A NEW MYLODON. 331 



character is absent in the South American Mylodon robustus, but is found in 

 Megatherium "through a great proportion of the posterior part of the dorsal 

 region." In connection with the shape of the skull and rostrum it may indicate 

 an adaptation for a browsing rather than a grazing habit through allowing an 

 increased mobility of the trunk in reaching upward for leaves and twigs. (See 

 Plate 4, figs. 17, 18). 



The vertebral spines deserve a passing mention. Those of the 3d and 4t]i 

 vertebrae are low, stout, and rugged, expanded terminally. The remaining 

 cervical spines are destroyed but seem to have become thinner and higher. The 

 8th, or first dorsal, has a spine some 135 mm. from the median edge of the arch 

 to the tip. The anterior portion is compressed but becomes thickened pos- 

 teriorly. The spines of the 10th and 11th vertebrae are the longest, about 140 

 mm. from the Up of the foramen. From this point they increase somewhat 

 in thickness, but diminish slightly and regularly in length, and more in the 

 degree of elevation, so that the posteriormost are much more flattened than 

 those at the anterior end of the column. The summits of the dorsal vertebrae 

 are at first oval (46 X 25 mm. in the 10th vertebra), in outline, but become suc- 

 cessively longer, narrower, and from the 16th on, more nearly triangular in out- 

 Ime, with the pointed end anterior. The summit of the 21st vertebra measures 

 56 mm. in length and 31 in breadth at the posterior end. There is no reversal 

 of the slant of the spines nor any material change in their general shape in the 

 posterior part of the column, as is likewise true of M. robustus. 



The lumbar and sacral portions of the skeleton had evidently been long 

 exposed above ground, so that nothing but fragments of the pelvis remain, 

 barely sufficient to reconstruct part of the right ilium. The terminal fourteen 

 vertebrae are, however, nearly intact and the centra of three more large caudals 

 Ukewise are present though somewhat distorted. The 11th to 14th caudals, 

 counting from the terminal one, are of essentially similar appearance. The 

 anterior and posterior faces of the centrum are of practically the same size, nearly 

 circular and about 53 mm. in diameter, but the anterior end is sUghtly the higher 

 above a transverse plane, and this feature is noticeable in all but the last few 

 caudals. The transverse processes arise along nearly the entire side of the 

 centrum, and measure in the 12th \'ertebra from the end, 70 mm. from anterior 

 point of union with the centrum to the extreme tip. They are directed back- 

 ward, and rapidly decline in size to mere lateral ridges in the 7th to the 3d 

 from the end of the series. The last vertebra to have caudal articular facets 

 is the 11th from the end, so that the 10th is consequently the last to have cranial 



