nidad,
but all are insufficiently mature to show subspecific
characters distinctly. Until adequate series are available
from southwestern Las Animas County it seems best to regard
all specimens from the three localities as representatives of
a single uniform population which is intermediate between
_fallax_ and _scopulorum_ but more nearly like the latter.
Unfortunately no other specimens are available from the
foothill zone south of the Arkansas River where morphological
intergradation and ecological transition between _fallax_ and
_scopulorum_ might reasonably be expected to occur.

Three specimens from the north side of the Arkansas River,
about 26 miles below Canyon City, Pueblo County, are like
_fallax_ in size, dorsal profile of the skull, and shape of
the interorbital constriction; but they approach _scopulorum_
in shape of the interparietal, size of the rostrum, and size
of the molars. They are intergrades referrable to _fallax_.

_Neotoma mexicana_ was first reported from Oklahoma by W.
Frank Blair in 1939 (Amer. Midl. Nat., 22:126) who referred a
specimen from Tesequite Canyon, Cimarron County, to _N. m.
fallax_. I have seen one specimen (MZ 80469) from Tesequite
Canyon and refer it to _scopulorum_.

Of _scopulorum_, each of eight skulls, of the 28 skulls
examined, has an anteroexternal enamel fold on the m3 and one
(BSC 35222/47487 [Male]) has an anterointernal fold on the m3.
Of the other 19 mandibles, a few are too old to show such a
fold, which tends to be obliterated with wear in later age,
and the others lack the fold.

Two other wood rats (_N. albigula warreni_ and _N. micropus
canescens_) occur at many of the same localities as _N. m.
scopulorum_. The dens of _scopulorum_ almost always are
situated among rocks, but the dens of _warreni_ and
_canescens_ are in a variety of other situations as well as
among rocks. Houses of sticks or cactus joints piled up around
the base of a juniper (_Juniperus monosperma_), thicket of
skunkbush (_Rhus trilobata_), clump of soapweed (_Yucca
glauca_) or tree cactus (_Opuntia arborescens_) have been
found to shelter only _N. a. warreni_ or _N. micropus
canescens_. When these wood rats are associated with
_scopulorum_ among the rocks, their dens can be recognized by
th