JM> Merriam Rediscovery of the Mexican Kangaroo Rat. 



1 mm. for the thickness of the skin over the end of the nose, 

 the measurements given by Wagner for the skeleton of his 

 Macrocolushalticus (converted into millimeters) are : Total length, 

 270; tail vertebrae, 168 ; hind foot, 39.5. The averages of 23 

 adult specimens of Dipodomys phillipsi collected in the Valley 

 of Mexico by Mr. E. W. Nelson are: Total length, 270; tail 

 vertebrae, 168; hind foot, 41.1, the agreement being surprising. 

 The measurements and description of the skull and skeleton 

 also agree with those of D. phillipsi and not with D. merriami or 

 any other species. The number of tail vertebra? is stated by 

 Wagner to be 31. In two skeletons from Tlalpam the number 

 is 32. No other species of Dipodomys is known to have more 

 than 29, and no species of Perodipus more than 28. Further- 

 more, if additional evidence is needed, the drawing of the skull 

 shows conclusively (if even approximately correct) that the 

 animal is D. phillipsi, the interorbital breadth of the frontals 

 being considerably greater than in any other species, and the 

 mastoids being only slightly developed for a Dipodomys, the 

 consequent breadth of the cranium across the mastoids but 

 slightly exceeding the breadth across the maxillary bridges of 

 the orbits. 



It has been shown by the process of elimination that Wagner's 

 animal could not belong to any known species other than 

 Dipodomys phillipsi ; and it has been shown by direct compari- 

 son of his description with duplicate types of the latter species 

 that it does agree with this species in every particular. It seems 

 safe to infer, therefore, that Macrocolus halticus of Wagner is 

 Dipodomys phillipsi of Gray. 



