_Megatherium._[96]—The typical genus _Megatherium_, as being the longest known representative of the family, may be noticed in some detail. A nearly complete skeleton, found on the banks of the River Luxan, near Buenos Ayres, and sent in 1789 to the Royal Museum at Madrid, long remained the principal if not the only source of information with regard to the species to which it belonged, and furnished the materials for many descriptions, notably that of Cuvier, who determined its affinities with the Sloths.[97] In 1832 an important collection of bones of the Megatherium was discovered near the Rio Salado, and secured for the Museum of the College of Surgeons of England; and these, with another collection found at Luxan in 1837, and now in the British Museum, supplied the materials for the complete description of the skeleton published by Sir R. Owen in 1861. Other skeletons have subsequently been received by several of the Continental museums, as Milan and Paris, and also by those in South America; and consequently our knowledge of the organisation of the Megatherium, so far as it can be deduced from the bones and teeth, is as complete as that of any other animal, recent or extinct. [Illustration: FIG. 61.—Oral surface of mandible of _Megatherium americanum_. _a_, Condyle; _b_, masseteric process; _c_, angle; _d_, symphysis. (After Owen.)] The remains hitherto spoken of are all referred to one species, _Megatherium americanum_ of Blumenbach (_M. cuvieri_ of Desmarest), and are all from the newest or Pleistocene geological formations of the Argentine Republic and Paraguay, or the lands forming the basin of the Rio de la Plata. Dr. Leidy has described, from similar formations in Georgia and South Carolina, bones of a closely allied species, about one-fourth smaller, which he has named _M. mirabile_. Three other South American species have been described; but _M. laurillardi_, of Lund, founded upon remains found in Brazil, has been made the type of the genus _Ocnopus_. [Illustration: FIG. 62.—Skeleton of _Megatherium_, from the specimen in the Museum of the Royal College of Surgeons. × ¹⁄₂₅.]