306 University of California Publications in Zoology (Vou. 17 
point midway between eye and nostril, when laid forward; anterior 
border of auricle strongly convex from the well developed basal notch 
to about middle, where it becomes straight and continues so almost 
to the broadly rounded tip; posterior border concave immediately 
below tip, then strongly convex to basal notch; basal lobe well devel- 
oped, separated from main auricle by a deep notch, and joining face 
at a point slightly below and behind angle of mouth. Tragus less 
than half height of ear, slightly blunt at tip, and curved forward 
(text-fig. L). The western bat and the Merriam bat are the only 
small bats of California having the tragus curved, and this feature 
is sufficient to distinguish them at once from the several small species 
of Myotis. 
Limbs and Membranes.—Wing short and broad, length of fifth 
metacarpal almost equaling that of third. Wing membrane attached 
at base of outer toe. Calear very slightly lobed at tip. Tip of tail 
projecting somewhat beyond edge of interfemoral membrane. Foot 
small, tibia short; length of former scarcely less than half that of 
latter. Tail about equal in length to forearm. 
Pelage-—Fur everywhere full and soft, 3 to 4 millimeters in length 
on body. Dorsal surface of ear furred only on its basal third; a 
seanty sprinkling of fine hairs over whole ventral (inner) surface 
of ear. Wing membranes naked both above and below, save for a 
very narrow strip of fur, about one millimeter in width, which extends 
out from side of body. Basal third of interfemoral membrane 
sprinkled with fine hairs, both above and below. Toes scantily 
clothed, both above and below, with very short, fine hairs. 
Color—Hairs everywhere plumbeous-black at bases. Distal two- 
thirds of fur on upper surface light buff, brightest on top of head; 
on lower surface a very pale tint of light buff, almost white; pelage 
everywhere given a grayish cast by the showing through of the darker 
bases of the hairs. Ear, muzzle, and wing and tail membranes, 
blackish, save that wing membrane is narrowly bordered with pale 
eray between foot and fifth finger. 
Skull—Form and general characteristics as for the genus. In 
general, as has been suggested, the skull of this bat reminds one of 
a miniature Lasionycteris. 
Measurements—Average and extreme measurements in milli- 
meters of a series of twenty western bats, from the Colorado River 
Valley, are as follows: ten males: total length, 66.4 (extremes, 62.0— 
72.0) ; tail vertebrae, 26.5 (24.0-30.0) ; tibia, 10.6 (10.0-11.5) ; foot, 
5.0; forearm, 27.8 (26.6-30.0); greatest leneth of cranium, 11.5 
(11.3-11.9). Ten females: total length, 72.9 (69.0-80.0) ; tail verte- 
brae, 29.9 (26.0-33.0) ; tibia, 11.2 (10.0-12.0); foot, 5.2 (5.0-6.0) ; 
forearm, 29.8 (27.3-30.7); greatest length of cranium, 11.9 (11.7- 
112.3). 
A comparison of the above averages will show that the females are 
as a rule somewhat larger than the males. 
Synonymy and History.—The western bat was described by H. 
Allen (1864, pp. 48-44) under the name Scotophilus hesperus from 
material obtained at Fort Yuma, California, and ‘‘Posa Creek.’’ 
According to True (1887, p. 515), Dobson in his catalogue of the 
