Plate VI. 



EXAMPLES OF PTYCTODONT DENTITION FROM THE 

 IOWA UPPER DEVONIAN. 



All figures are of the natural size. 



A miscellaneous assortment of detached tritors, all more or 

 less worn by use, and otherwise rolled and abraded, this being 

 the usual condition in which remains of this sort are found in 

 the Old State Quarry beds near North Liberty, in Johnson 

 county, Iowa. The greater number of these tritors belong to 

 Ptyctodus calceolus Newb. and Worthen, and are shown of the 

 natural size. Originals in the Museum of Iowa State Univer- 

 sity. Page 133 



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