52 MAMMALIA. 



Vol. XL VI., p. 447). The patterns of the three teeth which are 

 preserved agree with those of Trogontherium, the folds of enamel 

 being open exteriorly for only a short distance from the summit 

 of the tooth, indeed, the three outer folds of each tooth have 

 become shut off from the outside, and the single inner folds are 

 very nearly in the same condition. The largest of these teeth 

 (p.m. 4) which is closing in to form the fang, is 18 mm. long, 

 and 8 mm. wide. The much smaller size of this specimen as 

 well as its occurrence at a lower horizon has led to its receiving 

 the distinctive specific name of T. minus. The tooth from the 

 Norwich Crag of Sizewell Gap, near South wold, noticed by Sir 

 II. Owen as Beaver (Brit. Foss. Mamm., p. 192, 1846), and pre- 

 served in the Museum of the Geological Society, is provisionally 

 included in this species. 



Genus MUS, Linnaeus. 



MUS SYLVATICUS, LINNAEUS. 



(Field Mouse.) 

 (Vert. Forest Bed, p. 93, PLATE XIV., FIGS. 11, lla.) 



Jaws and limb bones of Mus sylvaticus have been found in the 

 Forest-bed at West Kunton, and the species is now living 

 throughout Europe. 



Genus MICROTUS, Schrank (ARVICOLA, Lacepede). 



MICROTUS (ARVICOLA) AMPHIBIUS? LINN&US. 



Water Vole. 



It is very doubtful whether A. amphibius occurs in beds of 

 Pliocene age. The form alluded to by Messrs. R. and A. Bell 

 (Prqc. Geol. Assoc., Vol. II., p. 212, 1872) from the Norwich Crag 

 is no doubt Arvicola intermedium (Mem. Geol. Surv., Vert. Forest 

 Bed, p. 83, 1882), the only specimens I have seen from that 

 horizon being referable to that species. Miost of the Arvicola 

 remains which occur in the Forest-bed are likewise A. inter- 

 medius, but possibly some of the larger teeth may be A. amphi- 

 bius (Vert. Forest Bed, p. 87). 



This species is found in Pleistocene deposits ; it is now living 

 throughout Europe and possibly in China. 



MICROTUS (ARTICOLA) ARVALIS, PALLAS. 



(Vert. Forest Bed, p. 88, PLATE XIV., FIGS. 2-5 and 7.) 



Teeth and bones agreeing with those of Arvicola arvalis have 

 been found in the Forest-bed at West Runton. Although the 

 species is extinct in Britain it is still living on the continent. 



