002 GEOQEAPniCAIr IIACES OP THE COMMON FIELD VOLB. [May 19, 



M. cu/restis and M. neglectus may be, there can hardly fail to exist, 

 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 tliere was only open to naturalists the binomial 

 system of nomenclature. It seems to nie, however, that there is 

 here a good case for the use of the trinomial system, especially as 

 it can be done without inventing any now name. 



The Volfs constitute so difficult a genus that it is not surprising 

 that the distinguishing characters laid down by even such good 

 naturalists as jenyus and De Selys-Longchamps are not very 

 clear, especially as they appear to have been given partially with a 

 view to distinguish M. neijhctus 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. bntannicus ; while, to further add to the confusion of 

 ideas, the differences between M. agrestis and M. arvalis were very 

 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 think, 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 sub- 

 species : — 



MiCEOTUS AGEESTis (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, the upporsido wanting the reddish tinge 

 of British specimens, and the underside being of a purer white 

 colour, most British examples having tlie 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 Lemming- 

 like in appearance, being much flattened and having the zygomatic 

 ai'ch very deep. 



Mr. Bonhote informs me that the Norway Voles were very 

 Lemming-like in appearance when alive and he found them in- 

 habiting the same burrows as Lemmings. 



MiCKOTUS AGEESTIS NEGLECTUS, Jenyus. 



This is a smaller animal, not averaging more than about 110 

 millims. when fully grown. It may be distinguished by the cha- 

 racters 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, whicli, 

 when present, is very distinctive. 



