15 



with that characterizing the genus Mylodon : certain modifications in the shape cf 

 the teeth indicated the specific distinction of the fossil of the Plata from both 

 the Patagonian Mylodon Darwinii and the North American Mylodon Harlani, 

 hut showed it to be more closely allied to the latter species. 



The differential characters of the Mylodon rohustus, as it is proposed to call 

 the present species, are further and very satisfactorily illustrated, in regard to 

 the Mylodon Darwinii, by the different proportions of the lower jaw itself, as will 

 be seen by comparing Plate VI. of the present memoir with Plate XVIII. of the 

 description of the Fossil Mammalia collected in the Voyage of the Beagle. The 

 distinction of the Mylodon rohustus from the Mylodon Harlani was demonstrated 

 by a comparison of the bones of the latter species in the collection of Missouri 

 fossils* exhibited in the present year (1842) by Mr. Koch, in London, with the 

 corresponding bones of the Mylodon rohustus. 



The more obvious modifications by which the dental and osteological charac- 

 ters of the genus Mylodon differ from those of the genera Megatherium, Mega- 

 lonyx and Scelidotherium, are pointed out in the detailed comparisons succeeding 

 the descriptions of the several parts of the present skeleton, and are succinctly 

 defined in the concluding synopsis of the families, genera and species at present 

 known to constitute the Phyllophagous division of the Edentate order. 



General Description of the Skeleton of the Mylodon rohustus. 



The singularly massive proportions of the skeleton of the Mylodon rohustus f 

 arrest the attention of every observer, and are not less calculated to excite the 

 surprise of the professed comparative anatomist. 



A trunk, shorter than that of the Hippopotamus, is terminated behind by 

 a pelvis, equalling in breadth and exceeding in depth that of the Elephant. This 

 capacious bony basin rests on two massive but short hind extremities, terminated 

 by feet as long as the femora, set at right angles to the leg, as in the plantigrade 

 animals, but with the sole slightly turned inwards. 



A tail equalling the hind limbs in length, and proportionally as thick and 



* These are the bones noticed by Dr. Harlan in the Proceedings of the American Philosophical 

 Society above cited, 

 t Plate I. 



