MICROTUS 66 < 



loop the inner re-entrant angle extends across to outer side, 

 isolating a second inner closed triangle and leaving the posterior 

 limb of crescent as a broad, rounded, backward-projecting, simple 

 loop, the inner side of which sometimes bears an incipient 

 re-entrant angle. First lower molar with posterior transverse 

 loop, three inner and two outer closed triangles, and a large 

 anterior loop indented by a deep re-entrant angle on inner side 

 and a shallow, more posterior reentrant angle on outer side, the 

 latter sometimes deep enough to meet point of inner re-entrant 

 angle subtending the terminal loop, thus isolating a third outer 

 triangle and reducing the loop to a crescent much like that 

 terminating m^ in its simpler form ; rarely the extreme antero- 

 internal border of loop shows traces of a supplemental re-entrant 

 angle ; inner side of tooth with five well developed salient 

 angles and a rounded anterior projection (rarely showing a 

 tendency to divide into two), and five well developed re-entrant 

 angles (rarely a rudimentary sixth) ; outer side of tooth with 

 three deep, definite re-entrant angles and a shallow fourth, and 

 four well developed salient angles and a broadly rounded anterior 

 convexity which sometimes develops a slight basal projection ; 

 outer re-entrant angles wider and shallower than those of inner 

 side, their points curved forward, the contrast between the two 

 sides much more noticeable than in the maxillary teeth ; outer 

 triangles about equal in size to those on inner side of m^, inner 

 triangles decidedly larger and more transversely elongated ; 

 posterior loop somewhat oblique, narrowly crescentic, slightly 

 curved, its inner limb much the longer, its transverse diameter 

 about equal to that of greatest width of crown. Second lower 

 molar with transverse posterior loop, two inner and two outer 

 closed triangles, two re-entrant and three salient angles on each 

 side, the elements essentially like the corresponding portion of 

 m^ but slightly smaller ; occasionally the anterior (external) 

 triangle develops on inner side a slight basal projection which 

 may become sufficiently pronounced to add a rudimentary salient 

 and re-entrant angle to those normally present. Third lower 

 molar with three transverse loops, each side with three salient 

 and two re-entrant angles, those of inner side much the deeper, 

 the antero-external re-entrant angle often obsolete ; posterior 

 -Oop larger than either of the others, more broadly crescentic in 

 outline than terminal loops of 7h, and m^, though not essentially 

 different in form, the outer limb practically absent ; first and 

 second loops somewhat irregular and variable in form, the first 

 usuUy truncate externally, the second usually with an angular 

 projection at outer side. 



Remarlis. — This species is recognizable among the European 

 voles by the presence of the well developed postero-internal loop 

 in the second upper molar. Externally it cannot always be 

 distinguished with certainty, particularly in dry specimens. 

 Throughout the greater part of its range, where the only other 



