I regret that I lost, during my residence at Buenos Ayres, the opportunity of making what too late I learnt would have been very acceptable additions to our zoological collections; but I never imagined that our public museums were so entirely destitute, as I found them upon my return, of specimens of the commonest objects of natural history, from a country with which we had been so many years in, I may say, almost daily intercourse. Mr. Darwin, and the officers of His Majesty's ship Beagle, have since done much to supply these deficiencies; but we still want, I believe, specimens of by far the greater part of the birds and beasts of which Azara gave us the description nearly forty years ago. The collections of some of the museums on the Continent are, I believe, much more complete; especially those of Paris, to judge from the accounts of the acquisitions made by M. Alcide d'Orbigny, the fruits of many years spent in those countries, to which he was sent in 1826, expressly, I believe, to collect information and specimens for the Museum of Natural History. Instigated first by Dr. Buckland, I made those inquiries for fossil remains, the results of which I flatter myself have been of no common interest both to the geologist and comparative anatomist. The examination of the monstrous bones which I sent to this country, by the learned individuals who have taken the pains to describe them, assists us to unravel the fabulous traditions handed down by the aborigines respecting a race of Titans, whilst it proves indisputably that the vast alluvial plains in that part of the world, at some former period, the further history of which has not been revealed to us, were inhabited by herbivorous animals of most extraordinary dimensions, and of forms greatly differing from those of the genera now in existence. To the account of the Megatherium, and other extinct animals, I am now enabled, by a delay which has unavoidably occurred in the publication of this volume, to insert the representation of another extinct monster, the Glyptodon, which has been very recently discovered at no great distance from the city of Buenos Ayres, apparently in a very perfect state, and which I trust ere long will be in England. Mr. Owen, of the College of Surgeons, has been good enough to draw up for me the description of it, which I have added in a note at the end of the tenth chapter. It is, perhaps, not unworthy of a passing observation here, that, amongst all the remains of extinct animals which we have now obtained from the Pampas, most of which too seem to have been singularly provided with a structure for self-defence, no instance, I believe, has as yet been satisfactorily proved of the occurrence of any portion of a _carnivorous_ animal.