Mylodon harlani, from Rock Creek, Texas. 349 



Dimensions. 



Centrum, length 36 mm 



depth 43 



breadth . _ _ . . 60 



Neural canal, height (estimated) 14-5 



width 53-5 



Neural arch, ant.-post. diameter over zygapophyses 5T5 



diameter of rib facet 21 



width over prezygapophyses .... 117 



pedicel, ant.-post. diameter 28*5 



transverse diameter 24 



Width over transverse processes 180 



Summit of spinous process destroyed so that its 

 height cannot be ascertained. 



Dorsals. — Third dorsal. — A detached neural arch of what 

 was apparently a third dorsal begins to exhibit the antero- 

 posterior expansion of the dorsal wall of the neural cavity so 

 characteristic of the later vertebrae of both ancient and modern 

 sloths. The neural canal was almost triangular in section and 

 nearly equilateral in the relative extent of its boundaries. 

 The transverse processes are massive and exhibit a clearly 

 defined facet for the tuberculum of the rib. This facet looks 

 downward and slightly outward. The anterior zygapophyses 

 are somewhat similar to those of the first dorsal, but the pos- 

 terior ones lie entirely beneath the neural arch and present a 

 flat rather than a curved facet. The facet looks downward 

 and inward but only slightly backward. 



Dimensions. 



Breadth across prezygapophj^ses . - _ 123*o mm 



" over transverse processes 181 



" of neural canal ._ __ 55 



Height " " " 45 



Seventh? dorsal. — The probable seventh dorsal is a well- 

 preserved bone lacking only the epiphyses and the tip of the 

 spinous process. It represents an individual not fully mature, 

 though of nearly equivalent size to the vertebras already 

 described. Here the backward slope of the spinous process is 

 strongly marked, the bone resembling the modern sloth, Choice- 

 pus, more than Mylodon robustus in this regard and in the 

 slenderness of the element. The centrum is rather small and 

 distinctly triangular in outline, because of the prominent ven- 

 tral keel flanked as before by nutritive foramina. Another 



