ing of the Society, in June of 1954. Unless otherwise
indicated, specimens are in the University of Kansas Museum of
Natural History. Specimens in other museums are designated beyond
as follows: American Museum of Natural History (AMNH); Museum of
Zoology, University of Michigan (Mich); Chicago Natural History
Museum (Chi); United States National Museum (USNM); Biological
Surveys Collection (USBS); Museum of Vertebrate Zoology, Berkeley,
California (MVZ); Colorado Museum of Natural History, Denver
(Denv); E. R. Warren collection, Colorado College, Colorado Springs
(ERW); University of Colorado Museum, Boulder (UC).

ACCOUNTS OF SUBSPECIES

Microtus pennsylvanicus modestus (Baird)

_Arvicola modesta_ Baird, Repts. Expl. and Surv...., pt. 1,
Mammals, p. 535, July 14, 1858.

_Microtus pennsylvanicus modestus_, Bailey, N. Amer. Fauna,
17:20, June 6, 1900.

_Type._--Immature specimen (sex not specified), skin and skull,
number of skin 594, number of skull 1717, deposited in the
collections of the Smithsonian Institution, obtained by F.
Kreutzfeldt, Sawatch Pass, Rocky Mountains [=Saguache Pass or
Cochetopa Pass, Saguache County, Colorado], exact date unknown. I
have not examined the type specimen.

_Range._--Northern New Mexico, and southern Colorado (see list of
specimens and Fig. 2).

_Comparisons._--For comparison with the subspecies newly described
below from northern Colorado see the account of that subspecies.
The subspecies _M. p. aztecus_ has been compared with _M. p.
modestus_ by Hall and Cockrum (1952:308) who reduced _aztecus_ to
subspecific rank. Although _aztecus_ is separated by approximately
100 miles from _modestus_, and although no proof of intergradation
is available, my studies of variation in this species lead me to
agree with Hall and Cockrum that "the morphological differences
between the two kinds of animals are of the degree and kind that
separate subspecies, rather than species." A more adequate series
of adults of _aztecus_ is needed to clarify even the subspecific
differences between _aztecus_ and _modestus_.

_Measurements._--Averages, extremes, and standard deviations of a
number of series are included in Table 1 in order to facilitate
comparisons between different subspecies.

_Remarks._--The dividing line between _M. p. mode