402 MB. G. T.. II. BARRETT-HAMILTON ON [-^P r - 3, 



like so many other local forms, were put aside with the remark 

 that they could be only regarded as " varieties of Mus sylvaticus " l . 

 Irish naturalists, however, well knowing the tendency of the 

 elements of our fauna to become darker in the west of the country, 

 have all along suspected that Jenyns's suggestion was well worthy 

 of attention. Hence they have been gradually accumulating a 

 series of Field-mice from Ireland, with the result that I think I 

 may now say definitely that we have, in the west of Ireland, a small 

 dark subspecies of Field-mouse, which nearly corresponds to Jenyns's 

 description, aud which is quite unlike the Field-mice of the greater 

 part of Europe, of England, or, what is equally interesting, of the 

 east and centre of Ireland. For this small subspecies I propose 

 the name Mus sylvaticus celticus. 



The first specimens of this Mouse received at the Museum were 

 a series of six, collected by Col. J. W. Yerbury, at Caragh Lake, 

 Co. Kerry, between Nov. 27th and Dec. 1st, 189-4. These, although 

 some allowance must be made for the winter coat, are darker and 

 smaller than any English specimens which I have seen even of 

 that season. In spite of these characters, I at first hesitated 

 to regard the specimens as conclusive evidence of the truth of 

 Jenyns's hypothesis. It was possible that in such a mild climate 

 the mice might continue breeding to a late date in the year, so 

 that examples showing the characteristics of immaturity might 

 be obtainable even in December, and hence Col. Terbury's speci- 

 mens might possibly be regarded as not wholly adulr. The colour 

 of the underside, however, did not suggest immaturity, it being as 

 white and as clearly marked off from that of the upperside as in 

 any English examples, nor were the skulls those of immature spe- 

 cimens. Hence I felt sure that I should eventually obtain others 

 like them from the west of Ireland. These were forthcoming in 

 1896, when Mr. E. F. Hibbert sent me four small dark J\J ice from 

 "Woodpark, Co. Gal way. The date at which they had been taken 

 (February and March) was such as to almost preclude the possi- 

 bility of their being immature, and they were further supplemented 

 by a third set of the small dark western Mouse sent by Mr. Gr. A. 

 Passingham, from Fermoyle, Castlegregory, in the very same 

 county which bad produced both Jenyns's and Colonel Yerbury's 

 specimens. 



The interest of these specimens was heightened when I found 

 them exactly matched in colour and size by three collected at 

 Eisken, in Lewis, in the Outer Hebrides, in October and November 

 1895, and by one sent to the British Museum of Natural History 

 by Mr. J. Steele Elliott, from Skve, in the same year. These 

 specimens seem to indicate that this small "Western subspecies of 

 Mus sylvaticus is not confined to the west of Ireland, but is found 

 in similar localities in the Western Scotch Isles. The late date of 

 capture (June 24tb) of the Skye specimens shows that the dark 

 colour is not characteristic of winter, but is retained throughout the 

 year. It is remarkable that I should have seen a perfectly similar 

 1 See Bell's ' British Quadrupeds,' ed. ii. p. 296 (1874). 



