DAKOTA AND NEBRASKA. 147 



The last premolar resembles the ordinary form in other ruminants, the crown con- 

 sisting of a transverse pair of lobes separated by a crescentic interspace. The 

 penultimate premolar has a broader crown than the former, but is not so broad as its 

 predecessor. It corresponds in form with the outer lobe of the tooth behind, in an 

 exjianded condition, but with less depth. Small offsets, projecting inwardly from the 

 two extremities, may be viewed as rudiments of the internal lobe of the last premolar. 

 The premolar in advance appears to have been nearly of the same size and form. 



In front of the latter tooth in the specimen commences the hiatus, as in the young 

 skull above described. The infra-orbital foramen is situated over the last premolar. 



The measurements of the premolars are as follow : 



Lines. 



Antero-posterior diameter of second premolar, . . . . 4J 



Antero-posterior diameter of third premolar, . . . . 4i 



Antero-posterior diameter of fourth premolar, . . . . 4i 



Transverse " . " " • • • -Si 



PEOCAMELUS. 



The genus Procamelus was established on a number of fossil fragments of jaws with 

 teeth of several different species, discovered by Dr. Hayden on the Niobrara River. 

 The fossils belong to the pliocene formation, or bed F of Dr. Hayden's section, as 

 indicated on pages 16. 20, 21. The specimens generally belonged to old animals, 

 as proved by the much worn condition of the teeth, and they are mostly much 

 mutilated. 



In anatomical character the fragments exhibit a nearer affinity with the corres- 

 ponding parts of the existing Camel family than they do with those of any other 

 ruminants. 



As far as can be ascertained and inferred from the imperfect specimens, the formula 

 of dentition appears to have been as follows : 



3 4? , 1? . . ? 



True molars -, premolars — , canines — , incisors - 



3 *^ 4 1 3 



Thus, in comparison with the permanent or adult series of teeth of the Camel, 

 Procamelus is distinguished by the possession of an additional premolar to the upper 

 series, and two additional ones to the lower series. In its dentition it would thus 

 appear that Procamelus, in its relation with the living members of its family, repre- 

 sents their earlier or less mature condition, or that before they have shed those 

 premolars which reduce the number to that observed in their adult condition. 



The true molars and premolars, excepting the first of the latter, form unbroken 

 rows, as in the smaller number of the corresponding teeth in the recent members of 

 the Camel family. 



