Late Pleistocene Voles and Lemmings 35 



and Southern Europe *. It is distinguished from the living 

 members of the latter group not only by its more highly 

 specialized occipital region, but by the greater specialization 

 of the pterygoid region and its larger size. So far as is 

 known, the species is confined to the latest portion of the 

 Pleistocene period in Britain, and has hitherto only been 

 found in the deposits of the Ightham Fissures. 



Microtus corneri, sp. n., foss. 



Type. — An adult skull in the collection of Dr. Frank Corner 

 from the Ightham Fissures (Late Pleistocene). 



Characters. — Skull essentially as in M. orcadensis and its 

 allies ; nasals and maxillary tooth-row a little shorter, 

 diasteme a little longer proportionally than in any of the 

 living members of the group ; incisors a little straighter and 

 more protruding than in M. orcadensis ; upper surface of 

 superior ramus of maxillary root of zygoma thickened, fusi- 

 form expansion of maxilla and jugal more extensive than 

 in M. orcadensis and sandayensis ; interparietal shorter in 

 proportion to width than in adult M. orcadensis, the adult 

 M. corneri presenting the interparietal form of young 

 M. orcadensis ; brain-case differing from that of M. orca- 

 densis in being somewhat narrower and more depressed, from 

 M. sandayensis in being considerably narrower, and from 

 that of M. samius in being proportionally broader. Taking 

 the distance from interorbital constriction to lambdoid crest 

 as| 100, the breadth of the brain-case at front edge of squa- 

 mosal root of zygoma amounts to 



!95 in M. sandayensis westros. Type, B. M. 



03 in M. sandayensis. B. M. 6. 11. 18. 9. 

 190 in M. orcadensis. B. M. 5. 12. 13. 2. 

 ' 85 in M. corneri. Type. 



78 in M. samius. B. M. <J, 8. 9. 2. 27. Type. 



The constricted interorbital region is shorter than in 

 M. orcadensis, almost exactly as in M. sandayensis ; molar 

 teeth of normal arvalis pattern, very light. 



Measurements. — Typeskull : condylo-basal length 28'8 mm.; 

 zygomatic breadth 16*5 ; interorbital constriction 3'6; occi- 

 pital breadth 13'0 ; occipital depth (median) 7*0; nasal 7*9; 

 diasteme 9*1 ; maxillary tooth-row Q'2. 



/Specimens examined.— One perfect and more than a dozen 

 fragmentary skulls, including one example from the Lang- 

 with Cave, Derbyshire ; the others from the Ightham 

 Fissures. 



* Miller, Proc. Biol. Soc. of Washington, 1910, March, pp. 19-22. 



3* 



