332 University of California Publications in Geology [Vol. 8 



and is no doubt specifically identical with them. The writer agrees 

 with Allen's determination of the Walsenburg specimen as M. harlani. 



The Colorado skull described by Cockered exceeds in length the 

 largest specimen in the Rancho La Brea series by 27 mm. and is, 

 therefore, the largest skull of M. harlani yet reported. This extensive 

 elongation may account for the greater distance between the last 

 alveolus and the postpalatine notch than in Brown's specimen, though 

 the distance does not appear to depend entirely on the elongation of 

 the skull. The pterygoids in the Rancho La Bi'ea skulls are normally 

 as prominent as in Brown's specimen and are possibly broken in the 

 Colorado skull. 



Although the skull of Mylodon garmani as described by Allen 18 

 is apparently distinct from the Rancho La Brea series, certain of its 

 characters are closely approached in specimens from the asphalt beds. 

 M. garmani differs principally in the extremely narrowed cranial por- 

 tion of the skull and in the antero-posterior elongation of the last 

 inferior tooth. The depth of the mandible below the front teeth and 

 the height of the anterior end of the symphysis are characters equally 

 marked in no. 21576 of the Rancho La Brea skulls. The greatest pre- 

 dental width across the symphysis of the lower jaw in M . harlani may 

 be less than that in M. garmani or may exceed the measurement in 

 that species. In general the fourth superior tooth in skulls from 

 Rancho La Brea is not as much compressed antero-posteriorly as in 

 M. garmani. The configuration of the last superior tooth may, how- 

 ever, be very closely, if not exactly approached in one (no. 21172) 

 of the skulls of M. harlani. From the great amount of variation shown 

 in the dentition of the mylodont sloths from the asphalt deposits, it 

 appears unsafe to base primary specific differences on the size or 

 form of the teeth. 



The Rancho La Brea skulls are generally larger and relatively 

 more slender than the South American species, Mylodon robustus, 

 described by Owen. 19 . In the South American species the muzzle 

 reaches its greatest width at the anterior end of the skull, while in 

 M. harlani the muzzle widens at about the middle and narrows again 

 at the anterior end. Posteriorly the supra-orbital region widens more 



is Allen, G. M., A New Mylodon, Mem. Mus. Comp. Zool. Harv. Coll., vol. 40, 

 pp. 319-346, 4 pis., 1913. 



is Owen, E., Description of the Skeleton of an Extinct Gigantic Sloth, Mylodon 

 robustus, Owen, with Observations on the Osteology, Natural Affinities, and 

 Probable Habits of the Megatherioid Quadrupeds in General (London), 4 to., 

 176 pp., 24 pis., 1842. 



