THE FAMILIES AND GENERA OF BATS. 57 
Number of forms . — About 70 forms of P ter opus are now recog- 
nized. 
Characters . — Dental formula : 
- 2 3. 1. - 2 3 4 5 6 - .2-2 1-1 3-3 
1 2-1. - 2 3 1 5 6 7 '' 2-2 ,C l-l ,pm 3-3’ 
m 
2-2 
3-3 
34. 
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 2 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 1 , and pm 3 , pm 4 , m 1? 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 1 and m 15 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 3 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 
