The name of a number of small jerboa-like, chiefly North, American rodents belonging to the family Geomyidae, and constituting the genus Perognathus and Heteromys. They are nearly allied to the American kangaroo-rats (see KANGAROO-RAT), but differ in having rooted molar teeth. The typical pocket-mouse P. fasciatus, which is a native of Montana, Missouri, and Wyoming, is a sandy-coloured rodent marked with black lines above and with white beneath, and measuring about 6 in. in length, this length being equally divided between the head and body and the tail. (See RODENTIA.)