MEGATHEEIID^E. Ill 



Mylodon gracilis, Burmeister \ 



Syn. Lestodon myloides, P. Gervais 2 



Pseudolestodon myloides, H. Gervais and Ameghino 3 . 

 Pseudolestodon gracilis, H. Gervais and Ameghino 4 . 

 The identity of M. gracilis with L. myloides is on the authority 

 of Burmeister (loc. cit.) ; and although this is not accepted by Gervais 

 and Ameghino, there seems no doubt of its correctness. Burmeister's 

 specific name, although of later date than that given by Gervais, is 

 adopted on account of the inappropriateness of the latter in con- 

 junction with the term Mylodon. 



The species is of rather more slender build than M . robustus, the 

 plane of the occiput is less oblique, the plane of wear of the anterior 

 teeth very oblique, and the fore and aft edges of the first lower tooth 

 bear a distinct ridge ; the last lower tooth is much elongated, and 

 has been compared to a figure of 8. 



Hab. South America (Argentine Eepublic). 



M. 2500. The nearly entire skeleton ; from the Pleistocene of 

 Buenos Ayres, Argentine Eepublic. The skull agrees 

 precisely with the type specimen figured in De Blainville's 

 ' Osteographie,' Genus Megatherium, pi. i. figs. 8, 9, 18. 



Purchased, 1885. 



Genus MEG ALOW YX, Jefferson 5 . 



Including Meyalochnus, Leidy 6 (= Myomorphus, Pornel). 



In this genus, which is confined to North America, the teeth are 

 | ; the hinder teeth form suboval or triangular prisms, with an 

 angle directed outwards ; there is a long diastema between the first 

 and second teeth, the first Cupper tooth being curved and having an 

 oval section, with a horizontal plane of wear. There is an ente- 

 picondylar foramen to the humerus. The astragalus is very like 

 that of Mylodon ; the terminal phalangeals are strongly curved, and 

 there is no anchylosis of the phalangeals. 



Megalonyx jeffersoni, Desmarest 7 . 

 Syn. Meyalonyx laqueatus, Harlan 8 . 

 This is the type species ; the identity of the so-called M. laqueatus 



1 An. Mus. Buenos Aires, vol. i. p. 166 (1864-69). 



2 Mamruiferes Possiles de 1'Amerique Meridionale(Castelnau's Voyage), p. 47 

 (1855). 



3 Mammiferes Fossiles de 1'^merique Meridionals, p. 160 (1880). 



4 Ibid. p. 164. 5 Trans. Amer. Phil. Soc. vol. iv. p. 248 (1799). 



6 Proc. Ac. Nat. Sci. Philad. 1868, p. 180. 



7 Mammalogie, p. 366 (1822). 8 Med. Phys. Eesearch. p. 319 (1835). 



