MEGA THERIID& 



189 



the feet differ considerably from those obtaining in the type genus. 



S. leptocephalum, the type of the genus, occurs in Patagonia and 



Argentina but 



other species are 



found in Brazil 



and Chili. The 



genus Mylodon, in 



its widest sense, 



may be taken to 



include a number 



of comparatively 



large Edentates, 



some of which have 



been described 



under the names of 



Grypotherium, Lest- 



odon, and Pseudo- 



lestodon. The teeth 



of the upper jaw 



are generally of an 



OVal Or Subtrian !!- Fl ' 63 -~ skeleton of Mylodon robvstus (Pleistocene, South 



America). From Owen. 



lar section ; and in 



the more typical forms the first and second teeth are separated 

 by a short interval, the former being horizontally worn. In 

 other species, however, like M. (Lestodon) armatus, there is a 

 considerable space between the first and second teeth, and the 

 first is worn obliquely. The skull is exceedingly like that of 

 the Sloths in general contour ; and there is not the descending 

 process at the angle of the mandible found in Megatherium. 

 The humerus has no entepicondylar foramen. The species 

 represented in Fig. 63 is from the Pleistocene of South America; 

 but the type of the genus is M. harlani, from beds of corre- 

 sponding age in Kentucky. The Patagonian M. (Grypotherium) 

 darwini is a remarkable form, characterised by the presence of a 

 bony arch connecting the premaxillse with the nasals, of which, as 

 already mentioned, there is an incomplete development in 

 Megatherium. Megalonyx, from the Pleistocene of Kentucky, differs 

 from Mylodon by the long interval between the first and second 

 teeth, and also by the presence of an entepicondylar foramen in 

 the humerus. Nothrotherium is a smaller form, occurring in the 

 deposits of the Brazilian caves, of which the dental features have 

 been already mentioned. The osteological characters of these and 

 other allied genera have been fully described in the works of 

 Cuvier, Owen, Burmeister. Leidy, Ameghino, Gervais, Reinhardt, 

 and others. 



Promegatherium. Two genera from the infra -Pampean beds 



