304 



ORDERS OF MAMMALIA. 



which the best known is the Mylodon robustus (fig. 612). In 

 its size, Mylodon robustus was smaller than the Megatherium, 

 but it reached a length of eleven feet. In many respects 

 Mylodon is very like Megatherium, and the number of the 

 teeth is the same — viz., five upper and four lower molars 

 on each side. The crowns of the molars, however, were fiat. 



Fig. tili.— Skeleton of Mi/lodun mhustus. Post-Plioeeue, South Aiiiericii. 



instead of being ridged, and the anterior upper molars were 

 separated by a gap from those behind them. The fore-feet 

 are pentadactylous, and the posterior tetradactylous, the two 

 external digits being nailless. Like Megatherium , the genus 

 Mylodon is known to have ranged into North America. 



Scclidotherium is another South American genus, closely 

 allied to Mylodon, but comprising forms of smaller size and 

 less massive construction, while the skull was elongated in 

 shape, and other osteological differences existed as well. 



Megalonyx, again, comprises large Sloth-like Edentates from 

 the Post-Pliocene of iSTorth America. It has the same dental 

 formula as Megatherium and Mylodon, but the crowns of the 

 molars are excavated centrally and have a prominent margin, 



