THE MAMMALIA OF THE UINTA FORMATION. 487 



rilOTOREODDX S. & O. (PI. VII, Figs. 1-s). 



This genus is the most perfectly known and after TriplopuK the most abundant 

 of all the Uinta mammals. The Princeton collection contains portions of a large 

 number of individuals representing nearly all the important parts of the skeleton and 

 pertaining apparently to two species. The genus is to be defined as follows : " Sel- 

 enodont Artiodactyla with unreduced dentition ; inferior canines with the form and 

 function of incisors, first lower premolar cuniniform ; superior molars of five crescents, 

 the unpaired one nuicli reduced and situated in the anterior half of the crown, outer 

 wall erect and flattened ; crowns very low and broad, valleys widely open ; inferior 

 molars much like those of AgriocJia'rtis with conical inlernal crescents. ^N'o diaste- 

 mata in lower dental scries and a very short one behind the u])per canine. Cranium 

 narrow and very much elongated, orbit open behind, apparently no lachrymal pit. 

 Lunar resting more directly upon the magnum than in Oreodon ; inanus pentadactyl ; 

 pes tetradactyl and inadaptively reduced. 



Before proceeding to describe the osteology of this remarkable genus it may 

 be well to glance at previous notices of the Uinta selenodonts. The first one de- 

 scribed is the Arfriochmrus yumiluii Marsh (No. 8, p. 250), which is founded upon the 

 inferior dentition. It seems highly imi)robable that this White River genus should 

 occui- in the Uinta, and the lower molars of Protoreodon being, as we have already 

 seen, much like those of Agriochoerus, one is led to infer that this supposed A'jrio- 

 chuinis belongs to Protoreodon, 1)ut in the absence of the upper molars this cannot l)e 

 certainly determined. Prof. Marsh (No. 9, pp. 361-5) subsei[uently named three 

 genera fi'om this formation, of which he says : " In the Diplacodoii horizon of the 

 Upper Eocene, the selcnodont dentition is no longer doubtful, as it is seen in most of 

 the Artiodactyla yet found in the^c beds. These animals ai'e all small, and belong to 

 at least three distinct gencia. Oni' of these, IiJomeryx, closely resembles Ilomacodon 

 in most of its skeleton, and lias four toes, but its teeth show well-marked crescents 

 and a |)artial transition to iliu tfftli of Ilijopotanuis from the Eocene of Europe. 

 With this genus is another (Parameryx), also closely allied to Homacodoii, iuit appa- 

 rently a straggler from the true line, as it has Init three toes behind. Tlu^ most pro- 

 nounced selcnodont in the Upper Eocene is the Oromeryx, which genus apjjcars to 

 be allied to the existing deer family, or Cproidr,, and if so is the oldest known repre- 

 sentative of the group." "The least specialized, and apparently' the oldest, geiuis of 

 this group [the oreodonts] is Ayriochrrrn-i, which so nearly resembles the older Ily- 

 opolatiiits, and the still more ancient Eomeryx, that we can hardly doubt that they 

 all belonged to the same ancestral line." ''A most interesting line, that leading to 



