36 BULLETIN 57, UNITED STATES NATIONAL MUSEUM. 
This is well illustrated by the genera Anthorhina (canines small, 
lateral motion of mandible free, outer portion of upper teeth well 
developed), Phyllostomus (canines large, with strongly trenchant 
edges, lateral motion reduced, outer portion of upper teeth relatively 
less developed), and V ampyrus (canines very large, lateral motion 
nearly absent, outer portion of upper teeth noticeably degenerate), a 
series which also shows the exceedingly nice adjustment betAveen the 
different parts of the cutting apparatus, since the gradually increas- 
ing size of the canines is closely followed by alterations in the cusps 
throughout the series of molar teeth. 
MODIFICATIONS OF CUSPS. 
While the majority of bats retain, together with their insectivo- 
rous habits, the typical primitive dentition almost unmodified, the 
members of certain groups show conspicuous changes in the form as 
well as in the function of the teeth. These alterations, Avhich pro- 
ceed chiefly by suppression of the original cusps, follow two main 
lines, one leading to a flat-crowned type of tooth effective for crush- 
ing the pulp of fruits, the other to a narrow, blade-like form most 
perfectly developed in those bats which subsist on blood. 
Among insectivorous bats a third line of divergence seems to be 
incipient. In this the molars tend to assume a single-cusped form 
closely resembling the fourth premolar. This is accomplished by the 
reduction of the styles and commissures and by the blending of the 
protocone and paracone with the metacone and of the paraconid and 
metaconid with the protoconid. In the most extreme instance knoAvn, 
hoAvever, it is not complete, as the three cusps are still recognizable. 
The first step in this direction is seen in various unrelated genera and 
consists in the reduction of the mesostyle together with the second 
and third commissures, accompanied by a distinct draAving together 
of the three main cusps, a noticeable diminution in the size of the 
protocone and paracone, and the partial fusion of the latter with 
the metacone. In the mandibular teeth the corresponding change is 
seen in the reduced area of the- triangle formed by the protoconid, 
paraconid, and metaconid as compared with the basal area of the 
croAvn. This condition occurs in the Nycteridse, Megadermidse, the 
genus V ampyrus (Plates I, II, fig. 3) and in Pachyotus (Plates I, 
II, fig. 2). In the Megadermidse it shows various degrees of develop- 
ment, being well advanced in Megaderma , M aero derma, and Cardio- 
derma , merely suggested in Lavia. In Pachyotus (Plates I, II, fig. 2) 
it has reached the same stage as in Megaderma in the maxillary 
teeth, while the mandibular teeth are slightly further advanced, hav- 
ing the second triangle noticeably smaller than the first. The next 
stage occurs in the genus Harpiocephalus (Plates I, II, fig. 4). In 
this the mesostyle has disappeared, together with the second and third 
