170 University of California Publications in Geology [Vol. 10 



Coll. Palae., for example, the first tooth, present only on the right 

 side, was very diminutive. It is therefore not improbable that in some 

 skulls the development of the first tooth may have been completely 

 arrested. 



As already stated, there are no mandibles directly associated with 

 nos. 642, 643, and 646. A fragmentary lower jaw does, however, 

 accompany no. 695, in which the fourth lower tooth is well preserved. 

 This tooth is relatively as much elongated anteroposteriorly as that 

 in the Nebraska specimen. It agrees also with Brown's specimen in 

 the direction of the anterior and posterior lobes with reference to the 

 long axis of the tooth-row. The anterior lobe has the usual oblique 

 position with reference to that axis. The posterior lobe is placed trans- 

 versely to the long axis of the tooth-row, in which respect the tooth 

 not only agrees with M T of the Nebraska skull, but with corresponding 

 teeth belonging to broader skulls from Rancho La Brea. The isthmus 

 connecting the anterior and posterior lobes is broadly convex on its 

 outer side, thus differing decidedly from the Nebraska specimen, in 

 which a pronounced external fold is developed. In no. 696, a skull of 

 the broad type, the external fold, or middle lobe, of the fourth inferior 

 tooth is much more distinctly developed than in no. 695, although 

 much less so than in no. 21156 Univ. Calif. Coll. Palae. The latter 

 specimen approximates most closely the type of fourth inferior tooth 

 seen in the Nebraska skull. An examination of twenty or more lower 

 jaws in the Museum of History, Science and Art of Los Angeles, in 

 various stages of completeness, failed to reveal a fourth lower tooth 

 showing exactly the same stage of development as in the Nebraska 

 specimen. 



It may perhaps be urged that in no. 695 the abnormality shown 

 by the presence of an extra tooth may have extended itself to the 

 dentition as a whole, and thus invalidate any conclusion which may 

 be drawn from a study of the fourth inferior tooth. The first inferior 

 tooth in no. 695 appears to be more compressed anteroposteriorly, 

 giving a subcircular rather than an oval or reniform section, which 

 is the usual type in Rancho La Brea skulls. The remaining lower 

 teeth show no characteristics which are not to be seen in other skulls, 

 and apparently have developed normally. 



Further modifications of the fourth inferior tooth, remarkable for 

 its variability, may be noted. The anterior lobe of the tooth may be 

 narrow oi' broad. It may have the usual, transverse position with 

 reference to the long axis of the tooth-row as in no. 696 for example, 



