46 BULLETIN 57, UNITED STATES NATIONAL MUSEUM. 



Geographic distribution. — The same as that of the Megachiroptera 

 (p. 44). 



Characters: — Premaxillaries separate, though usually in contact 

 anteriorly, retaining their distinctness throughout life; bony palate, 

 narrowing gradually behind tooth rows, the width of interpterygoid 

 fossa, including hamulars, distinctly less than distance between pos- 

 terior molars; canines parallel when jaws are closed; cheek teeth well 

 developed, without unusual development of cusps ; tongue not specially 

 elongated. 



Principal subdivisions. — The Pteropinse, the largest group of the 

 Pteropidae, includes at least 19 genera. 



KEY TO THE GENERA OF PTEBOPIN.*:. 



Occiput so little deflected that alveolar line projected backward falls out- 

 side of skull or at most passes through condyle. 

 Upper cheek teeth more than 3-3. 



Upper incisors with widened, trenchant crowns ; calcar absent. 



Sphwrias, p. 53. 

 Upper incisors styliform ; calcar present. 



Lower incisors 2-2; outer upper incisor nearly as long as 

 inner. 

 Dentition normal ; canines with secondary cusp ; crown of 

 cheek-teeth without median ridge. 



Crowns of molars longer than broad, without evident 



median cusp Gynopterus, p. 47. 



Crowns of molars subquadrate, pm t and m - x with 

 distinct terete cusp slightly in front of middle of 



crushing surface Niadius, p. 49. 



Dentition unusually heavy; canines without secondary 

 cusp ; crown of pm t and m 1 with distinct median ridge. 



Thoopterus, p. 50. 

 Lower, incisors 1-1 ; outer upper incisor conspicuously shorter 

 than inner. 



Upper cheek teeth 5-r5 , Balionyctcris, p. 52. 



Upper cheek teeth 4-4. 



Rostrum nearly straight above ; tail present. 

 v_ Ptenochirus, p. 51. 



Rostrum strongly concave above; tail absent. 



Megwrops, p. 51. 

 Upper cheek teeth 3-^3. 



Cheek teeth all subterete Scotonyeteris, p. 64. 



Cheek teeth not all subterete. 



Dorsal and ventral profiles of skull strongly converging ante- 

 riorly ; lower molars with one cusp on outer side. 



Epomophorus, p. 65. 



Dorsal and ventral profiles of skull nearly parallel; lower 



molars with two cusps on outer side Hypsignathus, p. 67. 



