138 yETT MAMMAL.'^ mOM MEXTCAX BOBDER—MEAHyS. vor.xis. 



PEROMYSCUS MERRIAMI, new species. 



.so^■ovTA DKsKirr .mousk. 



Tfipc.So. 5')234, U.S.N.M., skin and skull (Coll. International 

 Boundary Commission). Adult female, from the villa<fe of Sonoyta, on 

 the Sonoyta liiver, 8onora, Mexico. Collected hy l^lgar A. Mearns 

 and F. X. Holzner, January 21, 181)4. Original number, 2815. 



Description of tyiw. — Very similar in appearance to Peromysciis ere 

 hiicKs, with which it agrees in having the soles of the feet entirely bare, 

 the ears nearly naked, and the tail long, tapering, and sca^ntiiy haired, 

 without a terminal pencil. In coloration the two are identical except 

 that the light cinnamon extends down the outer side of the fore limbs 

 to the han<l ; and there is a large pectoral i)atch of cinnamon. . Length, 

 217 mm.; tail vertebne, 113; ear from crown, 20; length of hind foot 

 and claw, 23. Body stout and heavy as compared Avith i*. eremiviis. 

 The skull most resembles that of P. eremicns. It has the same poste- 

 riorly truncate nasals and general conformation, but ditiers notably in 

 havnig the rostral portion relatively longer, the zygomatic arches Avider 

 anteriorly, and the brain-case more highly arched. Its larger si/e 

 serves to identify the skull of this species at a glance, the two anterior 

 molar teeth about eijualing the lateral tooth-row of 1\ creniicus. Pero- 

 onyficns merriami and P. eremicns occur together at Sonoyta and Quito- 

 vaquito, on the Mexican line. 



PEROMYSCUS EREMICUS ARENARIUS, new subspecies. 

 EASTERN DESERT MOUSE. 



Typc.—:^o. Mjrh U.S.X.M. (Coll. International Boundary Commis- 

 sion). Adult male, from the Bio Grande, about six miles from El Paso, 

 Texas. Collected bj' Edgar A. Mearns and F. X. Ilolzner, February 

 25, 1892. Original number, 1513. 



Description of type. — Above pale ochraceous drab hnely mixed with 

 black, Avithout a darker median area; sides and rump pale ochraceous 

 buff: ears almost naked, but with a scant pubescence on the margin 

 and anterior band; tail, dusky drab above, mixed with hoary, i)ure 

 white below; under parts and feet ])ure white. The head is somewhat 

 grayish, and there is a dusky orbital ring. The outer border of the 

 first and second upper molars have but tliree salient and two re-entrant 

 loops or enamel folds, as is usual in the group of desert mice. Length, 

 108 mm.: tail vertebr;c, 10(1 (to end of hairs, 111); ear, from crown, 15 

 (from notch, IS)- distance between eyes, 9; diameter of eye, 4; length 

 of longest whisker, 42; distance from tii) of nose to eye, 13.5; to center 

 of pui)il, 10; to ear, 23; to tip of ear, 41; to occiput, 20; to end of out- 

 stretched hinder extremity, 138; fore limb, from olecranon i)rocess to 

 end of longest claw, 25; length of lore foot, 12; longest claw of fore 

 foot, 1.8; hind limb, from knee-joint to end of longest claw, 42; length 

 of hind foot, 21.5, longest claw of hind foot, 1.8. Skull, 25 by 12.7 mm. 



