DAKOTA AND NEBRASKA. 233 



The orbit has nearly the form and proportions of that of R. occidentalis, but has 

 its entrance less vertical, from its being less overhung by the supra-orbital promi- 

 nence of the forehead, so that it has a slight upward direction. The post-orbital pro- 

 cess of the frontal does not extend so far back, and therefore the orbit ajjpeai's more 

 open or less contracted behind than in R. occidentalis. The ant-orbital margin is on 

 a line with the back part of the ante-penultimate molar. It exhibits a compressed 

 conical lachrymal process, within the position of which there are two foramina, one 

 above the other. The orbital entrance is about an inch and a half in diameter, and 

 is situated nearly midway between the upper outline of the forehead and the alveolar 

 margin. 



The face in advance of the orbits is proportionately somewhat shorter than in E. 

 occidentalis. It also appears less vertical at the sides, but in all the specimens is too 

 much fractured to judge accurately of its original form and details. 



The infi'a-orbital foramen is situated an inch above the interval of the second and 

 third premolars. 



Upper view of the skull. — Above, the cranium appears ovoid, expanded towards the 

 summit and lateral borders of the inion, and jirolouged in front to expand into the 

 forehead. 



The sagittal crest is long and narrow, proportionately much longer than in R. 

 occidentalis. The temporal ridges diverge from its fore part at a less acute angle 

 than in the latter. 



The forehead has the same form nearly as in R. occidentalis, but is pi'oportionately 

 neither so long nor broad. It is more convex between the supra-orbital margins, but 

 is quite as much, if not more depressed along the middle. The frontal suture re- 

 mains open. 



The fronto-nasal suture, extending nearly the breadth of the forehead, has its 

 outer extremities descending to the lachrymals on a line with the ant-orbital margin. 

 It is in the form of a pair of crescents, between which extend the internal angular 

 processes of the frontals. The suture is much less advanced in position than in R. 

 occidentalis. 



The snout or upper fore part of the face is somewhat tapering. The nasals are 

 flat above and incline towards each other ; at the sides they are convex. Their 

 posterior broad scroll-like extremities articulate with the frontals and lachi'ymals, and 

 receive between them the obtusely angular processes of the former bones. Anteriorly 

 they are deeply notched, each terminating in a pair of long processes. 



The intermaxillary at the side of the face forms a narrow plate, slightly widening 

 in its ascent, and articulating with the nasal bone. The width of its upper end 

 where it joins the latter is ten lines, but at the middle it measures but half that 



30 



