DEVONIC FISHES OF THE NEW YORK FORMATIONS 



95 



stem, only the more generalized descendants of the latter having survived 

 until the present day. 



5 The primordial stock must have been autostylic, diphycercal, without 

 a maxillary arch and dentigerous dentary elements, and with a Uronemus- 

 like or Dipteruslike dentition ; characters which do not permit us to ascribe 

 the ultimate origin of Dipnoans to the Crossopterygii, but suggest rather a 

 descent from Pleuracanthid sharks. 



6 The recognition of Arthrodires as an order of armored Dipneusti 

 precludes their association with Ostracophores in any sense whatever. The 

 recently revived group of " Placodermata " is, therefore, an unnatural 

 assemblage, and should be abandoned. 



7 In the light of present information, the progressive modifications 

 amongst early Dipnoans may be represented after some such scheme as 



follows : 



Neoceratodus 



Ceratodus 



Ctenodtis 



Uronemus 



Phaneropleuron 



Scaumenacia 



Dipterus 



Titanichthys 

 Coccostens, Dinichthys 

 Afylostoma, Dinomylostoma 

 Homosteus 



Macropetalichthys 



Primitive Ceratodonts 



It would be superfluous to present here a fresh demonstration of the 

 close structural agreement between Arthrodires and Ceratodonts. One 



