THE FAMILIES AND GENEEA OF BATS. 57 



Number of forms. — About 70 forms of Pteropus are now recog- 

 nized. 

 Characters. — Dental formula : 



-23. 1. -2345 6- .2-2 1-1 3-3 2-2 „. 



12-1.-234567 2-2' 1-1'^ 3-3' 3-3" 



Incisors (Plates VII, VIII, fig. 1) , terete with slightly differentiated 

 crowns, the lower bluntly rounded, the upper with a fairly defined 

 cutting edge. The upper incisors are in contact or nearly in contact 

 with each other, but are separated from canine by wide diastema. 

 They form a slightly convex row, and the outer tooth of each pair is 

 distinctly shorter than the inner. Lower incisors separated from each 

 other and from canines by minute spaces, the row slightly convex and 

 the inner tooth of each pair smaller than the outer. Canines sim- 

 ple, without secondary cusps, the cingulum rather prominently 

 developed on posterior and inner sides, and the shaft, especially 

 of the upper teeth, marked by conspicuous longitudinal furrows. 

 Anterior premolar (pm 2 and pm 2 ) small, that in upper jaw 

 much smaller than incisors and deciduous, its crown bluntly 

 pointed, that in lower jaw slightly larger than outer incisor, per- 

 manent, its crown rounded in outline, the surface concave, the 

 outer edge usually somewhat higher than inner. Posterior molars 

 (m * and m 3 ) essentially like anterior lower premolar in size and 

 form, but m 2 usually with a more prominent inner edge and often 

 with a distinct outer anterior cusp or tubercle. The remaining cheek 

 teeth (pm 3 , pm 4 , m % and pm 3 , pm 4 , m 15 m 2 ) rather closely resem- 

 ble each other and are all formed on the same general plan of a sub- 

 quadrate or somewhat elongated crown with distinct median furrow 

 in long axis of jaw and a well developed outer and inner ridge, each 

 ridge tending to rise into a cusp a little in front of middle. The 

 outer ridge and cusp is. always larger than the inner, and in the 

 region between the cusps the longitudinal groove is usually con- 

 stricted or partly obliterated. This type of structure is most per- 

 fectly shown by m * and m t , the ridges and cusps tending to become 

 obsolete in the more posterior teeth, while they successively increase 

 at the expense of the median furrow in the two large premolars, so 

 that pm * and pm 3 assume almost the aspect of short canines, each 

 with a well developed, or at least distinctly indicated, secondary 

 cusp on inner side, the longitudinal groove having been made almost 

 vertical by the elongation of the cusps. Skull (fig. 8) moderately 

 elongate, the length of rostrum considerably greater than lachrymal 

 breadth. Premaxillaries well developed, in contact anteriorly but 

 not fused, their breadth along nasal suture at least equal to that at 

 alveolus of outer incisor. Occipital region strongly deflected and 

 distinctly tubular, the floor of the braincase forming so great an angle 



