112 



University of California Publications. [Geology 



In Isurus planus and Isurus tumulus, the base of the tooth is 

 much broader, at least two-thirds the height of even the largest 

 teeth. 



Three other teeth of this species are from a point three miles 

 west of Coalinga, in Fresno County. These are from rocks of 

 the San Pablo formation, in the Pliocene. It is barely possible 

 that these teeth are median teeth from the jaws of Isurus tumu- 

 lus, but at any rate it seems best to give them a distinctive name. 



The species is named for Dr. James Perrin Smith, palaeon- 

 tologist of Stanford University. 



16. Isurus dcsorii (Agassiz)?? 



Another species of this type is represented by a single speci- 

 men in the sandstone of the Chico formation of the Upper Creta- 

 ceous. It is long and slender, flexuous, without basal denticles. 

 The base seems to be narrower. We cannot distinguish the speci- 

 men from Isurus smithii, though it is found in a much older for- 

 mation. It much resembles Isurus desorii (Agassiz) of the Euro- 

 pean Cretaceous, with which it may be provisionally and very 

 doubtfully identified. 



Genus Carcharodon Andrew Smith. 



17. Carcliarodon rectus Agassiz. 



(Agassiz, 1. c. p. 274; Ocoya Creek.) 



Agassiz separates this species from Carcharodon angustidens 

 by the absence of "accessory points on each side at base." 

 Carcharodon angustidens belongs to a different section of the 

 genus, differing from Carcliarodon by the presence of basal den- 

 ticles, as Lamna differs from Isurus. Among our many speci- 

 mens of Carcharodon I find none identifiable as Carcharodon 

 rectus. The nearest is the specimen from Oil City, called below 

 Carcharodon branneri. The figure of C. rectus shows a tooth 

 about two inches high, rather narrowly triangular and flat, with 

 a serrated protuberance on each side at base corresponding to a 

 lateral denticle. The tip of the tooth is entire. The serrations 

 are small, close-set, about fifty on each side, besides about eight on 

 each lateral denticle. The edge of the tooth is straighter than in 



