14 



only four molars in the upper jaw and three in the lower jaw, and to be repre- 

 sented by a species of the size of the Tapir ; the other, called Sphenodon, is 

 not larger than a Hog*. 



These indications of an extensive family of most singular quadrupeds, once 

 spread over the American continents from the latitude of New York to Patagonia, 

 cannot, it is presumed, be pondered on without exciting the strongest interest 

 and desire to obtain further and more definite insight into their habits, their 

 natural affinities, and the business assigned to them in the organic economy of 

 a former world. 



The skeleton of the Megatherium of Madrid, hitherto the most complete expo- 

 nent of the type of this extinct race, exists under conditions which have raised 

 doubts even as to its representing one and the same animal : and if the additional 

 evidence obtained by Sir Woodbine Parish has proved that its anomalous pro- 

 portions were actually such as once characterized a living being, yet comparative 

 anatomists, who, with Cuvier, have admitted the authenticity of the Madrid ske- 

 leton in this respect, still lament its inadequacy to give the much-desired in- 

 formation as to the exact structure of the locomotive extremities : and we have 

 already seen that it has failed to afford a true knowledge of the number and form 

 of the teeth which rightly characterize the genus. 



In the absence, therefore, of a second skeleton of a Megatherium, more com- 

 plete, and more authentic in regard to its discovery and mode of articulation 

 than the existing one, further light on this subject can only be obtained, as it 

 were, by reflexion from such a skeleton of some nearly allied species. The 

 subject of the present memoir happily fulfils all the required conditions ; and 

 the desire to derive every possible advantage in the solution of this interesting 

 problem in Comparative Anatomy from the singularly perfect skeleton of the 

 Mylodon rohustus, must plead as the excuse for any apparently undue detail in 

 the following descriptions and comparisons. 



Generic and Specific Characters of the Mylodon robustus. 



On the reception of the bones composing the present skeleton, the lower jaw 

 was immediately examined, and was found to present a dentition conformable 



* Loc. cit. and Compte Rendu de I'Academie des Sciences, Paris, Avril 1839, p. 574. 



