THE YELLOW-NECKED FIELD MOUSE S47 



has been discovered in deposits older than the late Pleistocene. A 

 large lower jaw (i6-2 mm. long) mentioned by Woldrich {Sitzungsb. 

 Akad. Wien. math.-nat. CI., 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 Iv. 

 424, 1899) has described, first under the name of Mus abbotti (not of 

 Waterhouse) and subsequently as Mus kwisi, 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, Ann. and Mag. Nat. Ht'st., June 1915, 582). 

 The fossil species clearly is closely related to A. flavicoUis, 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. lewisi 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 sylvaticus ; 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 sylvaticus, 3m6. 

 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 sylvaticus 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 sylvaticus ; 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 bullae are relatively large. 

 The diastemata are proportionally about as long as in sylvaticus, but the 

 incisive foramina are relatively shorter (see table at p. 518 above). 



The cheek-teeth are a little larger than in sylvaticus, but they are 

 of the same form and structure. \n m^ the anterior " accessory " cusp 

 (p. SOI 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. lewisi. 



Geographical variation: — Two sub-species are now recognised. 

 One of these, the typical continental form, A. f. flavicoUis, has the 



