Subclass Dipneusti, or Lung-fishes 6 1 3 



In these the jugular plate is present, as in Uronemus. Dipterus 

 valenciennesi is the best-known European species. Dipterus 

 nelsoni and numerous other species are found in the Chemung 

 and other groups of Devonian rocks in America. 



In the CtenodontidcB the tail is diphycercal, and no jugular 

 plates are present in the known specimens. In Ctenodus and 

 Sagenodus there is no jugular plate and there are no marginal 

 teeth. The numerous species of Ctenodus and Sagenodus belong 



Fig. 383. — Phaneropleuron andersoni 'H.uxley; restored; Devonian. (After Dean.) 



chiefly to the Carboniferous age. Ctenodus wagneri is found in 

 the Cleveland shale of the Ohio Devonian. Sagenodus occiden- 

 talis, one of the many American species, belongs to the coal- 

 measures of Illinois. 



As regards the succession of the Dipneusti, Dr. Dollo re- 

 gards Dipterus as the most primitive, Scaumenacia, Uronemus, 

 Ctenodus, Ceratodus, Protopterus, and Lepidosiren following 

 in order. The last-named genus he thinks marks the terminus 

 ■ of the group, neither Ganoids nor Amphibians being derived 

 from any Dipnoans. 



Order Sirenoidei. — The living families of Dipneusti differ 

 from these extinct types in having the cranial roof-bones re- 

 duced in number. There are no jugular plates and no marginal 

 teeth in the jaws. The tail is diphycercal in all, ending in a 

 long point, and the body is covered with cycloid scales. To 

 these forms the name Sirenoidei was applied by Johannes 

 Muller. 



Family Ceratodontidae. — The CeratodontidcB have the teeth 

 above and below developed as triangular plates, set obliquely 

 each with several cusps on the outer margin. Nearly all the 

 species, representing the genera Ceratodus, Gosfordia, and Con- 

 chopoma, are now extinct, the single genus Neoceratodus still 

 existing in Australian rivers. Numerous fragments of Cera- 

 todus are fovmd in Mesozoic rocks in Europe, Colorado, and 



