Habits and taxonomy of species of the following genera are discussed: Aconaemys, Ctenomys, Chelemys, Geoxus, and Notiomys. In degree of adaptation to a burrowing mode of life, these five Patagonian genera fall between Thomomys bottae and Microtus californicus. Sympatry occurs frequently among most of the Patagonian genera, a condition permitted by dietary, size and habitat differences. The two studied species of Ctenomys remain allopatric, as well as the two species of Aconaemys.
New specimens of Notiomys edwardsii confirm the uniqueness of that genus. Chelemys and Geoxus are considered to be generically distinct. Chelemys angustus is an Akodon, and Chelemyscus fossor is a composite of Chelemyscus macronyx (skin) and Euneomys (skull). Two distinct species of Aconaemys are recognized; one of them is described as new.