546 MURID^E— APODEMUS 



the latter regards it as one of the phases of sylvaticus, which "is a 

 polymorphic species." According to both writers, sylvaticus and 

 flavicollis intergrade; and both may be found mingled in the same 

 colony. Still, the broad fact remains, according to Collett, that in 

 southern Norway the vast majority of the Field Mice of the coastal 

 lowlands are typical sylvaticus, the vast majority of those dwelling in 

 the high mountain pastures are typical flavicollis, while the intermediate 

 ground between the two situations is the most usual habitat of the 

 intermediate mice. Further, it is a remarkable fact that although 

 Britain has been occupied, but perhaps not continuously, by members 

 of the sylvaticus group since the Upper Pliocene (Forest Bed) period, 

 and that although their fossil remains have been found in several 

 horizons of widely different ages, it is not until the late Pleistocene of 

 Ightham that remains of a form {A. lewisi, Newton) similar to, if it 

 be not identical -with., flavicollis are met with. It is also a fact that 

 A. flavicollis has not found its way into any of the islands other than 

 Britain. Thu stztus oi A. flavicollis is, 3.5 is the case with other Field 

 Mice of the sylvaticus type, undoubtedly a difficult thing to determine ; 

 but the facts just cited seem to support the opinions of de Winton and 

 Miller. Some small proportional differences in certain regions of the 

 skull, described below, also support the claims oi flavicollis to specific 

 recognition. 



Distribution: — A. flavicollis is distributed throughout Central 

 Europe, ranging from at least southern Skandinavia and Finland south- 

 wards to the Pyrenees and Alps, and from Britain eastwards to Greece, 

 Rumania, and western Russia. How far to the north its range 

 extends is unknown. It is represented in the Himalayas by close 

 allies, and the range of the group may extend still further eastwards. 



In Norway, according to Collett, A. flavicollis is the predominant 

 Field Mouse of the wooded valleys of the interior and the adjoining 

 sub- Alpine tracts ; A. sylvaticus, on the other hand, being restricted 

 principally to the lowland coastal region. Mice which appear to be 

 intermediate in character are met with in the intervening belt of 

 country. A. flavicollis ascends to the mountain pastures, or a height 

 of about 3000 feet. From Fatio's description of the Swiss Field Mice 

 (p. 212) it would appear that flavicollis is the prevalent mountain form 

 in the Alps ; he mentions specimens taken in the Oberland at a height 

 of about 1900 m., and others from the Engadine at about 2500 m. ; 

 from the context it would appear that these were flavicollis rather than 

 sylvaticus. 



In Britain it is not known to occur further north than Northumber- 

 land ; the British form is regarded as sub-specifically distinct from the 

 typical continental flavicollis. 



Distribution in time : — As stated above, no trace of this species 



