THE FAMILIES AND GENERA OF BATS. 
167 
Premolars both above and below strongly resembling each other and 
canines, from which they differ chiefly in more reduced height and 
greater triangularity of outline of main cusp. Each has a large tren- 
chant outer cusp and the two upper teeth a distinct inner cusp high 
and well developed in pm 4 , low and obsolete in pm 3 . The lower pre- 
molars lack inner cusps, but the concave inner surface of the tooth is 
divided by a ridge extending from inner margin of tooth nearly to 
extremity of main cusp and strongly angled near middle. There is 
no indication of such a ridge in the upper premolars except a faint 
trace near summit of main cusp in pm 4 , and the inner concave sur- 
face is very well developed, slightly roughened posteriorly in pm 4 . 
First upper molar not strik- 
ingly different from last pre- 
molar in form, but longer, less 
concave, and the main cusp 
(paracoiie) not as high. On 
its inner side are the low proto- 
cone and liypocone, occup 3 ung 
about the same relative position 
as in the second molar of Artib- 
eus. From paracone a low, 
trenchant commissure extends 
along outer edge of tooth, near 
the posterior extremity of 
which is the rudimentary meta- 
cone. Outer and inner cingula 
very slight and irregular. 
Crushing surface concave, 
closely and finely wrinkled. 
Second u p p e r m o 1 a r with 
barely one-fourth area of first, fig.23.— pygoderma bilabiatum. ' sapucay, para- 
i 'ji ji ii • " GUAY. No. 105685. X If . 
but with the three mam cusps 
indicated, and a small, wrinkled, concave median surface. First 
lower molar of the usual Stenodermine type, the outer cusps low, or 
rather joined by a high commissure, the two inner cusps well de- 
veloped and in the normal position. A high, distinct ridge extends 
along anterior border of crown. Second lower molar less than half 
the size of first, its outer cusps obsolete, its two inner cusps rela- 
tively large. Skull (fig. 23) remarkable for its very deep, cuboidal 
rostrum, short, roundish palate (the inner line of the toothrows forms 
almost a circle except where broken posteriorly), and for the struc- 
ture of the interpterygoid region. The pterygoids are rather short 
and moderately divergent posteriorly, with short straight hamular 
processes, but below and behind each hamular (when skull is viewed 
from below) extends a plate conspicuously concave on inner side and 
