244 University of California Publications in Zoology [Vou.17 
birds or reptiles, being for the most part of somber grays or browns, 
with the ventral surface a lighter tint of the same color that pervades 
the back. Among exotic bats there are notable exceptions to this 
rule, but among our Californian species only two diverge in color from 
the quiet tones of their fellows. These are the spotted bat (Huderma 
maculatum), which is black on the dorsal surface, with three large 
white patches; and the western red bat (Nycteris borealis teliotis), 
which varies in color from bright rufous-red or fawn to yellowish gray. 
Young bats, while of the same general color as adults of the same 
species, are usually darker and duller than their parents. 
All color names used in the following pages are taken from Ridg- 
way’s Color Standards and Color Nomenclature (1912). 
AGE VARIATION 
In determining the age of bats the writer has followed the sugges- 
tion of Miller (1897b, pp. 8-9), who finds that in adults the finger 
joints are small and compact, the epiphyses no longer visible, and the 
phalanges of essentially the same diameter throughout; whereas in 
young specimens the joints are ‘‘large and loosely formed, with 
epiphyses separate from the ends of the phalanges and metacarpals, 
both of which are distinctly enlarged for some distance from the 
joint.’’ 
The matter of determining the age of individuals is important 
because of the fact that young bats, even when nearly full grown, 
present characters different enough from those of the adults to cause 
confusion in identification. In general, the fur of immature speci- 
mens is shorter and more woolly than that of adults, and the color is 
darker and duller. The young of Lasionycteris, however, are a notable 
exception to this rule, the pelage of young examples being long and 
silky, and the hairs having beautiful silvery tippings, which in the 
adults are less perfectly shown. 
SEXUAL VARIATION 
There is but little sexual variation among North American bats, 
and in those inhabiting California I have found such as is present to 
consist only of a slightly greater average size of the females in a 
few of the species, for example, in Pipistrellus. 
