THE FAMILIES AND GENERA OF 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 H arpiocephalus 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 
Pteropidee, but is found in various intermediate conditions in mem- 
bers of the Phyllostomidse. As no transitory stages are known in the 
Pteropidae, the conditions in the Phyllostomidse present much the 
greater interest. 
Among the Chilonycterinae and Phyllostominae, the two most prim- 
itive groups of the Phyllostomidae, 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 V ampyrus 
(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 w T ell 
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- 
a See Gidley, Proc. Washington Acad. Sci., VIII, p. 94, July 10, 1906. 
