1. Soles of hind feet densely haired; interparietal less than greatest width of skull; maxilla with enlarged and laterally projecting flange above root of zygomatic arch: genus Dipodomys, 2
1'. Soles of hind feet naked, or furred only to plantar surface; interparietal more than greatest width of skull; maxilla with very small laterally projecting flange: 4
2. Maxillary breadth more than 22 mm; tip of tail white: Dipodomys spectabilis.
2'. Maxillary breadth less than 22 mm; tip of tail not white: 3
3. Hindfoot with four toes; lateral aspect of dentary ramus molded so as to suggest the bases of the teeth: Dipodomys merriami.
3'. Hindfoot with five toes; lateral aspect of dentary ramus flatter: Dipodomys ordii.
4. Bullae larger, in dorsal view comprising more than one-half of transverse distance across skull through middle of interparietal; hair on end of tail usually not longer than hair near base of tail: genus Perognathus, 5
4'. Bullae smaller, in dorsal view less than half of transverse distance across skull through middle of interparietal; hairs on end of tail longer than those at base or not: genus Chaetodipus, 6
5. Length of tail usually 60 mm or more; total length usually 120 mm or more; length of skull usually more than 21 mm: Perognathus flavescens.
5'. Length of tail usually less than 60 mm; total length usually less than 120 mm; length of skull usually less than 21 mm: Perognathus flavus.
6. Hairs at end of tail not longer than those near base; tubes of auditory bullae projecting lateral of mastoids in dorsal view: Chaetodipus hispidus.
6'. Hairs at end of tail noticeably longer than those near base; tubes of auditory bullae not projecting as above: 7
7. Rump spines usually present; rocky habitats: 8
7'. Rump spines absent; habitat various: 9
8. Total length more than 180 mm; premaxilla extending distinctly farther posteriorly than nasal: Chaetodipus nelsoni.
8'. Total length less than 180 mm; premaxilla extending posteriorly about the same distance as nasal: Chaetodipus intermedius.
9. Tail much longer than head and body; head and body usually more than 95 mm; interparietal width equal to or less than least interorbital width: Chaetodipus baileyi.
9'. Tail slightly longer than head and body; head and body usually less than 95 mm; interparietal width exceeds least interorbital width: 10.
10. Sonoran Desert, barely reaching into extreme southwestern New Mexico (separated from C. eremicus on genetic data): Chaetodipus penicillatus.
10'. Chihuahuan Desert, including southern New Mexico; range stops short of the Arizona border: Chaetodipus eremicus.
Last Update: 4 Jan 2008