Late Pleistocene Voles and Lemmings. 37 



Measurements.-Ty V e skull : condylo-basal length 26*9 mm.; 

 zygomatic breadth U'O ; interorbital constriction I'l \ occi- 

 pital breadth 11-9 ; occipital depth (median) 64 ; nasal < L , 

 diasteme 8'7 j molar series (alveolus) 6'4. 



Specimens examined.— Two nearly perfect and a very laige 

 series of imperfect skulls from the Ightham Fissures and 

 numerous specimens from other Late Pleistocene deposits. 



Remarks.— This species has long been known to paleon- 

 tologists as a conspicuous element in the Late Pleistocene 

 fauna of Western Europe, and they have hitherto followed 

 the lead o£ Nehring ia referring it to M. gregahs ot Pallas. 

 The skull-measurements given by Pallas show that whatever 

 the imperfectly known M. gregalis may be it certainly Has 

 little to do with the fossil animal. The zygomatic and 

 occipital breadths, when compared with the skull-length taken 

 as 100, amount to 45'5 and 364 respectively in M. gregalis, 

 and to 52-0 and 44'2 in M. anglicm. Among the living 

 species of " Stenocranius" of which I have seen skulls or 

 descriptions M. tianshanicus, Biichner, appears to make the 

 nearest approach to M. anglicus in skull and dentition ; it 

 differs principally in the narrower palate, narrower and 

 shorter rostrum, and lighter zygomatic arches. 



Dicrostonyx henseli, sp. n., foss. 



Type.— A perfect adult skull in the collection of Mr. Lewis 

 Abbott from the Ightham Fissures. 



' Characters.- Size small. Skull: dorsal outline gently 

 convex ; combined nasal width little more than a third ot 

 nasal length ; zygomatic arches flaring more than in U. tor- 

 guatus (Discovery Bay) ; palate feebly sculptured with com- 

 plete postero-lateral bridges; auditory bullae very small, 

 egg-shaped, and not inflated anteriorly; presphenoid reduced 

 to a slender rod ; molars heavy. 



Dentition : in the anterior upper molar the fourth or 

 uostero-internal prism is reduced, its hinder wall has lost its 

 primitive curvature and passes into the posterior wall ot the 

 U„il fourth outer triangle without forming any minute 

 nosterO-mternal accessory (i. e. vestigial) angulation ; m the 

 Uond upper cheek-tooth the third inner prism is similarly 

 reduced antero-external triangle of last lower molar much 

 ™«1W t'h'aP Rft <™d one, and passes in front into the anterior 

 smaiiei tnaa w~~. . . . . » r antero-external 



wall of the tooth without forming arty lliA, 

 vestigial angulation. 



Measurements. — Type skull : condylo-basal length 28'6 ram. ; 

 zygomatic breadth 19'8; interorbital constriction 4-0; occi- 



