THE MAMMALIA OF THE DEEP RIVER BEDS. 155 



very obliquely downward and backward, and its antero-external border is thickened 

 and rugose and curved upward in a way that is not found in the other genera of the 

 family ; there is no vertebrarterial canal. 



The axis is not very well preserved in any of the specimens, but nevertheless 

 some characters of importance may be determined. The centrum is long and de- 

 pressed, with a prominent inferior keel and slightly concave posterior face. The 

 odontoid process is peculiar ; for most of its length it is broad and depressed, with 

 flat superior and convex inferior surface and irregularly semicircular free margin ; 

 just before joining the centrum the vertical thickness of the process is suddenly 

 increased, so as to form a step-like elevation on the upper surface along this line. 

 The lateral borders are elevated for a short distance from the centrum, giving the 

 process a spout-shaped section, but at the step already mentioned these raised borders 

 abruptly cease and more than two-thirds of the dorsal face of the process is flat. 

 The neural canal is notably small, with its greatest diameter directed transversely. 

 The neural spine is enlarged into a great plate, which apparently is continued into 

 a posterior spine-like process, as in Eporeodon, though this is not altogether certain. 



The remaining cervicals have rather short, broad and depressed centra, with 

 opisthoccelous and somewhat oblique articular faces ; on the ventral side is a promi- 

 nent keel, which bifurcates behind and into two tubercular ridges, which enclose 

 between them a narrow triangular depression ; on each side of the median keel is a 

 deeply concave fossa. The neural canal is very small and of subcircular shape. The 

 neural arch is broad and short and has a nearly flat dorsal surface. The zygapo- 

 physes are broad and flat and present nearly vertically and are but slightly oblique 

 in position; the posterior pair considerably exceed the anterior in transverse breadth. 

 The spine forms a low ridge on the third vertebra, but on the fourth it is well marked 

 and becomes longer on the succeeding vertebras, though it is still very short on the 

 fifth. The transverse processes are variously developed on the different vertebra?; 

 the pleurapophysial plate is very large and massive on the third, and especially so on 

 the fourth, while on the fifth it is smaller and its posterior portion extends outward 

 instead of backward. In all, except the seventh, the vertebrarterial canal is very 

 large. As a whole, the neck of Merycochcerus was obviously rather short but heavy, 

 as the structure of the vertebras indicates the presence of massive and powerful 

 muscles. 



The thoracic vertebras are represented by several from different parts of the 

 column, belonging to one individual. In the anterior part of the region they have 

 short, broad and depressed centra, with spines much heavier than usually occur in 

 the oreodonts. Posteriorly, the centra become longer and assume the trihedral form 



