tween
basisphenoid and presphenoid completely closed; nasals rounded
anteriorly; permanent P4 and p4 show no wear through enamel layer; wear
through enamel layer of molars noticeable, especially through
protocones; peglike permanent P3 slanting only slightly posteriorly;
skull only slightly convex dorsally; parietals solid and resistant to
pressure; lambdoidal crest weakly developed; 4 to 10 months of age.

_Adults._--Lambdoidal crest well developed; supraorbital ridges
pronounced; P4 and p4 show wear through enamel layer and frequently as
worn as molars; noticeable wear on lophs and lophids of molars;
occlusal pattern always visible; ten months to 2 years of age.

_Old adults._--Ridges and crests extremely well developed; occlusal
pattern of molariform teeth obliterated or nearly so; P3 noticeably
worn; 2 to 4 years or older.

The hypohyal and ceratohyal bones of the hyoid apparatus are distinct
from one another in juveniles and young, but are fused in subadults,
adults, and old adults.

Lack of suitable material prevented me from studying chipmunks younger
than juveniles. The patterns of growth of these younger chipmunks
probably closely follow the changes described by Hall (1926) for
_Citellus beecheyi_.

The tip of the baculum in juveniles and young is proportionally longer,
in relation to the shaft, than in subadults, adults, and old adults.

Juvenal (juveniles and young) pelage in chipmunks is characterized by
silkiness and sparseness, especially on the venter. The coloration of
this juvenal pelage resembles that of adults in winter pelage which is
duller than adult summer pelage. Adult pelage (subadults, adults, and
old adults) is not so silky as juvenal pelage, but there are more
hairs, especially on the venter. The color pattern is the same in both
juvenal and adult pelages.

Chipmunks are born naked and blind and in about two weeks the "body is
covered with silken hair clearly demonstrating the color pattern so
characteristic of chipmunks...." (Shaw 1944:282). This "silken hair" is
replaced by adult summer pelage, and juvenal chipmunks which are
molting into adult summer pelage closely resemble the adult males, and
later on in the summer, the adult females. Adult females molt later, as
a rule, than adult males probably because of lactation. Summer molt
begins, on chipmunks in Wyoming and South Dakota, in the latter part of
June and is completed by the latter part of August or the first part of
Septemb