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University of California Publications. 



[Geology 



forms of the teeth, it is not easy to determine species in this 

 genus. 



This species is distinguished by the flatness and breadth of the 

 crown of its teeth. The inner edge of the tooth is quite flat, the 

 outer or front not much convex. We refer to Isurus planus, 

 about 200 specimens of various sizes, but all relatively short and 

 broad. These are from Barker Ranch, in Kern County, and from 

 near Oil City. Some are nearly erect, and narrowly triangular. 



Fig. 9. Isurus planus (Agassiz). Miocene of Kern County, California. 



Some which we suppose to be outer teeth are very much more 

 curved, and have a marked reentrant angle. These would seem 

 at first sight to indicate a distinct species, but we are convinced 

 that both straight and hooked teeth came from the same shark. 

 The root in Isurus planus is very broad, and its basal margin is 

 but little curved, usually not crescent-shaped. The largest teeth 

 of this type are one and one-half to two inches in length. The 

 largest specimen of all, two and one-fifth inches high, was ob- 



