188 Mr. M. A. {". Hintoiio;i 



(b) Forest-Bed Beavers, 



Fovsy til Major * lias shown that two species of Castor 

 occur in the Forest-Bed lioiizon exposed at East Runton, 

 Norfolk. One, characterized by its broader incisors, slightly 

 larger cheek-teeth, and, above all, by the " complex and 

 elegant plication " of the enamel of its molars, is identical 

 with C. plicidens, Major, a species described from the Upper 

 Pliocene of the Val d'Arno ; the other, with narrower iricisors, 

 smaller molars, and much less plicated enamel, makes a 

 nearer appioach to the recent s))ecies, and it is the only form 

 which has been found hitherto in the Upper Freshwater Bed 

 at West K.uuton. Recently Mr. Savin has found in the latter 

 deposit two young upper cheek-teeth of Castor^ each being 

 eit iier the right Elii or ^^ (PI. VIII. figs. 2 & 3). Each tooth 

 presents the usual enamel pattern, and in each the enamel, as 

 exposed at the grinding-surt'ace (figs. 2 a, 3 a), is free from 

 plication. An examination of tiieir bases shows that, while 

 in the smaller tooth the enamel would remain uncrimj)ed 

 ( fig. 3 U), in the larger one (fig. 2 h) it acquires in deeper strata 

 of the crown the comj>lex and elegant plication of C. plicidens. 

 Boscof has shown that the jaw from the Val d'Arno, on 

 which Forsyth ^lajor based his C. rosinai\, is, in fact, a 

 young jaw of C. ]dicidens ; the enamel at the grinding- 

 surface of the little-worn teeth of this jaw is free from plica- 

 tion, but a section made through the basal parts of the teeth 

 shows that the typical plication is developed in the deej)er 

 portions of the teeth, just as in the West Runton specimen, 

 it may be mentioned, further, that whereas in the molars of 

 the lower jaw from East Runton figured by Forsyth ]\Iajor 

 the plication princi])ally affects the enamel of the first and 

 third inner folds, in the West Runton tooth all three of the 

 corresponding outer folds display it. 



Mr. Savin possesses a large light ramus from the Forest 

 Bed of Bacton with all the teeth in plac^'. It belonged to an 

 old itidividual. The molars are griatly worn and some of 

 them arc mutiUited ; their crowns still show, j)articularly in 

 the antero-inlernal fold of each tooth, traces of a strong 

 plication of the enamel. The incisor is very broad. This 

 jaw also may, peihaps, be referable to C. plicidens. 



* Forsyth Major, i'loc. Zonl. Sue. 11)08, p. 030. 



t liosco, op. cit. p. 88. 



+ Forsylli Major, Arch, per rautrop. o rctiiogrnliii, vol. vi. p. yir>(187f)). 



