34 THE MERYCOIDODONTID/E 



Mandible: The symphysis is nearly straight in profile, with a 45° symphysiodental angle. 

 The mental tubercle is well developed. The inferior border of the horizontal ramus is almost 

 straight, and the angle is not well demarcated. A ridge parallels the posterior border of the ascend- 

 ing ramus, as it does in P. fumilus. The coronoid process is moderately wide anteroposteriorly, as is 

 the sigmoid notch. The condyle is placed above the posterior part of the angle. 



Foramina: The infraorbital foramina are above the interval between P 3 and P 4 , somewhat 

 farther aft than in the other species, though fairly close to the position found in P. fumilus. 



Dentition: There are three incisors above and below. The premolars have the same develop- 

 ment as that seen in P. parvus, but the protoconule of the upper molars is reduced. P 1 is isolated. 

 The superior molar-premolar index is 1.17 and that of the lower series 1.01. 



Skeleton: The skeleton as a whole is rather more like that of a carnivore than are the skele- 

 tons of the later merycoidodonts. The neck is medium in length, the body moderately long, and 

 the tail very long, while the limbs are relatively long and slender. There are but six lumbar and 

 three sacral vertebras, one less in each series than in Merycoidodon. The bones have the same 

 general characters as those of Merycoidodon., except that the odontoid process of the axis is more 

 peg-shaped. In the manus the shifting of the lunar upon the unciform is indicated but has not 

 advanced so far as it did in the later genera of this family. The lunar rests partly upon the magnum, 

 and the scaphoid only partly covers the latter. The pollex is relatively a little better developed 

 than in Merycoidodon. Scott ( 1 899, p. 94) has described the tarsus of this genus, based upon 

 material at Princeton and at the American Museum, which corresponds with Peterson's material. 

 Scott's description follows: 



The astragalus is somewhat narrower and has a rather more asymmetrical proximal trochlea; in the 

 distal trochlea the cuboidal facet is even narrower than in the White River types. The calcaneum has a much 

 more slender tuber, and the sustentaculum is more prominent, though very inconspicuous, which is characteristic 

 of the entire family. The cuboid is higher, narrower, and more deeply incised by the calcaneal facet, while the 

 astragalar surface rises higher proximally. The navicular also has a greater proximodistal diameter. The meso- 

 and ecto-cuneiforms are coossified, though their limits are still clearly visible, and, as in the White River types, the 

 former is a little shorter than the latter. The whole tarsus is conspicuously higher and narrower than in the sub- 

 sequent genera of the family, in which the tendency was continually to become short and broad. 



The metatarsals are likewise long, and a rudimentary hallux is present in P. fumilus but not 

 in P. medius. The phalanges are longer and slenderer, and the unguals have not assumed the small 

 hoof-like shape but are longer and narrower and are in form more like those in Agriochoerus. 



Discussion: In the Duchesne Valley area this species is by far the most abundant, while the 

 smaller forms are comparatively rare. It is quite possible that the horizon is somewhat later than 

 that of the other species, as P. medius indicates a slightly more advanced evolutionary stage. 



The pes figured by Scott (1899, pi. 3) apparently belongs to this species, as Peterson (1919, 

 p. 84) first pointed out, the dimensions and characters of the bones agreeing well with Peterson's 

 specimens. 



Protoreodon minor Scott 1899 

 Figs. 9-10 



Original Reference: The selenodont artiodactyls of the Uinta Eocene. Trans. Wagner Free Inst. Sci., 

 Phila., VI, p. 95, pi. Ill, fig. 23. 



Type Localities: Kennedy's Hole, White River, Utah (HT); six miles east of Myton, Utah (PLT). 



Geologic Horizon: Upper Eocene (Uinta — Hor. C). The holotype was found in the upper gray clays of 

 the Telmatotherium cornutum beds. 



Types: Holotype, Cat. No. 11339 P.U.M., upper and lower dentition and part of skeleton. Plesiotype, 

 Cat. No. 3032 CM., skull and jaws, six cervicals, and parts of both fore limbs. 



Specific Characters: This is the smallest species of the genus, with a skull about three- 

 fourths as large as that of P. medius. The superior contour of the skull is more arched than in any 



