1)() Merrhnn — Jicdiscovcry of the Mexican. Kdiujaroo Rat. 



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

 the measurements given hy Wagner for the skeleton of liis 

 Macrocohis halticus (converted into millimeters) are : Total length, 

 270; tail vertehra;', 168 ; hind foot, 39.5. The averages of 28 

 adult specimens of Dipodnmys jjhiltrpsi collected in the \\alley 

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

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

 The measurements and description of the skull and skeleton 

 also agree with those of D. philllpsl and not with D. inerrlami or 

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

 Wagner to be 31. In two skeletons from Tlalpam the numl^er 

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

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

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

 shows conclusively (if even approximately coi'rect) that the 

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

 Ijeing considerably greater than in an}- other species, and the 

 mastoids being only slightly developed for a Dlpodomys, the 

 consequent breadth of the cranium across the mastoids l)ut 

 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 

 Dlpodomys phUllp-n ; and it has l)een shown 1)}^ direct compari- 

 son of his description with duplicate types of the latter species 

 that it does agree with tliis species in every ])articular. It seems 

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

 Dlpodomys pJiltllpsl of Gra}'. 



