DAKOTA AND NEBRASKA. 203 



diameter exceeding that fore and aft, and with the height about half the former 

 measurement. In the unworn condition (6gure 1, c) they are composed of five 

 pyramidal lobes, four of which hold the same relative position as their homologues in 

 living ruminants ; the fifth lobe intervenes between the anterior pair as existing in 

 the latter. The outer sides of the lobes are concave, but interrupted by a median 

 elevation ; the inner sides are angularly convex, and separated from the former by 

 an acute ridge diverging from the summits of the lobes outwardly towards their 

 bottom. The outer lobes are longer than the inner ones, which partially embrace 

 the bases of the former. 



The front and back of the crowns of the upper true molars are embraced by a 

 tliick angular basal ridge, which is more or less indented. The bases of the external 

 pair of lobes where contiguous bulge outwardly, and conjoin in the formation of a 

 remarkably broad and convex buttress as in AgriocJicerus. The fore part of the 

 base of the antero-external lobe in like manner bulges outwardly and forms a similar 

 buttress, which is continuous with the anterior basal ridge of the crown. A much 

 reduced buttress of the same kind also occupies the back part of the base of the 

 postero-external lobe, continuous with the posterior basal ridge of the crown. The 

 presence of these prominent convex buttresses to the crown renders the depth of the 

 concavity of the outer faces of the external lobes greater than in the internal lobes. 

 See figures 1, 2. 



The median transverse valley is deeper than that antero-posteriorly. It is 

 especially deep at its outer part, where its bottom is closed by the conjunction of the 

 outer lobes. The fore and back part of the lobes, or the sides of the transverse 

 valleys of the crown, are more or less strongly corrugated. 



The upper true molars are inserted by three fangs, — two external, and a bi'oad 

 internal one involving a connate pair. These teeth strongly resemble the corres- 

 ponding ones of Agriochoen^s, with the introduction of a fifth lobe between the 

 anterior pair. 



In the specimens, the last true molar, figure 1, c, is unworn. In the second true 

 molar, figure 1, h, the postero-external lobe is worn along its acute borders so as to 

 expose narrow lines of dentine ; the summits of the anterior lobes are nearly worn to 

 a level, and exhibit exposed crescentoid dentinal tracts, of which those of the antero- 

 internal and median lobe are continuous through a narrow isthmus. In the first 

 molar, figure 1, a, the separation of the anterior three lobes is obliterated, leaving a 

 broad concave tract of dentine bordered by enamel. The separation of the posterior 

 pair of lobes is yet indicated by the remains of the crescentoid interspace. 



The teeth represented in figure 3, plate XXI, which I suppose, from their resem- 

 blance to the corresponding ones of Anthracotherium magnum, to be the second and 

 third premolars, are contained, in apposition together, in a small fragment of the jaw. 



