Plate V. 



EXAMPLES OF PTYCTODONT DENTITION FROM VA- 

 RIOUS DEVONIAN LOCALITIES. 



All figures reduced a trifle less than natural size. 



Originals preserved in the Museum of Comparative Zoology. 



Figs. 1-17. Ptyctodus calceolus Newb. and Worthen. State 

 Quarry beds (Upper Devonian) ; Johnson county, Iowa. The 

 distinction between upper and lower dental plates is apparent 

 from the configuration of the syniphysial portion, a prominent 

 beak and obtuse descending process being developed in the lower, 

 and the corresponding region of the superior being gently 

 rounded. The lower beaks are preserved in the originals of 

 Figs. 1, 5-9, 16, the last being a nearly complete specimen. 

 Page 133 



Figs. 18-27. Ptyctodus compressus Eastman. State Quarry 

 beds (Upper Devonian) ; Johnson county, Iowa. Syniphysial 

 beaks of the lower dentition well shown in Figs. 23-27. Page . 135 



Figs 28-30. Ptyctodus molaris Eastman. Middle Devonian; 

 Eifel District, Rhenish Prussia. The holotype, shown in Fig. 

 28, is a nearly perfect example of the lower dental plate, and 

 shows traces of sutural attachment with its fellow of the oppo- 

 site side. 



Figs. 31-34. Ptyctodus panderi Eastman. Middle Devonian; 

 Eifel District, Rhenish Prussia. Figs. 31, 32 show collectively 

 the greater portion of the Rhynchodus-like inferior dental plate, 

 the oral surface of which, however, displays punctate tritoral 

 areas. Detached examples of the tritors are shown in Figs. 

 33, 34. 



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