476 University of California Publications in Zoology | Vou. 17 
While the coloration of adults and young is similar, the latter are 
woollier and grayer in general appearance than in the former. 
Age Variation —Cranially there is a tendency for the sutures be- 
tween the nasals posteriorly, the premaxillaries and the frontals to 
remain open longer than is the case in other species. The interorbital 
constriction undergoes a proportional and with some exceptions an 
actual decrease with age. The zygomata are heavier in adults than 
in the young and tend to be more bowed outward, or squarer, ante- 
riorly. Temporal lines or ridges come closer together with age. In 
some old adults of this species they almost coalesce anteriorly, while 
remaining only four or five millimeters apart posteriorly. Although 
the mastoid process tends to grow laterad more rapidly than the audital 
tube with age, in almost all the available specimens the latter exceeds 
the former in length. 
Sexual Differences—The erania of males tend to be larger than 
those of females in nearly all measurements; zygomata are heavier 
in males; and the temporal lines or ridges tend to be more accentuated 
and more closely approximated. The females tend to have interptery- 
goid fossa proportionally broader than the males. In seven out of 
eleven males measured the mandible, transversely across angular pro- 
cess, is greater than the maximum for the females. Examination of 
the material before me confirms C. Hart Merriam’s (1886, pp. 327, 
328) conclusions regarding cranial differences due to sex in this species 
except in certain details respecting the suture which separates the 
frontal bones from the premaxillaries and nasals, and in the outline 
of the postzygomatie notches. In Merriam’s material the suture in 
question is open in the females and closed in males, while in the 
material before me there is nearly as strong a tendency toward efface- 
ment of the suture in females as in males. In Merriam’s material 
the postzygomatic notches are larger in females, while in the material 
now available no constant sexual differences in this respect can be 
made out. Our specimens like those examined by Merriam have the 
skulls of the females less heavy and massive than those of the males, 
the oceipital crest not so highly developed, and the zygomatic arches 
not so much bowed outward. 
Molt and Seasonal Change. 
ing takes place during late summer and early fall. The earliest molt- 
ing specimen examined is a female taken July 21. Most examples 
taken during August and September are well along in the molting 
process, while those secured in October show its last stages, and a 
As in other subspecies of rufa, molt- 
a 
