702 



RODENTIA 



the underfur a dull, buflfy wood-brown (2 mm.) at tip, the longer 

 hairs black, those of sides and rump with conspicuous bulFy tips 

 or sub-terminal areas about 4 mm. in length. In both specimens 

 the long hairs are more conspicuous than in any other European 

 Microtus that I have examined. On sides the bufFy wood-brown 

 is nearly clear and distinctly more yellow than the cream-bufF of 

 Ridgway, but on back it is coarsely and conspicuously "lined" 

 with black, the general effect of the two colours approaching 

 olive or bister. Underparts yellowish cream-bufF irregularly 

 clouded by the slaty bases of hairs. Feet a dull, light, brownish 

 buffy. Tail obscurely bicolor, pale 

 butfy below, dull brownish above. 



Skull. — The skull differs from that 

 of all other known European species 

 of Microtus in its very highly arched 

 brain-case, which gives the dorsal 

 profile a uniform convexity that is ex- 

 ceedingly characteristic. Interorbital 

 region, in the two skulls examined, 

 rather broad, with distinct median 

 longitvTdinal concavity and low but 

 evident lateral ridges.* Nasals 

 slightly tapering, their width pos- 

 teriorly about three-fourths that 

 anteriorly, their posterior termination 

 square, slightly exceeded by nasal 

 branch of premaxillary. In both of 

 the skulls examined the length of 

 nasal decidedly surpasses that of 

 diastema, a condition not observed 

 in other European species. Palatal foramina large, their width 

 relatively to that of rostrum greater than in 

 M. arvalis. Auditory bulL-e not peculiar, their 

 size relatively about as in M. ari-alis. 



Teeth.— The teeth are strictly of the M. 

 arvalis type. Terminal loop of both m'^ and 

 n*! shortened as compared with the other 

 European members of the arvalis group, so 

 that in the former the third inner re-entrant 

 angle is very shallow, and the extreme pos- 

 terior portion of tlie tooth is a nearly straight 

 loop, almost as wide -as long, and evenly con- 

 stricted from both sides proximally, while in 

 the latter the outer re-entrant angle is prac- Microtus cahrerx. x 5. 

 tically absent, this peculiarity being carried 

 to a greater extreme than in M. sandayensis sandayensis, the 

 only other European Microtus in which it is known to occur 



* The ridges may eventually unite ; but the form of the interorbital 

 region in the young adult is different from that in any of the other 

 European species at the same stage. 



Fio. 14". 

 Mii-rotun cahrene. Nat. size. 



