MEGACEROPS TYLERI 449 



represented by a deep notch as in the rhinoceros, which our specimen 

 also resembles in the lack of a vertebraterial canal and in the relative 

 widths of the anterior and posterior facets. 

 The dimensions of the atlas are: 



Total width -__-___■_. 0.320 

 Width across atlar-occipital facets . 204 



Width across atlar-axis facets ------, 255 



The axis. — The axis is a massive bone with a high neural arch, 

 the spine being an equilateral triangle in mid-section. On its posterior 

 face a shallow groove arises between the zygopophyses which fades 

 out about two-thirds of the way to the summit. The prezygopophyses 

 overhang the atlas in front, but present no articular facets. The 

 odontoid process is a truncated cone, and is not so prominent rela- 

 tively as in Palaeosyops, being about one-third the length of the cen- 

 trum measured along its inferior face. The latter exhibits a low 

 longitudinal ridge below, but is not deeply excavated on either side, 

 as in Palaeosyops. The transverse processes of the specimen are 

 broken away, but the bases of its two supports are seen, indicating 

 the position of the vertebraterial canal, which is placed rather high 

 on the centrum, though not on a line with its upper surface, as is 

 Palaeosyops. 



The postzygopophyses look downward and outward; their hori- 

 zontal axes, if continued, would intersect at an angle of 90 . Alto- 

 gether both atlas and axis resemble those of a rhinoceros much more 

 than those of Palaeosyops. 



The measurements of the axis are as follows: 



Total height to summit of spine ----- 0.295 

 Greatest breadth -------- 2 ^\ 



Length of centrum including odontoid - - - - .133 



The remaining cervicals are distinctly opisthoccelous, with zygo- 

 pophyses which widely overlap one another. With the exception 

 of the sixth, they are quite poorly preserved, and the sixth is so badly 

 crushed as to make measurements very unreliable. 



Of the dorsals, nine only are referable to the type specimen, though 

 three others are added in the mount. The opisthoccelous centra 

 are preserved, but the spines and transverse processes are lacking. 



The ribs. — Portions of thirteen ribs from both sides of the body 



