torum scalopsoides_, to
which subspecies they are here referred.

Microtus pennsylvanicus aztecus (Allen)

1893. _Arvicola (Mynomes) aztecus_ Allen, Bull. Amer. Mus. Nat.
Hist., 5:73, April 28, type from Aztec, 5900 ft., San Juan County,
New Mexico.

Allen (_loc. cit._) described this species on the basis of two
specimens from Aztec, New Mexico, and three from La Plata, New Mexico.
He characterized it as "Size large; pelage very full and soft; tail
short; skull very narrow.

"Above grayish brown with a tinge of pale buff; fur blackish plumbeous
beneath the surface, tipped with pale yellowish brown, and varied with
longer, projecting, black-tipped hairs; below grayish white, the fur
plumbeous beneath the surface and tipped with white, giving a whitish
gray effect. Feet dusky; tail dusky brown above, dull white below."

Allen identified as this species "a large _Arvicola_ from Estes Park,
Colorado, which I have before been unable to allocate. I am unable to
find that it differs in any particular from the specimens from New
Mexico." He pointed out also (_op. cit._:73-74) that "The type and only
positively identified specimen of Baird's _Arvicola modesta_ [=
_Microtus pennsylvanicus modestus_ (Baird)] from Sawatche Pass,
Colorado, is a very young specimen in poor condition. An examination of
a series of adult and young examples from the type locality will be
necessary in order to determine its relationships to _A. alticolus_ [=
_Microtus longicaudus alticolus_ (Merriam)] and _A. aztecus_."

Bailey, in his revision of the American voles of the genus _Microtus_
(N. Amer. Fauna, 17:20), showed _Arvicola modesta_ Baird to be a
subspecies of _Microtus pennsylvanicus_ but retained _Microtus aztecus_
(Allen) as a distinct species. In describing _M. aztecus_ he wrote "the
size similar to _M. pennsylvanicus_, but with shorter tail and larger
hindfoot; skull long; braincase narrow; interparietal long ..." and
remarked that "_Microtus aztecus_ belongs to the _pennsylvanicus_
group. Externally it is not very different from _modestus_, but none of
the specimens show any signs of intergradation; and the skull
characters are so well marked that there seems no doubt of its full
specific rank."

Subsequent to the publication of Allen's (_op. cit._) account and
Bailey's account (_op. cit._), additional material was collected that
helps to clarify the relationships of _Microtus aztecus_. A comparison
of six adult to