468 MURIDAE—LOCALLY EXTINCT VOLES 
/ 
Ightham probably marks the date of the arrival of the species 
in Britain, since no arvadzs-like “‘ vole” is represented among the 
many microtine fossils recovered from the Crayford brickearth, 
a deposit one stage older than that of Ightham. 
Microtus anglicus (Hinton, Azz. and Mag. Nat. Hist., July 
1910, 36, first referred by Nehring to a little-known existing 
species, JZ. gregals, Pallas) is a very remarkable species 
belonging to the highly specialised Asiatic group which 
Kastchenko calls Stenocranius. The 
skull is very long and narrow, with 
the long inter-orbital region greatly 
constricted and bearing a sharp median 
crest ; the median septum of the hinder 
= ; palate is long and thin. The upper 
Pe eee a itis ie cheek-teeth are similar to those of 
M. anglicus of the late Pleistocene 7. avvalts. m, (Fig. 75) is of peculiar 
of England ; (2) of Micros rai- form ; it has the posterior loop and five 
ceps (K. and B.); Pleistocene of 3 5 
Bneland’=letimes life size closed triangles of normal J7/7crotus, 
but the fourth outer angle (counting 
from behind) is reduced, and the fourth outer fold obsolete; the 
outer border of the anterior loop is long and straight, and the 
tooth has only three outer salient angles. 2; has the third outer 
angle obsolete. The Stexocranius group is regarded by Hinton 
as an offshoot of the avvals group, its cranial and dental 
peculiarities being apparently results of an increased develop- 
ment of the temporal muscles ; this specialisation is similar in 
kind, though more intense in degree, to that described in the 
orcadensts group at p. 453. It is thus possible that instead of 
there being any specially close affinity between JZ. anglicus 
and the similarly modified forms of central Asia, the former 
may afford an instance of parallel evolution from a common 
arvaloid stock. 
M. anglicus first appears in Britain in, and is perhaps the 
most characteristic element of, the late pleistocene fauna 
(Ightham), and it, or closely allied forms, had a wide range in 
western and central Europe. So far as is known, all such forms 
are now extinct in this region. 
Microtus ratticeps (Keyserling and Blasius, Zem. Acad. Imp. 
Set. Nat., St Petersburg, iv., 3, 333, 1841 (1845) ; described from 

