FIELD BOOK OF MAMMALS 



with two tunnels leading downward into the bog on opposite 

 sides. The distance between them here, as in the nests, is 

 about 4 to 6 inches. Likewise the platform, as in the nests, 

 rises barely above the water level. . . . 



"Where the muck or the moss of the prairie rise close to or 

 above the water level, runways are generally seen in the 

 vicinity of the nests. They consist of more or less cleared 

 passages, about 3 inches wide, that extend over the surface 

 of the sphagnum and muck among fern, maiden cane, and 

 the like. . . . 



"From these meager data it appears that the breeding 

 season extends from January at least to April, and very 

 likely into the fall." 



Genus Ondatra [= Fiber of various authors]^ 

 Dentition: Incisors, {; Canines, g ; Premolars, g; Molars, f = 16. 



Muskrat. — Ondatra zibethica 



and related forms 



Names. — Muskrat; Musquash. Plate XXVII. 



General Description. — A large Rat with robust form; short 

 legs; broad feet, specialized for swimming, hind feet partially 

 webbed; tail long, laterally compressed, scaly and sparsely 

 haired; ears scarcely showing above fur; pelage dense and 

 composed of two types of hair, a close, waterproof underfur 

 and longer, glistening guard-hairs; perineal glands strongly 

 developed and secreting a pronounced musky odor; always 

 living near water. 



Color. — Sexes colored alike; Seasonal variation not con- 

 spicuous. 



Upperparts. — Dark brown, slightly darker on head; sides 

 chestnut; pelage glossy; underfur slate-colored at base. 



Underparts. — Like pelage of sides, but washed with tawny 

 and lighter in appearance, approaching whitish on throat and 

 belly; a blackish spot on chin and blackish about wrists and 

 heels; tail black; feet dark brown. 



Paler and duller in worn pelage. Occasionally occurs in a 

 black phase in which upperparts are black and underparts 

 dark. 



I For a full revision of the genus see N. Hollister, North American 

 Fauna, No. 32, 1911. 



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