274 University of California Publications in Zoology [Vou.17 
large (7.9 to 9.1 millimeters long) and strong, larger in proportion 
to size of body than in any other member of the genus Myotis. Gen- 
eral color of back cartridge buff; of lower surface, whitish. 
Description: Head.—EKar when laid forward reaching just beyond 
tip of nose; tip of ear narrow and abruptly rounded off. Tragus 
slender, about half height of ear, and pointed, its posterior border 
erenulate. 
Limbs and Membranes.—Membranes thicker than those of other 
small members of the genus. Foot large, broad, and strong, its length 
more than half that of tibia. 
Pelage.—Hairs longest on middle of back, where they average 
about 5 millimeters in length. 
Color—An example (no. 171508, U. S. Nation. Mus.) taken at 
Fort Mohave, Arizona, March 14, 1911, is colored as follows: hairs 
everywhere blackish at base; terminal half of fur on back and sides 
cartridge buff; beneath, whitish. Feet, ears, wings, and tail nearest 
avellaneous of Ridgway’s Color Standards; wing and tail membranes 
faintly edged with whitish. A specimen from Carroll Creek, Inyo 
County, is very similar in coloration, save that the ears, feet, and 
wing and tail membranes are nearest clove brown. Two specimens 
(coll. U. S. Nation. Mus.) from Colonia Lerdo, on the Colorado River, 
below Yuma, in Sonora, Mexico, agree closely in coloration with the 
Fort Mohave specimen; while a specimen (no. 138556, coll. U. S. 
Nation. Mus.) from Rancho San Antonio, Lower California, at the 
west base of the San Pedro Martir Mountains, varies in the direction 
of specimens of Myotis ywmanensis sociabilis from Fort Tejon, Kern 
County, California. 
SkulltIntermediate in size between that of Myotis californicus 
and Myotis lucifugus (total length, about 13.4 millimeters). Rostrum 
and interorbital constriction broader in ywmanensis than in califor- 
nicus. Skull of ywmanensis smaller and more slender than skull of 
lucifugus, and brain-case more inflated in frontal region. 
Measurements—The example of M. y. yumanensis (no. 16306, 
Mus. Vert. Zool.) taken at Carroll Creek, Sierra Nevada Mountains, 
Inyo County, September 9, 1911, measures in millimeters as follows: 
total length, 84.0; tail vertebrae, 37.0; tibia, 14.8; foot, 9.5; forearm, 
34.4; greatest length of cranium, 13.4; zygomatic breadth, 8.0; breadth 
of brain-ease, 7.0; interorbital constriction, 3.8. 
Synonymy and History.—tThis bat was described under the name 
Vespertilio yumanensis by H. Allen (1864, pp. 58-59) from material 
obtained at Fort Yuma, Imperial County, California. According to 
Miller (1897), p. 67) this bat is also the Vespertilio macropus and 
Vespertilio nitidus macropus of the same author, Dr. Harrison Allen. 
Distribution —Muiller (1912, p. 56) gives the range of the species 
as the Austral zones and lower edge of the Transition zone from the 
southwestern United States to San Luis Potosi and Michoacan, Mexico. 
The distribution in California is given by J. Grinnell (1913), pp. 
276-277) as follows: Lower and Upper Sonoran zones throughout 
southern California, both east and west of the desert divides; north 
