MicROTns 681 



Teeth. — While in no way essentially difterent from those of 

 the other small races of Microtus acjrestis the teeth of M. a. 

 rozianus appear to be relatively a little larger (see measurements, 

 p. 679), though the difference may prove to be merely an 

 individual peculiarity in the two skulls seen. In one of these 

 specimens there is a minute postero-internal triangle in the first 

 upper molar. 



Measurements. — External measurements of adult female from 

 Villalba, Lugo, Spain : head and body, 100 ; tail, 39 ; hind foot, 

 18' 8, For cranial measurements see Table, p. 679. 



Specimens examined. — Three, from tlie following localities in Spain : 

 La Corufia, 1 ; Villalba, Lugo, 2. 



2 al. Villalba, Spain. Dr. V. L. Seoane (c & p). 94. 1. 1. 14-15. 

 1 al. Corufia. Dr. V. L. Seoane (c & p). 95. 4. 29. 3. 



MICROTUS ARVALIS Pallas. 

 (Synonymy under subspecies.) 



Geographical distribution. — Continental Europe from the 

 Baltic to the Pyrenees and northern Italy, and from the Atlantic 

 coast eastward. 



Diagnosis. — Size less than in Microtus agrestis (hind foot, 15 

 to 18 '6 mm.; condylobasal length of skull in fully adult 

 individuals, 23 "4 to 26 6 mm.); plantar and palmar tubercles 

 relatively smaller ; second upper molar without small postero- 

 internal loop ; first lower molar with four re-entrant angles on 

 inner side ; skull slender or moderately broad (ratio of zygomatic 

 breadth to condylobasal length ranging from 50 to 57), never 

 conspicuously flattened and never assuming a " fossorial " aspect, 

 the upper incisors nearly perpendicular. 



External characters. — In general not essentially different from 

 Microtus agrestis, but ear less hairy and with meatal lobe much 

 less developed, barely half as high ; feet as in agrestis except that 

 the tubercles on both palm and sole are relatively smaller, those 

 on fore foot occupying scarcely more than half area of palm (that 

 at base of thumb barely more than twice as large as thumb itself), 

 those on hind foot occupying distinctly less than half region in 

 which they occur ; in form the tubercles all tend to be more 

 evenly i-ounded than in M. agrestis, owing to the less degree of 

 crowding. 



Skull. — Apart from its smaller size the skull differs from that 

 of Microtus agrestis in the broader, shorter, more depressed brain- 

 case, the outline of which when viewed from above is distinctly 

 rounded both in front, behind, and at the sides, seldom if ever 

 showing any trace of the squaring characteristic of the larger 

 animal ; postorbital process low, not distinctly angular ; inter- 

 parietal with antero-posterior diameter, exclusive of median 

 pi'ojection, obviously more than half transverse diameter, the 



