DAKOTA AND NEBRASKA. 151 



Thickness of alveolar portion below last premolar, 

 Thickness at middle of hiatus back of first premolar, 

 Antero-posterior diameter of last molar, 

 Antero-posterior diameter of first molar, 

 Antero-posterior diameter of last premolar, . 

 Antero-posterior diameter second premolar, . 

 Height of crown of do. 



'o' 





p. robustus. 



Camel. 





Inch. 



Lin. 



Inch. Lin 



• 





8 



1 







10 



10 



. 



. 1 



11 



2 



, 



. 1 





1 1 



, 





9 



9 



• 





5 





An isolated specimen of a well preserved upper true molar, probably the first one, 

 represented in figures 3, 4, plate XV, perhaps belongs to Proeamelus robustus. It 

 bears a near resemblance to the corresponding tooth of the Camel. It measures 

 fifteen and a half lines antero-posteriorly at the outer part of the triturating surface 

 and eight lines wide at the prominent points of the anterior lobes. Near the base of 

 the crown it is about as wide from before backward as at the triturating surface, but 

 at the anterior lobes from without inwardly is eleven lines wide. 



Peocamelus occidentalis. 



Most of the fossil remains of Proeamelus under examination are referable to a 

 smaller species than the preceding, to which the above name has been given. It is 

 estimated that the animal was about two-thirds the size of the existing Camel, 



The specimens on which the species is founded consists of fragments of jaws, with 

 teeth, of several difierent individuals, mostly of old animals, and much mutilated. 

 The best preserved specimens are as follow : 



1. The greater portion of the right side of the lower jaw, containing the last pre- 

 molar and the succeeding molars. It is represented in figure 5, plate XV, two-thirds 

 the diameter of nature and with the caniniform premolar and the succeeding two pre- 

 molars ideally restored from other specimens. The side of the jaw has lost its sym- 

 physial portion, the greater portion of its base, and the coronoid process. 



The construction of the jaw clearly resembles that in the Camel and Lama more 

 than in any other ruminant, but is nearer that of the latter animal than of the 

 former one. 



The body or dental portion of the bone nearly resembles in its form and propor- 

 tions that of the Lama, but back of this the jaw is relatively broader. The ascending 

 portion is also relatively wider and shorter than in the Lama, but still bears a 

 nearer resemblance to its condition in this animal than in the Camel. As in 

 the former it is furnished with an external concavity or masseteric fossa, but much 

 better developed. 



