Mylodon harlani, from Rock Creek, Texas. 379 



area of the astragalar facet in the angle of which lie nutritive 

 foramina. The cnboidal articulation is also triangular and 

 concave in all dimensions. The huge, rugged, posterior por- 

 tion which, as Owen says, makes the os calcis of the Mylodon 

 equal in size that of the elephant, is here missing. In the 

 remaining portion of the bone I see no characters in my limited 

 opportunity for comparison which would be of taxonomic 

 value. 



Dimensions. 



Antero-posterior diameter of calcaneal facet 98 mm 



Preserved width of calcaneal facet .. 60 



Antero-posterior diameter of cuboidal facet 27 



Width of cuboidal facet 55 



Taxonomic Summary. 



Chester Stock, a pupil of that inspiring teacher, Professor J. 

 C. Merriam, of the University of California, who is responsible 

 for the paleontological awakening of the Pacific Coast, has had 

 a splendid opportunity for the study of mylodont variation as 

 shown in the great series of sloths from the Rancho La Brea. 

 Mr. Stock's studies are not yet complete, but a summary of his 

 conclusions regarding the skull and dentition has just appeared.* 

 He finds the Pancho La Brea Mylodons to be extremely varia- 

 ble and to include within the limits of their variation the 

 generic characters assigned by Brown to Paramylodon and the 

 specific features shown in Mylodon harlani, M. renidens Cope, 

 M. suloidens Cope, and the skull described by Cockerell from 

 near Walsenburg, Colorado. All of these forms, together with 

 those from Pancho La Brea, he refers without question to the 

 original species, M. harlani Owen. 



M. garmani of Allen, Stock considers apparently distinct 

 from the Pancho La Brea series, although certain of its charac- 

 ters are closely approached in specimens from the asphalt, 

 garmani differing principally in the extremely narrowed cra- 

 nial portion of the skull and in the antero-posterior elongation 

 of the last inferior tooth. In certain other characters M. gar- 

 mani finds its parallel in one or another of the Pancho La 

 Brea skulls. Stock deems it unsafe to base primary specific 

 differences on the size or form of the teeth, as the dentition is 

 so very variable in the mylodont sloths. 



The Texan material which has been the basis of this memoir 

 emphasizes the variability in the rest of the skeleton as well. 

 It must be remembered that but a single Pancho La Brea 



* Stock, C, Skull and dentition of the mylodont sloths of Rancho La Brea. 

 Univ. of Calif. Pub., Bull. Dept. Geology, vol. viii, No. 18, pp. 319-334, 6 

 text figs., Dec. 5, 1914. 



