00 TRANSACTIONS OF WAGNER 



oo 



UINTA SELENODONTS 



pressed and trenchant than in the White River genus. The first premolar is 

 caniniform and is more slender and pointed than in Orcodon ; it is succeeded 

 by p^ after an interval which, though very short, is distinctly longer than in 

 the latter genus. P-^ is a small, simple, and much compressed cone ; p-^ is 

 larger, especially in the fore-and-aft dimension, and is obtusely pointed ; from 

 the apex a quite prominent ridge runs down the inner side of the crown, 

 partially enclosing a posterior fossette. In p T this inner ridge has become a 

 well-marked cusp, much like that in Leptoreodon. 



Leidy's admirable description of the lower premolars of Orcodon will 

 show the changes -which characterize that genus : " Their crown is a broad, 

 trapezoidal pyramid, widest behind, and with an acute crescentoid border 

 rising in a median point. From the latter an oblique ridge descends in- 

 ternally, and in the third [fourth] premolar terminates in a large, trilateral, 

 pointed tubercle, which springs from the middle of the base of the crown and 

 rises nearly as high as the principal point. In the premolars in advance the 

 tubercle just mentioned is nearly obsolete, and the oblique ridge appears to 

 expand into the base of the crown. Back of the oblique ridge the crown 



presents a fossa more or less closed internally by a tubercle or ridge 



In advance of the oblique ridge mentioned, the inner part of the crown forms 

 a broad, sloping concavity, usually enclosed at bottom by a narrow, festooned 

 basal ridge." ('69, p. 82.) 



The molars are much more primitive than those of the upper jaw and 

 have many points of resemblance to the lower molars of Agrioclmriis. The 

 internal cusps are conical rather than crescentic, and the outer ones, while cres- 

 centic, are quite thick ; the valleys are very broad and shallow ; the anterior 

 pair of crescents is separated from the posterior pair by a deep depression ; 

 small basal tubercles are developed on the inner cusps. M3 has a very large, 

 basin-like heel. In Orcodon the lower molars have become typically seleno- 

 dont, almost as much so as in the deer, while Agriochcents retains a structure 

 very closely like that of Protoreodon, — a significant fact. 



The milk dentition is only imperfectly known, but one specimen which 

 retains m- 1 - and dp^ displays some points of interest. The deciduous pre- 

 molar is completely molariform, but has more the molar pattern of Agrio- 

 chxrus than have the true molars of Protoreodon. This approximation to 

 Agriochcents is manifest (1) in the greater concavity of the external crescents ; 



(2) in the more massive and rounded shape of the antero-external buttress ; 



(3) in the greater breadth of the external median buttress, which is not com- 



