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 Vampyrus (canines very large, lateral motion 

 nearly absent, outer portion of upper teeth noticeably degenerate), a 

 series which also shows the exceedingly nice adjustment between 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, which 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 known, 

 however, 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 drawing 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 

 crown. This condition occurs in the Nycteridse, Megadermida;, the 

 genus Vampyrus (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, Macroderma, 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 



