EDENTATA OF THE SANTA CRUZ BEDS. 333 



size and form in the various parts of the thorax. The individual vertebrae 

 resemble those of Hapalops, though on a much larger scale and with 

 several characteristic modifications. Compared with the vertebrae in the 

 hinder part of the thorax, the first thoracic is very small and shows that 

 the neck was probably more slender than in Hapalops ; the centrum is 

 short, broad, much depressed, with feebly convex, D-shaped anterior face, 

 and with two parallel, widely separated, thick and very prominent ventral 

 keels, which do not occur in any of the preceding genera ; the anterior 

 facets for the rib-heads are large, slightly concave, and placed partly on 

 the centrum and partly on the neural arch, while the small posterior facets 

 project quite prominently from the postero-lateral angles of the centrum. 

 The transverse process is very prominent and heavy and has a large facet 

 for the tubercle of the first rib ; the prezygapophyses are lateral in position, 

 concave, very heavy and prominent, while the postzygapophyses are 

 small, convex and placed on the neural arch. 



The next vertebra of the series is one which corresponds in form to 

 the tenth or eleventh thoracic of Hapalops (Plate LX, fig. 4) ; the cen- 

 trum is relatively small and of quite a different shape from the first, hav- 

 ing subtriangular faces and nearly equal transverse and dorso-ventral 

 diameters ; the neural canal is remarkably large, its diameters exceeding 

 those of the centrum ; the pedicles of the neural arch are high and narrow, 

 the arch and spine extending far behind them; the spine is relatively 

 short and slender and has a very strong backward inclination ; the trans- 

 verse process is shorter than on the first vertebra, but very prominent 

 and heavy. 



Behind the middle of the thorax the centra increase steadily in size, 

 but the gradual way in which this increase is effected is strong evidence 

 that the backbone was nearly or quite as elongate as in Hapalops. In 

 the posterior part of the region the vertebrae are exceedingly large and 

 have assumed the appearance of lumbars ; the centra are massive, short, 

 broad and thick, with subquadrate faces ; the ventral foramina are nearly 

 obsolete ; on the last two vertebrae, at least, there are no facets for the 

 tubercles of the ribs ; the neural spines are shorter than in the middle of 

 the thorax, and less inclined, but they are very heavy and much thick- 

 ened at the free end ; the transverse processes are very short, broad, 

 sharply upcurved, and heavy and rugose at the distal end. The mode of 

 articulation of these vertebrae is almost the same as in Hapalops, but the 



