OREODONTOIDES 



215 



unite to form a sagittal crest — a character that is unique in the adult merycoidodonts, so far as I 

 recall. This causes the posterior part of the skull to appear to be very much depressed. The supra- 

 occipital crest is broken away, but I am certain that it was low. The brain case is low but unusually 

 expanded transversely. The postorbital constriction is of great width also. This species undoubtedly 

 had bulls, but they are missing, as is the external auditory meatus. The U-shaped palatonarial 

 border lies just back of the line of M 3 . The palate is narrow and moderately vaulted posteriorly, 

 while anteriorly it is much uparched. The basicranial axis is but slightly inclined. The glenoid 

 surface is convex downward to a moderate degree. The postglenoid process was small but stocky, 

 being three-fourths as wide anteroposteriorly as long transversely. Index: 0.60a. 



Mandible: The symphysis is proportionally long and strong, with a symphysiodental angle of 

 40°. The face of the symphysis is nearly straight. The depth beneath the tooth row increases very 

 slightly from P 2 to M 2 . 



Fig. IS 8. — Oreodontoides oregonensis Thorpe. 

 Superior view, fragmentary mandible. PLT. Cat. 

 No. 12638 Y.P.M. 2/3 nat. size. (After Thorpe, 

 1924.) 



Fig. 159. — Oreodontoides oregonemis Thorpe. 

 Fragmentary ramus. PLT. Cat. No. 12638 Y.P.M. 

 2/3 nat. size. (After Thorpe, 1924.) The in- 

 cisors and canine in this figure and in Fig. 158 are 

 restored from PLT. Cat. No. 12635 Y.P.M. 



Foramina: The infraorbital foramen lies above the interval between P 3 and P\ The supra- 

 orbitals are obscure. They are small and appear to be rather close to the sagittal suture. The basi- 

 cranial foramina cannot be discerned. The posterior palatine foramina are opposite P\ 



Dentition: The teeth are brachyodont. The premolar length is but slightly less than the 

 molar, the index being 0.95. The premolars do not overlap, nor do they appear markedly to be 

 obliquely placed. There is a suggestion of obliquity in P 1 and P 2 . The anterior parts are not so 

 much reduced as in Merychyus. The parastyles and mesostyles increase in prominence from molars 

 1 to 3. These styles are almost straight, thus producing an outline to the base of the paracone and 

 metacone that is more nearly square than in Merycoidodon, for example. 



Inferior: The three incisors are cylindrical in cross section, are directed well forward, and 

 increase slightly in size from Ii to I 3 . The crown of the canine is triangular in cross section, with 

 the external face smooth and flat. The lingual area, approximately twice the size of I 3 , is divided 

 into two surfaces by a median ridge. The caniniform premolar (Pi) is laniariform and was appar- 

 ently an excellent cutting tooth. In cross section it is elliptical, with the anteroposterior diameter 

 twice that of the transverse, 8x4 mm. The premolars are unusually narrow, and P x , P 2 , and P 3 are 

 so crowded that they set obliquely. 



Referred specimen: Cat. No. 10149 Y.P.M., consisting of the median part of an immature 

 skull, seems to be referable to this genus and species. However, the matrix is green, indicating a 

 middle John Day horizon, whereas in all the other specimens of this species the matrix is gray. The 

 locality whence it came was Clarnow Bottom, which is in the John Day Valley but some distance 

 from Turtle Cove, the type locality. 



Discussion: Loomis (1924B, p. 14) considered this to be a species of Merychyus, "slightly 

 less advanced than the eastern representatives." The characters common to both are the size, a skull 

 that is low and wide, with the highest point about at the postorbital constriction, large and moder- 

 ately elevated orbits, unreduced frontals, zygomatic arches that are probably light, deep lacrimal pit, 



