Any of about 30 species of nocturnal North American rodents constituting the genus Perognathus (family Heteromyidae), having fur-lined, external cheek pouches that open alongside the mouth. Pocket mice are yellowish brown to dark gray and are 2.5–5 in. (6–13 cm) long, excluding a tail of about the same length. They are usually solitary and inhabit dry and desert regions. They carry food (mainly seeds) in their pouches and store it in their burrows. Spiny pocket mice (most in the genera Liomys and Heteromys; family Heteromyidae), found from Mexico through Central America, are gray, brown, or black nocturnal burrowers that inhabit wet, forested regions as well as dry country.