MAMMALS OF THE MEXICAN BOUNDARY. 411 



Luis Mountains and scorched plains — impassable barriers to it. This 

 mouse is probably of Mexican origin, and, south of the United States 

 border, these two species (P. tornillo and P. arizonx) may come to- 

 gether and intergrade, in which case P. tornillo would become a sub- 

 .species of P. arizonse. The size of the two species is about the same, 

 though P. tornillo appears to be the stoutest, and has a smaller ear, 

 more massive skull, and larger teeth (see figs. 85 and 87), with a pecu- 

 liarity of the anterior upper molar, in which the marginal intermediate 

 subsidiary cusp is obsolete ; and the coloration is much paler. 



I have compared the specimens of this species in our collection with 

 the type of Sitomys americanus arizonse of Allen, and find that they 

 are unquestionably the same. 



Ilahits and local distribution.— In 1885 Doctor Merriam sent me a 

 "delusion" mouse trap, which I set under some driftage beside the 

 Verde River, Arizona, on September 23. The morning after it was 

 missing, a curious raccoon having carried it off; but I followed the 

 tracks of the raccoon and luckily recovered the 

 trap, in wliich I caught two Arizona wood mice 

 the next day. This was the beginning of my 

 systematic mammal trapping and of my ac- 

 quaintance with the present species, wliich I sub- 

 sequently caught quite often in the cottonw^ood 

 and willow groves bordering the Verde River. 

 Some were also caught in the post hospital at fig"87.-peromvscus''ari- 

 Fort Verde. Two species of wild mice infested zon^. crowns of molar 

 the hospital — the present species and Peromyscus Tlmv^n sEmEs. ^^^^^^' 

 eremicus anthonyi. Both were taken at the same 



time, in this same trap, set in a closet, in the hospital. On October 

 10, 1885, I found a nest of Peromyscus arizonse, in the hospital dis- 

 pensary, in a drawer that was opened many times each day. The 

 nest was composed of a small quantity of cotton and shreds torn 

 from muslin bandages. It was soft, nicely felted, and altogether a 

 snug little dwelling, in which I found a single mouse, just born, of 

 bright pink color, and destitute of hair. This is the common mouse 

 of the Verde Valley, ranging between 3,000 and 4,000 feet above sea 

 level, in which range it associates with Peromyscus eremicus antJionyi. 

 The higher mountains of this region are the habitat of Peromyscus 

 sonoriensis rujinus. I did not find any form of the Peromyscus hoylii 

 group north of the Gila River, in Arizona. 



At the Morris ranch, on Clear Creek, near Fort Verde, on February 

 3, 1887, 1 discovered a nest of this mouse under a big stone in an alfalfa 

 field. I put them in a box, together with some pocket -gophers 

 ( Thomomys) . The gophers "ate them all up, beginning at their tails. 

 On May 14, 1887, I saw a mouse running about under the cotton- 



