284 University of California Publications in Geology [Vol. 10 



grada is a distinctly more advanced character than the separation of 

 the phalanges in the Miocene gronnd-sloths from the Santa Cruz beds. 

 In the Pleistocene forms in which the co-ossification habitually occurs 

 a large median ungual is present, while in Mylodon, where the first 

 and second phalanges are usually separate, the ungual is tending to 

 become reduced. The co-ossification of the two phalanges noted in 

 M. harlani is presumably secondary and may be an age characteristic. 



In M. harlani only two elements of the fourth digit are present, 

 while in Scelidotherium the three phalanges are represented, the first 

 and second having co-ossified and the third being rudimentary. In 

 this respect Mylodon harlani is more advanced than Scelidotherium. 



Relation of Mylodont Pes to Supposed Human Footprints in 

 Pleistocene Strata at Carson City, Nevada 



Occurrence of fossil footprints in Pleistocene strata at ("arson, 

 Nevada, first attracted scientific attention some thirty-five years ago. 

 The imprints were uncovered in working the stone quarries of the 

 Nevada State Prison. Joseph LeConte 31 in a description of these 

 footprints states : 



The whole surface of the shale exposed in the prison yard is literally covered 

 with tracks of many kinds, but the mud was so soft when the tracks were made 

 that the nature of many of them can only be guessed. Some were probably 

 those of a horse; some probably of a wolf; some certainly of a deer; many were 

 those of long legged wading birds. But the most interesting are those of the 

 mammoth and the problematical so-called human tracks. 



The sitpposed human footprints referred to by LeConte measured 

 18-20 inches in length and 8 inches in breadth. These tracks, occur- 

 ring in associated right and left series, appeared to have been formed 

 by a bipedal creature. They were considered by Harkness 82 to be 

 impressions of the sandaled foot of primeval man. This belief created 

 not a little discussion 33 at the time of its presentation. LeConte, 34 

 however, pointed out certain obvious objections to this interpretation, 

 namely, the large size and the shape of the individual imprint and 



si Letter to Nature, vol. 28, pp. 101-102, 1883. 



32 Harkness, H. W., Footprints found at the Carson State Prison, Proc. Calif. 

 Acad. Sci., 7 pp., 5 diagrams, August 7, 1882. 



3S A delightful sketch written by the great American humorist, Mark Twain, 

 on the ' ' human ' ' footprints at Carson, was published in The San Franciscan, 

 February 16, 1884. 



34 LeConte, J., On certain remarkable tracks found in the rocks of Carson 

 quarry, Proc. Calif. Acad. Sci., 10 pp., August 27, 1882. 



