A NEW MYLODON. 327 



Immediately following it, as in the former, is a slight convexity which is further 

 developed in Paramylodon to form a small but fairly well-defined lobe. The 

 extreme length of the tooth is 64 mm., against 55.5 in M. harlani and 56.4 in 

 Paramylodon. Its greatest breadth is 23 mm., across the posterior end. 



The hyoid apparatus (Plate 3, figs. 5, 6) is complete, and apparently for 

 the first time allows the description of these bones in the genus. The stylo- 

 hyal is the longest, 130 mm. in extreme length, with an irregularly rounded 

 stem, expanding dorsally into a squarish plate at whose anteroventral corner 

 is a rounded projection for articulation with the skull. Distally it bears a trans- 

 verse articular surface. What corresponds to an epihyal articulates by a fiat 

 surface with the ventral end of this bone. It is compressed laterally and its 

 distal portion is transversely expanded with an elliptical articular facet, 14 X 10 

 mm., on its posterior face. Its extreme length is 62 mm., or about half that 

 of the stylohyal. A third and smaller bone of trapezoidal outline, with a small 

 eUiptical facet on each of its convergent sides, serves for the articulation of the 

 epihyal with the body of the hyoid. This series of three bones is present on 

 both sides, and the two smallest, or ceratohyals, articulate each with the facet 

 of a protuberance marking either end of the body or basihyal. The last is thor- 

 oughly ankylosed with the thyrohyals to form a V-shaped bone, whose sides 

 are a httle expanded dorsally and whose point is widely emarginate at its pos- 

 terior border. A small facet at the posterior tip of each cornu probably marks 

 the attachment of cartilage. Leidy has figured (1855, pi. 7, figs. 7, 8) the cor- 

 responding bone in Megalonyx jeffersoni, but it differs in having the tips of the 

 cornua much smaller, tapering from the body. 



The correspondence of the hyoid bones with those of the Nine-banded 

 armadillo, as described by Burmeister (1871) is complete, though his figure of 

 these bones in a young animal indicates that the articular protuberances of 

 the V-shaped arch are actually the ends of the thyrohyals, while the basihyal 

 is a small piece wedged in between them. In the armadillo the stylohyal is 

 shown to be smaller than the epihyal; and the ceratohyal as in Mylodon, is a 

 small ossicle. 



Vertebrae. — Of the vertebral column, the cervicals, several dorsal, and a 

 few caudal vertebrae are preserved, but the sacral region and most of the pelvis 

 are lacking. 



The atlas (Plate 4, fig. 19) is in general .similar to that of M. robustus as fig- 

 ured by Owen, but at its anterior end is slightly more emarginate in dorsal 

 outline medially. The lateral boundaries are more nearly parallel instead of in- 



