On a New Exogyra from Del Rio Clay 15 



higher horizons may not be intimately related, notwith- 

 standing the very similar shape, but rather be convergent 

 forms. 



A monograph of the Texas Cretaceous Exogyras would 

 probably show a still much greater variety of forms which 

 were derived from the same original tribe, and at the same 

 time it would not at all be difficult to demonstrate that in 

 Europe, Northern Africa and Asia quite a similar -evolution 

 has taken place. 



