Diagnosis.—Size small (see measurements). Color dark, entire dorsal surface (h) between Cinnamon and Sayal Brown, purest on sides and flanks, upper parts strongly suffused with black; posterior surfaces and fold of pinnae of ears, white; arietiform markings, plantar surfaces of hind feet, inside of pinnae of ears, dorsal and ventral stripes of tail, blackish. Skull small; nasals long; rostrum long and narrow; interorbital region relatively wide; degree of inflation of auditory bullae about average for species; zygomatic arches light and bowed laterally; pterygoid fossae subcircular; braincase but slightly vaulted.
Comparisons.—From Dipodomys ordii ordii, D. o. palmeri differs as follows: Size somewhat larger; color darker; skull larger; nasals longer and flaring distally; interorbital width greater; narrower across auditory bullae; interparietal region narrower; breadth across maxillary arches greater; zygomatic arches bowed laterally as opposed to relatively straight; pterygoid fossae more nearly circular; rostrum longer and narrower.
From Dipodomys ordii sennetti, D. o. palmeri differs in larger size, darker color, longer tail and longer skull.
For comparisons with Dipodomys ordii obscurus and Dipodomys ordii fuscus see accounts of those subspecies.
Remarks.—Specimens from Berriozobal, Zacatecas, in the width of the rostrum and the configuration of the nasals, are intermediate between Dipodomys ordii fuscus and D. o. palmeri. In color these animals are more nearly like typical representatives of D. o. palmeri. The animals from Jalisco and Guanajuato are not typical but the characters differentiating them from D. o. palmeri are merely modifications of such slight degree that they all have been placed with that subspecies.
Specimens examined.—Total, 56, distributed as follows:
Zacatecas: Canitas, 3 (USBS); Berriozobal, 10 (USBS).
San Luis Potosí: Potrero Santa Ana, 7.6 mi. S Matehuala, 2 (MVZ); Jesus Maria, 12 (USBS); 2 mi. NW San Luis Potosí, 8 (MVZ).
Aguascalientes: 1 mi. N Chicalote, 1900 m., 4 (MVZ).
Jalisco: 9 mi. N Encarnación, 1900 m., 1 (MVZ).