some Remains of Rodenfs. 



195 



verse crest starting from its posterior part instead of from 

 cusp 5. As a result of tiiese differences the anterior and 

 ])osterior transverse valleys are less extensive, the central 

 one, on tiie other hand, wider and deeper than in S. vulgaris. 

 Viewed from the front, the fossil is seen to be rather more 

 brachyodont than the recent tooth. Like the latter, the 

 fossil has three roots, viz., a large fang sn[)porting' the inner 

 cone and two small ones on the outer side ; in the fossil the 

 outer fangs are of approximately equal size, but in jS'. vulgaris^ 

 owing to the greater size of cusp 1, the antero-external fang 

 is stouter than the j)Ostero-external one. As the following- 

 dimensions show, the fossil is considerably smaller than the 

 recent tooth : — 



EXPLANATION OF PLATE VIII. 



Fiff. I. Castor veterior, Lankester. Part of a right ramus, witn ^, i^, 

 and iSTTa, from the Red Crag- of ^Yoo^^bridge, Sntiolk. Major 

 Moore's collection. A, inner, 13, outer view; 0, crown view 

 of cheek-teeth. 



Fig. 2. Castor plicidcns, Forsyth Major, from the Upper Freshwater Bed 

 of West Kuntcn, Norfolk. «, crown, h, basal view. 



Fifj. .3. Castor sp., from the Upper Freshwater Led of West Ronton. 

 «, crown, b, basal view. 



Figs. 4 & 5. Trogontherium. Lateral and sectional views of two young 

 left upper incisors from the Upper Freshwater Bed of' West 

 \in\\U)i\. 



Fig. G. Trogontheriitm. Left lower incisor from the Upper Freshwater 

 Led of West Runton. 6 a. Posterior view of tip. 6 6. Ante- 

 rior view of tip. (G a and 6 6 much enlarged.) 



Fig. 7. Trogontherium cuvieri, Fischer. Right navicular fiom the Upper 

 Freshwater Led, West Runton. A = proximal, L = distal, 

 C = tibial, and D = tibu]ar views. Facettes: a, astragalean; 

 c, cuboid ; III., II., and 1., cuneiform, n.t., naviculare tibinle. 



Fig. 8. Castor Jiber, Linn. Right na\icular from the alluvium of the 

 Thames. Li ttering as in tig. 7. 



Fig. 9. Scitirus vulgaris, Linn. Right P™ < , recent. X 9. 



liy. 10. Scmrus whitei, pp. n. Right !""■ 4 iroiu the Upper Freshwater 

 Bed, West Runton. X 9. 



(Except where otherwise noted, all figures are of natural size.) 



