_Type._--Male, adult, no. 90029, Museum of Zoology, University of Michigan; San Juan, 12 mi. W Lerdo, 3,800 ft., Durango, Mexico; obtained on March 1, 1946, by F. and F. Hammerstrom. _Range._--Known only from the type locality. _Diagnosis._--Size small (see measurements). Color pale, entire dorsal surface (c) between Light Ochraceous-Buff and Ochraceous-Buff, purest on sides, flanks and cheeks; upper parts but slightly washed with black; arietiform markings, lateral parts of pinnae of ears, plantar surfaces of hind feet, dorsal and ventral stripes of tail, brownish; medial part of pinnae of ears flesh-colored. Skull medium in size; rostrum wide and relatively long; braincase but slightly inflated; least interorbital width great; interparietal region relatively narrow; upper incisors strongly recurved; zygomatic arches relatively heavy and slightly bowed laterally; auditory bullae greatly inflated ventrally, laterally and posteriorly. _Comparisons._--From _Dipodomys ordii ordii_, _D. o. idoneus_ differs in: Size smaller; color lighter; skull larger; nasals longer and somewhat more inflated distally as opposed to straight; interorbital width greater; breadth across maxillary arches greater; interparietal region narrower; auditory bullae more inflated posteriorly, laterally and ventrally and projecting anteriorly into orbit; extension of nasals anterior to upper incisors less; zygomatic arches heavier and more bowed laterally; paroccipital processes smaller; foramen magnum elongate as opposed to nearly circular. From _Dipodomys ordii obscurus_, _D. o. idoneus_ differs as follows: Size smaller; color lighter; skull larger, rostrum wider; nasals shorter and more expanded distally; interorbital region wider; width across maxillary arches greater; interparietal region narrower; auditory bullae more inflated laterally, posteriorly and ventrally; zygomatic arches shorter, heavier and less bowed laterally. From _Dipodomys ordii palmeri_, _D.o. idoneus_ differs in: Size smaller; color lighter; skull larger; rostrum shorter and wider; nasals shorter and more expanded distally; interorbital region wider; auditory bullae more inflated laterally, posteriorly and ventrally; zygomatic arches heavier. From _Dipodomys ordii fuscus_, _D. o. idoneus_ differs as follows: Size smaller; color lighter; skull smaller; rostrum narrower and shorter; interorbital width greater; braincase more vaulted; nasals longer; interparietal region generally wider; auditory bullae less inflated; breadth across maxillary arches greater; zygomatic arches heavier and more bowed laterally; pterygoid fossae ovoid as opposed to subcircular; occipital condyles more anterior to dorsal evagination when viewed ventrally.