FOSSIL MAMMALIA. 63 



and it consequently recedes the furthest amongst the Edentata, in this, as in most 

 other particulars of the cranial organization, from the Glossothere. The chief 

 distinctive peculiarity in the cranium of the Glossothere, so far as it can be studied 

 in the present fragment, and compared with that of other Edentata, is the deep, 

 well-marked, semicircular styloid depression, above described. 



A question may arise after perusing the preceding evidence, upon which the 

 present fossil is referred to a great Edentate species nearly allied to the Oryete- 

 ropus, whether one or other of the lower jaws, subsequently to be described, and 

 in like manner referable, from their dentition, either to the Orycteropodoid or Dasy- 

 podoid families of Edentata, may not have belonged to the same species as does 

 the present mutilated cranium. I can only answer, that those jaws were dis- 

 covered by Mr. Darwin in a different and very remote locality,— that no fragments 

 or teeth referable to them were found associated with the present fossil ; and that, 

 as it would be, therefore, impossible to determine from the evidence we have now 

 before us, which of the two lower jaws should be associated with Glossotherium ; 

 and as both may with equal if not greater probability belong to a totally distinct 

 genus, it appears to me to be preferable, both in regard to the advancement of 

 our knowledge of these most interesting Edentata of an ancient world, as well 

 as for the convenience of their description, to assign to them, for the present, dis- 

 tinct generic appellations. 



The figures in Plate XVI. preclude the necessity of a table of admeasure- 

 ments of the cranial fragment of Glossotherium. 



DESCRIPTION OF A MUTILATED LOWER JAW AND TEETH, ON WHICH IS FOUNDED 

 A SUBGENUS OF MEGATHERIOID EDENTATA, UNDER THE NAME OF 



M Y L O D O N. 



The genus Megalonyx, as is well known, owes its name and the discovery of the 

 fossil remains on which it was founded, to the celebrated Jefferson,* formerly Pre- 

 sident of the United States. Cuvier, from an examination of a single tooth, and 

 the casts of certain bones of the extremities, especially the terminal ones, deter- 

 mined the ordinal affinities of this remarkable extinct quadruped.f But while he 



* Transactions of the Philosophical Society of Philadelphia, vol. iv. p. 246. 



t Its relations to the Edentata, previously conjectured by Dr. Wistar, are proved in the Annates du Museum, 

 torn v. p. 358 ; its more immediate affinities as an annectant form in that group are discussed in the edition of 

 the Ossein. Fossiles, of 1833, torn. v. pt. 1. p. 160. 



