1914] 



Stock: Mylodont Sloths of Ranch o La Brea 



331 



tooth as reconstructed by Cope 12 the width anteriorly is less in pro- 

 portion to the greatest length of the tooth than in the Rancho La Brea 

 series. The greatest width of the anterior lobe in the fifth superior 

 tooth is twice the width of the posterior lobe. These dimensions are 

 never reached in the Rancho La Brea skulls, and the tooth in Cope's 

 series apparently corresponds to a third superior tooth. 



Cope 13 also established a species, Mylodon renidens, to which he 

 referred several upper and lower teeth from Petite Anse, Louisiana. 

 The specific characters of the teeth of M. renidens noted by Cope lie 

 within the range of individual and age variations of the Rancho La 

 Brea specimens. The third inferior tooth as described by Cope is 

 identical with the corresponding tooth in skulls from the asphalt 

 deposits. 



The beveling of the postero-internal angle of the third inferior 

 tooth, given as characteristic of Mylodon sulcidens by Cope 14 and 

 noted in M. garmani by Allen, occurs also to a varying degree in the 

 Rancho La Brea skulls. The fourth superior tooth of M. sulcidens 

 described and figured by Cope 15 may possibly be a third inferior tooth. 



In the light of the previous meager knowledge of Mylodon harlani, 

 the Nebraska skull described by Brown 16 appeared entirely distinct. 

 The Rancho La Brea collection, however, has demonstrated a surpris- 

 ingly wide range of skull and dental variations. The characters noted 

 by Brown in the skull and dentition of the Nebraska Mylodon are 

 now seen to lie within the range of variation exhibited by the skull 

 series of Mylodon harlani from the asphalt deposits. Some of the 

 more salient features of the Nebraska specimen, as the absence of the 

 first tooth on each side of the palate and the trilobate outline of the 

 last inferior tooth may occur, also, in Mylodon harlani. There appears 

 at present to be no single character or group of characters constant 

 enough to warrant a subspecific separation of Brown's specimen. 

 Possibly the Nebraska skull represents a female individual. 



The ground-sloth recorded from near Walsenburg, Colorado, by 

 Cockerell 17 does not differ essentially from the Rancho La Brea forms, 



" Cope, E. D., op. ext., pi. 10, fig. lc, 1895. 



is Cope, E. D., op. cit., pp. 460-462, pi. 1.0, fig. 3, pi. 11, figs. 5 and 6, 1895. 

 i4 Cope, E. D., op. cit., p. 463, 1895. 



is Cope, E. D., op. cit., p. 463, pi. 11, figs. 7, la and 7b, 1895. 



is Brown, B., A New Genus of Ground Sloth from the Pleistocene of Nebraska, 

 Bull. Amer. Mus. Nat. Hist., vol. 29, pp. 569-583, pis. 50-51, 1903. 



i7 Cockerell, T. D. A., A Fossil Ground-Sloth in Colorado, Univ. Colo. Studies, 

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



