DAKOTA AND NEBRASKA. 1-25 



bounded by a more deeply sinuous border externally than in M. elegans. (Compare 

 with figures 3, 4, plate XI.) 



On the triturating surface of the first molar, figure 5, a crescentoid enamel islet, 

 including a narrow depression, occupies an intermediate position to the posterior pair 

 of lobes. On the triturating surfaces of the last two molars there is seen a pair of 

 median angular crescentoid bars. These are sections of the remaining enamel invest- 

 ment of the inner faces of the external constituent lobes of the crown, and are nearly 

 as thick as the enamel at the outer border of the latter, but they thin out to nothing 

 at the extremities, before and behind. The bars appear to come in direct contact 

 with the dentine of the inner lobes, as there is no visible separation, but most proba- 

 bly there intervenes an imperceptibly thin layer of enamel, the remains of the invest- 

 ment of the outer faces of the internal lobes. 



The fourth premolar is like that of Merycliyus elegans, excepting that it exhibits 

 upon the triturating surface a central bar of enamel, as in the back true molars, 

 instead of a conspicuous crescentic enamel pit. 



The third premolar also resembles that of M. elegans, except that the postero- 

 internal fossa extends more deeply into the crown and is more open at the bottom 

 antero-internally. Nearly the same difference exists in the second premolar of the 

 two animals. The first premolar is alike in both. 



The upper canine has the same form as in M. elegans, but like the other teeth is 

 smaller. 



The specimen of the nearly complete, but much fractured skull above mentioned, 

 in a perfect condition, independently of the lower jaw, appears as if it had been propor- 

 tionately more depressed and wider than in Orcodon. An upper view of one-half the 

 specimen is represented in figure 1, plate XII, but the side view is too much muti- 

 lated to exhibit any of the important characters of the skull, except the lower jaw, 

 which is represented in figure 2. 



The cranium, in its present condition, appears of great breadth and proportionate 

 shallowness, compared with that of Oreodon. The difference, I suspect, is at least 

 partially due to the specimen having been crushed downwardly and spread outwardly, 

 though the appearance of such crushing and spreading is not very obvious. The face 

 likewise appears proportionately low to the cranium, and it is broader posteriorly and 

 more tapering anteriorly than in Oreodon. 



The sides of the cranium are occupied, as in the latter, by large temporal fossae, 

 separated by a prominent sagittal crest. The anterior temporal ridges are more 

 divergent than in Oreodon. 



The forehead is broad and generally flat, compared with that of the genus just 

 mentioned. It is slightly elevated along the middle, and feebly depressed between 

 the latter position and the temporal and supra-orbital borders. The supra-orbital 



