56 



MICROTIN^ 



enamel, and cement is present in the re-entrant folds. The 

 enamel pattern is closely similar to that of Microtus, but m^ 

 has only three closed triangles in front of the posterior loop, 

 the fourth and fifth triangles being more or less broadly con- 

 fluent with each other and with the anterior loop. In some 

 species w^ shows some interesting phases in its reduction. 



Fig. 4a 



Fig. 5a 



Fia. 29a.— Cheek-teeth of Neodon. 

 a. Right upper molars. 



1. N. sikimensis Hodgson (B.M., No. 15.9.1.218). 



2. N. forresti Hinton (type). 



3. N. irene Thomas (B.M., No. 12.3.18.13). 



4. N. carruthersi Thomas (B.M., No. 9.4.3.93). 



5. N. oniscus Thomas (B.M., No. 11.11.1.3). 



In face of the severe competition offered to it in Europe and 

 N. America by the very numerous species of Microtus, Pitymys 

 has been forced to adopt fossorial habits; it owes not only its 

 continued existence, but its outward and cranial specialization, 

 and probably its present wealth in species, entirely to these 

 habits. 



In those parts of the highlands of South-eastern Central 



