200 MICROTUS. 



299. oregoni. [Arvicola], Bachm., Journ. Acad. Nat. Scien. Phila. , 



1839, viii, p. 60. 



morosus. Elliot, Pub. Field Columb. Mus., 1899, 1, p. 227, Zool. 



Type locality. Astoria, Oregon. 



Geogr. Distr. Pacific Coast region from northern California to 

 Puget Sound. 



Genl. Char. Size small; tail long, ears prominent. Skull: brain 

 case rather flat and narrow; interparietal large, squarely rectangular; 

 zygomata considerably bent outward. 



Color. Above brownish bister; under parts buffy. Tail, black- 

 ish above, paler below. 



Measurements. Total length, 140; tail vertebras, 42;hindfoot, 17. 



300. serpens. {Microtus), Merr., Proc. Biol. Soc. Wash., 1897, p. 75. 

 Type locality. Agassiz, British Columbia. 



Geogr. Distr. " Southern British Columbia and northern Wash- 

 ington, between the Cascade Mountains and Puget Sound." 



Genl. Char. Tail shorter than that of M. oregoni, color darker. 



Color. Summer Pelage. Above very dark brown, dusky on lower 

 back and everywhere mixed with black; under parts deep plumbeous, 

 belly washed with buffy. Tail, dusky above, whitish below. 



Winter Pelage. Paler above; fur thinner, ears projecting. 



Measurements. Totallength, 130; tail vertebrae, 31; hind foot, 18. 



301. bairdi. {Microtus), Merr., Proc. Biol. Soc. Wash., 1897, p. 74. 

 Type locality. Glacier Peak, Crater Lake, Oregon. Altitude, 



7,800 feet. 



Geogr. Distr. Known from type locality only. 



Genl. Char. Size small, ears and tail short; colors pale. 



Color. Above pale grayish bister, tinged with reddish brown; 

 under parts whitish. Tail, dark above, whitish beneath. Feet 

 whitish. 



Measurements. Total length, 131; tail vertebrae, 33; hind 

 foot, 17.5. 



F. Arvicola. 



Palate slightly abnormal; lower third molar with occasional 

 closed triangles; first lower molar normally with three to five closed 

 triangles and seven to nine salient angles; upper third molar nor- 

 mally with two or three closed triangles, and six to eight salient 

 angles. Mammas, eight, four pectoral and four inguinal. Plantar 

 tubercles, five; sole almost naked. Musk glands present on sides of 

 body. (Miller.) 



302. richardsoni. {Arvicola), De Kay, N. Y. Zool., 1842, i, p. 91. 

 riparius, Richards, (nee Ord.), Faun. Bor. Amer. , 1829, p. 120. 



