During Triassic and Jurassic Periods 207 



So In the evolution of the great families Pholidophorl- 

 dae, Oligopleurldae and Leptolepidae, a definite and easy 

 transition Is made, during the period from the upper Trias- 

 sic to the close of the Jurassic, from the ancient Proto- 

 spondylll or scaled ganoids to the great group of the Teleo- 

 stei that was destined gradually to displace all of the other 

 groups In individuals. In genera, In geographic distribution, 

 and In adaptive contrivances. 



