DAKOTA AND NEBRASKA. Ill 



site Fort Laramie. They were discovered in a stratum of " dull reddish-brown 

 indurated grit," or bed D of Dr. Hay den's section of the miocene formation, as 

 indicated on pages 17, 20. 



The chief differences between Merycoclioerus p^'oprius and the species of Oreodon 

 observed in comparing the specimens of the former with the corresponding portions 

 of the skulls of the latter, are briefly as follows : 



In Meri/cochoerus the infra-orbital arch, as formed by the malar bone and its con- 

 junctions, is remarkable for its great absolute and relative depth, being double that 

 in the Hog, and two and a half times as great as in 0. major. It is directed much 

 more abruptly inward to the face than in Oreodon. The external surface of its 

 anterior abutment, formed by the malar and maxillary bones, constitutes a deep 

 vertical plane, sloping with a gentle curve inwardly and subsiding entirely on a line 

 with the fore-part of the second molar tooth. 



In Oreodon the fore part of the infra-orbital arch forms a convex ridge proceeding 

 forward and inward and gradually subsiding over the position of the middle 

 premolars. 



In consequence of the comparatively abrupt termination of the infra-orbital arch, 

 the face appears abruptly narrowed at the position of the interval of the first and 

 second molai's, compared with its condition in Oreodon. The face appears also 

 relatively moie prolonged, giving it a narrow snout-like appearance as iu the Hog. 

 From the interval of the first and second molars it gradually narrows to the position 

 of the third premolar, and then widens to the position of the canine alveolus, from 

 whence it is abruptly rounded upon the incisive border. The side of the face appears 

 to be relatively higher than in Oreodon, and it forms a wide unbroken, transverse 

 concavity from the infra-orbital arch to the position of the canine alveolus. 



The infra-orbital foramen is situated above the interval of the first and second 

 molars, and is as large as in the Hog. In all the species of Oreodon it is situated 

 above the third premolar, and is comparatively small. 



In consequence of the great relative depth of the infra-orbital arch, the orbit is 

 more elevated in position than in Oreodon. Its anterior border is on a line with the 

 interval of the second and third molars. In Oreodon it is on a line with the fore-part 

 of the second molar. 



From a remaining fragment of the lachrymal bone, its facial surface appears to 

 have been relatively much smaller and narrower than in Oreodon, and appears not 

 to have been depressed into a deep lachrymal fossa, though it does appear to have 

 contributed, together with the maxillarj", to form a broad concave fossa, nearly as in 

 the Hog. The suture, between the lachrymal, malar, and maxillary, descends at first 

 almost vertically and curves backward at its lower part. In Oreodon it proceeds 

 more obliquely backward and downward. 



