71 



same lobe a third but less conspicuous ridge extends directly to the lobe 

 within. 



In the last molar the fifth lobe has a crescentoid summit declining from a 

 median point. The outer arm of the summit joins the contiguous arm of the 

 lobe in advance, and the inner arm joins the base of the postero-internal lobe. 



The minutely detailed description of these teeth, and the same may be 

 said of those of other fossils, is essential to the distinction of generic characters. 



From the back molars of Lophiodon, those of Lophiotherium especially 

 differ in the distinction of four instead of two lobes to the crown ; though the 

 two lobes in the teeth of Lophiodon and Tapirus represent the four of Lo- 

 phiotherium in a connate condition. 



The jaw-fragment of the fossil referred to Lophiotherium sylvaticum pre- 

 sents nothing peculiar. The outer, vertical surface is slightly convex, and ihe 

 base fore and aft is also moderately convex. 



The measurements of the fossil are as follows . 



Lines. 



Depth of lower jaw below middle of last premolar 5^ 



Depth of lower jaw below middle of last true molar G£ 



Autero-posterior diameter of last premolar 3£ 



Anteroposterior diameter of first true molar 3| 



Antero-posterior diameter of second true molar 3f 



Anteroposterior diameter of last true molar. . 54 



Transverse diameter of last premolar : 2 ; \ 



Transverse diameter of true molars .' -.] 



Should the duplication of the summit of the antero-internal lobe of the 

 crown of the lower back molars not be a character present in the Loph'w- 

 therium cervulum of France, it would probably be a concomitant of other 

 characters in the upper teeth, now unknown to us, which would distinguish 

 the American animal as generically distinct from Lophiotherium. 



In the American Journal of Science for 1871, Professor Marsh notices 

 some remains, from Grizzly Buttes, which he attributes to a species about 

 two-thirds the size of the former, and names it Lophiotherium Ballardi. 



TROGOSUS. 



Trogosus castoridens. 



One of the most curious of the extinct mammals of the Bridger Tertiary 

 fauna is an odd-toed pachyderm about the size of the larger living peccary, 

 which, with the usual complement of molar teeth, was apparently devoid of 

 canines, and was provided with a large pair of incisors like those of rodents. 



