92 Merriam Rediscovery of the Mexican Kangaroo Eat 



is produced anteriorly beyond the plane of the adjoining part 

 of the mastoid, a condition not found in any other species ex- 

 cept D. merriami, from which it differs in shape, being narrower 

 and having the greatest projection on the inferior surface, while 

 that of D. merriami is bluntly rounded anteriorly. The inflated 

 mastoids are both relatively and actually smaller than in any 

 other species and are separated on top of the skull by at least 

 3 mm. The forks of the supra-occipital enclose a broadly oval 

 interparietal. The top of the skull is considerably arched both 

 antero-posteriorly and transversely, the highest point being the 

 middle of the fronto-parietal suture. The mandible is rather 

 light and slender, and the angular processes are less strongly 

 developed than in any other member of the genus. 



Geographic Distribution. The Valley of Mexico and adjacent, 

 mountain slopes on the south, and the plains of Puebla from 

 Canada Morelos and Esperanza north to Huamantla, Tlaxcala, 

 and Perote, Vera Cruz. 



) Fanned Position. From Mr. Nelson's account of the haunts 

 of this species it appears to be an inhabitant of the Transition 

 Zone (or perhaps of both the Upper Sonoran and Transition), 

 in which respect it agrees with the California species which it 

 most closely resembles (D. cali/omicus), and differs from all 

 others of the genus the others being Lower Sonoran. 



Variations in Dipodomys phillipsi. 



The area inhabited by Dipodomys phillipsi is so small that the 

 characters of the species are very constant, as would be expected. 

 In 28 specimens from Tlalpam and Ajusco the length of the 

 white tip of the tail, beyond the black hairs that overlap its base, 

 varies from 5 to 15 mm. 



The dark facial crescents and connecting band across the nose 

 vary somewhat in different specimens from the same locality, 

 but average much broader and blacker in those from the plains 

 of Puebla than from the Valley of Mexico. 



The tail averages shortest in specimens from Perote, Vera 

 Cruz (163.4 mm.), and longest in those from Huamantla, Tlaxcala 

 (175 mm.). 



