ORDERS CHIMEROIDEI AND DIPNOI. 



957 



former ; and it is also recorded from strata in Illinois and Texas 

 which are correlated with the European Permian. 



As members of this order, but perhaps indicating one or more dis- 

 tinct familes, we may class the following genera : Palcedaphiis^ from 

 the Devonian of Europe and Ohio (the species from the latter area 

 having been separated as Ife/iodus), is a moderately large form in 

 which the mandibular teeth (fig. 885, 4) are very broad, and carry 



Fig. 885. — 1, Upper and lower jaws of Difiterus Valenciennesi; from the Devonian. xx, 

 Palatal ; xxx, Mandibular teeth ; n, n, Narial processes ; g, Palatopterygoid. 2, Palate of 

 Ctenodus tuberculatus ; Carboniferous. 3, Mandible of Ctenodus imbricatus ; Carboniferous. 

 4, Mandible of P al&daphus insignis ; Devonian. All reduced. 



only four low ridges. Holodus, from the Devonian of Russia, is a 

 smaller form very imperfectly known, but apparently allied to the 

 preceding ; while Conchodus is known by teeth from the same de- 

 posits in both Scotland and Russia. Ganorhynchus, of which the 

 horizon is unknown, may also be provisionally placed here. From 

 North America we have Ptyonodus and Gnathorhiza from the Per- 

 mian, and Mylostoma from the Devonian, of which the full affinities 

 require further elucidation. 



