64 PTEROPTTS. 



iu one or other direction (either by eiilnrgemeiit of the posterior 

 basal ledges of tlie molariform teeth, or development of an inner 

 basal ledge in the lower cheek-teeth, or tendcnc}- to splitting of 

 inner ridges of certain lower cheek-teeth, or reduction of m^ and 

 m^, or excessive development of cingulum of canines and incisors, 

 or by several of these modifications combined). Compare skull and 

 numdible of I'leralojx'.v. 



I 



Fig. 



-A, typical Plei-oijine skull (Pt. hyjjomdn hilh tomci^i, 94.7.14.2); see text 



p. Gl. B, skull of a species with short rostrum and heavy dentition 



(Pt. cnieliam(f, 7. 1.1. 2;" 6) ; text p. 63. C, skull as modified in species 



with excessively weak cheek-teeth (Pt. icapulatus,&lX>A.2); text p. (iS. 



All figures \. 



The three principal types of Pteropine skulls described above as 

 (2), (;i), and (4) must not be considered sharply separated. There 

 is, on the contrary, a perfectly gradual transition from (2) to (3) 

 (viz. by species showing various stages of reduction in the sizes of 

 the teeth, and therefore also more or less pronounced leanings 

 towards the cranial charactei's of weak-toothed species), and several 

 transitional stages betAveen (2) and (4) (some of the most instructive 

 examples are found in the I't. iiselajiliut group ; certain jieripheral 



