In addition to the inguinal region and the inner side of the thighs, the hands, feet, and tail are often white. The outer hind toes are reduced, and there is webbing between the middle hind toes. The soles are hairy from the back of the heel to the base of the outer digits. The ears are fairly large. Each upper incisor has a deep median groove.
Females have eight mammae.
The coney rat inhabits pampas, cultivated fields, stony hills, and sandy coasts. It either digs its own burrows or utilizes, with or without modification, the abandoned burrows of Dasypus and other fossorial mammals or natural crevices and holes among the rocks. Barlow found Reithrodon to be strictly nocturnal in his study area but noted that this may simply have reflected a low population level at the time. Reithrodon is pastoral, feeding mainly on grasses, other plants with tuberous rhizomes, and roots. In Barlow's study area in Uruguay the nearness of burrows to each other suggested that Reithrodon may be variously gregarious or solitary.