134 THE MAMMALIA OF THE DEEP RIVER BEDS. 



more rugose. The posterior articular surfaces for the axis are larger in both dimen- 

 sions than in the latter genus, but especially in width. 



The axis is very different from that of the Oregon genus. The atlanteal facets 

 are broader and higher, descending more below the level of the centrum and separated 

 by a more decided medio-inferior notch, but not, as is the case in Eporeodon, divided 

 above by deep notches from the bases of the pedicels of the neural arch. The odon- 

 toid process is wider, more depressed and spout-like, with more elevated margins and 

 with the articular surface for the inferior arch of the atlas rising higher upon its 

 sides. The odontoid process is thus in an analogous stage towards the assumption 

 of the spout-like character as it is in Protolabis among the camels and Miohippus 

 among the horses. The transverse processes are longer and heavier than in Eporeo- 

 don. The neural spine is of very different shape from that of the latter, a change 

 which is chiefly brought about by an elevation of the anterior portion, so that it 

 forms a large hatchet-like plate, quite different from the spine found in the other 

 members of the subfamily and more like that of AgriocJicerus. The postzygapo- 

 physes are more horizontal in position than in the Oregon genus, presenting more 

 directly downward and less obliquely outward and backward. The pedicels of the 

 neural arch are not perforated for the second pair of spinal nerves. 



The remaining cervicals are rather short, with slightly opisthocoelous centra, 

 which are keeled on the inferior side. The transverse process and pleurapophyseal 

 plate are well developed and the latter reaches great size on the sixth vertebra. The 

 neural spine is a mere ridge on the third, fourth and fifth cervicals, on the sixth it is 

 much higher, slender and inclined forward, while on the seventh it is still higher and 

 heavier. In proportion to the size of the head, the neck is of about the same length 

 as in Eporeodon, but the vertebrae are more heavily built. 



The thoracic vertebras are not different in any very important respect from those 

 of the Oregon genus, except for the better development of the spines. On the first 

 of the series the spine is considerably higher and thicker than on the last cervical, 

 but is much surpassed in both respects by the spine of the second, in which this pro- 

 cess reaches almost bovine proportions. The other anterior thoracic vertebra? have 

 broad, compressed spines, though none of the specimens are sufficiently complete to 

 allow a determination of the length of these processes. 



The remaining regions of the vertebral column are represented by numbers of 

 isolated centra, from which the processes have been broken away, and which there- 

 fore do not require any detailed description. So far as they go, these bones differ but 

 little from the corresponding vertebras of Eporeodon. 



The anterior ribs are rather short, broad and compressed, and of triangular 



