158 ON THE EXTINCT MAMMALIA OF 



HOMOCAMELUS. 



HOMOCAMELUS CANINUS. 



An extinct animal belonging to the Camel family, apparently distinct from any of 

 those previously indicated, is represented by several fragments of jaws, with teeth, 

 contained in Dr. Hayden's Niobrara collection of fossils. 



The specimens, derived from the same individual, consist of a portion of the right 

 maxilla, containing three premolars ; a portion of the right intermaxilla, with a cani- 

 niform incisor; and a third specimen, consisting of portions of the left maxilla and 

 intermaxilla, with the caniniform incisor, the canine tooth and three premolars. 



A series of these teeth, with the corresponding portions of the maxillary and inter- 

 maxillary bones are represented in figure 17, plate XIV, as recomposed of the frag- 

 ments from the two sides of the face. 



The portions of the maxillary and intermaxillary bones of the fossils have nearly 

 the same form as the corresponding portion of the upper jaw in the Camel. The fore 

 part of the face, as in this animal, was produced in a narrow snout-like prolongation. 

 The breadth of the face outside the canine alveoli measured about seventeen lines, 

 opposite the first premolars about fifteen lines, and opposite the middle of the second 

 premolars about nineteen lines. The hard palate was more deeply vaulted than in 

 the Camel. No palatine foramen exists in the fossils in advance of the posterior 

 broken border, which is on a line with the middle of the position of the third pre- 

 molar. 



The caniniform incisor, the canine, and the first premolar, as represented in figure 

 17, were all separated from each other and from the succeeding continuous row of pre- 

 molars and true molars by wide arching intervals. 



The second and third premolars, figures 16, 17, forming the advanced pair of teeth 

 of the closed molar series, difler from those occupying the jaw fragments ascribed to 

 Procamelus occidentalis, both in shape and relative position to each other. In P, occi- 

 dentalis the antero-posterior diameter of the two teeth mentioned extends along the 

 same line, and this is parallel with the alveolar border. In the present fossil the 

 two teeth have their antero-posterior diameter directed obliquely, so that the back 

 part of the first premolar is external to the fore part of the second. Both teeth are 

 inserted by distinct pairs of fangs. 



The crown of the second premolar, figures 16, 17, d, slightly worn, is moderately 

 compressed conical, with its posterior portion curving outward and backward in a 

 wing-like expansion. Internally it is bounded by a crescentoid basal ridge. 



The crown of the third premolar, figures 16, 17, e, is a more developed form of that 

 of the preceding tooth. The internal basal ridge is produced into a thick fold or pro- 



