322 University of California Publications in Geology [Vol. 8 



CEANIUM 



In the following discussion the Raneho La Brea series of specimens 

 is shown to have a wide range of variation in the skull and dentition, 

 but is considered to represent a single species, Mylodon harlani 

 Owen. There appear to be no characters sufficiently important and 

 constant to necessitate the recognition of more than one form. A 

 subdivision of the group may, however, be necessary when the skeleton 

 is known in greater detail. 



Viewed from above the skulls are essentially similar to the specimen 

 described by Brown as Paramylodon nebrascensis (Amer. Mus. Nat. 

 Hist. Coll., no. 2780) and to the Colorado skull described by Cockered. 

 It differs from the South American Mylodon robustus in being gener- 

 ally larger and relatively more slender. None of the specimens 

 approach Mylodon garmani in the extreme narrowness of the brain- 

 case. The muzzle is somewhat inflated at the middle and narrows to 

 a greater or less extent anteriorly. In M. robustus the muzzle widens 

 from the region anterior to the malars to the front end of the skull. 

 The nasals are more or less constricted at the middle. The fronto- 

 nasal suture is usually V-shaped as in the Nebraska skull described 

 by Brown. In two skulls (no. 21172 and no. 21577) this suture has 

 in part almost disappeared. The nasal in these specimens has either 

 developed a secondary outgrowth posteriorly, which gives the element 

 a rectangular outline, or has united with a small portion of the frontal. 



The supraorbital region in the Raneho La Brea skulls does not 

 widen backward toward the postorbital processes as much as in M. 

 robustus, and in some specimens may be narrowed posteriorly. The 

 nearly flat, dorsal surface of the cranium is never as wide as in M. 

 robustus, or as narrow as in M. garmani. 



The supraoecipital may at first descend gently from the dorsal 

 plane of the skull toward the foramen magnum for about a third of 

 its length, continuing from this point downward with a steeper slope, 

 as in Brown's specimen, or it may descend directly from the dorsa] 

 plane to the foramen magnum without a noticeable change in slope. 

 As in P. nebrascensis and in the Colorado skull, the width of the 

 occiput in Raneho La Brea specimens is much greater than the height 

 and thus differs from M. garmani. 



The majority of the skulls agree with Brown's specimen and with 

 .1/. robustus in dorsal contour, though a few are more highly arched 

 in the mid-cranial region. The malar is generally found separate 



