It seems that the Rio Grande serves as a barrier to the dispersal southward of kangaroo rats from the north side and vice versa. _D. o. fuscus_ ranges from the type locality to Nuevo Laredo and has not been found on the north side of the river, being replaced there, up-river, by _Dipodomys ordii medius_ and down-river by _Dipodomys ordii sennetti_. _Specimens examined._--Total, 53, distributed as follows: =Coahuila=: San Juan Neponuceno, 5 mi. N La Ventura, 4 (MVZ); La Ventura, 7 (USBS). =Tamaulipas=: Nuevo Laredo, 2 (USBS); Miquihuana, 14 (4 USBS; 9 MVZ; 1 AMNH); Juamave, 8 (USBS); Tula, 5 (UM); 3 mi. N Lulú, 5 (MVZ): Lulú, 8 (MVZ). =Dipodomys ordii longipes= (Merriam) _Dipodops longipes_ Merriam, N. Amer. Fauna, 3:72, September 11, 1890. _Perodipus ordii_, Allen, Bull. Amer. Mus. Nat. Hist., 5:71, April 28, 1893 (part--the part from Bluff, Utah). _Cricetodipus longipes_, Trouessart, Catalogus Mammalium, 1:581, 1897. _Perodipus longipes_, Elliot, Field Columbian Museum, Zool. Ser., 2:239, 1901. _Perodipus ordii longipes_, Goldman, Proc. Biol. Soc. Washington, 30:113, May 23, 1917. _Dipodomys ordii longipes_, Grinnell, Journ. Mamm., 2:96, May 2, 1921. _Dipodomys ordii cleomophila_ Goldman, Journ. Washington Acad. Sci., 23:469, October 15, 1933, type from 5 miles northeast of Winona, Coconino County, Arizona. _Type._--Male, no. 17703/24639, U. S. Nat. Mus. Dept. Agric. Coll.; foot of Echo Cliffs, Painted Desert, Arizona; obtained on September 22, 1889, by C. Hart Merriam, original no. 512. _Range._--Southeastern Utah, northeastern Arizona to immediately south of the Little Colorado River, northwestern New Mexico and extreme southwestern Colorado; marginal occurrences are: in Arizona, 20 mi. NE Lees Ferry, Foot Echo Cliffs in Painted Desert, 5 mi. NE Winona, Winslow and Holbrook; in New Mexico, 10 mi. SW Quemado, Riley, Laguna, Chama Canyon and Shiprock. _Diagnosis._--Size large (see measurements). Color dark, entire dorsal surface between (_16''_) Pinkish Cinnamon and Cinnamon-Buff, purest on sides and flanks with but slight suffusion of black on upper parts; cheeks white; arietiform markings, pinnae of ears, plantar surfaces of hind feet, dorsal and ventral stripes of tail, brownish. Skull large; rostrum long and narrow; nasals long and thin; auditory bullae greatly inflated; styloid processes project on ventral surface of auditory bullae beyond middle of external auditory meatus. _Comparisons._--From _Dipodomys ordii chapmani_, _D. o. longipes_ differs as follows: Size larger; color lighter; skull larger in all measurements taken; auditory bullae much more inflated.