INTRODUCTION. 



Among the most remarkable of all extinct mammalia are the gigantic sloths, which 

 inhabited the western continent during the pleistocene, or drift period, contempo- 

 raneously with the better known Elephant and Mastodon. 



The remains of the sloth tribe discovered in South America, have been amply 

 described in the works of Pander and d' Alton, Cuvier, Owen, and Lund, and the 

 object of the present memoir is to give an account exclusively of the remains of the 

 same family, which have been found in North America. The memoir was com- 

 menced six years ago, and during a portion of this time new discoveries afforded 

 me an opportunity of giving a much more complete account of the osteology of the 

 animals to which the memoir relates, than I could have anticipated. 



Besides having had access to the cabinets of the Academy of Natural Sciences 

 and American Philosophical Society of Philadelphia, of the New York Lyceum of 

 Natural History, and of the National Institute in Washington, for the examination 

 of remains of extinct sloths, I further had the opportunity of examining a large 

 collection of specimens loaned to me by Dr. D. D. Owen, of New Harmony, Lidiana, 

 and others loaned by B. L. C. Wailes, Esq'r, of Jefferson, Mississippi, Prof. Jeffries 

 Wyman, of Boston, Prof. J. D. Dana, of New Haven, and Prof. F. S. Holmes, of 

 Charleston ; to all of whom I offer my sincere thanks for the interest they have 

 taken in the preparation of the work I now lay before them and the public. 



