A PECULIAR MODIFICATION AMONGST PERMIAN 

 DIPXOANS. 



C. R. Eastman. 



than a dozen species, of which only three have been described 

 from the Permian of Texas. These are S. dialophus, S. pcriprion 



size. The presence of a fourth species, different from any 

 hitherto described, and displaying quite unusual modifications 

 amongst ceratodonts, is indicated by several well preserved 

 mandibular and palatine dental plates which have recently been 

 brought to light by Dr. E. C. Case, of the State Normal School 

 at Milwaukee, and kindly placed by him in the hands of the 

 writer for description. 



The present species occupies a unique position amongst fossil 

 dipnoans in having a dentition adapted for cutting instead of 

 crushing, thus paralleling the conditions found in certain 

 Palaeozoic sharks and in recent Gymnodonta. This divergence 

 is the more striking in view of the singularly uniform type of 

 dental system pervading lung-fishes throughout their entire 



correlated with the change from marine to brackish-water condi- 

 tions that took place during the Permian, with its very pronounced 

 effects upon the environment and food-supply, may perhaps be 

 plausibly conjectured. 



