The Thespian grass mouse is gray-brown, with little contrast between back and belly and a long tail. It is recorded in humid Yungas forests from southern Peru into Bolivia.
The account describes a uniformly gray-brown coat with little contrast between back and belly, no eye-ring, a whitish chin spot in many specimens, and a dark tail about as long as the head and body.
Records extend from humid Yungas cloud forest to the edge of high-elevation grasslands. In Bolivia, animals were trapped on a humid forest floor; one was found in grassland near a stream.
Near Yanahuaya in southern Peru, it was collected in forest with epiphyte-laden trees, Cecropia, bamboos and tree ferns.
The head and muzzle are long and the eyes small, giving it a different appearance from many close relatives with blunter snouts.
An extinction-risk assessment has not been added yet.