178 THE MERYCOIDODONTIMi 



Paroreodon the width is but slightly less than the length. There is, however, a similarity in con- 

 struction of the P 3 and P 4 in both genera. 



With Poatrephes we have a closer approach to Paroreodon, the latter differing chiefly in the 

 smaller size of skull, relatively greater diameter of postorbital constriction, much shorter and lower 

 sagittal crest, somewhat reduced brachycephaly, much smaller taper to the muzzle, relatively higher 

 skull, differently shaped bulls, orbits much larger and more elevated, and posterior of skull much 

 more depressed. In the dental series the premolar length is greater than the molar length in 

 Poatrephes, while the paracones and metacones are nearly in line in that genus. P 3 is less developed 

 anteriorly, and P 4 is relatively considerably wider transversely. 



Paroreodon is closest to Merycoides in the structure of the teeth. Both have about the same 

 m.-pm. index, M 3 has the same offset metacone, and the structure of P 3 and P 4 is close. The major 

 differences in the skull are that Paroreodon is much smaller, with relatively larger brain case, shorter 

 and lower sagittal crest, more brachycephaly, relatively longer face, shorter nasals, greater depres- 

 sion posteriorly and anteriorly, much steeper basicranial axis, deeper malar, and differently shaped 

 bulla? and paroccipital processes. 



I believe that Paroreodon is the West Coast early representative of the Ticholeptus line. A 

 comparison with that genus shows that the former has a skull fully as deep, with nearly the same 

 postorbital constriction diameter, frontals as wide, and zygomatic arches as short, as in the later form. 

 The teeth have the same general construction but are more advanced. The metacone of M 3 is offset 

 in both, and M 2 and M 3 are nearer of a size than are M 1 and M 2 . 



The major differences in Paroreodon are the smaller size, relatively larger brain case, shorter 

 nasals, more brachycephalic skull than is average in Ticholeptus, longer face, lower and shorter 

 sagittal crest, outer faces of P 3 and P 4 not on a line at their point of contact, and M 1 wider than long. 



The evidence seems to point to Eporeodon as the ancestor of Paroreodon, the latter being as 

 much advanced over the former as Ticholeptus is over Paroreodon. In the Promerycochosrus- 

 Pronomotherium division we find very considerable divergences, the nearest contemporary being 

 Mesoreodon, but even here the differences are so marked that a detailed comparison is unnecessary. 



Etymology: Paroreodon (near + Oreodon). 

 Species: P. mars hi Thorpe 1921. Genotype. 



Paroreodon marshi Thorpe 1921 



Figs. 129-131 



Original Reference: John Day eporeodons. Amer. Jour. Sci. (5), II, pp. 109-110, figs. 14-16. 

 Type Locality: Haystack Valley— Turtle Cove area, John Day Valley, Oregon. 

 Geologic Horizon: Upper Oligocene (middle John Day). 



Type: Genoholotype, Cat. No. 12415 Y.P.M., skull with incomplete zygomata and without crowns of 

 incisors, of canines, and of P 1 and P 2 . 



Specific Characters: The skull is decidedly heavy and robust, about the length of that of 

 Merychyus a. minimus, but markedly uparched, being in this respect distinctly unoreodont, and is some- 

 what brachycephalic, with the maximum expansion probably just in advance of the glenoid surface. 

 The malar is thick and deep below the orbit. The facial vacuities are triangular in shape, with a 

 maximum diameter of nearly 12 mm., and are located in front of the orbits, at which point they are 

 bounded by the lacrimal, frontal, and maxillary bones. The posterior part of the nasal bones is 

 abruptly truncated. The bones increase gradually in width anteriorly to a maximum probably at the 

 contact between the nasals and maxillaries and are very gently convex from side to side. The 

 lacrimal bone is subtriangular, and the lacrimal fossas are large and moderately deep, with the long 

 diameter nearly vertical. The frontals are wide and flat, projecting about 3 mm. farther forward 

 than do the lacrimals, with the anterior termination as abruptly truncated as is that of the posterior 



