MAMMALS OF THE MEXICAN BOUNDARY. 383 



e. Length more than 210 nun.; hind fool 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. 143). 



ee. Length less than 210 nun.: hind fool less than '_'() nun.; skull less than 26 



nun.: 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 . ./'( romyscus stephensi (p. 127). 



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 nun.; coloration dark'; tail quite hairy. 



Peromyscus tiburonensis (p. Ill . 

 gg. Size larger; hind foot more than 20 mm.; length. 1!M); tail vertebrae, 

 100; ear from crown, 16; hind foot, 21 ..Peromyscus eremicus (p. 131 - 

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

 arches moderately com crgeiit . A'< romyscus i it micus anthonyi I p. 138 i. 

 M. Coloration paler than /'. eremicus; size medium; skull with zygomatic 

 arches strongly convergent ...Peromyscus < /< micus mi narius 'p. Ill 

 bb. 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 Hush with, or behind, the nasal branches of the pre- 

 maxillary bones. 

 /. Coloration dark: upper surface broccoli brown, skull elevated, with interptery- 



goid fossa long and narrow Peromyscus boylit (p. lb! 



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

 tened, with interpterygoid fossa short and narrow. 



Peromyscus boylii pinalis (p 1 1 * > 

 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 boylit attwateri (p. -123). 

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



Peromyscus boylit penicillatus (p 422). 

 an. Tail shorter than head and body. 



m. Ear from crown more than 19mm '....Peromyscus martirensis <p 125 



mm. Ear from crown less than IS mm. 



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

 mole-like, resembling thai otOnychomys, with a ianuginous tuft ol bail at ante- 

 rior base of eat; tail thick, with a narrow dorsal stripe; coronoid process o| 

 mandible elongated and uncinate. 

 o. Coloration pallid. 

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

 68; ear from crown, 11 .">; length of hind foot and claw 21 5. 



/'< romyscus \onorii nsis h/tun/us p .'is'.) ■■. 

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

 tebrae, 7o: ear from crown, L5; length of hind foot and claw, 22. 



Peromyscus sonoriensis deserticola (p. 394 

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



Peromyscus michigant nsis paUesa ns(p. M)l). 

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

 oo. Coloration dark. 



r. Color n descent Peromyscus sonorit nsis i ufinus l p 



rr. Color not decidedly rufescent. 



