221 and 90 uncatalogued specimens in
preservative; Mancos River, 6200 ft., 69382-69385; back of Park
Museum, 6930 ft., MV 7857/507; Mesa Verde, 25 mi. [by road] SW
Mancos, 149093 USNM; Cornfield, MV 7878/507.

The most abundant mammal is the ubiquitous deer mouse. Series of
specimens taken in August (by Anderson in 1956), in September (by
Shepherd in 1958 and 1959), and in November (by Alcorn in 1957) make
possible the following comparisons of age, reproductive conditions, and
molts.

The specimens obtained in August and November were placed in five
categories according to age (as judged by wear on the teeth). These
categories correspond in general to those used by Hoffmeister (1951:1)
in studies of _Peromyscus truei_. From his descriptions I judge that
wear in _Peromyscus maniculatus_ differs from wear in _Peromyscus truei_
in that the last upper molar is not worn smooth before appreciable wear
appears on the first two molars, and the lingual and labial cusps wear
more nearly concurrently. The five categories differ as follows:
category 1, last upper molar in process of erupting, showing no wear;
category 2, some wear apparent on all teeth, but most cusps little worn;
category 3, greater wear on all teeth, lingual cusps becoming rounded or
flattened; category 4, lingual cusps worn smooth, labial cusps show
considerable wear; category 5, all cusps worn smooth. The condition of
the pelage was noted for each prepared skin. Hoffmeister (_op. cit._: 4)
summarized changes in pelage that he observed in _Peromyscus truei_, and
he summarized earlier work by Collins with _Peromyscus maniculatus_. In
_P. maniculatus_ a grayish juvenal pelage is replaced by a postjuvenal
pelage in which the hairs are longer and have longer, pale, terminal or
subterminal bands giving a paler and more buffy or ochraceous hue to the
dorsal pelage. The postjuvenal pelage is replaced by an adult pelage
that is either brighter or, in some cases, is not distinguishable with
certainty from the postjuvenal pelage. Not only is the juvenal pelage
distinguishable from the postjuvenal pelage, but the sequence of
ingrowth of postjuvenal pelage follows a regular pattern that is usually
different from that of subsequent molts. The loss of juvenal hair is
less readily observed than the ingrowth of new postjuvenal hair on
account of the greater time required for the growth of any individual
hair than for the sudden loss of a hair.

Molt was observ