710 RODENTIA 



agrestis or perhaps a trifle less. Enamel pattern agreeing with 



that of M. arvalis in the absence of all trace of a postero-internal 



loop in mi 2 , as well as in the characters of m 1 , m 2 and m 3 , common 



to nearly all the European members of the sub-genus ; there is 



everywhere, however, less contrast in size and depth between 



the inner and outer angles and triangles. Third upper molar 



frequently of the more complicated type described under 



M. agrestis, the posterior loop with its inner limb isolated as a 



definite, well-developed, second inner closed triangle, and the 



projection on its outer side tending to assume the form of a 



small but almost closed third outer triangle. 



First lower molar highly characteristic and 



readily distinguishable from that of all the 



other European members of the sub-genus ; 



posterior loop, three inner and two outer closed 



triangles as in M. agrestis, except for the less 



contrast in size between the elements of outer 



and inner side ; anterior loop so short that it 



bears no re-entrant angle on outer side, while 



that of inner side is reduced to a shallow, 



inconspicuous concavity, some trace of which 



is, however, apparently always present ; angle 



Fia. 147. subtending terminal loop on outer side broad 



Microtus rattweps. -, ., ° , T1 r , . . , . . t 



Enamel pattern, x 5. and rather shallow ; antero-internai triangle 



usually communicating with anterior loop, this 



communication when broadly open frequently converting the two 



elements into a secondary terminal loop of irregularly crescentic 



form not unlike some of the variants of posterior loop of m 3 . 



While differing conspicuously from that of the other European 



species of true Microtus this tooth is essentially like that of the 



members of the sub-genus Ghionomys. Isolated specimens may 



usually be distinguished by the less contrast between size of inner 



and outer triangles, and by the absence of any conspicuously 



projecting angle at outer base of anterior loop ; in certain forms 



of Chionomys, however, the latter peculiarity is almost exactly 



reproduced. 



Measurements. — Average and extremes of nine adults from 



Lappmark, Sweden : hind foot (dry), 19 - 9 (19-4-21). Adult from 



Csallokoz-Somorja, Pressburg, Hungary: hind foot, 20 • 8. Adult 



female from Texel Island, Holland : head and body, 130 ; tail, 62 ; 



hind foot, 20 ; ear, 13. For cranial measurements see Table opposite. 



Specimens examined. — Twenty-eight, from the following localities : — 



Norway. — Gausdal, 4 ; Hjerkin, Kristiansamt, 1 ; Dovre Field, 1 

 (U.S.N.M.). 



Sweden. — Medelpad, W. Norrland, 1 ; Karesuando, Norrbotten, 3 ; 

 Lappmark, 5 (B.M. and U.S.N.M. ; near Stockholm, 1 (U.S.N.M.). 



Finland. — Muonionniska, Uleaborg, 5 (B.M. and U.S.N.M.). 



Germany. — Colpm, Brandenburg, 1 ; near city of Brandenburg, 1 (Berlin 

 Agrio. ; ootype of stimmingi Nehring). • 



Austria-Hunqary. — Csall6koz-SomorJ8, Pressburg, Hungary, 1. 



