122 THE MERYCOIDODONTID^ 



Promerycochcerus gregoryi loomisi Schlaikjer 1934 

 PI. XIII, figs. 1-2; PI. XLVI, fig. 2 



Original Reference: Three new oreodonts. Proc. Boston Soc. Nat. Hist., XL, pp. 225-229. 



Type Locality: N.W. }4> Sec. 36, T. 20 N., R. 62 W., Bear Creek Mountain, Goshen County, 

 Wyoming. 



Geologic Horizon: Lower Miocene (lower Harrison). Approximately 200 feet above the Brule — lower 

 Harrison contact. 



Type: Holotype, Cat. No. 2820 M.C.Z., nearly complete skeleton. Collected by E. M. Schlaikjer, 1930, 

 and named in honor of Professor F. B. Loomis. 



Specific Characters: The skull of this species is the longest known in the genus. It is also 

 the most dolichocephalic of the three species with a long, narrow skull, the other two being P. mon- 

 tanus grandis and P. microcephalus. The muzzle is long and narrow. The maximum expansion 

 of the zygomatic arches lies opposite the glenoid surfaces. The malar is deep, and the ridge from 

 the anterior zygomatic pedicle fades out above P\ The malar sends an inferior process backward 

 almost to the glenoid surface. The squamous portion is relatively weak. It extends forward to a 

 position beneath the postorbital bar, from which point aft it is nearly horizontal at first and then 

 rises abruptly to the crest above the anterior of the postglenoid process. Its superior surface is 

 about on a line with the middle of the orbit. The nasals are narrow, very long, and unreduced, 

 extending from the incisor border aft nearly to a line through the antorbital margins. They are 

 posteriorly pointed. The 'pars facialis of the lacrimal bone appears subtriangular in outline, and the 

 antorbital fossa is deep and large. The frontals are narrow, unreduced, and flat, with a medium 

 amount of decurvature above the orbits. The latter are subcircular, with the greater diameter 

 vertical, and are above medium in size. The temporal ridges unite above the anterior of the glenoid 

 surfaces to form a high, narrow sagittal crest, about a fourth of the skull length. The crest rises but 

 slightly above the nearly straight superior contour of the skull. The supraoccipital crest is very 

 narrow and produced well beyond the plane of the occipital condyles, and the wings are very 

 slightly open. The brain case is very narrow and small but has, however, very prominent lateral 

 ridges. The external auditory meatus is large and is situated above the base of the paroccipital 

 process. The palate is anteriorly broad and flat, while posteriorly it is narrow and considerably 

 vaulted. The basicranial axis is steep. The glenoid articular surface is slightly oblique to the 

 sagittal plane. The postglenoid and the paroccipital processes are very near together, but otherwise 

 they appear to be normal. Index: 0.42. 



Mandible: The chin profile is somewhat concave, and the mental tubercle is not especially 

 prominent. The symphysiodental angle is about 33°. The inferior border of the horizontal ramus 

 is straight, and the angle is prominent. The condyle is very slightly inset, the sigmoid notch is 

 narrow but open, and the coronoid process is short and slender. The ridge descending from the 

 coronoid process is at first glance suggestive of the peculiar construction in this area in P. m. grandis. 

 The masseteric fossa is small but deep. 



Foramina: The infraorbitals are above P 4 . 



Dentition: In general this is of the Promerycochcerus pattern. There is a faint internal cingu- 

 lum on P 4 , on M 2 , and on M 3 . P 4 has a small pit in the anteroexternal corner on the right side but 

 none on the left. P 1 is moderately isolated. The superior and inferior incisors are transversely 

 placed, and the canines are large. The superior molar-premolar index is 0.98 and that of the 

 lower series 1.13. 



Skeleton: Schlaikjer states that the vertebra are very much like those of P. carrikeri, except 

 that they are lighter and have shorter neural spines. His description continues: 



The pelvis is of light construction. It is shorter, narrower and much less robust than P. carrikeri. The 

 appendicular skeleton is very similar to this species. In keeping with the other dimensions of the postcranial 

 skeleton, however, the limbs while of approximately the same length as those of P. carrikeri are rather lighter in 



