THE FAMILIES AND GENERA OP BATS. 37 



commissures, and the parastyle and metastyle are closely approxi- 

 mated, though distinct and unusually large. The three main cusps 

 are much closer together than in any other genus of bats, and the 

 protocone and paracone are so reduced as to appear like mere append- 

 ages to the large metacone. The whole tooth thus rather closely 

 resembles a normal fourth premolar, the first and fourth commissures 

 representing the anterior and posterior cutting edges, respectively, 

 and the metacone the main cusp. In the lower molars all of the cusps 

 except the protoconid are so reduced that the teeth approximate the 

 form of the lower premolars. While Harpiocephalus represents the 

 extreme of this peculiar variation so far as at present known, it would 

 not be surprising to find genera in which the metacone alone remains, 

 thus forming the complete parallel to the similar changes which 

 have resulted in the suppression of all but the paracone in such 

 genera of Insectivora as Centetes, Ericulus, and others. 



The next and more important series of changes is that leading to 

 the flat-crowned crushing tooth. This type of dentition, character- 

 istic of fruit-eating bats, reaches its highest development in the 

 Pteropidse, but is found in various intermediate conditions in mem- 

 bers of the Phyllostomidse. As no transitory stages are known in the 

 Pteropidse, the conditions in the Phyllostomidse present much the 

 greater interest. 



Among the Chilonycterinse and Phyllostominse, the two most prim- 

 itive groups of the Phyllostomidse, the teeth usually show no special 

 modifications (Plates III, IV, fig. 1). The premolars, and occa- 

 sionally the canines, are trenchant, and the molars retain their outer 

 cusps and commissures well developed and functional, except where 

 the lateral motion of the jaws is lessened by the excessive development 

 of the canines, the extreme of which condition is seen in Vampyrus 

 (Plates I, II, fig. 3). Such modification as occurs tends, therefore, 

 rather toward the narrow, blade-like type. 



In the Glossophaginse the first stage in the flattening process is 

 clearly seen (Plates III, IV, fig. 2) . The molars of the upper jaw have 

 nearly lost the mesostyle, while the parastyle in m 1 and in m 2 is prac- 

 tically indistinguishable from the base of the paracone. The meta- 

 style, however, remains long, though low; fourth commissure well 

 developed, but the other three reduced to a mere trace. In m 3 the 

 parastyle remains long, while it is the metastyle that has disappeared. 

 Paracone and metacone well developed, the metacone, as usual, the 

 larger. Protocone low and broad, extending backward along inner 

 margin of crown as a noticeable ridge. The three main cusps are 

 wide apart, and the space between the protocone and those of the 

 outer row is less encroached upon by the bases of the cusps. It thus 

 suggests the first trace of the flattened crushing surface. The man- 



* See Gidley, Proc. Washington Acad. Sci., VIII, p. 94, July 10, 1906. 



