50 SCOTT. [Vol. V. 



continued up into the overlying Loup Fork. This animal 

 retains the full number of teeth, but the superior premolars 

 (the inferior are not known, unless, as is very improbable, Pro- 

 tomeryx, Leidy, should belong to the same form), are much 

 reduced in size and especially in antero-posterior length, as 

 compared with those of Pcebrotheriiim. The canine is longer 

 and more pointed, and the external incisor has become canini- 

 form and larger than the true canine. The true molars are still 

 very brachyodont. In the Loup Fork species of Protolabis, P. 

 heterodontus, the external incisor and canine have become very 

 large, quite as large in proportion as in the camel and much 

 larger than in Procamelus. I suspect, however, that this species 

 will prove to belong to the genus Homocamelus, Leidy. Leidy 

 describes the teeth of this genus as follows : " The caniniform 

 incisor, the canine, and the first premolar were all separated 

 from each other, and from the succeeding continuous row of 

 premolars and true molars by wide-arching intervals. 



"The second and third premolars (Figs. 16, 17), forming the 

 advanced pair of teeth of the closed molar series, differ from 

 those occupying the jaw fragments ascribed to Procamelus occi- 

 dcntalis, both in shape and relative position to each other. In 

 P. occidentalis 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, slightly worn, is moder- 

 ately 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 is a more developed form 

 of that of the preceding tooth. The internal basal ridge is 

 produced into a thick fold or process before and behind, extend- 

 ing towards the triturating border. It has nearly the constitu- 

 tion of the corresponding tooth, or first premolar, of the camel, 

 but is relatively shorter and wider, and has the antero-internal 

 fold relatively better developed. The worn triturating border 

 exhibits a uniform surface of dentine, with the notch outward " 

 (No. 19, p. 158). 



