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Show 602 GEOGRAPHICAL RACES O F T H E C O M M O N FIELD VOLE. [May 19, M. agrestis and M. neglectus may be, there can hardly fail to in countries on the boundary-line of their respective ranges intermediates whose presence would render it impossible to regard the two as distinct species. No doubt this was the right course to take so long as there was only open to naturalists the binomial system of nomenclature. It seems to me, however, that there is here a good case for the use of the trinomial system, especially as it can be done without inventing any new name. The Voles constitute so difficult a genus that it is not surprising that the distinguishing characters laid down by even such good naturalists as Jenyns and De Selys-Longchamps are not very clear, especially as they appear to have been given partially with a view to distinguish M. neglectus from the Continental species M. arvalis, which was at that time supposed to occur in Great Britain, or to be represented there by a supposed nearly allied species M. britannicus; while, to further add to the confusion of ideas, the differences between M. agrestis and M. arvalis were verv imperfectly recognized, if at all. I think, however, that De Selys- Longchamps's remarks show that he applied the name of neglectus to one of the forms to which this paper refers: hence, if it be considered desirable, as I submit it is, to distinguish these two distinct forms by different names, the British and Southern form should, I thiuk, be distinguished as M. agrestis neglectus, Jenyns, while the name of M. agrestis (Linn.) should be restricted to the more Northern form. The following are the characters of the two forms or subspecies :- MICROTUS AGRESTIS (Linn.). This is a large Vole reaching when adult a length (head and body) of 130 millimetres and upwards. It differs in coloration from the Southern form, tbe upperside wanting the reddish tinge of British specimens, and the underside being of a purer white colour, most British examples having the underside washed with yellow. The skulls of the Northern form are much larger and stronger than those of the Southern, and the postorbital and other crests are more prominent. The whole skull is very Lemminglike in appearance, being much flattened and having the zygomatic arch very deep. Mr. Bonhote informs me that the Norway Voles were very Lemming-like in appearance when alive and he found them inhabiting the same burrows as Lemmings. MICROTUS AGRESTIS NEGLECTUS, Jenyns. This is a smaller animal, not averaging more than about 110 millims. when fully grown. It may be distinguished by the characters given above, viz., the size, cranial characters, and coloration. There is usually a reddish tinge on the upper surface of the adults and a yellowish wash to the belly, especially in summer, which, when present, is very distinctive. |
