166 MK. E. T. NEWTON ON A SKULL OF TROGONTHERIUM CUVIEEI 



It is proposed in the first place to describe this new specimen in detail, at the same 

 time comparing it with the skull of the Beaver, to which it is nearly allied, and then 

 to institute a comparison between it and Fischer's type ; and finally to consider its 

 relation to the skull from the Pliocene of Saint-Prest, called by M. Laugel in 1862 

 Conodovtes ioisvilleffii \ which is believed to be referable to the same genus and species. 



There has been much diversity of opinion as to the genus to which these Forest Bed 

 lemains should be referred, and consequently the synonymy is very perplexing ; this 

 has, however, been explained in the Memoir of the Geological Survey already i-eferred 

 to, and the new specimen seems to me fully to confirm the opinions there expressed, 

 lleferences to the authors who have written upon the subject will be found at 

 the end of this paper. 



2. Description of the Skull of Trogontheriumym« East Runton. 



This Forest Bed skull has very nearly the same parts preserved as Fischer's type ; it is 

 of a dark brown colour, and is much impregnated with iron. The nasal bones, as might 

 be expected, have fallen away ; and both the incisor teeth are absent, but their alveoli 

 are intact. The jugal arch on both sides is broken off close to the cranium, leaving 

 only the bases of the maxillary and squamosal buttresses. The bony external auditory 

 meatus is wanting on the right side, and the thin laminae of the palatines and ptery- 

 goids are broken away. There has evidently been a strong supraoccipital crest, 

 probably as well developed as in the Beaver ; but it is now much abraded. 



As this skull (Plate XIX.) bears a very close resemblance to that of a Beaver, its 

 description will be most intelligible if given in terms of comparison with that animal ; 

 and it is so little longer than the specimen from the fens, which will be used for 

 comparison, that the relative proportions, indicated by the measurements given in the 

 table on page 173, will be very obvious. 



When viewed from above (fig. 1) the difference in general proportion between the 

 two skulls is clearly seen. The length of the cavity exposed by the removal of the 

 nasal bones is about the same in both specimens, but is much the widest in the 

 Troqont/ierium. The fronto-premaxillary suture in the Trogontherium is opposite the 

 middle of the maxillary buttress for the jugal arch, and the premaxilla is consequently 

 almost wholly in front of the maxillary buttress. In the Beaver this buttress is further 

 forwards, and the premaxilla extends for some little distance behind it. The frontals 

 are longer and wider in Trogontherium than in the Beaver; and the postorbital process 

 is about halfway between the anterior and posterior buttresses of the jugal arch, while 

 in the Beaver this process is further forwards. The parietals are much shorter than 

 they are in the Beaver, and the same may be said of the interparietal. On each 

 parietal, near the sagittal suture, there is a ridge, which, running backwards, meets its 

 fellow at their junction with the triangular interparietal, and they are continued as a 

 • BuU. Soe. Geol. Fr. ser. 2, vol. xix. p. 167 (1802). 



