700 THE BRIDGER FAUNA. 



rami of the mandible, with complete dentition, of a third. The species is 

 distinguished by the details of the dental structure, and by the superior 

 size. It exceeds, in this respect, the Palceosyops major Leidy; in which 

 the three posterior lower molars measure M. .108 in length, while the same 

 teeth of the present animal measure M. .145. The last superior molar of 

 another specimen measures M. .051 in length; in a third, the first true 

 molar is M. .038 in length, while the last inferior molar is .057 inches long. 

 The peculiarity in the structure of the superior premolars consists in the 

 existence of two strong transverse ridges, which connect the inner tubercle 

 with the outer crescents, inclosing a pit between them. In the premolars 

 is also found the peculiarity of the almost entire fusion of the outer cres- 

 cents into a single ridge. These united crescents are narrower than in P. 

 major, and the summits of all the crescents are relatively more elevated. 

 The external vertical ridge is weaker than in the other species of the genus. 

 The number of inner tubercles is the same as in that species; all the teeth 

 have very strong basal cingula, which extends on the inner side on the pre- 

 molars only. The inferior molars are relatively narrower than in P. major, 

 and the posterior tubercle of the last is larger and longer, and is an elevated 

 cone. The inner tubercles in all the lower molars have broader bases and 

 less acumination than in that species. 



The bones containing the maxillary and mandibular teeth were not 

 found together in any instance, so that it is possible that the different series 

 may represent different species. No other species of the genus was, how- 

 ever, found in the localities to which the respective parts could be referred. 

 Should these prove not to pertain together, the lower jaws may be regarded 

 as typical of the species. 



The mandibular rami are less robust than in P. major, and are rather 

 thin posteriorly. The dentary portion is compressed, and presents a longi- 

 tudinal concavity on the inner side above the inferior border. There is 

 a large mental foramen below the second premolar. The first premolar is 

 one-rooted. The second has no antei'ior basal tubercle, and supports a 

 principal cusp and a heel, which has an oblique median ridge. The fourth 

 premolar has the two Vs, but the anterior ridge of the anterior one and the 

 posterior ridge of the posterior one ai-e weak. The true molars increase 



