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34 Mr. M. A. C. Hinton on new 



IV. — Some new Late Pleistocene Voles and Lemmings. 

 By Martin A. C. Hinton. 



As some considerable time will elapse before my work dealing 

 with the British Fossil Voles and Lemmings can be published, 

 and as some of the Late Pleistocene forms throw considerable 

 light upon certain problems of geographical distribution at 

 present confronting zoologists, it seems advisable to publish, 

 the following diagnoses. I have, firstly, to thank Mr. W. J. 

 Lewis Abbott, Dr. Frank Corner, Mr. A. S. Kennard, Dr. H.O. 

 Male, and the Rev. E. Mullins for the loan of material, 

 Mr. Oldfield Thomas for the facilities he has kindly afforded 

 for examining the recent material in the British Museum, and 

 Mr. Gerrit S. Miller for much valuable assistance and advice. 



Arvicola abbotti, sp. n., foss. 



Type. — An adult skull in the collection of Mr. Lewis 

 Abbott from the Ightham Fissures (Late Pleistocene). 



Characters. — Size large (condylo-basal length of adult 

 skull 41'0 mm.). Skull showing extreme fossorial specializa- 

 tion ; incisors straightened and protruding, the straightening 

 far more pronounced than in any living member of the 

 A. scherman group ; incisive foramina very small ; postorbital 

 squamosal crests very weak ; occiput, in adults, sloping 

 forwards conspicuously, the interparietal becoming reduced and 

 its posterior margin boldly convex instead of nearly straight; 

 lambdoid crest markedly sinuous and ridge for ligamenium 

 nuchce prominent ; mesopterygoid fossa very narrow, postero- 

 lateral palatal pits extensive, the fossae for origin of ptery- 

 goideus internus muscle correspondingly increased in exten- 

 sion ; mandible with very small angular process, the inci^'- 

 root ascending nearly to condyle and making a strong hurw 

 externally j molar teeth very light, enamel pattern substan- 

 tially as in A. amphibius. I 



Measurements. — Type skull : condylo-basal length 41 mm. \ 

 zygomatic breadth 25 2 ; interorbital constriction 4 - 8 ; occi- 

 pital depth (median) 10*1; diasteme 140; molar series 

 (alveolar) 9"5; condyle to alveolus of last molar 15*6. 



Specimens examined. — Four complete and about a dozen 

 fragmentary skulls from the Ightham Fissures. 



Remarks. — A. abbotti is of great interest, since it affords 

 the highest expression of that fossorial specialization which 

 is seen beginning in the Scandinavian A. terrestris, and 

 which is well developed in the A. scherman group of Central 



