MIMOMYS 



379 



Almost all stages of growth are represented in the long 

 series of examples of the m^ now before me. As in other 

 species the young teeth are of especial importance, for they 

 throw light upon the significance of certain characters which, 

 though minute, are very commonly present in the adult m^ of this 

 and other species. In this connection, and also in order to show 

 what range of variation is seen in the ;«i of this species, attention is 

 called in the following notes to the more interesting specimens so 

 far examined. 



In a slightly worn w^, from the " peat " at West Runton 



Fio. 104. — CroT\Ti views of w,j of Mimomys majori Hinton and 

 31. cantianus Hinton. 



a. M. 7najori. Right nii very young; a' anterior part of outer surface. 



b. M. majori. Right m^ very young. 



c. M. majori. Right Wj adult. 



a, h, and c, all from the Upper Freshwater Bed of West Runton. 



d. M. cantianus. Right m^ adult (type of sj)ecies); High Terrace of the 



Thames, near Greenhithe, Kent. 



(Fig. 104a), the grinding surface displays the usual juvenile con- 

 I fluency of the dentinal spaces and several of the ephemeral 

 peculiarities in the form of the posterior loop and salient angles 

 <liscu.ssed above at jip. 110-115. The " prism-fold " is extremely 

 weak ; but the third outer valley is represented by a deep and 

 perfectly persistent re-entrant fold. On the outer side of the 

 tooth, just in front of this fold and at the level of the present 

 '.grinding surface, there is a minute tubercle {n') and inime- 

 liately below this tubercle there begins a .shallow but well- 

 ilefined and quite persistent vertical groove (iv') which, as the next 



