112 THE MERYCOIDODONTIMi 



is rather small, and the pit for the Ugamentiim teres is unusually deep. The cotyloid notch is deep 

 but narrow. The ischial tuberosity is high and robust. The large obturator foramen is ovate in 

 outline. 



The femur also has a close similarity to that of P. montanus. The second trochanter, however, 

 is larger. The rotular trochlea is asymmetrical, as in P. montanus. This is interpreted as a modern- 

 ized character and is not seen in the earlier genera. The large patella is very convex and rugose on 

 the anterior face and has the usual form. The tibia and fibula are short and coossified. The former 

 is heavy, with the head much expanded in both diameters and with a very prominent cnemial crest, 

 and the internal malleolus is especially well developed. The shaft of the fibula is slender, with the 

 head expanded and the distal end anteroposteriorly expanded. The calcaneal facet occupies approxi- 

 mately half of the anterointernal face. 



The tarsus is low, broad, and massive but otherwise is similar in construction to that in earlier 

 genera. The ectocuneiform and mesocuneiform are coossified as usual. The entocuneiform articu- 

 lates with the navicular, mesocuneiform, and Mt. II in such a manner as completely to interlock the 

 proximal end of the latter. The metatarsals are short and heavy but are longer than the meta- 

 carpals. Mts. II and V are subequal in length; Mt. II, which is but 12 mm. shorter than Mt. Ill, 

 is slightly the longer, whereas generally in this family Mt. V is the longer. Mt. Ill is heavy and 

 relatively much shorter than in Merycoidodon. Mt. IV is a trifle longer than Mt. Ill, while Mt. V 

 is the shortest of the series. The phalanges are relatively slightly longer and less broad than those 

 of the manus but are otherwise very similar. 



In summary, this species was somewhat larger than Sits scrofa. It had a short, robust neck, 

 long, heavy body, short legs, and broad tetradactyl feet. 



Discussion: As Peterson has pointed out, the general body configuration, as well as certain 

 structural features of the skeleton of this species, are hippopotamoid. The animal was heavy and 

 doubtless sluggish in its movements. 



Peterson considered this species to be "most nearly allied to P. chelydra Cope," but he pointed 

 out many differences, several of which I believe separate these two forms much more than Peterson 

 appreciated. 



Promerycochoerus chelydra (Cope) 1884 

 Figs. 71-73 



Original Reference: Synopsis of the species of Oreodontidx. Proc. Amer. Philos. Soc, XXI, pp. 523- 

 526 (Mcrycochcerus chelydra). 



Type Locality: Bridge Creek, John Day Valley, Oregon. 



Geologic Horizon: Lower Miocene (upper John Day). 



Type: Holotype, Cat. No. 7430 A.M.N.H., skull, well-preserved except that the anterior extremity of the 

 nasals and the premaxillary border are missing. Collected by the late J. L. Wortman. 



Specific Characters: The skull is the length of that of P. Iiollandi. It is much shorter than 

 the skull of P. macrostegus but has a slightly greater bizygomatic diameter. The outstanding char- 

 acter is the great breadth of this skull in proportion to its length, although it is exceeded in this 

 respect by P. carrikeri. This maximum width is equal to the distance from the paroccipital process 

 to the canine. The muzzle is compressed and laterally divided by the ridge that continues forward 

 from the anterior zygomatic pedicle. Above and below this ridge the face is concave. The maxi- 

 mum zygomatic expansion lies about at the middle of the zygomatic foramen. The malar is deep 

 and flat and is more vertical than the plane of the orbit, extending posteriorly to a point just behind 

 the line of the postfrontal process. The squamous portion of the zygoma arises below the postfrontal 

 process, descends at first, and then rises abruptly and nearly vertically to its highest point, which is 

 almost as high as the sagittal crest. It is very heavy and massive, and the inferior surface is as wide as 



