MIMOMTS 369 



occur rarely in the " shelly sand " ( ? Weybourne Crag) at East 

 Runton ; but they are among the most abundant fossils of all 

 three parts ("Lower Sandy," "Middle Peat," and upper 

 " Monkey-Gravel ") of the Upper Freshwater Bed at West 

 Runton. On the continent, remains certainly referable to this 

 species have been found only in the Upper Pliocene or earliest 

 Pleistocene deposits of Hungary, at Beremend and at Nagy- 

 Harsany. 



Characters. — Size medium ; jaws about as large as in the 

 smaller species of Arvicola (e.g., A. scherman) ; lower tooth-row in 

 adults from 7-8"5 mm. Distinguished from M. savini by the 

 form of ??ii, in which, in adults, the third outer angle is not 

 complicated by a prism-fold. 



Skull known only from fragments ; temporal ridges well 

 marked in adults but remaining widely separated in the 

 interorbital region ; outer wall of the infraorbital canal not 

 essentially different from that of modern voles, the maxillary 

 zygomatic process extending as far back, the jugal no further 

 forwards than in Arvicola ; ascending branches of premaxillaries 

 extending slightly further backwards than the nasals; frontals 

 perfectly coalesced in adults and sending a small process forwards 

 between the posterior ends of the nasals. Palate (PI. XIV, 

 fig. 1) essentially as in Arvicola, quite unlike that of Evotomys; 

 in its fore-part, lateral grooves and median spear-shaped 

 ridge more or less prominently sculptured ; point of spear-shaped 

 ridge jutting in between the anterior palatine foramina from 

 behind ; the foramina extending backwards to a point some- 

 what in advance of the front edges of the tooth-rows ; postero- 

 lateral bridges complete and massive ; post-palatal lateral 

 pits deep ; the intervening, or posterior median sloping septum, 

 short, wide, and sometimes grooved ; interpterygoid fossa square 

 or slightly rounded anteriorly, very slightly indenting the palatal 

 shelf in the middle line ; maxillo-palatine suture extending 

 forwards to a point nearly opposite the middle of m^. In the 

 figured specimen a longitudinal median fissure seems to suggest 

 that occasionally, at all events, the median palatal suture 

 persisted in adults. 



Mandible in general appearance much like that of a small 

 species of Arvicola; angular and coronoid processes well de- 

 veloped ; lower incisor crossing from lingual to labial side of jaw 

 between m^ and m^ (the former tooth wholly labial, the latter 

 wholly lingual to the shaft of the incisor) and ascending the 

 condylar process to a point about level with the dental foramen. 

 Muscular impressions on outer surface sharply defined and 

 indicating that the two divisions of the masseter medialis muscle 

 agreed with those of Arvicota as regards their arrangement and 

 insertion (PI. XIV, fig. 2). 



Cheek-teeth.— Enamel well differentiated; re-entrant folds 

 partly filled with cement; teeth provided with roots in old age 



