1 8 University of Texas Bulletin 



Paralegoceras inceirtuin, n. sp. 



Agathiceras Frechi, n. sp. 



Marathonites vidriensis, n. sp. 



Manathonites sulcatus, n. sp. 



Marathonites, J. P. Smithi, n. g. n. sp. 



Vidrioceras Uddeni, n. g. n. sp. 



Vidrioceras irregulare, n. sp. 

 Hess formation: 



Prothalassoceras Welleri, n. g. n. sp. 



Marathonites Hargisi, n. sp. 

 Leonard formation: 



Medlicottia Whitneyi, n. sp. 



Gastrioceras altudense, n. sp. 



Perrinites vidriensis, n. g. n. sp. 



Perrinites compressus, n. sp. 



Paralecanites altudensis, n. sp. 

 Word formation: 



Medlicottia Burckhardti, n. sp. 



Gastrioceras roadense, n. sp. 



Gastrioceras sp. nov. indet. 



Paraceltites multicostatus, n. sp. 



Paraceltites aff. elegans Girty. 



Agathiceras Girtyi, n. sp. 



Adrianites marathonensis, n. sp. 



Stacheoceras Bowmani, n. sp. 



Staeheoceras gilliamense, n. sp. 



Waagenoeeras Dieneri, n. sp. 



This list demonstrates that the formations distinguished here are 

 real paleontological zones; not one species passes from one forma- 

 tion to the other and there are even very few genera which occur in 

 several of our subdivisions. 



Every one of our formations is characterized by the great develop- 

 ment of some genera and this permits us to establish stratigraphical 

 zones which may be used instead of the meaningless local geographi- 

 cal names whenever a comparison with beds of other localities can 

 be made. We can thus establish the following four zones : 



Zone of Waagenoceras=Word formation. 

 Zone of Perrinites=Leonard formation. 

 Zone of Prothalassoceras=Hess formation. 

 Zone of Uddenites^Wolfoamp formation. 



