2 ANNALS OF SCOTTISH NATURAL HISTORY 



islands had been regarded as the Short-tailed Vole (Microtus 

 agrestis], a species which is common and widely distributed 

 over the mainland of Great Britain. 



It would not have been so surprising had this Vole 

 proved to be a racial form of some European species, 

 but that it should be entirely distinct from any of its con- 

 geners is certainly a most remarkable fact. Indeed it is 

 not too much to aver that this little mammal is, from a 

 scientific standpoint, among the most interesting and im- 

 portant of existing British Vertebrates. 



Microtus orcadensis, though undoubtedly quite a distinct 

 species, shares certain peculiarities with both the Water 

 Vole and the Field Vole. Thus, in stoutness of build, in the 

 comparative prominence of the ears, in the density and 

 colour of the fur (especially the tint of its under surface), 

 and, broadly, in its cranial characters, it resembles the Water 

 Vole. While in the shortness of its tail, and to some 

 extent in its dental characters, it approaches the Field Vole. 

 In size it is somewhat intermediate between these species, 

 large specimens being nearly half as large again (40 per 

 cent) as the latter, though it is decidedly smaller than the 

 Water Vole. 



In colour it is sandy-brown above (the apical portion of 

 the hairs being yellowish-brown, the basal slaty-gray) with 

 long protruding black hairs interspersed ; below it is sandy 

 rufous. Half-grown examples are duller in colour, being 

 darker than the adults on both the upper and under surface, 

 and in this respect they resemble the Water Vole of similar 

 age. 



Mr. Millais' largest male measured 6.75 ins. (head and 

 body 5.5, tail 1.25 ins.). The following are the comparative 

 measurements and weights of the largest specimens ot 

 Microtus orcadcnsis and M. agrestis in the collections of 

 the Royal Scottish Museum : 



