420 ME. G. E. H. BARRETT-HAMILTON ON [Apr. 3, 



19. MUS SYLVATICUS LEWISI. 



Mus abbotti, E. T. Newton, Quart. Journ. Geol. Soc. vol. vii. 

 pt. 2, no. 198 (May 1, 1894). 



Nee Mus abbottii, G. K. Waterhouse, P. Z. S. July 25, 1837, 

 p. 77, which is a form of M. musculus Linnaeus. 



Mus lewisi, E. T. Newton, P. Z. 8. 1899, p. 381. 



Type. A skull, being one of those collected by Mr. Lewis 

 Abbott in the ossiferous fissure at Ightham, Kent, and now in the 

 Geological Museum, Jerinyn Street, London, 8.AV. 



Description (skull only). Similar to M. sylvaticus, but differs 

 from it in the absence of the anterior pointed tubercle of the first 

 lower molar. 



Distribution. Known only from the typical series. 



General Remarks. The absence of a small dental tubercle seems 

 to be a very small point on which to base a species, especially as 

 the skulls of M. lewisi were accompanied by others which were 

 indistinguishable from those of M. sylvaticus. But the validity 

 of the specific character must depend on its constancy or incon- 

 stancy in skulls of modern sylvaticus. I have examined 49 of 

 these with a view to deciding this point, with the result that in 

 47 the tubercle in question is conspicuously present, while in two 

 only (viz., no. 98.2.2.22, from Cintra, Portugal, and no. 95.10.25.1, 

 from Lewis, Scotland, the type of Mus. s. hebridensis) had the 

 wearing down of the teeth made it. indistinct. The specimens 

 were of all ages, with the teeth both worn and unworn, and from 

 widely different localities, yet in all the tubercle shows clearly, 

 and must therefore, I think, be considered characteristic of 

 present day sylvaticus. 



We cannot tell what external features were present in M. s. 

 lewisi in correlation with this slight peculiarity of dentition. 

 These may have been conspicuous, or they may have been non- 

 existent. The material in our hands permits us merely to examine 

 the skulls, and from them alone, according to my treatment of 

 Mus sylvaticus, I can only admit M. lewisi to subspecific rank as 

 representing a side development of the Mus sylvaticus stock. 



MUS ARGENTEUS. 



Mus aryenteus, C. J. Temminck, Faun. Jap. p. 51, pi. xv. fig. 1 

 (1845) (on the date of this work see Sherborn & Jentink, P. Z. S. 

 Feb. 19, 1895, p. 149). 



Type locality. Japan. 



Distinguishing Characteristics. Pesembles Mus sylvaticus in 

 arrangement of colours, but has the upperside of a peculiar, 

 deeper, more uniform M. minutus-like red, of a shade that I have 

 never seen in M. sylvaticus. In the specimens at my disposal 

 there is no breast-band and none of the black-tipped hairs of 

 M. sylvaticus. The size is that of M. musculus. Temminck states 

 that the general size and the ears of M. aryenteus are as in 

 M. musculus, and the tail is longer than the head and body. Of 

 the colour he writes that " tout le dessus du corps, jusqu'a la 



