MAMMALS OF THE MEXICAN BOUNDARY. 388 



e. Length more than 210 mm.; liiud foot more than 22 mm.; .skull more than 26 

 mm. in total length; zygomatic arches almost parallel to cranial axis; chest 



and wrists colored Peromyscus merriami (p. 443). 



ee. Length less than 210 mm.; hind foot less than 20 mm.; skull less than 26 



mm.; zygomatic arches anteriorly convergent; chest without a colored spot 



(except occasionally — especially in P. e. anthonyi), and wrists all white. 



/. Coloration pallid; grayish — or ochraceous — buff; upper profile of skull 



straight and strongly declined anteriorly . .Perornvscus stephensi (p. 427). 



ff. Coloration darker; grayish drab, tinged with cinnamon- or tawny-ochra- 



ceous; upper profile of skull more arched. 



g. Size small; hind foot less than 20 mm.; coloration dark; tail quite hairy. 



Peromyscus tiburonensis (p. 444). 

 gg. Size larger; hind foot more than 20 mm.; length, 190; tail vertebrae, 

 100; ear from crown, 16; hind foot, 21 ..Peromyscus eremicus (p. 431). 

 h. Coloration darker than P. eremicus; size larger; skull with zygomatic 

 arches moderately convergent. .Peromyscus eremicus anthonyi (p. 438). 

 7ih. Coloration paler than P. eremicus; size medium ; skull with zygomatic 

 arches strongly convergent... Peromyscus eremicus arenarius (p. 441). 

 bl. Two front upper molars with distinct subsidiary cusps and corresponding enamel 

 loops; soles of feet usually hairy from the heel to the tubercles; tail hairy through- 

 out, with a distinct brush at the tip. 

 i. Nasal bones ending in a point flush with, or behind, the nasal branches of the pre- 

 maxillary bones. 

 j. Coloration dark; upper surface broccoli brown, skull elevated, with interptery- 



goid fossa long and narrow Peromyscus boylii (p. 413). 



jj. Coloration pale; upper surface pale grayish drab, sometimes buffy, skull flat- 

 tened, with interpterygoid fossa short and narrow. 



Peromyscus boylii pinalis (p. 416). 

 ii. Nasal bones truncated posteriorly, and ending in front of the hinder extremity of 

 the nasal premaxillaries; soles of feet naked 

 Jc. Color above, tawny brown, much mixed with black along the median dorsal area. 



Petomyscus hoylii attwaten (p. 423). 

 hh. Color above, dral)-gray, without a distinctly darker median dorsal area. 



Peromyscus boylii penicillatus (p 422). 

 aa. Tail shorter than head and body. 



m. Ear from crown more than 19 mm Peromyscus marttrensis (p 425). 



mm. Ear from crown less than 18 mm. 



71. Soles of feet densely hairy, with the metatarsal tubercles small, pelage den.se and 

 mole-like, resembling that of Onychomys; with a lanuginous tuft of hair at ante- 

 rior base of ear; tail thick, with a narrow dorsal stripe; coronoid process of 

 mandible elongated and uncinate. 

 o. Coloration pallid. 



p. Color grayi.sh drab. Skull lightly built Length, 160 mm.; tail vertebra, 

 68; ear from crown, 14 5; length of hind foot and claw, 21.5. 



Peromyscus sonoriensis blandus (p. 389). 

 pp. Color ochraceous drab. Skull strongly built. Length, 170 mm.; tail ver- 

 tebrae, 75; ear from crown, 15; length of hind foot and claw, 22. 



Peromyscus sonoriensis desetticola (p. 394). 

 q. Length less than 140 mm.; vertebral area distinctly darker. 



Peromyscus michiganensis pallescens (p. 401). 

 qq. Length more than 1.50 mm.; vertebral area not distinctly darker. 

 00. Coloration daik. 



r. Color lufesccnt Pe/omyscus sonoriensis rujinus (p. 391). 



rr. Color not decidedly rufescent. 



