DICROSTONYX. FIBER 211 



Color. Summer Pelage. Upper parts save rump rich chestnut, 

 base of hairs mottled with white; rump blackish gray mottled with 

 white; dorsal stripe blackish; face gray; ear patches chestnut. Sides 

 and under parts tinged with rusty; breast between fore legs chestnut. 

 Feet white. Pelage in change, central portion of upper parts mixed 

 chestnut and yellowish white, darker posteriorly; remaining pelage 

 yellowish white with fulvous markings, viz. : a patch on either side, 

 one on breast, reaching to neck and ears, and ring around base of 

 tail. Median dorsal stripe dark brown. 



Winter Pelage. Pure white. 



Measurements. Total length, 132-165; tail vertebrae, 2i;hind foot, 

 18-19. Specimen from Point Barrow, Alaska. 



c.— richardsoni. (Du-rostony.x), Merr. , Proc. Wash. Acad. Scien., 1900, 

 p. 26. 



Type locality. Fort Churchill, Hudson Bay. 



Genl. Char. Size large; third nail of fore foot larger than fourth; 

 bulla' broadly rounded and somewhat depressed. Enamel pattern of 

 molars like D. nelsoni. 



Color. Summer Pelage. Unknown. 



Winter Pelage. White. 



Measurements. Total length, 143; tail vertebr;c, 14; hind foot, 20. 



57. Fiber. 



I. i=i; M. 5=5 = 16. 



i-i 3-3 



Fiber. G. Cuvier, Lerons d'Anatomie, i, 1800. T\'pe Castor zibetlii- 

 cus, Linn. 



Ondatra, Lacep., Less. Man., 1827, p. 286. 



Size large; hind feet oblique to the leg; tail flattened sideways 

 for nearly its entire length and fringed with stiff hairs; ears very small, 

 deeply buried in fur; muzzle furry except nasal pads, which are naked. 

 Palms and soles naked, fringed with hairs, 5-tubercled ; dentition 

 and skull arvicoline; squamosals much expanded: parietals reduced; 

 interparietal nearly as long as broad, upper incisors almost a circle in 

 shape within and without the jaw, lower incisors enter jaw to root of 

 the condylar process; descending process of condyle hamular and 

 much twisted. Palate terminates opposite middle of last molar and 

 has a median azygos protuberance; pterygoid fossa wide and deep; 

 nasals narrow posteriorly, widening rapidly anteriorly, tumid, and 

 terminating behind the incisors; interorbital constriction excessive. 

 Processes of squamosal and maxilla have their ends in contact; the 

 jugal being merely a splint, not necessary for the continuity of the 

 zygomatic arch. 



