102 



Georgia, and with additional pieces sent to liim by Dr. Habersham. 

 As the North American Megatherium had, upon theoretical grounds, 

 been described from a few fragments as a distinct species from the 

 South American one, by Dr. Leidy, it was an interesting question to 

 ascertain how far this theoretical distinction was well founded. For- 

 tunately, the fragments, which had been found by Professor Agassiz 

 and Dr. Habersham, were exceedingly characteristic, and included 

 portions of bones which enabled Professor Agassiz to satisfy himself 

 of the specific difference of the Patagonian and of the North Amer- 

 ican Megatherium. He then exhibited to the Society a portion of 

 the ulna and radius with the perfect articulating surface of the elbow. 

 The ulna of the two species is about the same size, the North Amer- 

 ican being somewhat shorter and blunter, while the olecranon Is very 

 prominent In the South American species. The articulating surfaces 

 of the radlu3 were very different, showing a much greater power of 

 rotation In the northern species, while the great development of the 

 articulating surface must have restricted the rotation In the southern 

 species to much narrower bounds ; and other minor differences between 

 the heel-joints and the spinous processes, which all tend to prove 

 that the North American Megatherium must have been more flexible 

 than the southern species. The question then arises how far it is pos- 

 sible for these two animals to have been generlcally distinct, as the 

 differences which have thus far been pointed out are structural differ- 

 ences. Professor Agassiz was inclined to believe that the differences 

 which he had pointed out were not simply specific, but that they were 

 generic. This view he supported by making a short revision of the 

 Edentata, and showing that the three groups into which Owen had 

 subdivided them were of such a character that he considered them as 

 suborders. The Megatherolds would be divided into two families, as 

 the presence of a trunk indicated by the structure of the anterior 

 portion of the skull In Megatherium would warrant its separation, 

 as a separate family, from Megalonyx, in which we have a short 

 snout. This subdivision into families would simply be applying to the 

 Edentata the same principles of classification which are adopted in 

 the Pachyderms. 



In reply to a question of Di*. C. Pickering, Prof. Agassiz 

 stated that he had no satisfactory conclusive evidence in 

 regard to the exact geological age of the dej)osits in which 

 the North American Megatherium is found. 



Dr. Pickering said that he had seen the deposits of the 

 Rio Negro, where the South American Megatherium was dis- 

 covered, and was inclined to consider them as belonging to 

 the age immediately preceding our own. 



