106 PROCEEDINGS OF THE NATIONAL MUSEUM vol. no 



a tendency to synonymize it under the name Plecotus. However, 

 there seems to have been no study of specimens to support the con- 

 tention that Corynorhinus and Plecotus are congeneric, or to determine 

 the relation of Idionycteris to them. 



Classification of Big-Eared Bats 



While agreeing with the basic outline of Tate's (1942, p. 225) 

 classification of vespertilionid big-eared bats, I prefer a slightly 

 modified version: 



Subfamily Vespertilioninae 

 Group Myotini 



Genera: Euderma 

 Plecotus 



Subgenera : Idionycteris 

 Plecotus 

 Corynorhinus 

 Group Pipistrellini 

 Genera: Histiotus 

 Laephotis 

 Group Nycticeini 



Genus: Otonycteris 



In my opinion, the degree of difference between the nominal genera 

 Idionycteris, Plecotus, and Corynorhinus is of subgeneric or specific 

 rather than generic grade. Idionycteris is a basal or relict form, 

 whereas Plecotus and Corynorhinus represent more advanced or later 

 evolutionary stages. Corynorhinus has evidently differentiated more 

 rapidly than Plecotus, and has approached the point of generic dis- 

 tinction from its near relatives. Inasmuch as these forms represent 

 different stages of evolution and since they form a disjunct series, at 

 least one of the steps of which contains more than one species, it seems 

 best to regard the degree of difference between the three forms of as 

 subgeneric rather than specific magnitude. Evidence in support of 

 this thesis is presented in the following pages. 



Characters and Comparisons 



Cranial characters relating Euderma and Plecotus and distinguishing 

 them from other big-eared bats {Histiotus, Laephotis, Otonycteris, 

 Nyctophilus, Pharotis, and Antrozous) of the family Vespertilionidae 

 are: 



1. Rostrum relatively weak, narrow, and shallow. 



2. Brain case elongated and vaulted in the frontal region. 



3. Zygomata parallel (in dorsal view) and not bowed out posteriorly. 



4. Dentition weak (teeth not robust). 



5. Cusps of teeth high and sharp-pointed. 



6. P4 not so high as Mi. 



7. Teeth reduced in number only slightly from the chiropteran maximum. 



