92 Merrifvm — Bediscoverij of the Mexican Kangaroo Bat 



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 shajie, l)eing 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 botl 

 antero-posteriorly and transversely, the highest point being the 

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

 light and slender, and the angular processes are less stronglj 

 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. 



Fdunal Position. — From Mr. Nelson's account of the hauntsl 

 of this species it a})pears to be an inhabitant of the Transition] 

 Zone (or perhaps of both the Ui^per Sonoran and Transition),! 

 in which respect it agrees with the California species which iti 

 most closely resembles (D. ccdifornicns), and differs from all] 

 others of the genus — the others being Lower Sonoran. 



Variations in Dipoclomys phillipsi. 



The area inhabited by Dipodomys phillipsi is so small that the 

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

 In 28 specimens from Tlalpam and Ajusco the length of the 

 white tip of the tail, beyond the 1)lack hairs that overlap) its base,] 

 varies from 5 to 15 mm. 



The dark facial crescents and connecting l)and across the nosej 

 vary somewhat in different specimens from the same locality,] 

 Init average much broader and blacker in those from tlie plainsj 

 of Puebla tlian from the Valle}^ of iNIexico. 



The tail averages shortest in specimens from Perote, Vera! 

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

 (175 mm.). 



