138 THE MERYCOIDODONTID/E 



portion. The nasal bones are unreduced, extend nearly to the plane of the incisive border, and are 

 gently convex transversely and moderately straight fore and aft, except for the slight downward 

 curvature at the anterior tip. They appear to be posteriorly truncated. The pars facialis of the 

 lacrimal is triangular in outline, and the lacrimal fossa is well marked, moderately deep, and blends 

 gradually into the superior concavity that is formed by the convex ridge from the anterior zygomatic 

 pedicle which divides the face laterally. The canine convexity is prominent. The unreduced f rontals 

 rise posteriorly from front to back and are markedly decurved above the orbits. The latter are large 

 and roughly triangular in outline, with the apex downward and forward, and they look almost 

 entirely sidewise. The temporal ridges sweep backward very gradually to unite in a plane nearly 

 above the posterior of the glenoid surfaces, thus forming a short but very thin and high sagittal 

 crest. 



The extremely small, narrow brain case is one of the remarkable features of this peculiar skull 

 and suggested the specific name. The lateral ridge is only prominent anteriorly. The external 

 auditory meatus is situated low on the skull and is directed mainly outward but also slightly upward. 

 The basicranial axis is steep. The palate is narrow and moderately vaulted. The glenoid articular 

 surface is small and convex. The postglenoid tubercle is robust. The paroccipital process is moder- 

 ately strong and is directed downward almost parallel to the postglenoid process, and the two 

 processes do not enclose the auricular fossa below. There are very deep lateral fossa; above the 

 condyles. The bullae are large and extend below the postglenoid processes. Index: 0.45. 



Mandible: The mandible is deep, and the symphysis has an angle of about 40° and a nearly 

 straight profile. The large mental tubercle is very prominent. Its angle is but slightly demarcated 

 and blends into the inferior border of the horizontal ramus. The masseteric fossa is deep but not 

 large. The condyle is very slightly inset from the posterior border. The coronoid process is low, 

 and the sigmoid notch is wide and shallow. 



Foramina: The infraorbital foramina are above the anterior of P\ The supraorbitals cannot 

 be seen. The posterior palatines are opposite the anterior of P 4 . 



Dentition: There are no internal cingula on the superior molars and but a faint one on P\ 

 The metastyle of M 3 is large. P 1 is isolated. The premolar pattern is typical of the genus. The 

 superior molar-premolar index is 0.83 and that of the inferior series 0.89. 



Discussion: As this skull is laterally crushed on one side, the lateral measurements are based 

 on the uncrushed left half. 



Promerycochcerus montanus (Cope) 1884 

 PI. XVII 



Original Reference: Synopsis of the species of Oreodontidae. Proc. Amer. Philos. Soc, XXI, pp. 521, 

 531-535 {Merycochcerus montanus). 



Type Locality: Smith River Valley, Montana. 



Geologic Horizon: Upper Miocene (Deep River), vide field records; probably lower Miocene (Harrison). 



Type: Holotype, Cat. No. 8107 A.M.N.H., skull, lacking muzzle in advance of M 1 . There are also 

 fragmentary rami and skeletal parts belonging to other individuals. Collected in 1880 by J. C. Isaac. 



Specific Characters: This skull has a general resemblance to that of P. montanus grandis. 

 The zygomata attain their maximum lateral expansion at the anterior edge of the glenoid sur- 

 face. The malar is flat and deep, with a groove along the narrow inferior edge. The squamous 

 portion of the arch is slender and flat, rising gradually aft to the crest which stands above the 

 middle of the postglenoid process and which is on a level with the upper portion of the orbit. The 

 lacrimal fossa appears to have been small but deep. The wide unreduced frontals are nearly flat, 

 except for being somewhat decurved above the orbits. The latter are large and subcircular, with the 

 greater diameter vertical. The temporal ridges unite above the glenoid surface to form a well- 



