958 A. W. GRABAU THE TULLY LIMESTONE 



occurred was the same as that which permitted the interdispersal of the 

 Traverse and the Mid-Devonic European faunas, as well as the Upper 

 Devonic coral and Brachiopod fauna of Europe and the lowan Upper 

 Devonic basin. But whether //. cuhoides is a derivative of the American 

 H. intermedia, from which H. venustula was also derived, and b}^ west- 

 ward migration reached Asia and Europe in Upper Devonic time, or 

 whether our species are immigrants from Europe is not easy to determine. 

 The fact that the European varieties are frequently characterized by a 

 high antero-median extension, whereas the west American species are less 

 specialized in that respect, lends some support to the interpretation that 

 migration was westward, and that tlie Cuboides type originated in Amer- 

 ican waters in Hamilton (Traverse) time. 



