The dorsal pelage is dark brownish gray, and the underside is white, with dark bases to individual hairs. Head and body length averages 85 mm and the tail length 54 mm. Animals are sexually mature by 60 days age. The estrous cycle is five days. Gestation is 22 days, except in lactating females where it is delayed by 4-5 days to 26 or 27 days.
Breeding is optimized when animals are continuously retained in breeding pairs.
The females enter postpartum estrus about 12 hours after delivery and remate. Thus, serial litters are born at 26-27 day intervals. There may be a lag in breeding during midwinter under natural lighting. Mean number per litter is 4.2. Usual litters are 3-6 and rarely exceed 8.