54 



The articulating surface corresponds with that of the same part 

 in the Megatherium. It consists of two deep depressions, sep- 

 arated by a sharp ridge ; the inner depression is a segment of a 

 nearly spherical surface, and the outer forms a broad groove of 

 considerable length, and traverses the end of the bone obliquely 

 from before backwards and inwards. These surfaces correspond 

 Avith the peculiar configuration of the astragalus, which in Mega- 

 theroid animals is quite characteristic. 



The dimensions of the fragment are as follows: — 



Inches. 

 Breadth at the lower extremity . . . .13 



Thickness of do .... 8 



Breadth of upper extremity, fractured ... 8 

 Thickness of do .... 4.5 



Transverse diameter of spherical concavity . . 4 

 Antero-posterior diameter of do ... 4.7 



Transverse diameter of elongated articular surface . 4.7 

 Antero-posterior (oblique) do . 9.5 



The circumference of the bone around the lower extremity, 

 without the fibula, is two feet seven inches ; that of the Madrid 

 specimen with the fibula is 2 feet 6^ inches. 



The breadth of the Madrid specimen with the fibula is 12J- 

 inches, and that of the specimen from the Brazos River, without 

 the fibula, is 13 inches. The latter, therefore, must have belonged 

 to a much longer animal than the former. 



In North America, the Megatherium has hitherto been found 

 only in two localities, viz : Skiddaway Island, on the coast of 

 Georgia, and on the banks of the Ashley River, in South Caro- 

 lina. Dr. Leidy, in his Memoir on the Extinct Sloth Tribe of 

 North America, gives a list of all the remains of the Megatherium 

 which have been discovered in the United States ; the upper half 

 of a tibia is described, but in no instance is the lower portion 

 mentioned. Since the animals, whose structure is known, from 

 North and South America, are of different species, he thinks the 

 North American Megatherium forms a distinct species, which he 

 calls M' mirabile. I have had no means of making a direct com- 

 parison of the bone from the Brazos River with the correspond- 

 ing part of the skeleton from South America ; and as the same 

 portion of bone from the M. mirabile has not yet been discovered, 



