Fig. 25. Known occurrences and probable geographic range of the subspecies of Dipodomys ordii in the northeastern fourth of the range of the species. 1. D. o. richardsoni 8. D. o. terrosus 18. D. o. montanus 2. D. o. oklahomae 10. D. o. uintensis 24. D. o. priscus 5. D. o. evexus 11. D. o. sanrafaeli 31. D. o. longipes 6. D. o. medius 15. D. o. luteolus 33. D. o. nexilis
Fig. 25. Known occurrences and probable geographic range of the subspecies of Dipodomys ordii in the northeastern fourth of the range of the species. 1. D. o. richardsoni 8. D. o. terrosus 18. D. o. montanus 2. D. o. oklahomae 10. D. o. uintensis 24. D. o. priscus 5. D. o. evexus 11. D. o. sanrafaeli 31. D. o. longipes 6. D. o. medius 15. D. o. luteolus 33. D. o. nexilis
| Fig. 25. Known occurrences and probable geographic range of the subspecies of Dipodomys ordii in the northeastern fourth of the range of the species. | |||||
| 1. | D. o. richardsoni | 8. | D. o. terrosus | 18. | D. o. montanus |
| 2. | D. o. oklahomae | 10. | D. o. uintensis | 24. | D. o. priscus |
| 5. | D. o. evexus | 11. | D. o. sanrafaeli | 31. | D. o. longipes |
| 6. | D. o. medius | 15. | D. o. luteolus | 33. | D. o. nexilis |
From Dipodomys ordii obscurus, D. o. extractus differs as follows: Size larger; color lighter; skull larger in all respects, notably in least interorbital width, greatest length of skull and breadth across auditory bullae; zygomatic arches less robust and straight as opposed to robust and bowed laterally; pterygoid fossae subcircular as opposed to circular; auditory bullae more inflated ventrally.
From Dipodomys ordii idoneus, D. o. extractus differs in: Size larger; color lighter; skull larger in all measurements taken except least interorbital width and breadth across maxillary arches which are smaller; nasals longer and narrower; braincase less vaulted; zygomatic arches less robust and more nearly straight; auditory bullae less inflated ventrally.
Remarks.—This subspecies of Dipodomys ordii is the palest of any of the known races from Mexico. It inhabits an area of light-colored sandy soil at the type locality.
The only subspecies with which D. o. extractus really needs comparison is Dipodomys ordii ordii from which it differs as described above. The series which is herein described contains two individuals that resemble D. o. ordii cranially and three that resemble it in color although they are somewhat paler. One specimen, MVZ no. 76560, is the palest of any of the series, has a short tail and in these respects resembles the pale form of Dipodomys ordii compactus. It is apparent from the skull of this latter individual that it is not D. o. compactus but D. o. extractus.
Dipodomys ordii ordii inhabits, in most of its range, dark-colored soils, whereas D. o. extractus inhabits light-colored soils. Possibly the differentiation that has occurred is a result of an ecological separation much as occurs with Perognathus on the white sands and black lavas of the Tularosa Basin of New Mexico (see [Benson], 1933).