28 BULLETIN 57, UNITED STATES NATIONAL MUSEUM. 



invariably the outer that disappears first. This tooth may be seen in 

 every stage of degeneration among the genera with 2-2 upper incisors, 

 while in none is it distinctly more developed than its fellow, though in 

 some of the long-tongued Pteropidse and in certain genera of Gloss- 

 ophaginse it is slightly the larger. 



In the lower jaw the incisors become reduced from the outer side, 

 a process mostly associated with narrowing of the anterior portion 

 of the mandible. This process is especially well illustrated in the 

 Molossidse. The third incisor exists in some species of Nyctinomus 

 and in Mormopterus, though reduced in size and crowded beneath the 

 cingulum of the canine, the prominent cusp of which has assumed its 

 function. In Chcerephon, Eumops, Promops, and most species of 

 Nyctinomus it has disappeared. In some species of Molossops the 

 narrowing of the mandible has reduced and distorted the second 

 incisor, the cingulum cusp of the canine in turn taking the functions 

 of this tooth, while in other species of Molossops, in Eomops, Cheiro- 

 meles, and Molossus the second incisor has disappeared. There is 

 little doubt that a similar course" has been followed throughout the 

 Microchiroptera. In the Megachiroptera no genera are known with 

 3-3 lower incisors, and it has been assumed by Winge that the first 

 tooth is absent, a conclusion based chiefly on the correspondence in 

 position of these teeth with, the second and third of the upper jaw. 

 The probability of this view seems heightened by the almost univer- 

 sally larger size of the outer tooth as compared with the inner, while 

 in the Microchiroptera the reverse is normally the case. In the fruit- 

 eating Phyllostomidse, however, there is a similar reduction in the 

 size of the inner incisor as compared with the outer, probably due to 

 the aotion of the tongue, and I prefer to assume that the frugivorous 

 habits of the Pteropidse account for the relative size of these teeth 

 also, and that the course of reduction in this group forms no exception 

 to the rule, so far at least as regards the disappearance of the outer 

 tooth first. The next incisor to disappear is, however, probably i t , 

 acted, upon, as it must have been, by the tongue. In the genera 

 Dobsonia, Nesonycteris, and Notopteris i , is therefore the remaining 

 tooth. 



Premolars. — Both above and below it is probably the first pre- 

 molar that is permanently absent, though of this there is no proof. 

 In the upper jaw the next to disappear is either pm - or pm 6 . 

 Three premolars are present in members of the families Pteropidse, 

 Phyllostomidse, Natalidse, Thyropteridse, Myzopodidse, and Vesper- 

 tilionidse. The anterior tooth {pm 2 ) is the more reduced in four 

 of these, the Pteropidse, Phyllostomidse, Natalidae, and Thyrop- 

 teridse, while the median (pm 3 ) is the smaller in the two others, 

 ihe Myzopodidse and Vespertilionidse. While the evidence is there- 

 fore not conclusive for any of the other families, it appears safe to 



