168 ME. E, T. NEWTON ON A SKULL OE TROGONTHERIUM CUVIERI 



just in front of the anterior grinders. These depressions are not present in the Beaver. 

 The two rows of cheek-teeth diverge more rapidly than in the Beaver : the anterior 

 pair of teeth being nearer together, and the hinder ones further apart. 



The palatine bones end anteriorly in a more broadly truncated extremity than do 

 those of the Beaver ; but in both skulls there is a similar pair of foramina, placed one 

 at each angle of this truncation. Posteriorly the palatines are somewhat broken ; 

 but at the hindermost angle of each may be seen a large pit (or foramen filled with 

 matrix) placed just on the inner side of the last molar. This pit is not present in 

 the Beaver. 



The notch of the hinder palatal margin extends forwards to a little within the hinder 

 extremities of the last molars ; it is narrower than in the Beaver, and there is no median 

 process. In the Beaver the palatine notch is altogether behind the last molars, and it 

 has a median process. The pterygoids seem to be entirely broken away. 



The under surface of the basioccipital bone is characterized by a median longitudinal 

 ridge with an oval depression on each side. Posteriorly the ridge widens and then 

 dividing joins the two occipital condyles ; these, however, are sepairated by a distinct 

 median groove. Anteriorly the ridge is lost in the wide groove which occupies the 

 front part of the basioccipital. In the Beaver the whole under surface of the basi- 

 occipital is occupied by a deep round fossa. Only a small part of the basisphenoid can 

 be seen in the fossil, this region being obscured by the hard sandy matrix. 



The tympanic bullas [th.) are not so rounded and inflated as they are in the Beaver, 

 and the ridge which runs up the external auditory meatus is not so strongly developed. 

 The mastoid portion of the periotic forms a well-marked prominence upon the side of 

 the occipital region (fig. 3), and is separated from the bony auditory meatus by a down- 

 ward process of the squamosal similar to, but not precisely like, that of the Beaver. 



The foramen magnum (fig. 4) is triangular, its height and width being about the 

 same ; while in the Beaver it is rather more rounded and is proportionally higher. 

 The exoccipitals form lateral plates, which, extending downwards on each side, become 

 paroccipital processes ; these are now denuded, but when perfect could not have been 

 so large as those of the Beaver. The exoccipital plate also extends upwards and 

 outwards, covering much more of the mastoid than it does in the Beaver ; and it may 

 be that it extends to the line seen near the outer margin of the occiput, thus almost 

 excluding the mastoid from the back of the skull ; it is not quite certain, however, 

 that this line is really a suture, and possibly the exoccipital only extends as far as the 

 large foramina seen in this region. Each exoccipital is marked by a deep depression, 

 just above the occipital condyle. The general contour of the back of the skull is 

 unlike that of the Beaver : for. even when allowance is made for the absence of the 

 occipital crest, the occiput is found to be much wider, the paroccipitals do not project 

 to the same extent, and the supraoccipital bone is certainly wider. 



Dentition. — The incisor teeth are absent, but the size and roundness of the alveoli 



