DEVONIC FISHES OF THE NEW YORK FORMATIONS 121 



Opercular elements, which have been variously interpreted by different 

 writers. 



Finally, and this is the most important test of all, we have to consider 

 the dentition. A serious difficulty in the way of correlating the several 

 parts, and of understanding accounts of earlier writers, is removed the 

 moment we perceive that the suborbital plate has nothing whatever to do 

 with the dentition. Its identification in Coccosteus on the part of some 

 writers as a " superior maxillary " is not only erroneous, but misleading, 

 since it implies the development of a secondary upper jaw amongst Arthro- 

 dires, and a secondary upper jaw does not occur. The suborbital is simply 

 a cheek plate, and corresponds to the three nonfused ossicles forming the 

 lower border of the orbit in Neoceratodus. The dental elements of both 

 jaws are precisely alike in Coccosteus and Dinichthys, as regards number, 

 form and arrangement. The whole matter of the dentition can be summed 

 up by saying that Coccosteus and Dinichthys exhibit the same close paral- 

 lelism with Protopterus and Lepidosiren as is observed between Mylostoma 

 and Neoceratodus. Coccosteus and Dinichthys represent a modification of 

 Dipnoan dentition adapted for cutting, and closely corresponding modifica- 

 tions exist in the modern fauna. Mylostoma and Dinomylostoma adhere 

 to the ancestral type of crushing or triturating dentition, which has been 

 preserved essentially unchanged until the present day amongst the most 

 generalized descendants of the primordial stock. 



It will be seen that the foregoing interpretation is at variance with the 



one recently proposed by Jaekel in his paper of 1902, to which frequent 



reference has been made. The dental plates of Coccosteus are identified 



in that contribution as maxillae and premaxillae, and their arrangement is 



expressed graphically by means of a restoration, concerning which the 



author speaks as follows : 



Ich bemerke dazu, dass ich dieses Bild durch sorgfaltige Praparation 

 einer ganzen Anzahl von Exemplaren erzielt habe, und dass sich dasselbe 

 von dem Traquairschen Entwurf namentlich unterscheidet durch den 

 Nachweis der Maxillen und Praemaxillen, durch die abweichende Lage der 

 Nasenoffnungen und der unteren Rumpfpanzerelemente, den Nachweis 

 des Beckens und den Hinweis auf paarige Extremitaten. 



