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384 University of California Publications. [Geology 



and more acute than those of the posterior teeth. Several of 

 the middle teeth represented in figure one have been truncated 

 by wear, but the crowns seem to present transition forms rang- 

 ing between the quite different types at the two ends of the 

 series. In nearly all of the teeth there is a distinctly constricted 

 neck region at the base of the crown. 



In the superior dentition, one row of teeth contains only a 

 single complete crown, the most posterior one (pi. 40, fig. 2). 

 The crown of this tooth is gently domed, and is compressed lat- 

 erally. The bases of several crowns anterior to the complete 

 tooth in this row show a rapid decrease in the size of the teeth 

 anteriorly, with a change in the form of the crowns from a 

 laterally flattened cross-section in the posterior ones to a nearly 

 circular section in the most anterior one. In the other superior 

 row, the few imperfectly represented tooth crowns are of the 

 smaller form with nearly circular cross-section, corresponding 

 to the anterior crowns of the superior series described above. 



The dentition of specimen 9853 represents four posterior 

 teeth in the upper, and four in the lower jaws (fig. 2). The 

 most posterior tooth present on the maxillary is situated only a 

 short distance in front of the anterior border of the orbit. 



The four teeth on the mandible are of nearly the same size. 

 The crowns are low, laterally-compressed domes, on which the 

 anteroposterior diameter considerably exceeds the height of the 

 crown from the base of the enamel to the summit. The sum- 

 mits of the crowns may show distinct radial furrows. The 

 heavy, laterally-compressed roots show a marked infolded or 

 furrowed structure of the lateral walls. The four teeth are 

 rather closely set in the jaw, but seem to be in pits. 



The teeth of the upper jaw are less closely set than those on 

 the dentary, and other teeth may originally have been present 

 in some of the interspaces. The most posterior tooth resembles 

 the two opposing teeth of the lower series. The second tooth 

 from the back of the series is considerably shorter anteroposte- 

 riorly than the last, but retains approximately the same trans- 

 verse diameter. The anterior pair of teeth are still shorter 

 anteroposteriorly. In the most anterior tooth the cross-section 

 shows only a slight lateral compression. The crowns of the 



