UNGULATA. 



359 



behind pm. 1. The milk-dentition is known, and remains in place until all 

 the true molars have appeared. The dental crowns are low, and each 

 upper molar exhibits four crescentic cusps, while the hindermost lower 

 molar has a third posterior lobe or talon ; the anterior premolars in 

 each jaw are antero-posteriorly extended. The canines are small. The 

 radius and ulna are fused together, and the upper and lower ends of 

 the imperfect fibula are fused with the tibia ; but the metapodials 

 (in, iv) are separate on each foot, and there are remnants of the upper 

 ends of metapodials nos. n and v at least in the hind foot. The typical 

 species, known by the greater part of the skeleton, is Poebrotherium 

 vnlsoni, from the Lower Miocene (White River Formation) of Nebraska, 

 Dakota, Wyoming, and Colorado. Its skull measures about 0'15 m. in 

 length. 



Fio. 205. 



Procamelua occidental}* ; skull from the superior (A) and lateral (B) aspects, 

 one-third nat. size. U. Miocene (Loup Fork Formation) ; New Mexico. 

 (After Cope.) 



Procamelus (fig. 205). More robust animals, ranging in size from that 

 of a sheep to that of a camel. There is a small irregular vacuity on each 

 side of the slender facial region of the skull, and the orbit is completely 

 surrounded by bone. The upper incisors are reduced to a single, widely- 

 separated pair, conical in shape, but the remainder of the dentition is 

 complete. The incisor, the canine, and the first premolar, all similar in 



