MERYCOCHCERUS 151 



from the anterior zygomatic pedicle divides the side of the broad muzzle into two concavities. The 

 squamosal portion of the arch is relatively weak, extending forward to a point below the posterior 

 of the orbit and rising sharply posteriorly to the crest above the glenoid surface. The unreduced 

 nasals are exceptionally long, reaching a point above the incisor border. They are markedly 

 decurved anteriorly and appear to be wide and posteriorly pointed. The antorbital fossa is broad 

 and shallow. The frontals are also unreduced, wide, and flat. The orbits are medium in size and 

 subcircular. The temporal ridges unite just behind the postorbital constriction to form a thin, high 

 sagittal crest, about a fourth of the skull length. The brain case is relatively fuller and more 

 rounded than that of some of the species, and the lateral ridge is well marked. The external 

 auditory meatus is small and directed somewhat upward and a trifle backward. The basicranial axis 

 is steep. The wide palate is well vaulted, and the V-shaped palatonarial border lies well behind the 

 molars and nearly below the postorbital bars. The slightly convex glenoid articular surfaces are 

 somewhat oblique to the sagittal plane and are about twice as long (transversely) as wide. The 

 postglenoid processes are large, with the greater diameter transverse. The bullae are moderately 

 large, subtriangular in section, with the apex forward, and do not extend below the level of the 

 postglenoid processes. The posteriors of the bulla and of the postglenoid process are nearly on the 

 same transverse line, but the anterior of the bulla is considerably in advance of that of the process. 

 The paroccipital processes are long and thin, extend downward and somewhat outward, and are 

 subtriangular in section. Index: 0.707. 



Foramina: The infraorbitals lie above the interval between P 4 and M 1 . The foramen ovale is 

 large. There appears to be a tiny foramen rotundum, but of this I cannot be positive. The posterior 

 palatine foramina, rarely observed in this genus, lie opposite M 1 . 



Dentition: The metastyle of M 3 is small. There are internal cingula on the molars, but this 

 cingulum is interrupted on P 4 . The premolars are simple and the anterior two compressed, with P" 

 obliquely placed. The canines are strong. The small incisors are more transversely placed in the 

 parapet than usually seen in this genus, which is due to the very blunt muzzle. The molar-pre- 

 molar index is 0.81. 



Skeleton: The feet are extremely short. 



Discussion: Loomis considers that this species has the characters of Promerycochcerus devel- 

 oped to an advanced degree and that it is a dwarf species rather than a primitive one. Both types 

 are thought by Loomis to be females. 



Genus MERYCOCHCERUS Leidy 1858 



Table 8 



Original Reference: Notice of remains of extinct Vertebrata. Proc. Acad. Nat. Sci. Phila., X, p. 24. 

 Genotype: M. frofrius Leidy 1858. 



Genoholotype: Cat. No. 156 U.S.N.M. nearly complete upper and lower dentition in contiguous parts 

 of skull and jaws (figured by Leidy 1869, pi. 10, figs. 1-4). 



Distinguishing Characters: Skull brachycephalic (indices ranging from 0.66 to 0.87) and 

 length from 286 mm. to 334 mm.; nasal bones much reduced and moved aft; premaxillaries usually 

 coossified; face, including orbits, about a third longer than remainder of skull and abruptly nar- 

 rowed anterior to M 2 ; cranial region foreshortened and brain case moderately large and laterally 

 expanded; antorbital fossa large; orbits elevated, in consequence of the great depth of the malar, 

 and moderately small; frontals wide, inflated, and moderately convex; occiput broad; zygomatic 

 arches widespread and squamosal portion medium to heavy; bulls small to moderately large and 

 usually oval in shape; mandible much as in Pr ornery cochcerus, with strong symphysis, inferior 



