TYPE MATERIAL AND TYPE LOCALITY: BMNH 4.1.5.48, the holotype by original designation, consists of the skin and skull of an adult male collected at “Sapucay” (= Sapucaí, at 25.67° S, 56.92° W; ca. 220 m), Paraguarí province, Paraguay.

SYNONYMS: ignitus Díaz et al., 2002.

DISTRIBUTION: Cryptonanus chacoensis occurs in grasslands and dry forests from central Brazil to Paraguay and northern Argentina (Fegies et al., 2021: fig. 1); the species might also occur in Uruguay (see Remarks).

REMARKS: For an emended description see Voss et al. (2005), who also tabulated measurement data from nine specimens. DNA sequence data obtained from the holotype of Cryptonanus ignitus (originally described as a distinct species), together with new information about ontogenetic character variation in C. chacoensis provide compelling evidence that these taxa are conspecific (Teta and Díaz-Nieto, 2019). Phylogenetic analyses of multilocus sequence data also suggest that specimens referrable to C. chacoensis belong to four morphologically cryptic phylogroups that probably diverged in the Middle Pleistocene (Fegies et al., 2021). Two of these phylogroups are known to contact one another in central Brazil, but the taxonomic interpretation of sympatrically collected specimens is not clear due to mitonuclear discordance. The identity of the Uruguayan specimens reported by D’Elía and Martínez, 2006) has yet to be determined, but some of them could be C. chacoensis.