13 



especially of the astragalus : the species is probably less than the Megalonyx 

 Jeffersonii, Desm. 



A nearly entire lower jaw, likewise discovered by Mr. Darwin in Bahia Blanca, 

 presented a dentition similar in the number and essential structure of the teeth 

 to that in Megatherium, Megalonyx, and Scelidotherium, but differing in the form 

 of the teeth as much as those genera differ in the same respect from each 

 other. For the genus thus indicated I have proposed the name of Mylodon, 

 from the Greek words signifying ' molar teeth,' or teeth adapted solely for 

 grinding* ; and I have shown that certain fossil jaws and teeth which had been 

 previously discovered in North America, and assigned to the Megalonyx, belong 

 in fact to this new genus, in which they form a second species. The name of 

 Mylodon Darwinii was assigned to the Patagonian species ; that of Mylodon 

 Harlani to the North American species, in honour of the naturalist by whom 

 it was first described f. 



Remains of the Mylodon Harlani have been subsequently described and figured 

 by Dr. H. C. Perkins J : these were discovered in the Oregon territory, near one 

 of the tributaries of the Columbia, twelve feet below the surface. Other re- 

 mains of the Mylodon Harlani, discovered by Mr. Koch in Benton County, Mis- 

 souri, were perceived by Dr. Harlan to be distinct from Megalonyx, and have 

 been noticed by him as indicative of a new genus and species, for which he has 

 proposed the name of Orycterotherium Missouriense^. 



In conclusion, I may observe that Dr. Lund has indicated two before unknown 

 extinct genera of large Sloth-hke quadrupeds, whose remains he has discovered 

 in the Brazihan caverns. One of these, called by him Cailodon, is stated to have 



* MiiXi) 7nola, oiois dens. See Fossil Mammalia of the Beagle, 4to, p. 63. It is to be observed 

 that canine and incisor teeth are absent in the other genera of Megatherioid animals ; but an objection 

 that such name, signifying the presence of molar teeth only, does not imply a peculiarity of the genus, 

 might equally be made to the term Megalonyx {fieyas, great, iji'vl, a claw), of which genus the known 

 species have not relatively longer or larger claws than the Mylodon and other Megatherioids ; all of 

 which, likewise, as well as the Scelidotherium ((Ti.e\is, kind-leg, Bripiov, beast), are remarkable for the 

 size of their hinder extremities ; nor can any of the known Megatherioids be termed other than great 

 animals, although the Megatherium proper (fieyas, great, dijpiov, beast) best merits that term. On 

 this principle of the nomenclature of the Megatherioid genera all the characteristic peculiarities of the 

 family are readily fixed in the memory. 



f Harlan, Medical and Physical Researches, 1835, 8vo, p. 334. 



I Silhman's Journal, vol. xlii. No. 1, January 1842. 



§ Proceedings of the American Philosophical Society for November 1841. 



