MAMMALS OK TIIK MEXICAN BOUNDARY. 



495 



central Arizona. (Type, skin and skull, in the American Museum of 

 Natural History, New York. I 



Geographical range. Sonoran Zone of the arid interior region of the 

 United Stales. Its aquatic habits necessarily rot rid it to the vicinity 

 of streams. On the Mexican Border we saw it only on the San Pedro 

 River, though it is said to occur on the lower Colorado River, where, 

 however, it was not detected by us, unless some tracks, seen imper- 

 fectly at the foot of a clay bluff near llanlons. were made by a musk- 

 rat. 



IK scription. —Similar to Fiber zibethicus (Linnaeus), bul smaller 

 and much paler in color. Size, two-thirds thai of the eastern musk- 

 rat. General color, rusty brown, paler and grayish beneath; under 

 furgray, tipped with rusty or yel- 

 lowish brown; coarse outer hair 

 scanty, glossy brown, reddish in 

 places: whiskers and scattered 

 hairs of tail, rich liver brown. 



Mi asun ments. — A v e r a g e of 

 nine adults (8 males and 1 fe- 

 male) from Fort Verde, Arizona: 

 length, 482 mm. (475-500); tail 

 vertebra-, 204 (171-220); greatest 

 depth of tail, 14 (12-16); distance 

 between eyes, 120 (23-28) ; earfrom 

 crown, 17.3; earfrom notch, 19.7; 

 length of head, 69.5 (67-71); 

 length of manus, 31 (28-32); 

 length of pes, 67 (62-70). Skull, 

 58.8 by 36.3. 



Cranial characters. — The skull 

 shows no constant differences 

 from that of the typical form 

 zibethiciis, except that it is much smaller (58.8 mm. against 65 in total 

 length). A detailed comparison, with ratios of the several measure- 

 ments to the basilar length, will be found in the original description. 



Habits and local distribution. — Muskrats abound in the waters of the 

 ( lolorado Basin, and are especially numerous on the Gila and its higher 

 tributaries, but less so near the mouths of the Gila and Colorado 

 rivers. I saw many on the Verde River, where they inhabit burrows 

 along the banks of the stream. At ]'i<-k^ Lake, where muskrats have 

 every advantage for building houses, they never do so, and probably 

 none are built in Arizona, as the weather is not cold enough to make it 

 necessary. I sometimes shot them in the smaller streams, irrigation 

 ditches, and sluices, as well as in the Verde River. On July 8, 1884, 



Fig. L23. 



-Feet or Fiber zibethk i s. a, fork- 



FOOT; ''. HINDFOOT. 



a Bull. Am. Mus. Nat. Hist., II. 1890, p. 281. 



