694 RODENTIA 



in both incisors and molai-s, the teeth do not differ from those 

 of Microtus arvalis. First lower molar with anterior outer 

 re-entrant angle normally developed. 



Measurements. — External measurements of type (adult 

 female) : head and body, 120 ; tail, 37 ; hind foot, 20 ; ear from 

 meatus, 14. Young adult male from La Granja, Segovia, 

 Spain: head and body, 100 ; tail, 38; hind foot, 19 ; ear from 

 meatus, 12 "8. For cranial measurements see Table, p. 707. 



Specimens examined. — Seven, from the following localities in Spain : — 

 Pajares, Leon, 3 ; La Granja, Segovia, 4. 



6, 2 9. Pajares, Leon, Spain. 0. Thomas (p). 8. 2. 9. 205-207. 



{N. Gonzalez.) (8. 2. 9. 206. Type of species.) 



2 (5,2 juv. al. La Granja, Segovia. Purchased (Escalera). 8.7.30.15-18. 



MICROTUS ORCADENSIS Millais. 



1904. Microtus orcadcnsis Millais, The Zoologist, 4th ser., viii, p. 244, 



July, 1904. 



1905. Microtus orcadensis ISIajor, Ann. and Mag. Nat. Hist., 7th ser., xv, 



p. 324, March, 1905. 

 1909. Microtus orcadcnsis Trouessart, Faune Mamm. d'Europe, p. 177. 



Tyjye localitij. — Pomona Island, South Orkney Islands, 

 Scotland. 



Geographical distribution. — South Orkney Islands ; known at 

 present from Pomona, Rousay, Shapinshay and South Ronald - 

 shay. 



Diagnosis. — Much larger than Microtus arvalis (hind foot, 18 

 to 20 mm., condylobasal length of skull in largest individuals 

 about 28 • 5 mm.) ; skull essentially like that of M. arvalis in 

 form, but slightly broader (ratio of zygomatic breadth to condylo- 

 basal length about 60 instead of about 56), the depth of brain- 

 case not however sensibly reduced ; teeth as in 31. arvalis, the 

 second upper molar with no trace of postero-internal loop, the 

 first lower molar with well developed anterior outer re-entrant 

 angle ; colour much darker than in any of the other European 

 species with the same pattern of enamel folding, the underparts 

 clear ochraceous-buff. 



Colour. — General effect of upper parts a rich, dark brown, 

 nearly approaching the mummy-brown of Ridgway. Individual 

 hairs slate-black at base, those of the underfur tipped (2 mm.) 

 with brownish ochraceous-buff, the longer hairs clear black but 

 producing a very slight effect of " lining." On sides the colour 

 gradually passes into the clear bright ochraceous-buff of under- 

 parts, this slightly obscured by the slaty bases of the hairs, 

 especially on chin and throat. Feet and under surface of tail 

 light grey tinged with ochraceous-buff. Upper surface of tail 

 blackish. 



Skull. — Except for its larger size and relatively shorter, more 



