442 



BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



pure white below; under parts and feet pure wliite. The head is some* 

 what grayer, and there is a dusky orbital ring. 



Cranial and dental characters. — The skull is longer and narrower 

 in front than in the more western forms of P. eremicus, with the 

 rostrum somewhat longer. The outer border of the anterior and 

 middle upper molars have but three salient and two reentrant loops 

 or enamel folds, as is usual in the group of desert mice. The sub- 

 sidiary (often paired) marginal cusps, usually present in Peromyscus, 

 are obsolete in the eremicus group; and they are wholly wanting in 

 the genus Onychomys. Peromyscus eremicus affords another striking 

 illustration of the difference in the mammal forms of the Eastern and 

 Western Desert tracts. 



Habits and local distribution. — The eastern desert mouse was found 

 in abundance about El Paso, where it lived among rocks, cacti, and 

 agaves, on both sides of the Rio Grande, specimens having been taken 

 from Texas and Chihuahua. Salt pork and oatmeal were attractive 

 bait. 



Measurements of 21 specimens of Peromyscus eremicus arenarius. 



Locality. 



Date. 



Sex and 

 age. 



El Paso, Texas. 



do 



do 



do 



....do 



....do 



....do 



....do 



.do. 

 .do. 

 .do. 

 .do. 

 .do. 

 .do. 

 -do. 

 -do. 

 .do. 

 .do. 

 -do. 

 .do. 



Chihuahua, Mexico, near Monu- 

 ment No. 1, on the Rio Grande. 



1892. 

 Feb. 

 Feb. 

 Feb. 

 Feb. 

 ...do 

 ...do 

 ,...do 

 ...do 

 Feb. 

 Feb. 

 ...do 

 Feb. 

 ....do 

 Feb. 

 ...do 

 ...do 

 Feb. 

 ....do 

 ....do 

 Feb. 

 Mar. 



cfad. 

 c?ad. 

 cf ad. 

 Sad. 

 cfad. 

 ?ad. 

 ?ad. 

 cfad. 

 c?ad. 

 d'ad. 

 d'ad. 

 ?ad. 

 ?ad. 

 d'ad. 

 d'ad. 

 Sad. 

 Sad. 

 d'ad. 

 dad. 

 dad. 

 dadr 



182 

 169 

 197 

 187 

 187 

 182 

 183 

 191 

 181 

 194 

 191 

 184 

 184 

 186 

 189 

 200 

 200 

 198 

 191 

 199 

 184 



87 

 105 

 95 

 103 

 96 

 96 

 100 

 92 

 112 

 101 

 105 

 100 

 94 

 96 

 107 

 HI 

 106 

 106 

 98 

 96 



mm. 

 21.0 

 21.0 

 21.0 

 21.0 

 21.0 

 21.0 

 20.0 

 21.0 

 20.5 

 20.6 

 21.5 

 19.5 

 22.0 

 20.0 

 21.0 

 21.0 

 21,0 

 21.6 

 21.0 

 21.0 

 20.0 



mm. 

 16.0 

 14.0 

 14.0 

 16.6 

 15.0 

 15.5 

 15.0 

 14.0 

 14.0 

 16.5 

 14.0 

 13.0 

 16.0 

 15.0 

 14.0 

 14.0 

 15.0 

 15.0 

 15.0 

 15.0 

 14.0 



