia and Langguth (1981) and Reig (1987). Species recognized here largely observe the generic review of Galliari and Pardiñas (2000).