148 ON THE EXTINCT MAMMALIA OF 



The inferior true molars have the same form and coustitution as in the Camel, but 

 are rather smaller in proportion with the size of the jaw. The superior true molars, 

 so far as can be judged from the generally much mutilated specimens, likewise hold 

 the same relations with those of the Camel. 



The fourth premolar in both jaws also closely resembles that of the latter animal. 



The third upper premolar is much better developed than the corresponding tooth 

 of the Camel, and the second one is in excess of the number existing in the perma- 

 nent series of that animal and the Lama. 



The third and second premolars of the lower jaw are in excess of the number 

 observed in the adult series of the Camel and Lama. 



The first lower premolar is separated from the others, and is caniniform, as in the 

 corresponding tooth of the Camel. The separation is less than in the latter, in conse- 

 quence apparently of the presence of the additional premolars occupying part of the 

 interval. The corresponding tooth is absent in the permanent series of the Lama. 



The lower jaw is of more robust proportions in relation with the size of the con- 

 tained teeth than in the Camel and Lama. Its fore part is relatively deeper, and the 

 symphysis much shorter; the back part is relatively of greater breadth, and the 

 ascending ramus shorter. 



Procamelus agrees with the recent Camel family in the possession of a post-coronoid 

 process to the lower jaw. The ascending ramus exhibits a well-marked external 

 concavity or fossa, which is comparatively feebly developed in the Lama, and does 

 not exist in the Camel and ordinary ruminants. 



Procamelus robustus. 



The largest species of Piveamelus, distinguished by the above name, is indicated by 

 a portion of the right side of a lower jaw, represented in figure 1, plate XV, two- 

 thirds the size of nature. It contains the premolars, except the third (which has 

 been introduced in the figure from another specimen), and the first and last true 

 molars. The specimen indicates an animal which apparently was about the size of 

 the existing Camel. The teeth are rather smaller than the corresponding ones of the 

 latter, but this difference is more than compensated by the greater number of molars, 

 the row of which is absolutely longer than in the Camel, and the jaw fragment is 

 deeper and thicker or more robust than its homologue in that animal. 



The jaw fragment bears a nearer resemblance of form and proportions to the same 

 portion in the Lama than the Camel. It is of more uniform depth than in the latter, 

 in which it rapidly decreases forward. 



Below the molars externally the jaw is as convex as in the Cainel, and of little 

 greater depth. Below the premolars, and above the thickened convex base, it is 

 comparatively flat, and is one-fourth greater in depth than in the Camel. In advance 



