Vol. XXllI, pp. 1-2 February 2, 1910 



PROCEEDINGS 



OF THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



DESCRIPTIONS OF TWO NEW JNIUSKRATS. 



BY X. HOLLTSTER. \<^ . 



■ A systematic study of the muskrats discloses two unnamed 

 subspecies, preliminary descriptions of which are herewith 

 presented. Both new forms are based upon specimens in the 

 collection of the United States Biological Surve3^ 



Fiber zibethicus mergens subsp. nov. 



Type from Fallon, Nevada. No. 156,880X1. S. National Museum, Bio- 

 logical Survey Collection. 9 adult, skin and skull. April 3, 11)08. 

 Collected by S. E. Piper. 



General characters. — Differs trom F. z. osoyoosensis in its much paler 

 color and distinct dorsal stripe, and from F. z. pallidus in its large size 

 and darker colors. 



Color. — Fresh pelage: Above grayish brown; head and dorsal area 

 blackish; cheeks, shoulders, and sides rusty; underparts creamy white 

 with central area pale cinnamon or russet; usual spot on chin blackish 

 brown. Fall specimens before the black hairs have come in are some- 

 times quite rusty above. Worn or washed out pelage: Above uniform 

 pale yellowish brown ; sides and underparts with little rusty. 



Cranial characters. — Skull smaller than that of osoiioosensis, with 

 shorter rostrum, more broadly spreading zygomata, and heavier jugal ; 

 much larger than that of pallidus. 



Measurements of type. — Total length, 540; tail vertebrae, 240; hind foot, 

 76. Skull: Basal length, 61.6; zygomatic breadth, 40; palatal length, 39. o; 

 length of nasals, 21 ; breadth of nasals, 9.8 ; alveolar length of upper molar 

 series, 15.5. 



Remarks. — Fiber z. mergens is a pale form of the osoyoosensis type, 

 occupying the northern part of the Great Basin. There is no evidence of 

 direct intergradation with the very different pallidus on the south. 



Fiber zibethicus zaiophus subsp. nov. 



Type from Becharof Lake, Alaska. No. 131,488 U. S. National Museum, 

 Biological Survey Collection. Skin and skull. October, 1903. Collected 

 by A. G. Maddren. 



1— Proc. Biol. Soc. Wash., XXIII. 1910. (1) 



