710 



RODENTIA 



Fig. 147. 

 Mierotas ratticeps. 

 Enamel pattern. 



X5. 



agrestis or perhaps a trifle less. Enamel pattern agreeing with 

 that of 31. arvalis in the absence of all trace of a postero-intei-nal 

 loop in m'^, as well as in the characters of m^, m„ and iHo, common 

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

 evei'ywhere, however, less contrast in size and depth between 

 tlie 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-enti'ant 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 

 subtending terminal loop on outer side broad 

 and rather shallow ; antero-internal 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^. 

 While differing conspicuously from that of the other European 

 species of true 3Iicrotus this tooth is essentially like that of the 

 members of the sub-genus Chionomys. 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 

 rejDroduced. 



Measurements. — Average and extremes of nine adults from 

 Lappmark, Sweden : hind foot (dry), 19*9 (19-4-21). Adultfrom 

 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, Kristiausamt, 1; Dovre Fjeld, 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. — Colpin, Brandenburg, 1 ; near city of Brandenburg, 1 (Berlin 

 Agric. ; coty]3e of stivimingi Nehring). 



Austria-Hungary. — Csallokoz-Somorja , Pressburg, Hungary, 1. 



