lls area of extreme northeastern Wyoming. Suitable
montane habitat is present and both _Microtus pennsylvanicus insperatus_
and _Microtus longicaudus longicaudus_ occur there. The arid basin of
the Powder River presumably is a barrier that has prevented _M.
montanus_ from reaching this area.

REFERENCES CITED

BAILEY, V.

1900. Revision of American voles of the genus _Microtus_. N. Amer.
Fauna, 17:1-88, June 6.

1917. A new subspecies of meadow mouse from Wyoming. Proc. Biol.
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CARY, M.

1911. A biological survey of Colorado. N. Amer. Fauna, 33:1-256,
August 17.

1917. Life zone investigations in Wyoming. N. Amer. Fauna, 42:1-95,
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DAVIS, W. B.

1939. The Recent mammals of Idaho. 400 p., front., illus., maps,
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DURRANT, S. D.

1952. Mammals of Utah, taxonomy and distribution. Univ. Kans.
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ELTON, C.

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GOIN, O. B.

1943. A study of individual variation in _Microtus pennsylvanicus
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HALL, E. R.

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HILL, E. A.

1935. Cranial foramina in rodents. Jour. Mamm. 16(2):121-129.

HOWELL, A. B.

1924. Individual and age variation in _Microtus montanus yosemite_.
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KELLOGG, R.

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MERRIAM, C. H.

1891. Results of a biological reconnaissance of south-central
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PIPER, S. E.

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WARREN, E. R.

1942. The mammals of Colorado, their habits and distribution.
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_Transmitted March 22, 1954._

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