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 *. 

 First upper molar not strik- 

 ingly different from last pre- 

 molar in form, but longer, less 

 concave, and the main cusp 

 (paracone) not as high. On 

 its inner side are the low proto- 

 cone and hypocone, occupying 

 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 upper molar with 

 barely one-fourth area of first, 

 but with the three main 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 



Pygodekma bilabiatum. Sapucay, Para- 

 guay. No. 105685. x ij. 



