12 BULLETIN 144, UNITED STATES NATIONAL MUSEUM 



The most widespread American species is Myotis lucifugiis, whose 

 range extends to tree limit in the north and to southern Mexico in 

 the south. It becomes modified into five geographic races under the 

 changing conditions of this geographical area, but its structural 

 characters remain very constant. The fact, therefore, is rather re- 

 markable that a genus whose members may be capable of pushing 

 their range so far should be absent from the West Indies except in 

 the southern Lesser Antilles (Grenada, Dominica), where the tropi- 

 cal Myotis nigricans has gained a foothold, having undoubtedly come 

 in from northern South America. A representative of the same species 

 occurs on the island of Curacao, Such a distribution, however, is in 

 line with the pronounced northern affinities of the genus; it also 

 serves, perhaps, to emphasize the long isolation of the Antilles from 

 the continent. We have too little accurate knowledge of the dis- 

 tribution of Myotis in tropical America to say whether or not the 

 known species are mainly found at the higher levels and in cool 

 forest, but such may not improbably be the case. 



In the northern continent a general correspondence may be traced 

 between some of the American species and those of the Eastern Hemi- 

 sphere. There appears to be little doubt that the long-eared Ameri- 

 can Myotis keenii, M. evotis, and M. thysanodes are not distantly 

 related to the Old World M. nattereri (with its Japanese race horrv- 

 hinus) and M. emarginatus. The Palearctic Myotis daubentonii has 

 characters allying it to M. lucifugus, while a Chinese species, M. 

 frater, seems to be the Old World counterpart of M. volans. Simi- 

 larly, the Chinese M. tnoupinensis may be regarded as the Old 

 World representative of M. calif ornicus^ which it closely resembles 

 in its small size, bodily proportions, delicate feet, keeled calcar, and 

 long fur. The range of the American species volant and calif ornious 

 now reaches as far north as the coast of southern Alaska, and that of 

 evotis and yumanensis nearly, if not quite, as far. Presumably, the 

 northward extent of their representatives in the Old World will be 

 found to be limited by corresponding isotherms on the Asiatic side, 

 and this fact, if it could eventually be substantiated, would be in a 

 measure indicative of the higher temperature that must once have 

 prevailed to the northward at the time when the ranges of these now 

 slightly differentiated species were continuous from Asia to America 

 by way of a northern land connection providing favorable climatic 

 conditions. For it is not unreasonable to suppose that by some such 

 immigration these American species were derived from Asia and 

 that by subsequent evolution specific differences have arisen. On the 

 other hand, there is no obvious explanation of the fact that the very 

 large species, such as the European and Asiatic Myotis nvyotis and 

 M. chinensis have no representatives in the New World; but in this 

 connection it should be recalled that these bats are not known to 



