MEGATHERIUM. 49 



The left half of the loAver jaw preserved with all its teeth. The bone in its 

 present condition measures ten inches from its posterior margin to the anterior 

 mental foramen, which is placed an inch and a quarter in advance of the position 

 of the first molar ; and its depth below the third molar is about two and a half 

 inches. Its form agrees with the corresponding portion of the jaw of Mi/lodon 

 rohustus but is more convex externally in accordance with its age. The teeth 

 have the same form and proportions as those in the adult fragment of jaw above 

 described, except that the first of the series in transverse section is more demi-oval 

 than reniform, and the anterior side of the second tooth is a little convex instead 

 of being a little concave. 



The malar bone of the left side. It presents the same trilobate appearance as in 

 Mijlodon rolmshis. 



Fourteen fragments of vertebroa. 



The scapula of the right side. Its glenoid articulation and coracoid process have 

 the same mode of development indicated in the account of the corresponding bone 

 of the young skeleton of the Megalonyx Jeffersonii. 



Both humeral diaphyses. These are nine and a half inches long, by seven and 

 a half inches in circumference at the middle. The deltoidal tract already presents 

 a j^rominent outline. 



The right ulnar diaphysis, which is eight and a half inches long, and its lower 

 third is six and a quarter inches in circumference. The coronoid process rises 

 almost from its middle. 



Both radial diaphyses. These are five and a half inches long, and four and a 

 half inches in circumference about the middle. 



One ilium, two ischia, and an os pubis. 



Both femoral diaphyses accompanied by the head of- one. Length of the 

 diaphyses eleven inches ; circumference about the middle ten inches. 



A tibial and fibular diaphysis. The former measures four and three-quarter inches 

 in length, and seven inches in circumference about the middle; and the latter is about 

 the same length, and two and three-quarter inches in circumference at tlie middle. 



lUEOATHERIUiVI, Cuvieu. 

 iTIe^atheriiiin iiiirabile, Leidy. 



The most wonderful of all the extinct sloth tribe, the huge Megadtciinm, finally 

 claims our attention. Its geographical range appears to have been equally exten- 

 sive with that of the Mylodon, but I think it may be questioned whether the remains 

 of this genus found in North and South America belong to the same species. In 

 no other instance, so far as investigations have been carefully made, has any species 

 of an extinct sloth been discovered common to the two American continents. 

 Under these circumstances, until it shall have been proved to be otherwise the case 

 by comparison of specimens or good figures, I propose to consider the North Ame- 

 rican Megatherium a distinct species with the name of M. mirahUe, while the older 

 name of M. Cnvicri appertains to the South American species. 

 7 



