HISTORICAL REVIEW 9 



In the first order was placed the Xenacanthida, including the Permian 

 Diacranodus and the Cladodontidcs. In the second order were placed all the 

 other families of the sharks. 



The Stegocephali was divided into the orders Ganocephali, with the families 

 Trimerorhachidee and Archegosauridce, the former without and the latter with 

 neural spines on the vertebrae; the Rhachitomi with a single family, the 

 Eryopida, in which is included the Labyrinthodontia; the Embolomeri, with 

 the single family Cricotidee; and the Microsauria with the families Branchio- 

 sauridee, Hylonomidce, Molgophidee, Phlegethontiidce. 



His synopsis of characters is as follows: 



"Subclass Stegocepkali. Basioccipital, supraoccipital, intercalare, and supra- 

 temporal bones present; propodial bones distinct. 

 a. One occipital articulation. 



Vertebral bodies represented by basal and lateral elements (inter- 

 centra and centra) Ganocephali 



aa. Two lateral occipital condyles. 



Vertebrae represented by distinct and incomplete intercentra and 



centra (pleurocentra); atlas segmented Rhachitomi 



Centra and intercentra complete, making two vertebral bodies to each 



neural arch Embolomeri 



No centra; intercentra each supporting a neural arch Microsauri" 



Smith-Woodward in the "Catalogue of Fossil Fishes in the British 

 Museum" (74) substituted Pleuracanthus for Cope's Didymodus. He gives: 



Subclass Elasmobranchii. 

 Order Selachii. 

 Family 



Genus Pleuracanthus. 

 Family Petalodontida. 

 Genus Janassa. 

 Genus Thoracodus. 



Subclass Dipnoi. 

 Order Sirenoidce. 



Family Lepidosirenidce. 



Genus Ceratodus. 

 Family Ctenodontidee. 



Genus Sagenodus (Ptyanodus). 



Subclass Teleostomi. 

 Order Crossopterygia. 

 Family Osteolepidce. 

 Genus Megalicthys {Ectosteorhachis). 



In the " Catalogue of the Fossil Reptilia and Amphibia of the British 

 Museum (N. H.), 1890," Lydekker (59) gives the following classification of 

 the Permian Amphibia from North America: 



