4 ( .»4 BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



Incisors broad, molars rootless or rooted, with flat crowns and 

 re-entrant angles. 



The subfamily Microtinse, which has been thoroughly revised by 

 Mr. Gerrit S.Miller, jr.," is represented on the Mexican Line by only 

 two genera, Fiber and Microtus. The former is confined to the 

 neighborhood of streams, and the latter principally to the Transition 

 and Boreal zones of the mountains, although one species inhabits the 

 Sonoran Zone in the coast belt of southern and Lower California. 



Genus FIBER Cuvier (1798). 



Fiber Cuvier, Tabl. Elem. de l'Hist. Nat. des Anim., p. 141, 1798; Lepons d'Anat. 

 Comp.. I. Tab. I, 1S00. 



Dentition.— I. \ ~ ; M. 3 if = 16. 



Type. — Castor zibeihicus Linnaeus. 



Upper incisors with anterior faces smooth. Lower incisors with 

 roots on outer side of molars. Molars rooted. Enamel pattern char- 

 acterized by approximate equality of re-entrant angles on outer and 

 inner sides of molars. Feet modified for swimming. Tail flattened 

 laterally. (G. S. Miller, jr.) (See figs. 128 and 124.) 



FIBER ZIBETHICUS PALLIDUS Mearns. 

 PALE MUSKRAT. 



Fiber zibeihicus paUidus Mearns. Bull. Am. Mus. Nat. Hist.. II, No. 4, Feb. 21, 1890, 

 pp. 2.S0-2N3 (original description). — Miller and Rehn, Proc. Bost. Soc. Nat. 

 Hist., XXX, No. 1, l),c 27, 1901, p. 131 (Syst. Results Study X. Am. Mam. to 

 close of 1900).— Elliot, Field Col. Mus., Zool. Ser., IV, 1904, p. 307, fig. 55 (Mam. 

 Mid. Am.). 



[F'iber zibethicus] paflidux, Elliot, Field Col. Mus., Zool. Ser., II, 1901, p. 213 (Synop. 

 Mam. X. Am.). 



Ti/]>e-locality. — Old Fort Yerde (now Camp Verde), Yavapai County, 



color; belly pinkish bull'. Similar in general to .V. U pida . but hind foot larger, differing also 

 in color and cranial characters. 



Color. — Type: Upper parts grayish bull", palest on head, becoming pinkish buff along 

 cheeks and sides, well mixed on dorsal region with brownish hairs; underparts strongly 

 washed with pinkish bull', this color spreading over entire belly and more or less irregularly 

 invading other parts; small areas on pectoral and inguinal regions, sometimes including 

 throat, pure white: ears thinly covered with grayish brown hairs; ankles dusky; feet white; 

 tail grayish brown, slightly paler below. 



Cranial charactt rs. -Skull small, short, and relatively broad; brain case large and smoothly 

 rounded; frontal region broad and flat; bulla 1 large; first upper molar with antero-internal 

 sulcus obsolete. Compared with N. lepida the skull averages larger, with decidedly longer 

 toothrow, larger interparietal, and smaller bulla?. ■ 



Measurements. Type: Total length, 310: tail vertebra 1 , 139; hind foot, 31. (Proc. 

 Biol. So . Washington, XVIII, 1905, p. 32. 1 



When living at Fori Verde, Arizona, I heard from miners of the existence of a small, 

 somewhat bushy-tailed wood rat on Squaw Peak and others of the Verde Mountains, and 

 now suppose it to have been Xeotoma stephensi. 



u North American Fauna, No. 12, July 23, 189<>, pp. 1-84, pis. i— in, text figures 1-40. 



