304 University of California Publications in Zoology [Vou.17 
to be migratory in at least the eastern portion of its range, and the 
same probably holds true here in California. The known facts relat- 
ing to its migration are recorded on page 232 of the present paper. 
Of nine specimens obtained by Joseph Dixon at Fyffe (3700 feet 
altitude), Eldorado County, between July 19 and 31, seven were adult 
females weighing from 10.2 grams to 12.1 grams each, one was an 
immature female weighing 6.3 grams, and one a male, probably imma- 
ture, weighing 8.5 grams. Some of the adult females showed evi- 
dences of having recently nursed young. 
Genus Pipistrellus Kaup 
This genus ranges in the Eastern Hemisphere from the northern 
to the southern limits of tree growth, and from Tasmania to [reiand. 
In the Western Hemisphere it occurs from the northern United States 
(except in the Boreal zone’) to southern Mexico (Barrett-Hamilton, 
1910, p. 102). The genus contains about forty species, only one of 
which occurs in the area under consideration, where it is represented 
by two subspecies. 
o BY ll 2=2 3-3 
Characters —Dental formula: 1 329’ © jay’ PMocg) M 3-3 — 34. 
Upper inner incisor about one-third higher than outer one. Lower 
incisors all of about equal size and with columnar shafts, separated 
from each other by spaces about one-third the width of the shaft; 
the abruptly wider crowns are imbricated and deeply trilobed. 
Upper canine conical and about twice height of lower canine, which 
is similar in form but with a more highly developed cingulum. First 
upper premolar minute and lying on inner side of tooth row, crowded 
in angle between canine and second upper premolar. Second upper 
premolar about midway in height between canine and first molar. 
First lower premolar about half height of second and closely crowded 
against cingulum of canine; cingulum of this premolar about equal 
in width to that of canine. Second lower premolar nearly equal 
in height to lower canine. Molar teeth normal for vespertilionid 
bats. 
Greatest width of skull about two-thirds of the total length of 
same. Brain-case distinctly flattened above and forming only a sight 
angle with rostrum. Auditory bullae large, their greatest diameter 
being distinctly greater than the width of the space between them. 
Zygomata slightly expanded. (See pl. 21, fig. 27, and pl. 22, 
fig. 39.) 
Ear in this genus distinetly longer than broad and tapering to a 
narrowly rounded tip. Tragus broadest below its center, its tip 
straight or shghtly eurved forwards. Dorsal surface of interfemoral 
membrane sprinkled with hairs on basal third. Mammae two. 
