TYPE MATERIAL AND TYPE LOCALITY: MVZ 144311, the neotype (designated by Voss et al., 2009a), consists of the skin and skull of an adult male collected on the Trans-Chaco Highway (Ruta Nacional 9) 460 km NW Villa Hayes (ca. 28.37° S, 60.20° W), Boquerón department, Paraguay.

SYNONYMS: bruchi Thomas, 1921; citellus Thomas, 1912; nanus Olfers, 1818; pulchellus Cabrera,1934; verax Thomas, 1921.

DISTRIBUTION: As recognized herein (see Remarks), Thylamys pusillus occurs in southeastern Bolivia, western Paraguay, and northern Argentina, including the Dry Chaco, Humid Chaco, Mesopotamian Savanna, and Humid Pampas ecoregions (Teta et al., 2009: fig. 1).

REMARKS: Teta et al. (2009) recognized Thylamys citellus and T. pulchellus as valid species distinct from T. pusillus, but Giarla et al. (2010: 41–43) were unable to distinguish these allopatric taxa morphologically and, therefore, treated them as synonyms. South American authors (e.g., Palma et al., 2014) have subsequently tended to follow Teta et al. (2009), so the binomina T. citellus and T. pulchellus remain in current use. Because geographic variation in morphology and isolation by distance remain plausible explanations for the reported phenotypic and genetic differences among these nominal taxa, it still seems an appropriately conservative option to treat them as conspecific.