284 University of California Publications in Zoology [Vol. 21 



Microtus mordax mordax (Merriam) 



Cantankerous Meadow Mouse 



Arvioola (Mynomes) mordax Merriam (1891, p. 61, pi. 2, figs. 3, 4). 

 {Microtus) mordax, Trouessart (1899, p. 564). 

 Microtus mordax, Bailey (1900, p. 48), part [Goose Lake]. 

 Microtus mordax mordax, Miller (1912, p. 221), part. 



24231 

 Type specimen. — Male adult; no. coll. Biol. Surv., U. S. 



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Nat. Mus. ; Sawtooth Lake (or Alturas Lake), east base of Sawtooth 

 Mountains, 7200 feet altitude, Blaine County, Idaho; September 29, 

 1890; collected by Dr. C. Hart Merriam and Vernon Bailey; original 

 no. 1903. 



Range. — Modoc or Great Basin region of northeastern California. 

 Vertical range from 4800 feet up to 8700 feet ; zonal range Transition 

 to Hudsonian. (See map, fig. CC.) 



Total number of specimens examined, 39, from the following locali- 

 ties in California. Modoc County : east face of Warren Peak, Warner 

 Mountains (8700 feet), 11; head of N. Fork of Parker Creek (7300 

 feet), 11; Parker Creek (5000-5500 feet), 9; Goose Lake Meadows 

 near Sugar Hill (4800 feet), 2 ; Goose Lake Meadows near Davis Creek 

 (4800 feet), 4 (1 Biol. Surv.); Lassen Creek (5600 feet), 1 (Biol. 

 Surv.) ; Goose Lake (5150 feet), 1 (Biol. Surv.). 



Diagnosis. — Size medium (hind foot, 21 to 22 mm., condylobasal 

 length of skull in largest individuals, 28.1 mm.) ; second upper molar 

 without posterior internal loop or triangle ; first lower molar with four 

 reentrant angles on outer side; skidl, medium, slender and lightly 

 built (ratio of zygomatic breadth to condylobasal length about 54 per 

 cent) ; interorbital region not developing a crest with age. Pelage 

 grayish and normally light colored; underparts nearly pure white; 

 ears moderate in size (10 to 13 mm.). 



Measurements. — Average of 9 specimens, including 2 topotj^'pes : 

 Total length, 177.55 mm. (168-185) ; tail vertebrae, 63.88 mm. (61- 

 70) ; hind foot, 21.27 mm. (20-22.5) ; condylobasal length, 26.84 mm. 

 (26.2-28.1) ; occipito-nasal length, 26.24 mm. (25.3-27.8) ; basilar 

 length, Hensel, 23.9 mm. (23.3-24.8) ; nasal length, 7.82 mm. (7-8.8) ; 

 zygomatic width, 14.96 mm. (13.9-16.1) ; interorbital constriction, 

 3.78 mm. (3.1-4.1) ; interparietal width, 8.56 mm. (8.1-8.9) ; shelf 

 of bony palate, 13.46 mm. (12.9-14.3) ; height cranium at bullae, 9.77 

 mm. (9.5-10.1) ; mastoid width, 12.22 mm. (11.3-12.8) ; length upper 

 molar series, 6.34 mm. (5.9-6.7) ; length mandible, 15.94 mm. (15.3- 

 16.7). 



Color. — Mass effect of dorsal area ranging from tawny olive to 

 light cinnamon brown, with varying admixture of long dark overhairs. 

 Dorsal stripe strongly contrasted with rest of upperparts. In fresli 

 pelage : hairs of upperparts blackish plumbeous basally, with light 

 tipped portion grading from cinnamon buff to dark clay color; the 

 long overhairs grading from bone brown to aniline black. Color of 



