MAMMALS OF THE MEXICAN BOUNDARY. 



415 



are compared. The characters of the skull and teeth are shown in 

 the accompanying figure (fig. 88) of the type-specimen. 



Local distribution. ^The California brush mouse is an abundant 

 mhabitant of brushy localities of the Pacific Coast Tract. It is com- 

 monlyfound in the chemizo thickets. Specimens taken at Nachoguero 

 Valley, Lower California, and on the Laguna ]\Iountains, California, 

 June 8 and 15, 1894, contained 2 and 3 fetuses, respectively. 



This elegant species, long since accurately described by Professor 

 Baird, is typical of the group of brush mice, which are somewhat inter- 

 mediate between the wood mice and desert mice. This group inhabits 

 the Sonoran — usually only the Ui)per Sonoran — and Transition zones 

 along the Mexican Boundary Line, from Texas to the Pacific; some- 

 times it penetrates the Lower Sonoran, or even crosses the Transition 

 Zone, reaching the lower edge of the Boreal. A straggler was taken 

 at the eastern base of the Coast Range Mountams, m California; one 

 was taken at Mosquito Springs, 

 Chihuahua (Monument No. 46); 

 one was found quite low on the 

 Franklin Range, in western Texas ; 

 and three were obtained at Fort 

 Clark, Kinney County, Texas. 

 These all came from the Lower 

 Sonoran Zone, where, however, 

 they are mere stragglers from the 

 higher zones, the brush mice being 

 mhabitants of brushy or forested 

 mountains in the altitudinal zone 

 between the habitats of the desert 

 and plains mice and the habitat 

 of the Arizona wood mouse ( Pero my scus sonoriensis rujinus). On the 

 Hachita, San Luis, San Jose, and Huachuca mountains the subspecies 

 pinalis ranged from base to summit, and P. sonoriensis rufinus was not 

 found ; but in the Chiricahua, ]\Iogollon,White, Graham, San Francisco, 

 and other high ranges of mountains in Arizona and New Mexico P. s. 

 rufinus occupies the Douglas spruce and aspen zone about the sum- 

 mits; and P. hoylii innalis is only found lower down, in the forest belts 

 of pine, pinon, alligator juniper, cedar, and brushwood. As a rule, at 

 least in the interior tract, the forms of P. hoylii do not descend to the 

 lowest valleys, even when these are wooded; and on the open 

 country — the habitat of the desert mice (Peromyscus eremicus group) 

 and plains mice {Peromyscus sonoriensis group) — it occurs only as an 

 accidental straggler. 



Professor Baird's type of Peromyscus hoylii was obtained on the 

 Middle Fork of the American River, in Eldorado County, California, 



Fig. 88. — Peromyscus boylii. Skull and teeth 

 of type, a, skull, dorsal view, b, crowns 

 OF LOWER molars; c, crown of upper molars. 



