76 



MICROTIN^ 



relationship and of the fact that each has been profoundly modified 

 for fossorial habits, they are very unlike. Each has solved the 

 problems of fossorial life in its own peculiar way. 



Among the characters common to the two genera may be 

 mentioned the brachyodonty of the cheek-teeth, which develop 

 roots in adult stages of growth ; the peculiar reduction of m| ; 

 the simplification of ?«,j ; the absence of cement from the re- 

 entrant folds of the teeth ; the remarkable relation of the roots 



Fig. 48. — Neofiber alleni True. 

 Ventral view of skull (enlarged). 



of mg to the shaft of the lower incisor. The lower incisor 

 passes from the lingual to the labial side of the jaw between OTj 

 and m^ as in other voles ; but the implanted part of m^ curves 

 sharply backwards and follows the curve of the dorsum of the 

 incisor upon its lingual aspect, instead of continuing straight down 

 transversely across the shaft of the incisor. 



Prometheomys, represented by a single species living in the 

 mountains of the Caucasus, is in many ways the more primitive 

 genus. It is a rather large vole, with long and soft fur, very 

 small eyes, and moderately large, naked and rounded ears which are 

 provided with a large antitragus and are not concealed by the fur. 



