662 MURID^— MUS 



one of Steele Elliott's specimens and others collected in 1898 by 

 Henry Evans, published a full description and figure of the animal, 

 and established a new species, his M. muralis, for its reception. He 

 thought that this mouse was "of at least several hundred years' 

 standing at St Kilda," and while realising that it was very closely 

 allied to M. musculus, he thought it better to regard it, pending further 

 research upon the status of the various described members of the 

 group, as a full species rather than as a sub-species oi musculus. In 

 1906 Barrett- Hamilton {Ann. Scott. Nat. Hist., 2) described a further 

 series of specimens collected by Waterston in June 1905. In the 

 autumns (September and October) of igioand 191 1 Eagle Clarke made 

 another collection, and he described these specimens in 1914 (^Ann. 

 Scott. Nat. Hist., 127). 



The status of M. muralis has been discussed by various writers. 

 Lydekker {Field, 30th April 1904) and Winge (1908) regard it as no 

 more than a local race, while Millais and Trouessart treat it as a sub- 

 species oi musculus. Barrett-Hamilton {Proc. Zool. Sac, 1899, 81) thought 

 that since this mouse was perfectly isolated, and not known to inter- 

 grade with the parent form {musculus'), it had " as much claim to be 

 accorded full specific rank as any other island species." After examining 

 all the European members of the genus. Miller came to the conclusion 

 that muralis is sufficiently well differentiated to receive full specific 

 rank. For reasons given above (p. 648), Miller's view has been 

 adopted here, although not without hesitation. 



If Miller's decision to regard the wild forms of southern and central 

 Europe {M. spicilegus) and the island House Mice {M. muralis and 

 fceroensis) as distinct species be really well founded, it is possible that 

 these species represent a more ancient stock of House Mice indigenous 

 to western Europe. The distribution of these forms is in favour of 

 such a theory ; and the large size of the jaw from the Kirkdale Cave 

 (see p. 636), assuming that specimen to be of Pleistocene age and really 

 referable to this genus, figured by Owen, could be explained by referring 

 it to a forerunner of muralis. Our knowledge of the matter, however, 

 is still far from sufficient to raise any such view above the rank of a 

 mere hypothesis. 



Description : — In outward form M. muralis agrees closely with 

 musculus, but differs in being rather larger, and in having the tail and 

 feet more robust. The width of the hind foot, measured across the 

 bases of the outer toes, is about 4 mm., instead of 3-5 mm., as in 

 musculus. 



In general colour the back is rather lighter than in ordinary 

 specimens of musculus, the bases of the hairs are slaty, and while most 

 of them have sepia-brown tips, a certain proportion are rufous-tipped, 

 and give the animal a grizzled appearance. The under parts are bright 



