Scapteromys tumidus (Waterhouse, 1837) . Proc. Zool. Soc. Lond., 1837:15.

TYPE LOCALITY: Uruguay, Maldonado .

DISTRIBUTION: Southernmost Brazil (Rio Grande do Sul), Uruguay and adjacent Argentina, E Paraguay.

SYNONYMS: aquaticus .

COMMENTS: Distribution and morphological identity reviewed by Hershkovitz (1966c). Massoia and Fornes (1964) realigned aquaticus as a subspecies of S. tumidus . The taxonomic significance of the reported karyotypic differences between aquaticus and tumidus warrants re-examination (see Brum et al., 1973, and Gentile de Fronza, 1970).