Eastman: Dipterus Remains from Colorado. 283 



The recent discovery of Diptcrine remains in the San Juan country 

 happily simplifies the problem, and appears to prove that the line of 

 communication between the Appalachian and Cordilleran regions 

 during late Devonian times was actually by way of the Ohioan and 

 Dakotan seas; also that interchange took place between the faunas 

 of the Elbert formation and the so-called State Quarry beds of Iowa 

 toward the close of the Devonian. 



Figs. 1-4. Dipnoan dental plates from the Upper Devonian of Colorado. 

 I, Synthetodont type of crushing plate. 2, Dipterus digilatus Eastm. 3, Dipterus 

 mordax juv. Eastm. 3, Dipterus pectinatus Eastm. (All figures natural size.) 



It is of some further interest to recall in this connection that the 

 earliest reported occurrence of Dipterine remains in this country is 

 that of a dental plate of Dipterus itself in the Columbus limestone of 

 Ohio,^" and that the only Elasmobranch species thus far described from 

 the Colorado Devonian (Cladodus formosus Hay) bears a not alto- 

 gether remote resemblance to C. concinniis from the Huron shale of 

 Ohio. 



'» Bull. 10, 4th Series, Geol. Survey Ohio, 1909, p. 196, pi. xvii. figs. 14-17- 



