114 



MICROTIN^ 



similar to that seen in the m^ of M. pUoccBnicus, after the 

 disappearance of the islet, is speedily brought to the surface 

 by wear. The youngest tooth of M. intermedius at present 

 known (Fig. 61a) shows two of the lowest crown tubercles 



Fig. 61. — Mimomys intermedins Newton. 



Crown views of young specimens of the nii and of the lower molars of the 

 type specimen; all from the Upper Freshwater Bed at West Runton. 



a. Left nil, very young, with third outer fold intact, and other youthful 



features. 



b. Right nil, slightly older than a. 



c. Right »«j, with third outer fold undergoing insulation. 



d and e. Two examples of the left Wj with the third outer fold represented 

 by an ephemeral enamel islet ; e', basal pattern of e for comparison 

 with the adult crown pattern shown in the type specimen /. 

 (In e' the dentinal spaces are lettered to illustrate the terminology 

 usually employed in descriptions of Microtine molars : p = 

 posterior loop; 1, 2, 3 closed triangles; a.l. anterior loop.) 



surmounting the fore-part of the anterior loop ; but wear has 

 proceeded too far to enable us to say whether a median valley 

 was originally present in the fore-part of the anterior loop, as 

 in Arvicola, or not. 



In the species of Mimomys so far mentioned the third outer fold 



