MERYCOIDODON 47 



Specific Characters: The skull is about intermediate in size between M. gracilis and 

 M. culbertsonii but is proportionally more mesocephalic and has a short muzzle. The malar is of 

 medium depth below the orbit, while the squamosal part of the zygomatic arch is light and rises 

 very gently posteriorly. The wide nasal bones are posteriorly obtuse and nearly flat in both 

 diameters. The -pars facialis of the lacrimal bone is large and subtriangular, with the long diameter 

 directed anterosuperiorly, and bears a deep but small fossa. The frontals are flat, except for the 

 usual supraorbital convexities, and extend about 8 mm. in advance of the lacrimal bones. The 

 orbits are moderately small. The temporal ridges unite near the postorbital constriction to form a 

 low and somewhat rugose sagittal crest, approximately a third of the skull length. The supra- 

 occipital crest is but slightly produced, and the wings are widespread. The low brain case is moder- 

 ately well rounded, with the normal convexities. The large external auditory meatus is somewhat 

 upwardly, as well as outwardly, directed. The gently vaulted palate is of medium width, and the 

 palatonarial border lies just posterior to a line through the after part of the last molars. The basi- 

 cranial axis is steep. The glenoid articular surface is typical of the genus. The postglenoid process 

 is transversely wide and moderately thin anteroposteriorly. The bullae are tiny, and the paroccipi- 

 tal processes are L-shaped in cross section. Index: 0.57. 



Mandible: The symphysiodental angle is 43°, with the chin profile nearly straight. There 

 is a small mental tubercle. The inferior border of the horizontal ramus is straight. The bone 

 increases in depth aft. 



Foramina: The infraorbitals lie above P 3 . The supraorbital foramina are 15 mm. apart. The 

 foramen ovale is medium-sized, while the foramen rotundum is small. The posterior palatine 

 foramina are opposite P 4 . 



Dentition: There is a pit in the anteroexternal corner of P 4 . The anterointermediate crest of 

 P 3 does not divide the anterior face equally, so that the anteroexternal basin is the larger, though 

 both basins are tiny. P" is more nearly normal. The superior molar-premolar index is 0.84 and 

 that of the inferior series 0.72. 



Discussion: Leidy thought that this might be a doubtful species and that perhaps it could be 

 considered as a large variant of M. gracilis or a small one of M. culbertsonii. However, it first 

 appears in the lower Oligocene, and it has certain characters which seem to make it a valid species, 

 albeit one which appears not to have been so prolific as some of the other species of this genus. 



Merycoidodon culbertsonii Leidy 1848 

 Figs. 3, 7, 21-23; PI. II, Figs. 3-6; PI. XL 



Original Reference: On a new fossil genus and species of ruminantoid Pachydertnata: Merycoidodon 

 Culbertsonii. Proc. Acad. Nat. Sci. Phila., IV, pp. 47-50, figs. 1-5. 



Synonyms: Oreodon friscum Leidy 1851A, pp. 237-238, milk teeth; Cotylop sfeciosa Leidy 1851A, 

 p. 239; Oreodon robustum Leidy 185 IB, p. 276; Oreodon culbertsonii Leidy 1852A, p. 548. 



Type Locality: Nebraska, and Badlands of White River, South Dakota. 



Geologic Horizon: Middle Oligocene (lower Brule); also lower Oligocene (Cypress Hills). 



Types: Genocotypes, Cat. Nos. 10727 and 10728 A.N.S.P., part of maxillary of young individual contain- 

 ing M 2 and M 3 , and portion of right ramus, also of young animal, with M, to M : , inclusive. These two frag- 

 ments may well belong to the same animal. Plesiotypes, Cat. No. 137, U.S.N.M., skull and jaws; and Cat. 

 No. 2506 U.S.N.M., another skull, with jaws. The species was named in honor of Alexander and Thaddeus A. 

 Culbertson, who collected and preserved the first specimens of this great group. 



Specific Characters: The skull varies in size from about 180 to 200 mm. in length, 

 and it is mesocephalic, although close to the border between dolichocephaly and mesocephaly. 

 The maximum expansion of the zygomata is just in advance of the glenoid surface. The malar 

 is the deepest part of the zygoma, but the entire arch is light and narrow and rises markedly 



