FROM THE rOEEST BED OF EAST EUNTOX. 171 



4. Comparison of the Forest Bed Skull with Fischer's Trogontherium cuvieri. 



It will be obvious, from the description of the Forest Bed skull given above, that it 

 differs widely from that of the Beaver, and confirms the view held by Sir E. Owen and 

 other writers, as to the Forest Bed rodent belonging to a genus distinct from Castor. It 

 now remains to be seen whether we are also justified in referring it to the Troqontherium 

 of M. Gotthelf Fischer, and finally to ascertain whether Conodontes boisvillettii is, or is 

 not, to be included in the same species. 



The skull from the Forest Bed agrees so closely with that of Trogontherium cuvieri, 

 so far as one can judge from a comparison with the published figures of Fischer's type 

 skull and with a cast of the original specimen, kindly sent me from Moscow by the late 

 Dr. Kowalewsky, that our purpose will be best served by pointing out the differences 

 between them, rather than by alluding to their many points of resemblance. 



Fischer's type is certainly larger than the Forest Bed skull, a diff'erence especially 

 noticeable in the premaxillary region ; but this cannot be looked upon as of much 

 importance, and certainly not as an indication of specific distinction ; for some of the 

 fragments from the Forest Bed, and more particularly a pair of premaxillary bones in 

 Mr. A. Savin's collection, must have belonged to larger skulls than Fischer's type, and 

 it is tolerably certain that the premaxillse of this Pliocene rodent became elongated in 

 proportion to the gradually increasing size of the incisor teeth. 



The cheek-teeth of Fischer's type (fig. 7) are a little larger than those of this English 

 specimen (fig. 5), though not so large as some teeth found in the Forest Bed ; the 

 patterns of the teeth, however, are essentially the same. The first and second molars 

 in the maxilla described by Sir R. Owen (fig. 6), and alluded to above, having only two 

 folds instead of four, it was thought impossible for it to belong to Fischer's genus ; but 

 we now know that the loss of folds is due to the stage of wearing of the teeth. The 

 Forest Bed skull forms an interesting link in the chain of evidence, for while the first 

 true molar (m. 1, fig. 5) has only three folds (that is, one more than in Owen's specimen, 

 m. 1, fig. 6), the second true molar (m. 2, fig. 5) still retains the four folds as in Fischer's 

 type (m. 1 & 2, fig. 7). Hitherto no English example of the upper third true molar 

 has been available for comparison ; but the present specimen has both these teeth 

 preserved (fig. 2), and the folds are essentially the same as in Fischer's type — that is, 

 one inner and four outer folds. It is true that in Fischer's specimen the hindermost 

 fold is represented by two small islands of enamel ; but this I regard as an individual 

 peculiarity, Jiaving seen a similar tendency in teeth from the Forest Bed. 



Much of the type specimen is obscured by the sandy matrix adhering to it, so that 

 the sutures and other details of structure cannot be compared. Nearly all the 

 minor differences which are seen on a close comparison seem to me to be due either to 

 this obscuring by matrix, or to the different condition of wearing. There is, however, 

 one point about which I am in some doubt; in the description of Fischer's type 

 attention is called to a deep fossa, situated on the base of the skull between the 



