408 University of Califorma Publications in Zoology [ Vou. 17 
californica (Oberholser, loc. cit.), and the same is true as between 
A. californica immanis of the Sacramento Valley, and A. hypoleuca 
of Cape San Lueas, but in each case the region between these forms 
is occupied by a race or races different from either. 
It seems to me that there is danger of giving too much emphasis 
to the resemblances noted, and of losing sight of the significant fact 
that there is no blending of characters where the different forms 
meet. For example, although in the three subspecies of Aphelocoma 
californica, as I would restrict them, californica, oocleptica, and 
immanis, there is such intergradation at the margins of the several 
habitats, nothing of the sort can be detected along the boundary 
between immanis and woodhouset. It is true that there is a specimen 
at hand that may be regarded as intermediate between these two 
latter forms (see beyond), but this is a single sporadic individual, and 
the circumstance appears to be exactly comparable with conditions 
observed to exist in Psaltriparus minimus californicus and P. plum- 
beus, of the same region. In both cases in this marginal region the 
populations in general of the several species are as typical in appear- 
ance as are those at opposite extremes in the birds’ ranges. It is 
just an occasional individual which shows any admixture of characters 
of the adjoining races. 
The manner of variation to be traced through the several sub- 
species of Aphelocoma californica differs in some respects from what 
may be observed among other variable species of birds. Aphelocoma 
is not an especially ‘‘plastic’’ group, the several species being for 
the most part rather sharply defined, and remaining uniform in 
appearance over a wide expanse of territory. In the three recogniz- 
able subspecies of A. californica occurring within the state of Cali- 
fornia, the manner of variation is unlike what is observed in the races 
of such species as Pipilo maculatus and Thryomanes bewicki, for, as 
shown in the accompanying table, in A phelocoma the several characters 
concerned vary, to all appearances, independently, and not always in 
the same direction. 
Characters which have been used to differentiate species and sub- 
species in the genus Aphelocoma pertain to size and color. Size char- 
acters consist of general size, length of wing, length of tail, length of 
bill and bulk of bill. Color characters used are: shade of the blue 
areas, of dorsum, of under parts, of under tail coverts. 
It should be noted that characters of color are quite as apparent 
in the juvenal plumage as in the adult, and, when the quill feathers 
