DAKOTA AND NEBRASKA. 153 



been. It resembles in form tliat of the Lama, but is relatively of less depth, ap- 

 proaching in this respect more the condition in the Camel. 



The base presents a stronger and shorter curve approaching the symphysis than 

 in the latter. 



The back part of the symphysis terminates, as in P. robustm, below the fore part of 

 the caniniform premolar. A vasculo-neural foramen, communicating with the dental 

 canal, is situated below the fore part of the last premolar. The mental foramen is 

 placed below the hiatus just in advance of the position of the caniniform premolar, 

 and a small foramen is situated just below the latter. 



The only perfect tooth in the fossil, the last premolar, is somewhat larger than in 

 the preceding specimen. From its less worn condition, it presents at the back part of 

 the triturating surface an elliptical enamel pit. The second premolar was provided 

 with a pair of fangs inserted into distinct sockets. 



The first or caniniform premolar occupies the same relative position as in P. 

 rohustus, and it appears to have had the same form. In advance of it, in the speci- 

 men, there exists a portion of a large canine alveolus. 



The measurements of the fossil are as follow : 



Lines. 



Depth of jaw below fore part of last pi'emolai', . . . .16 



Depth at hiatus in advance of premolars, , . . . . 10 J 



Depth at back part of symphysis,. . . . . . .13 



Space occupied by premolars, . , , . . .20 



From canine alveolus to fore part of last premolar, . . .36 



Hiatus between canine and first premolar, . . . . .10 



Hiatus between latter and second premolar, . . . .10 



Antero-posterior diameter of last premolar, . ... . .8 



3. An alveolar fragment of the left side of a lower jaw, containing all the molars 

 except the caniniform premolar. It belonged to an aged animal, the first molar 

 having its crown worn away to the fangs, and all the others worn in a proportionate 

 manner. In its worn condition, the crown of the third premolar, as represented in 

 figure 6, c (in which it has been introduced from this specimen), repeats the form of 

 that of the succeeding tooth in the same condition of abrasion. 



The fangs of the second premolar are confluent and not gibbous. The tooth has 

 lost the fore part of its crown. 



The last molar retains a crescentic enamel pit in the middle division of the tooth, 

 but in the other molars the corresponding pits are completely obliterated. 



The length of space occupied by the molar series, independent of the caniniform 



premolar, is within a couple of lines of five inches, of which the included premolars 



occupied a space of an inch and a half. 



20 



