1914] 



Stock: Mylodont Sloths of Bancho La Brea 



333 



in M. robustus than in M. Jiarlani, and the dorsal surface of the 

 cranium is wider in the former species. 



The superior tooth-rows in M. Jiarlani generally show less diverg- 

 ence anteriorly, and the last upper tooth is usually situated farther 

 from the postpalatine notch than in M. robustus. In the South 

 American species the first superior tooth may vary in size, but appears 

 never to have been absent on either side of the palate as in M. Jiarlani. 

 The first tooth is also separated from the second superior tooth by a 

 larger interval than in the North American species. The second 

 superior tooth is smaller than in the Rancho La Brea skulls and is 

 not so pronouncedly elongated antero-posteriorly. 



The lower jaw in Mylodon robustus is generally of greater depth 

 below the anterior teeth, and the predental region is of greater width 

 than in Mylodon Jiarlani. 



The South American genus GrypotJierium, originally described by 

 Owen, 20 and later determined on more complete skull material by 

 Bernhardt, 21 differs from Mylodon Jiarlani principally in possessing at 

 the anterior end of the skull a bony arcade connecting the nasals with 

 the premaxillaries. The lengthening of the skull in front of the 

 superior teeth is associated with an extreme forward extension of the 

 lower jaw anterior to the first inferior tooth. In mandibles belonging 

 to individuals of M. Jiarlani having the reduced superior dentition, 

 the extension of the jaw anterior to the first inferior tooth is no greater 

 than in individuals having the normal dentition. The reduction in 

 the superior dentition to four teeth on each side of the palate, con- 

 sidered by Reinhardt, 22 Woodward, 23 and others as being generically 

 distinctive of GrypotJierium, is seen to occur, also, in Mylodon 

 Jiarlani. In GrypotJierium the superior tooth-rows diverge less 

 anteriorly and the teeth, on the whole, have more simple outlines than 

 in M. Jiarlani. 



20 Owen, K., The Zoology of the Voyage of H. M. S. Beagle, etc., Part 1, 

 Fossil Mammalia, pp. 68-73, pi. 17, fig. 5, pi. 18, pi. 19, figs. 1-4, 1840. 



21 Reinhardt, J., Beskrivelse af Hovedskallen af et Kaempedovendyr, Grypo- 

 tJierium darivinii, fra La Plata-Landenes plejstocene Dannelser, Vidensk. Selsk. 

 Skr., 5. Eaekke, naturvidenskabelig og mathematisk Afd. Bd. 12, 4, pp. 351-380, 

 2 Tav., Copenhagen, 1879. 



22 Reinhardt, J., op. cit., p. 365, 1879. 



23 Woodward, A. S., On Some Remains of GrypotJierium (N eomylodon) listai 

 and Associated Mammals from a Cavern near Consuelo Cove, Last Hope Inlet, 

 Patagonia, Proc. Zool. Soc. Lond., p. 73, 1900. 



