62 PISCES. 



composed. One family, indeed, the Uronemidae, is characterized 

 by a patch of separate denticles on the bones which ordinarily 

 bear the grinding plates ; but it is as yet represented only by 

 one genus (Uronemus} from the Calciferous Sandstones and 

 Carboniferous Limestone of Scotland, and perhaps by one other 

 (Conchopoma) from the Lower Permian of Germany. 



Uronemus. The cranial roof-bones are arranged as in Dipterus (fig. 

 48). The anterior part of the palato-pterygoid bone on each side is 

 broad and flat and covered merely by small rounded tubercles, while 

 along its outer margin there is one row of laterally compressed, basal ly 

 confluent, short conical teeth. The median fin is continuous, not sub- 

 divided even in the anal region. The trunk is covered with very thin 

 cycloidal scales of moderate size. U. lobatus, the typical species, attains 

 a length of about O2 m. 



The Permian genus Conchopoma, which also seems to be 

 Dipnoan, resembles Uronemus in the non-fusion of the dental 

 tubercles and in the continuity of the median fin, but its scales 

 are smaller. The type species is C. gadiforme from the Lower 

 Permian of Rhenish Prussia. 



FIG. 49. 



Dipterus valenciennesi ; restoration by E. H. Traquair, one-fifth nat. size. 

 L. Old Bed Sandstone ; N. Scotland. 



The most characteristic Palaeozoic family of Dipnoi, however, 

 is that of the Ctenodontidae, in which the cranial roof-bones 

 are small and numerous, the dental plates complete, the median 

 fijis more or less subdivided, and the scales cycloidal. The 

 earliest genus is Dipterus and the latest Sagenodus, while 

 Phaneropleuron, Scaumenacia, and Ctenodus are also tolerably 

 well known. The endoskeletal supports of a dismembered 

 median fin have hitherto been observed only in the anal fin of 

 Scaumenacia. Here they are distinctly crowded, while at least 

 three basal elements are fused together (fig. 20, p. 22). 



