LOCALLY EXSINGE 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 Chzonomys 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 newer 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 (Vat. Sczence, iii., October 1893, 261-266) 
and by Scharff (European Animadts, chaps. vii., viii., and ix., 
and pp. 54 and 56). 
Hinton’s argument has been very remarkably substantiated 
by Mottaz’s rediscovery (Miller, Aun. and Mag. Nat. Hist., 
January 1908, 97; Hinton, Sez. Proc. R. Dublin Soc., N.S., 
xii., 264) of MW. lebrunit lebrunzi 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 Régne 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 J/zcrotus in its greater specialisa- 
