1 82 THE MERYCOIDODONTID/E 



Mandible: The symphysis is strong. It is not so concave vertically as in P. typus, and the 

 inferior tubercle is more rounded. The dentosymphysial angle is about 45°, thus making the chin 

 somewhat straighten The ramus is longer than that of the other species and appears to be straighter 

 along the inferior border, that is, the angle does not descend so much below this border. The con- 

 dyle is less inset from the posterior border, which is not so straight as in P. typus. The coronoid 

 process is short and less hooked, and the masseteric fossa is larger. The sigmoid notch is shallow 

 and wide open. 



Dentition: The teeth are very similar to those in P. typus, except that the molars are slightly 

 more delicate and the axis of the metastylid is not so much in line but has a more outward and 

 backward direction. 



Skeleton: The vertebras, so far as known, resemble those of P. typus. The fore limb is longer, 

 however, and the radius has a longer and relatively slenderer shaft that is rod-like throughout. The 

 hind limb, likewise, is longer and somewhat slenderer. The metatarsals are slightly longer, in fact 

 are very nearly as long as the metacarpals, in contrast to those in P. typus. 



Discussion: This species and P. typus are certainly contemporaries within a very small area. 

 The longer legs and larger size of P. munroensis might indicate a male, but the relatively longer 

 hind foot in relation to the manus and the slenderer molars may indicate more than sex or individual 

 variation. Until more material of both species comes to hand, I shall consider this form valid, 

 although perhaps subspecific rank is sufficient for it. Subsequently, it is entirely possible that 

 further collecting may invalidate the species, showing that it is merely a variant of P. typus. 



Phenacoccelus typus Peterson 1906 

 Figs. 5, 132-136; PI. XLIII, fig. 2 



Original Reference: The Miocene beds of western Nebraska and eastern Wyoming and their vertebrate 

 faunas. Ann. Carnegie Mus., IV, pp. 29-31, figs. 4-5. 



Type Locality: Head of Squaw Creek, Sioux County, Nebraska. 



Geologic Horizon: Lower Miocene (upper Monroe Creek). 



Types: Genoholotype, Cat. No. 1263 CM., major portion of skeleton. Paratype, Cat. No. 1276 C.M., 

 skull; plesiotypes, Cat. Nos. 1265, 1277, 1278, and 1335 CM. No. 1265 is a partial skeleton, while Nos. 

 1277, 1278, and 1335 are skulls. 



Specific Characters: The skull is about the size of that of Merycoidodon culbertsonii but 

 is more brachycephalic and slightly shorter. The zygomatic arches have their maximum width just 

 in front of the glenoid surface. The malar extends well forward of the orbit which gradually 

 trends outward nearly to the anterior of the orbit and is then directed backward and slightly out- 

 ward. It is relatively heavier below the orbit than in Merycoidodon and is invaded by the 

 squamosal as far forward as a point below the posterior of the orbit. The lower branch of the malar 

 extends back nearly to the glenoid surface and tapers almost to a point. The superior branch is 

 much shorter. The facial vacuities are much smaller than in Leptauchenia and lie mainly in the 

 lacrimal and maxillary bones. They do not invade the nasal bones and probably affect the frontals 

 very little, if at all. They are narrow, and their main axis is anteroposterior. There are also narrow, 

 elongate frontal vacuities, one on either side of the sagittal suture, extending from a point just in 

 advance of the supraorbital foramina to the nasofrontal suture. The nasal bones are unreduced, 

 extending forward nearly to a point above the incisors. Their widest point is at the nasomaxillary 

 contact, from which they decrease in width both fore and aft. They are truncated posteriorly. The 

 lacrimal bone occupies a considerable part of the face and bears a large and deep lacrimal fossa. The 

 premaxillaries are not coossified, are shorter and smaller than in Merycoidodon, and resemble more 

 nearly the condition in Merychyus. The orbits are subcircular in shape, are closed posteriorly by a 



