THE AMERICAN BATS OF THE GENERA MYOTIS AND 



PIZONYX 



By Gerrit S. Miller, Jr. 



Curator, Division of Mammals, United States National Museum 



and 



Glover M. Allen 



Curator of Mammals, Museum of Comparative Zoology, Cambridge, 

 Massachusetts 



INTRODUCTION 



The bats of the genus Myotis, though small and inconspicuous 

 mammals, present many features of unusual interest from the point 

 of view of systematic zoology. At nearly every point in its exces- 

 sively wide range the genus is represented by several species often 

 puzzlingly alike in superficial appearance though readily distinguish- 

 able from each other when the true differential characters are once 

 recognized. As these animals everywhere subsist, so far as known, 

 on small, soft-bodied insects, and their habits appear to be subject to 

 no conspicuous changes from species to species or from district to 

 district, we are forced to regard the process of specific differentia- 

 tion in the group as a whole as primarily dependent on some other 

 factor than any influence which might be exercised directly by the 

 environment. This is equally true of the species in most genera of 

 bats; but in no other genus do we find the process worked out in so 

 much variety of detail over a territory so nearly world-wide in 

 extent. 



In striking contrast to Myotis the nearly related genus Pizonyx is 

 not at present known to have any geographical " range " in the true 

 sense, as the few existing specimens have all been collected on islets in 

 the Gulf of California and on the neighboring mainland of Sonora. 

 Its peculiarities may prove to have an adaptational significance as 

 the animal has become specialized in a manner which somewhat paral- 

 lels the occasionally fish-eating Noctilio. The food habits are, how- 

 ever, not yet known. 



1 



