691 



1907. Microtus wrvalis incertus Mottaz, Mem. Soc. Zool. de Prance, xx, 



p. 32, September, 1907. 

 1910. Pitymys incertus Trouessart, Faune Mamm. d'Europe, p. 188. 



Type locality. — Near summit of St. Gothard Pass, Uri, 

 Switzerland. 



Geographical distribution. — Mountains of Switzerland and 

 Tirol, from the central Alps eastward. Details of distribution 

 very imperfectly known. 



Diagnosis. — Like Microtus arvalis, but skull tending to assume 

 a distinctly fossorial aspect, the occipital region depressed (ratio 

 of occipital depth to occipital width about 50 • 5 instead of 58), 

 the rostrum elongated (diastema 

 usually about 8 mm. in adults instead 

 of about 7 • 5 mm.), the upper incisors 

 projecting forward ; auditory bulla 

 small and flattened. 



External characters. — So far as 

 can be determined from skins, the 

 external characters are in all essen- 

 tials as in Microtus arvalis, though 

 from the peculiarities of the skull it 

 seems probable that the head is more 

 flattened and the incisors more pro- 

 truding ; fur tending to be longer and 

 less dense. 



Colour. — In a series of skins the 

 colour is, on the average, less buffy 

 above than in Microtus arvalis arvalis, 

 and the underparts are more fre- 

 quently a clear, slate-tinged grey. The colours are dull and 

 blended, with very slight indication of grizzling, even in 

 individuals with elements of the colour nearly as in M. arvalis 

 duplicatus. 



Measurements. — Adult male and female from Andermatt, 

 Uri, Switzerland: head and body, 114 and 108; tail, 41 and 

 37; hind foot, 16 and 15 '5. Adult male from Furka Pass, 

 Switzerland: head and body, 113; tail, 31; hind foot, 15-4. 

 Average and extremes of eight adults from Vulpera-Tarasp, 

 Grisons, Switzerland: head and body, 111 (104-119); tail, 36-5 

 (30-41); hind foot, 16-4 (15-6-17); ear from meatus, 11 '7 

 (11-13). For cranial measurements see Table, p. 692. 



Specimens examined. — Sixty-six, from the following localities : — 

 Switzerland : Furka Pass, 31 (B.M., U.S.N.M., Geneva and Mottaz) ; 

 St. Gothard Pass, 2 (B.M. and U.S.N.M.) ; Andermatt, Uri, 7 (U.S.N.M.} ; 

 Vulpera-Tarasp, Grisons, 16 (Rothschild); Campfer, Grisons, 7 (Roths- 

 child) ; Engadine, 1. 



Austbia-Hungary : Meran, Tirol, 1 ; Paneveggio, Tirol, 1. 



Bemarhs. — Microtus incertus is readily distinguishable from 

 ilf. arvalis by its flattened brain-case, small auditory bullae and 



2 y 2 



FIS. 135. 

 Mierotus incertus. Nat. size. 



