380 R. S. Zull — Pleistocene Ground Sloth, 



skull was available for comparison and the differences which 

 were emphasized in the present description might well have 

 disappeared had other asphalt skulls been accessible. There 

 seem to be no distinctions of specific rank and I know of no 

 reason for referring the Texan material to any other species 

 than that which includes the Kancho La Brea forms, namely, 

 Mylodon harlani. 



Comparison with the cast of the type of M. harlani shows 

 that the three Texan jaws exhibit collectively the same fea- 

 tures, some in one specimen and some in another, so that all 

 the important specific characters of the type jaw are to be seen 

 within the limits of variation shown by the Texas specimens. 



Moreover, the Perkins casts of other skeletal material from 

 Oregon which has been referred to the type species, M. har- 

 lani, are indistinguishable except for size and certain minor 

 proportions which may be expected in somewhat older indi- 

 viduals. I therefore unhesitatingly refer the Rock Creek 

 material to the variable and widespread species, Mylodon 

 harlani Owen. 



M. sodalis Cope is founded upon such meager material that 

 its validity may well be questioned. The type ungues are not 

 separable from those of the Texan form other than by slight 

 individual variations and the degree of preservation. 



The mylodont sloths of the Lower Pleistocene of North 

 America may therefore be referred first to : 



Mylodon harlani Owen, including material from the Big 

 Bone Lick, Kentucky ; Oregon ; Hay Springs, Nebraska ; Rock 

 Creek, Texas ; and Rancho La Brea, California. 



As synonyms of the species M. harlani the following 

 should be included : 



Mylodon sodalis Cope 



M. renidens Cope 



M. sulcidens Cope 



Paramylodon nebrascensis Brown. 



Mylodon , gar mani Allen alone probably represents a dis- 

 tinct though closely related form. 



BlONOMY. 



Much has been written concerning the probable appearance 

 and habits of the ground sloths. Sir Richard Owen, with his 

 marvellous insight and ability to appreciate anatomical charac- 

 teristics, has given an interpretation of habits which I see no 

 reason to question in the light of later discovery. 



Mylodon was of elephantine bulk although it by no means 

 attained the stature of the later Megatherium. The fore feet 



