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 topotypes of Microtus aztecus with a series of nine adults of M. p. modestus from 1 mi. S, 2 mi. E Eagle Nest, 8100 ft., Colfax County, New Mexico, with three adults from 1½ mi. E Manassa, Conejos County, Colorado, and with four adults from Saguache County, Colorado (all in KU), reveals that the supposed "well marked" external and cranial differences between the two forms are not nearly so evident as was indicated by Bailey.
The cranial differences that exist between these two forms (narrower nasals, slightly longer interparietal, slightly longer and narrower skull in aztecus) are evident only as averages. Although geographically intermediate specimens are lacking, the morphological differences between the two kinds of animals are of the degree and kind that separate subspecies, rather than species. We therefore judge M. aztecus (Allen) to be only subspecifically distinct from M. pennsylvanicus modestus and employ the name Microtus pennsylvanicus aztecus.
Microtus pennsylvanicus funebris (Dale)
1940. Microtus pennsylvanicus funebris Dale, Jour. Mamm., 21:338, August 14, type from Coldstream, 1450 ft., 3½ mi. SE Vernon, British Columbia.
Taylor and Shaw (Occas. Papers Charles R. Conner Mus., State College Washington, 2:24, December, 1929) list under Microtus nanus [= montanus] canescens material from Calispell Peak, Washington. Probably the basis for this record is a specimen in the Biological Surveys collection (adult male, 236474) taken on May 9, 1921, by G. G. Cantwell, and labelled as Calispell Peak, 9 mi. W Locke, 3500 ft., Pend Oreille County. An examination (by Hall and Kelson) of the specimen discloses that it is of the species Microtus pennsylvanicus, and that it falls within the geographic range ascribed to the subspecies Microtus pennsylvanicus funebris by Dalquest (Univ. Kansas Publ., Mus. Nat. Hist., 2:346, April 9, 1948).