VESPERTILIONID^ 269 



Length about loo mm. (3.95 inches) ; tail vertebras 40 

 (1.60) ; ear from crown 15 (.60). 



Type locality, eastern United States. 



Silvery^haired bats are common in the eastern United States, 

 but appear to be rare west of the Rocky Mountains. I have seen 

 no Californian examples and know of but eight having been 

 taken in the State. In the eastern States this species frequents 

 the vicinity of streams and the borders of hardwood forests. 



Genus Pipistrellus Kaup. (A bat.) 

 Size small ; skull small and lightly built ; ears longer than broad, 

 tapering to a narrow rounded tip ; tragus straight or curved for- 

 ward; basal fourth of interfemoral membrane thinly haired on 

 the upper side. 



Dental formula, I, 2 — 3; C, i — i ; P, 2 — 2; M, 3 — 3X2=34. 



Pipistrellus hesperus Allen. (\^^estern.) 



WESTERN BAT. 



Smallest California species of bat; ear short, barely reaching 

 .lostril when laid forward; ears widely separated; tragus rather 

 short, very blunt and bent forward; feet 

 small; interfemoral membrane of moderate 

 size, sparsely haired on the upper surface 

 near the body, the border not fringed ; face 

 and ears bare, black; color of pelage pale; 

 above very pale drab ; below brownish white ; 

 all the fur blackish at base ; winigs dull black. 



Length about 72 mm. (2.85 inches) ; tail vertebrae 30 (1.20) ; 

 ear from crown lo- (.40) ; expanse of wings 200 (7.90). 

 Type locality, old Fort Yuma, California. 

 Western Bats range from southern and eastern California 

 east to Colorado and Texas. They are a desert loving species and 

 are not common in the coast region of southwestern California. 

 Very few remain in California in winter. The northward migra- 



