156 



ON THE EXTINCT MAMMALIA OF 



The remaining specimens have the appearance as if they had been derived from 

 one individual, but there is no positive means of determining whether they belonged 

 to the same species as the premolar just described. They bear a due degree of rela- 

 tionship in size to that tooth, and even a form which approximates them. 



One of the specimens, an isolated tooth, represented in figure 15 h, plate XIV, is 

 apparently a third premolar of the lower jaw. It is slightly worn, and nearly 

 resembles in shape the fourth premolar above described. The form is a modification 

 of that of the lower premolar of the Camel. The crown is proportionately shorter 

 and wider, the width greatly exceeding the height. Viewed laterally it is oblong, 

 with the outer side moderately sloping, and the inner side presenting four ridges. 

 The back pair of the latter are separated by a short oblique valley ; the anterior by 

 vertical concave depressions. The tooth is trilobate, with the middle lobe largest and 

 highest, and the posterior lobe thickest and divided by the short oblique valley just 

 mentioned. 



Two of the specimens, of which one is represented in figure 15, c, plate XIV, are 

 second premolars of the right and left sides, and are inserted into small fragments of 

 the jaw by robust pairs of fangs. The crown of these teeth is oblong, wider than 

 high, convex externally, slightly trilobate internally, and with an acute biting edge 

 rising in a point in advance of its middle. 



The remaining specimen ai3pears to be a caniniform premolar, and is inserted into 

 a small fragment of the lower jaw by a pair of strong fangs, in the same relative 

 position as the caniniform premolar in Procamehis occidentalis. The crown is com- 

 pressed conical, wider than high, and has acute borders descending from a feebly 

 worn point. 



The tooth last described renders it probable that it and its companions, except the 

 fourth premolar belonging to a different individual, may pertain to the same genus, as 

 some fossils referred to Homocamelus caninus, hereafter described. 



The measurements of the specimens are as follow : 



Lines. 



Antero-posterior diameter of fourth premolar, . . . .6 



Antero-posterior diameter of third premolar, . . , . .5 



Antero-posterior diameter of second premolar, . . . . 3i 



Height of do., . . . . . . . .21 



Antero-posterior diameter of caniniform premolar, . . . .3 



Height of do., . . . . . . . . 2h 



Thickness of do., . . . . . . . . Ih 



The collection of fossils obtained in Dr. Hayden's trip to Dakota in 1866 contains 

 several small fragments of jaws, with teeth, of Procamelus, from Little White River, 



