378 MICROTIN^ 



impressed upon a surface of bare dentine, remains as an external 

 vestige of the fourth outer valley. The fifth inner angle is promi- 

 nent at the present grinding surface, but it would become nearly 

 obsolete with prolonged wear. The base of the crown shows that 

 in the adult the three triangles, widely confluent in the present 

 stage of wear, would be almost tightly closed and that the adult 

 pattern of this tooth would be much as in the teeth of M. newtoni 

 described above. The small size of the specimen also tends to 

 confirm my opinion. 



The second important tooth from Tegelen is a right m^, the 

 only example of the m^ of this species known to me. Having 

 regard to its small size, and to the character of the m^ found with 

 it, I think it can be safely referred to M. newtoni. This specimen 

 (Fig. '99, 23) has two roots; its postero-interual valley is persist- 

 ent, as in M. intermedius and the other species occurring in the 

 Upper Freshwater Bed at West Runton ; on the other hand, the 

 third inner and third outer angles are much more reduced than in 

 the West Runton forms. 



Of the other cheek-teeth, I have seen examples from East 

 Runton and also a left m^ from Tegelen, mentioned by Newton. 

 In addition to these, two examples of the m^ are figured by 

 Mehely. These teeth offer no character of importance beyond 

 what is mentioned in the diagnosis above. 



7. t Mimomys majori Hinton. 



1902. Mimomys intermedius "> Forsyth Major, P.Z.S., 1902, 1, p. 106, 



text-fig. 15, fig. 26, text-fig. 14, "fig. 13 

 1910. Mimomys majori Hinton, Proc. Geol. Assoc, 21, p. 491. 



T^/ye.— B.M., No. M. 6968e; Savin Collection ; an adult right 

 ???i figured by Forsyth Major (loc. cit. supra). 



Type horizon and locality. — Upper Freshwater Bed (Cromerian) 

 at West Runton, Norfolk. 



Range in time and space. — Remains of this species have been 

 found in the " shelly-sand " or crag of East Runton (Weybourne 

 Crag or Lower Cromerian). They occur abundantly in the lower 

 sandy portion of the Upper Freshwater Bed at West Runton and 

 are found also in the overlying peaty portion of the same deposit. 

 From the " Monkey Gravel," or stratum above the peat at West 

 Runton, the form in which the " prism-fold " of ?% is obsolete is 

 known. 



Characters. — Size and general character of the cheek-teeth as 

 in M. intermedius and M. savini; but m^ retains the third 

 outer valley as a deep re-entrant fold, which persists through- 

 out life instead of being reduced by insulation and more 

 or less completely obliterated in early youth. " Prism-fold" of 

 TOj variable, strongly developed and long persistent in some speci- 

 mens, weak and relatively ephemeral in others ; occasionally 

 absent altogether even in the youngest stages of wear. 



I 



