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 ther 
Pteropidae, includes at least 19 genera. 
KEY TO THE GENERA OF PTEROPIN^. 
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. 
Sphcerias, 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 Cynopterus, p. 47. 
Crowns of molars subquadrate, pm 4 and m x with 
distinct terete cusp slightly in front of middle of 
crushing surface .7 Nicidius, p. 49. 
Dentition unusually heavy ; canines without secondary 
cusp ; crown of pm 4 and m 1 with distinct median ridge. 
Thoopterus, p. 50. 
Lower incisors 1-1 ; outer upper incisor conspicuously shorter 
than inner. 
Upper cheek teeth 5-5 Balionycteris, p. 52. 
Upper cheek teeth 4-4. 
Rostrum nearly straight above ; tail present. 
Ptenochirus, p. 51. 
Rostrum strongly concave above ; tail absent. 
Megwrops, p. 51. 
Upper cheek teeth 3-3. 
Cheek teeth all subterete Scotonycteris, 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. 
