A FOSSIL GROUND-SLOTH IN COLORADO 31I 



32 .mm. The distance from the last alveolus to the posterior nares is 

 58 mm. Thus it seems that the teeth in our animal were both actually, 

 and in a slight degree relatively, larger than in Paramylodon. The dis- 

 tance from the' last alveolus to the posterior nares in Paramylodon, as 

 measured from Mr. Brown's figure, would be about 48 mm. 



The elongate skull, and inflated muzzle, given by Mr. Brown as 

 generic characters of Paramylodon, are equally noticeable in the Colo- 

 rado animal. The trilobed last molar of lower jaw, also said to be a 

 generic character of Paramylodon, is in some degree indicated in Mylodon 

 harlani, according to Leidy's figure in his Smithsonian Memoir of 1855. 

 The slope of the occipital region, as seen in lateral profile, is equally 

 characteristic of our skull and Paramylodon; so also is the broadening 

 of the muzzle anteriorly. These characters are equally well seen in the 

 existing sloth Choloepus hoffmanni, found in Costa Rica, but are much 

 less evident in the other living Central American genus, Bradypus. 

 Gray's figure (Proc. Zool. Soc, 187 1) of the skull of the Brazilian 

 Choloepus didactylus does not exhibit the occipital character at all, and 

 is surprisingly unlike C. hoffmanni; but Dr. J. A. Allen assures me 

 that the difference is due to immaturity, as De Blainville's figure of the 

 skull of C. didactylus shows no material difference from skulls of C. 

 hoffmanni. In the Pleistocene Megalonyx the slope of the occiput is 

 less extreme, and the whole skull is much less elongated than in Para- 

 mylodon. 



It is to be noted that a Mylodon fibula was found some years ago at 

 Seneca, Kansas, and described and figured by Dr. Williston in the 

 Kansas University Quarterly, January, 1895. Dr. Williston referred it 

 with doubt to Mylodon harlani, but the general measurements accord 

 better with those given by Brown for the fibula of Paramylodon, showing 

 merely an excess of ten millimeters. However, Mr. Brown writes me 

 that the Kansas fibula must certainly be referred to Mylodon, having 

 the tibial and astragalar facets separate, whereas they are continuous in 

 Paramylodon. The fibula of Paramylodon is also more slender than 

 that of Mylodon. 



Provisionally, it is perhaps justifiable to consider our skull referable 



