TRANSACTIONS OF WAGNER 

 IOO 



UINTA SELENODONTS 



Hyomeryx, which appears to be merely an abortive side-branch of the oreodont 

 stem that led to nothing. At the same time this genus and the species of 

 Protoreodon with reduced upper incisors would seem to have been the domi- 

 nant representatives of the oreodonts in the typical Uinta horizon (horizon C). 

 All the specimens of P. parvus which I have seen were found in the clays of 

 horizon B, and while the Uinta collections are not yet sufficiently complete to 

 give certainty upon such points, it seems exceedingly probable that in the Uinta 

 proper the main line of oreodont development was overshadowed by the tem- 

 porary abundance and importance of this short-lived group. This reasoning 

 proceeds upon the assumption that structures once lost are not regained, and 

 such certainly appears to be the normal course of evolution in the mammalian 

 phyla. At the same time it must be remembered that it is an assumption, that 

 possibly the incisors may have been partly suppressed and again redeveloped. 

 The series Protylopus , Pocbrotherium, Gomphotlierium, etc., shows us that teeth 

 may be greatly reduced in size and subsequently enlarge, and we cannot say 

 with entire confidence that the process of rehabilitation may not go farther, 

 and that teeth which are lost in the adult may not become functional again in 

 a descendant. It is most important that we should not dogmatize concerning 

 evolutionary processes on a priori grounds, and that we should await the 

 evidence before coming to a decision upon these problems. 



Family V. AGRIOCHCERID/E. 



Protagriochcerus gen. no v. 



Plate IV., Figures 26-28. 



This genus, which is represented by a species of considerably larger 

 stature than those of any other genus of Uinta selenodonts, is founded upon a 

 specimen belonging to the American Museum of Natural History (No. 1818). 

 It is much to be regretted that all the known material is so very imperfectly 

 preserved that many interesting phylogenetic questions cannot yet be settled. 

 The dentition (Plate IV., figs. 26, 27) is of a character intermediate between 

 the oreodonts and agriochcerids. 



The dental formula is : I-, C 1 , P-, MX The incisors appear to have 

 already undergone some reduction, and in the type specimen only the fang of 

 i-^ is visible; this fang is stout, of circular section, and is implanted quite near 

 to and in advance of the canine. If the other two incisors were present they 

 were probably small, as the premaxillary is so narrowed as hardly to allow 



