150 



ON THE EXTINCT MAMMALIA OF 



The third premolar, not existing in the adult state of the latter animals, in the 

 specimen has lost the greater part of its crown. In figure 1, c, it is represented as 

 restored from older or more worn teeth of another species. The crown appears to 

 have been a reduced form of that of the last premolar just described. 



The second premolar has a remarkable appearance. It is represented in figures 1, 

 2, h, — , in the latter of the natural size, in the former reduced one-third. From its 

 condition, it appears to have protruded at a comparatively late period. The crown 

 is laterally compressed conical, with trenchant borders and pointed summit, and with 

 the sides impressed approaching the borders. It is only slightly worn,— just below 

 the apex, about half the length of the posterior border. The tooth is inserted by a 

 pair of confluent, somewhat gibbous fangs, more robust than those of the succeeding 

 jDreraolar. 



The first or caniniform premolar, figure 1, a, is situated nearly in the same relative 

 position as in the Camel, that is to say, nearly the same distance from the correspond- 

 ing tooth, — the last premolar. The crown is much worn, but appears to have been 

 as well developed and to have had the same form as in the Camel — curved conical, 

 laterally compressed, with trenchant borders, and the sides impressed near the latter. 

 The fang is large and gibbous, and curves downward and backward. 



About eight lines in advance of the caniniform premolar the fossil presents part of 

 a large curved alveolus, which was sufficient to accommodate a canine tooth like that 

 of the Camel. All traces of incisive alveoli are lost in the specimen. 



The measurements of the fossil in comparison with those of a lower jaw of a recent 

 adult Camel are as follow : 



Distance from canine alveolus to back of last molar, 



Space occupied by closed row of six molars, . 



Space occupied by true molars and last premolar. 



Space from caniniform premolar to last premolar, 



Length of hiatus back of first premolar. 



Length of hiatus in front of do. 



Space occupied by true molars, 



Space occupied by back three premolars. 



Depth of jaw at fore part of last molar. 



Depth of jaw at last premolar. 



Depth of jaw at caniniform premolar. 



Depth of jaw at hiatus bacli of latter, 



Thickness of jaw below last molar, . 



Thickness of base below do. 



Thickness of base below last premolar, 



P. robustus. 



Inch. Lin. 



8 6 



Camel. 



Inch. Lin. 



9 2 



6 

 5 

 2 

 1 



4 

 1 

 2 

 2 

 1 

 1 

 1 



2 



2 

 1 



8 



o 

 O 



10 



8 

 7 

 4 

 9 

 9 



5 



2 

 2 



2 

 1 

 1 

 1 

 1 

 1 



6 

 5 



5 

 6 



7 

 10 



2 

 5 

 4 



o 

 O 



4 

 11 



