Hayden's Vole 
lOI 
Habits. — The Pigmy Vole seems to prefer the dryer prairie 
lands of the regions it inhabits, and is not found in such wet 
places as some of the other species. Its general habits seem 
to be essentially similar. 
Microtus ochrogaster haydeni (Grk. ochros, yellow, + 
gaster, stomach , haydeni, for Dr. F. V. Hay den). 
Hayden's Vole. 
Arvicola haydeni Baird, Mamrn. N . A. 543-544 (1857). 
Type locality. — Fort Pierre, South Dakota. 
Measurements. — Total length 6.5 ; tail vert., 1.45 ; hind foot, 0.85. 
Description. — (From a specimen taken at Wray, Yuma Co., 
Mar. 6th): Upper parts grizzled grayish brown, very similar to 
M. modestus; upper surfaces of feet and entire under parts buffy, with 
plumbeous bases of hairs showing through on belly. Tail buffy 
above, grayish below. The buffy color of the under parts serves 
to distinguish it at once from M. modestus, the only species which 
is found in the same range with it in Colorado. 
Distribution. — Hayden's Vole is found in the plains region of the 
following States; South Dakota, Nebraska, Kansas, Colorado, 
Wyoming, and Montana. In Colorado it is recorded from Larimer, 
Weld, Fremont, and Yuma counties. It is an inhabitant of the 
Transition Zone. 
Habits. — This species seems to prefer the prairie land as a 
place of residence. At the same time it may be found in 
the same locality as the Saguache Vole; at Wray, Yuma 
County, one of each species w^as caught at the same time 
near a spring in traps less than three feet apart. 
Genus EVOTOMYS (Grk. eu, well, + ous {ptis), ear, well-eared). 
Evotomys Coues, Proc. Acad. Nat. Sci., Phila., 1874, p. 186. 
Type E. rutilus. 
Revision, Bailey, Proc. Biol. Soc. Wash., xi., p 126 (1897). 
Small voles with short tails usually from ^ to ^ the total length ; 
eyes small and ears just projecting beyond the fur; back rufescent 
or reddish brown contrasting with the sides, this coloration is 
characteristic of all the species; skull with very weak flattened 
zygomata; dentition, i. |; m. f X 2 = 16; lower incisors with 
short roots, the latter falling short of the dental foramen; molars 
