MAMMALS OP THE MEXICAN BOUNDARY. 383 



e. Length more than 210 mm.; hind 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. anihonyi), and wrists all white. 



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



straight and strongly declined anteriorly . .Peromj/scus stephensi (p. 427). 



^. 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 iiburonensis (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). 

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

 arches strongly convergent... Peromysi^us eremicus arenarius (p. 441). 

 hb. 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 ioylii (p. 413) . 



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

 tened, with interpterygoid fossa short and narrow. 



Peromyscus hoylii pmalis (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. 



Peromyscus hoylii atiwaten (p. 423). 

 Teh. Color above, drab-gray, without a distinctly darker median dorsal area. 



Peromyscus hoylii penicillatus (p 422). 

 aa. Tail shorter than head and body. 



m. Ear from crown more than 19 mm Peromyscus martirensis {p. 425). 



mm. Ear from crown less than 18 mm. 

 n. Soles of feet densely hairy, with the metatarsal tubercles small, pelage dense and 

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

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

 mandible elongated and uncinate. 

 0. Coloration pallid. 

 p. Color grayish drab. Skull lightly built. Length, 160 mm.; tail vertebrse, 

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



Peromyscus sonoriensis hlandus (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 deserticola (p. 394). 

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



Peromyscus michiganensis pallescens {p. 401). 

 qq. Length more than 150 mm.; vertebral area not distinctly darker. 

 00. Coloration daik. 



r. Color tufescent Peromyscus sonoriensis rufinus (p. 391). 



rr. Color not decidedly rufescent. 



