166 University of California Publications in Geology [Vol. 10 



istie of Mylodon harlani from Rancho La Brea, and as these characters 

 are apparently constant and cannot be satisfactorily shown to grade 

 into the usual type of skull from the asphalt deposits, they are con- 

 sidered to represent a new subspecies. It may be possible to establish 

 a series with uniform and perfect gradations between the narrow 

 and broad types of skulls of M. harlani when the entire mylodont 

 sloth collection is reviewed, but at present it seems necessary to make 

 the distinction between the two forms. 



I desire to acknowledge my thanks to Mr. Frank S. Daggett, Direc- 

 tor of the Museum of History, Science and Art of Los Angeles, who 

 not only very kindly allowed me to examine the ground-sloth material 

 but rendered many personal favors during my stay at the Museum. 

 I desire also to thank the other members of the staff for many cour- 

 tesies shown me. The photographs of the skull of the new subspecies 

 were taken at the Museum by Mr. L. E. Wyman. 



CEANIUM 



Of the thirty-two skulls of mylodont sloths contained in the Rancho 

 La Brea collections of the Los Angeles Museum of History, Science 

 and Art, by far the greater number range approximately between 

 460 mm. and 525 mm. in length (from anterior end of maxillary to 

 posterior end of occipital condyles). None of the skulls attain the 

 length of the Colorado specimen described by Professor Coekerell. 2 

 With the exception of three, possibly four crania, this series is com- 

 posed of skulls having the general characteristics already discussed in 

 connection with a similar series contained in the palaeontological 

 collections of the University of California. 



Specimens 642, 643, 646, and 695 3 differ from the usual broad type 

 of skull of Mylodon harlani from Rancho La Brea in the decidedly 

 more slender cranium posterior to the postorbital processes. For skull 

 642 this is distinctly indicated in plate 3. In this respect they ap- 

 proach more closely the skull-form in Mylodon garmani, differing, 

 however, in being much less slender. With the least width of the 

 skull behind the postorbital processes as a convenient and suitable 

 index of slenderness of the cranial case, a series can be established 

 with gradations tending toward the broader type of skull. The speci- 



- Coekerell, T. D. A., A fossil ground-sloth in Colorado, Univ. Colo. Studies, 

 vol. 6, pp. 309-312, 2 pis., 1909. 



s All numbers used in this paper, unless otherwise stated, are the catalogue 

 numbers of specimens contained in the Rancho La Brea collections of the Museum 

 of History, Science and Art of Los Angeles. 



