MAMMALS OP THE MEXICAN BOUNBAKY. 293 



sidnally touch each other or are separated by an interval a few miles 

 broad or a few hundred feet in altitude. The narrow intermediate 

 zone is occasionally occupied by the Say chipmunk {Callospermo- 

 philus lateralis), which species, however, has almost the same area 

 of distribution as the Arizona chipmunk. At Stonemans Lake, on. 

 the northwestern slope of the Mogollon range, having an altitude 

 of 6,215 feet, this species is very numerous, finding in the rocky walls 

 of the lake basin a satisfactory abode; but between that point and 

 the summit of the mountain is a pine forest free from rocks quite 

 unsuited to the present species. In traversing this forest, which rises 

 gradually to near the summit of the range, Say's was the only chip- 

 munk found until a certain altitude (about 6,600 feet) was reached, 

 when the first Arizona chipmunks appeared, whereupon both species 

 (C alios fermo'pMlus lateralis and Eutamias cinereicollis) became 

 gradually more abundant until the top was reached. The large area 

 of Ton to Basin is bounded on the north by a nearly, vertical precipice, 

 or " rim-rock," hundreds of feet high, whose summit marks the back- 

 bone of the Mogollon Mountains. This is the typical home of Euta- 

 mias cinereicollis, while the basin itself is an equally populous strong- 

 hold of the Gila chipmunk. Nowhere have I seen so palpable a line 

 of division between two contiguous species, and I imagine that few 

 naturalists, seated on this fence, would hesitate about the separation 

 of these two distinct mammals, whose habitats touch each other, 

 while each retains all of its distinctive characters. 



West of the "Verde Valley, a few Gila chipmunks were noted March 

 26, 1885, in rocky places between Antelope and Bumble Bee post- 

 offices, in Yavapai County, Arizona; and some were seen farther 

 south, in Black Canyon, the next day. I saw some of them near 

 Mountain Spring, east of Tucson, Arizona, April 8, 1885. The banks 

 of Ash Creek, Agua Fria Valley, which were wooded with scrub oak 

 and lined by rocky bluffs, were inhabited by numbers of these chip- 

 munks May 19, 1885. 



The Gila chipmunk crosses the Mexican Boundary Line in a narrow 

 belt, including the San Luis and Guadalupe mountains (Monuments 

 Nos. 64 to 75). None were found east or west of this area. The ab- 

 sence of any species of chipmunk from the Huachuca Mountains is 

 remarkable. 



In the San Luis Mountains the young are apparently born during 

 July. Adults caught June 24, 26, and July 20, contained, respec- 

 tively, 3, 2, 8, and 7 fetuses. 



On the Mexican Border the vertical range of the Gila chipmunk 

 was noted as from 1,200 meters (in Guadalupe Canyon) to 2,498 

 meters (summit of San Luis Mountains, where it was fairly common). 

 In Cajon Bonito Canyon it is abundant; some had descended as low 

 as 1,200 meters, and were active; late in September, 1893. 



