PALEONTOLOGY ZORRITOS FORMATION 29 



species from the Cercado formation, of Burdigalian age, and 

 8 with Chipolan species. The remaining Burdigalian affin- 

 ities are scattered as shown by the table. 



Thirteen species either occur at Bowden or have close 

 relatives there. The latest opinion, based on unpublished 

 studies by Dr. W. P. Woodring, of the United States Nat- 

 ional Museum, is that the Bowden beds are Helvetian in 

 age ; however, most of the Bowden forms related to species 

 from Zorritos are of clearly older affinities, and the Zorritos 

 fauna contains few species closely related to that more 

 modern element in the Bowden fauna which indicates its 

 place in a higher stage. 



The species which occur elsewhere may be tabulated as 

 follows : 



Gatun 5 



Santo Domingo (Cercado) 3 



Santo Domingo (Gabb) 2 



Bowden 5 



Atlantic Miocene 2 



Chipola Marl I 



European Oligocene i 



The geologic discussion of the fauna will conclude with a 

 brief consideration of each of the constituent four groups. 



Upper Zorritos Fauna: The proportions of the Helvetien 

 and Burdigalien elements in the Upper Zorritos fauna have 

 already been discussed in general. Exact tabulation of rela- 

 tionships will be found in Plates 2, 3, and 4; it will suffice 

 to say here, statistically, that in the large Burdigalien 

 element represents about half of the total fauna, with the 

 Helvetien and Tortonien aggregating somewhat less than 

 a third. The Helvetien element is so characteristic and 

 profuse, however, that the numerical expression fails to por- 

 tray the situation fully. Although present evidence demands 

 consideration of the fauna as Burdigalian along with the 

 Variegated and Lower Zorritos, there is no doubt that it 



