THE YELLOW-NECKED FIELD MOUSE 547 
has been discovered in deposits older than the late Pleistocene. A 
large lower jaw (16-2 mm. long) mentioned by Woldrich (Sz¢zungsb. 
Akad. Wien. math.-nat. Cl, 84, Abt. i, 216, 1881) from the fissure 
deposit of Zuzlawitz, Bohemia, appears to be referable to this species. 
From Britain, Newton (Quart. Journ. Geol. Soc.,1., 195, 1894, and lv. 
424, 1899) has described, first under the name of Mus abdottz (not of 
Waterhouse) and subsequently as A/us dewzsz, remains of a large Field 
Mouse from the fissure deposit of Ightham (see above). A lower jaw 
from one of the upper strata of Kent’s Cavern, Torquay, yielding 
a typical assemblage of late Pleistocene rodents, is also referred to 
A. lewisi ; and skulls of the same form have been found in strata of 
similar age in the Happaway Cave, Torquay, and the Wye Cave, 
Forest of Dean (Hinton, Anz. and Mag. Nat. Hist., Jane 1915, 582). 
The fossil species clearly is closely related to A. flavicollis, and may 
well be identical with it; its real status, in the absence of good skull 
material, cannot at present be determined, and it is better for the 
moment, therefore, to regard A. /ewzs¢ as a distinct form. 
Description :—The Yellow-necked Field Mouse is distinguished from 
A. sylvaticus by its larger size (head and body of adults, 100 to 115; 
hind foot, 23 to 27; condylo-basal length of skull, 25 to 28-8 mm.), 
more intense and purer coloration, and by some cranial characters. 
The colour of the back and sides is brighter, with redder tints than 
in sylvatecus ; the belly is white, without any trace of a buffy suffusion, 
and the lateral line of demarcation is always sharply defined. The 
pectoral spot of yellowish-brown is usually larger than in sy/vaticus, and 
is often extended laterally so as to form a complete collar. 
The skull in adult or old animals (teeth half-worn or more) is 
distinguished from that of sy/vatzcus of equal age by its larger size and 
more massive build. The temporal ridges are relatively strongly 
developed, and impart an appearance of angularity to the skull, as a 
whole, which is never seen in sy/vaticus; anteriorly these ridges are 
continued almost to the lachrymal as sharp superciliary margins which 
are sufficiently salient to produce a slight but evident longitudinal 
furrow upon the frontals. The auditory bulla are relatively large. 
The diastemata are proportionally about as long as in sy/vadzcus, but the 
incisive foramina are relatively shorter (see table at p. 518 above). 
The cheek-teeth are a little larger than in sy/vaticus, but they are 
of the same form and structure. In mm, the anterior “accessory” cusp 
(p. 501 above) is frequently of small size, and is occasionally so incon- 
spicuous that, in moderately worn specimens, it may appear to be quite 
absent. Newton called attention to this character in his description of 
the pleistocene A. dewzsz. 
Geographical variation:—Two sub-species are now recognised. 
One of these, the typical continental form, A. f flavzcollis, has the 
