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University of California Publications. 



[Geology 



as the lateral teeth of I. planus. The chief distinction rests in the 

 basal thickness of the crown of the tooth, measured from front to 

 back. None of these teeth show a strongly curved crown or a re- 

 entrant angle on the outer margin. There is no median ridge as 

 is seen in Isurus mantelli, a related species from the Cretaceous 

 of Europe. 



The following notes are on teeth from near Santa Ana : 

 These teeth are very large, the largest teeth being two inches 

 long. The crown is flexuous, curved backwards in the median 

 teeth, curved forward in the lateral ones. The root is heavy, little 



Fig. 11. Isurus tumulus (Agassiz). Miocene of Santa Ana, California. 



cordate below, its form varying in the different teeth. Some teeth 

 are knife-like, the crown not one-third higher than the breadth at 

 base, the form suggesting that of Isurus planus. Other teeth, 

 supposed to be median, are less flattened, and nearly half higher 

 than broad at base. All are erect or nearly so, with entire edges. 

 Some of the smaller teeth are more curved, and more acuminate. 



Some of the teeth from near Oil City are still larger, with 

 thicker base, but are otherwise similar. One large tooth with a 

 thick crown and heavy base is curved strongly outward, with a 

 knife-like margin. This is probably an outer tooth of the same 

 species, but no teeth quite like this are found in the living species 



