A NEW MYLODON. 329 



Parts of sixteen dorsal vertebrae are preserved, in some cases enough to re- 

 construct nearly the entire bone. Vertebrae 8 to 13 are almost complete, but 

 of the eight following, the centra and pedicle portion are broken or imperfect 

 so that reconstruction is difficult. Probably' there were sixteen dorsals. In 

 Mylodon robustus there were sixteen pairs of ribs. 



The centrum of the first dorsal is roughly elliptical as seen from in front, 

 with a transverse diameter of 59 mm., and a vertical of 40 mm., as measured 

 on the articular surface. The posterior face is not so wide, and like the anterior, 

 bears the demifacets at the sides. The pedicles rise from the anterior upper 

 corners of the centrum, are short, thick, and oval in section. The cranial 

 articular facets are broadly elliptical, with their long axes nearly transverse. 

 The neural spine is some 145 mm. high from the anterior dorsal edge, thin and 

 compressed, but with a greater width posteriorly, where it is ridged vertically. 

 The summit is flattened, its sides diverging posteriori j'^ to a width of 21 mm. 



In the succeeding vertebrae the centrum becomes more or less triangular in 

 face view. This is first observable in the next but one, (tenth), the posterior 

 face of which is distinctly three-cornered with the ventral point rounded. The 

 sides also are concave. In the sixteenth vertebra the centrum is largest and 

 deepest (62 mm. anteriorly). 



With the eleventh vertebra the pedicle increases in length until it arises 

 from nearly the whole side of the centrum; at the same time it becomes gradu- 

 ally much reduced in thickness on successive vertebrae. The cranial demifacets 

 of the ninth ^■ertebra are borne on the anterior base of the pedicel; the caudal 

 demifacets at the dorsal corner of the centrum. The tenth vertebra is sunilar 

 but the cranial demifacets are more elongated vertically. In the eleventh 

 they become lateral. The caudal demifacets are mainly borne by the posterior 

 base of the pedicle, and seem to become obsolete at about the eighteenth ver- 

 tebra. 



The transverse processes, so far as preser\'ed, are at first broad and irregular 

 in shape, with a prominent anterior point- and two posterior ridges. A facet 

 for articulation with the tubercle is present externally. Posteriorly on succeed- 

 ing vertebrae the two ridges lengthen and diverge forming a Y on the 14th to 

 16th or 17th vertebrae. The inner fork of the Y at length becomes much the 

 longer until finallj' it forms a ridge with an obtuse angle. The entire transverse 

 process grows successively more elevated and longer, with a groo\-e of increasing 

 size that passes from the outer to the inner side of the ridge. 



The cranial articular facets of the 3d to the 8th vertebrae are all slightly 



