LOCALLY EXTINCT VOLES 471 



(which may also occur in the early middle terrace deposit 

 at Grays Thurrock, Hinton), which cannot be referred to 

 this sub-genus with any certainty, the later middle terrace 

 deposits yield abundant remains of nivaloid voles. Large series 

 of lower jaws from the Clevedon Cave, and from the brick-earth 

 of Crayford and Erith, have been studied by Hinton [Proc. 

 Geol. Assoc, 1907, 39, and 1910, 493), who cannot separate 

 them in the absence of skulls from those of recent members of 

 the group. 



The former wide distribution (in the lowland districts of 

 western Europe) of this group, usually associated with high 

 altitudes and perpetual snow, has contributed to the view that 

 these districts were afflicted during the pleistocene period with a 

 climate much more severe than that which they now enjoy. 

 Hinton combats this view, pointing out that Chionomys is a 

 southern group not now occurring north of the Alps and at no 

 time known further north than Norfolk or southern Germany, 

 and he suggests that it reached Britain from the south through 

 France. He regards it as an ancient lowland group which 

 has been forced to recede to mountain fastnesses before the 

 competition of new^er and stronger immigrants, and thinks that 

 it owes its survival to the present epoch solely to the fact that 

 it has been able to colonise the mountains, where it finds 

 security from competitors, enemies, and frosts, beneath the 

 Alpine snows, in accordance with the principle already advo- 

 cated by Bulman [Nat. Science, iii., October 1893, 261-266) 

 and by Scharff {European Animals, chaps, vii., viii., and ix., 

 and pp. 54 and 56). 



Hinton's argument has been very remarkably substantiated 

 by Mottaz's rediscovery (Miller, Ann. and Mag. Nat. Hist., 

 January 1908, 97 ; Hinton, Sci. Proc. R. Dublin Sac, N.S., 

 xii., 264) of M. lebrunii lebrimii on hot plains near the French 

 shores of the Mediterranean at Nimes. Glacial conditions are 

 thus shown to be anything but indispensable to the sub-genus. 



The genus Pitymys (MacMurtie, American edition of 

 Cuvier's Rdgne Animal, i., 134, 1831, renaming the pre- 

 occupied Psammomys of Le Conte, 1830, based on Psammomys 

 pinetorum, Le Conte, 1828, described from Liberty County, 

 Georgia) differs generally from Microtus in its greater specialisa- 



