Coloration is dark buffy above and gray below. The body form is stocky.
Females have eight mammae.
This genus resembles Punomys but can be distinguished by its longer tail. The Andean mouse lives on the Altiplano at elevations of 1,675-4,850 meters. It has been captured among rocks on the bank of a stream and in bushy thickets. It is nocturnal. Collectors have remarked that it lives in the branches of trees, where it makes its nest, and in round holes carpeted with very fine straw.