MIMOMYS 383 



variety stands in an exactly similar relationship to typical M. 

 majori as does M. savini to M. intermedius. 



In the Savin Collection (B.M.) there are several specimens 

 of the ?%, from the shelly sand or crag of East Runton, which 

 having the third outer valley unreduced and persistent may be 

 referred to this species. In these teeth the " prism-fold " is either 

 very faintly developed or obsolete. 



Remarks. — It is not improbable that the remains now referred 

 to M. majori represent more than one species. The unparalleled 

 richness of the Microtine fauna of the Upper Freshwater Bed 

 and the fragmentary condition of most of the specimens find a 

 probable explanation in what is known of the history of the 

 Cromerian deposits. These seem to have been laid down 

 in the fluctuating estuary of a large river, which apparently 

 included representatives of the Rhine and Thames as well as 

 of other streams flowing into the area that is now the southern 

 portion of the North Sea. The estuarine deposits of that ancient 

 river thus contain in all probability the sweepings of a very 

 large part of Western and Central Europe. It is therefore not 

 necessary to suppose that all the Cromerian species inhabited 

 Britain at one and the same moment; some of them, perhaps 

 the majority, may never have lived here at all. It is to the 

 future discovery of inland deposits of Cromerian age, deposits 

 free from contamination by streams of continental origin, that 

 we must look for information as to what species actually con- 

 stituted the late Pliocene Microtine fauna of Britain, and for 

 data that will enable us to appreciate the real systematic status 

 of the forms now recognized. 



8. t Mimomys cantianus Hinton. 

 1902. Microtus intermedius Hinton and White, Proc. Geol. Assoc, 



17, p. 414. 

 1910. Mimomys cantianus Hinton, Proc. Geol. Assoc, 21, p. 491 ; 



Duckworth, " Prehistoric Man," Cambridge Manuals Science and 



Lit., p. 88, 1912. 



Tyjpe. — A right m^ ; collected by Mr. Gilbert White (Figs. 

 99, 21 ; 1046; and PI. XIII, figs. 11, 11a). 



Tyj>e horizon and locality. — Early Pleistocene; High Terrace 

 Drift of the Thames, Ingress Vale, near Greenhithe, Kent. 



Range in time and space. — Known only from the type horizon 

 and locality. 



Characters. — Imperfectly known, the species being represented 

 by only a few detached teeth. Cheek-teeth developing roots 

 very late in life — later apparently than in the species found in the 

 Upper Freshwater Bed at West Runton. Re-entrant folds partly 

 filled with cement ; enamel differentiated as in other species of 

 Mimomys, thicker on convex, thinner on concave borders of salient 

 angles ; m^ with three outer and four inner salient angles, and with 



