MAMMALS OF THE MEXICAN BOUNDARY. 



495 



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

 Natural History, New York.) 



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

 United States. Its aquatic habits necessarily restrict 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 blutT near Hanlons, were made by a musk- 

 rat. 



Description. — Similar to Fiber zibethicus (Linnaeus), but smaller 

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

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

 fur gray, tipped with rusty or yel- 

 lowish brown; coarse outer hair 

 scanty, glossy brown, reddish in 

 places; whiskers and scattered 

 hairs of tail, rich liver browm. 



Measure m ents. — A verage of 

 nine adults (8 males and 1 fe- 

 male) from Fort Verde, Arizona: 

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

 vertebrae, 204 (171-220); greatest 

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

 between eyes, 26 (23-28) ; earfrom 

 crown, 17.3; ear from notch, 19.7; 

 length of head, 69.5 (67-71); 

 length of manus, 31 (28-32); 

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

 58.8 by 36.3. 



Cranial characters. — The skull 

 shows no constant differences 

 from that of the typical form 

 zibethicus, 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. " 

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

 Colorado 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 Picks 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. 12:?. 



Feet of Fiber zibethicus. a, fore- 

 foot; 6. hindfoot. 



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



