12 



bones of three digits, regarded by Cuvier, according to the analogy of the Ca- 

 bassou {Dasypus unicinctus, Gm.), as the index, medius, and annularis, the two 

 latter armed with powerful claws ; vestiges of a thumb and little finger ; a hu- 

 merus, radius and ulna ; from which bones Cuvier deduces the affinities of the 

 Megalonyx to the Sloth, and its specific distinction from the Megatherium*. All 

 these remains of the Megalonyx were discovered in the continent of North 

 America. 



Mr. Darwin's collection of mammalian fossils from South America contained, 

 besides portions of the Megatherium, characteristic remains of at least three 

 other species, indicating distinct subgenera of less gigantic Megatherioid animals. 

 Of these one was unequivocally the Megalonyx ; the teeth in the lower jaw 

 having an elUptical or oval crown, depressed in the centre, which is the form 

 characteristic of that genus f. 



The existence of the Megalonyx in South America had previously been af- 

 firmed by Professor DoeUinger, on evidence derived from fossil claw-bones dis- 

 covered by Drs. Spix and Von Martins in a bone-cave in Brazil. Dr. Lund| 

 has subsequently founded, on fossil remains from the same locality, three species 

 of Megalonyx distinct from the original Meyalonyx Jeffersonii ; but other genera 

 of Megatherioid Edentata appear to have been confounded with the true Me- 

 galonyx in his enumeration. 



A genus or subgenus distinct from both Megatherium and Megalonyx, but of 

 the same natural family, has been very satisfactorily estabUshed by a comparison 

 of a large proportion of the skeleton of a Megatherioid animal, discovered by 

 Mr. Darwin in the bay called Bahia Blanca in Patagonia. The bones were im- 

 bedded in the cliff so nearly in their proper relative positions, as to lead to the 

 belief that the carcase had been drifted to the spot in an entire state. Tlie cha- 

 racters of this genus, to which I have assigned the name of Scelidotherium^, are 

 taken from the modifications of the teeth and of the bones of the extremities, 



* " Quant a la comparaison entre le Megatherium et le Megalonyx, elle donne pour resultat des 

 rapports assez marques, et cependant des caractferes de distinction au moins specifiques." — Loc. cit. 

 p. 364. 



f Fossil Mammalia of the Voyage of the Beagle, 4to, 1838-40, p. 99, pi. 29. 



J Lund, loc. cit. and Compte Rendu de I'Academie des Sciences, Avril 19, 1839, p. 573. 



§ Fossil Mammalia of the Beagle, 4to, 1839, p. 73, plates 20-27. 



