CLA SSIFICA TION OF VER TEBRA TA 1 1 



2. Sub-CLASS DIPNOI, Mueller 



With gills and lungs. Heart trilocular, with mixed blood. 



Nasal ducts lead into the mouth-cavity. 



With archipterygium, no mixipterygium. Tectobranch. 



Conus with numerous series of valves. Membrane bones. 



Teeth and the acentrous but potentially chordocentrous 

 vertebral column much resembling Holocephalous conditions; 

 the same applies to the holostylic arrangement. Spiral valve. 



1. Order Arthrodira, Smith Woodward. Strong dermal 

 armour, also on the ventral side. 



Paired fins vestigial or absent. 

 With maxilla and premaxilla, which are toothless. 

 Teeth on mandible and palatal region. 

 Coccosteus. Lower Old Ked, Scotland. 



Dinichthys. 1 T ~ , . ~,. 



rr-i. i,i f Lower Carboniferous, Ohio. 

 Titamchthys.J 



2. Order Sirenoidei. Dermal plates restricted to the 

 head. Trunk with imbricating scales, or " naked." 



Paired fins present, archipterygial. 



Dipterus. No distinct maxilla and premaxilla. Jugular 



plates. Cycloid scales. Old Eed, England ; Eussia. 

 Phaneropleuron. Upper Old Red, Scotland. 

 Ctenodus. Carboniferous, British. 

 Ceratodus. No distinct maxilla and premaxilla. No 



jugular plates. Cycloid scales. Ehaetic, England 



and Wuerttemberg ; Jurassic, Colorado ; Karroo, S. 



Africa. Eecent, Queensland and West Australia. 



Muschelkalk and Keuper, Europe. Trias, India. 

 Protopterus. Eecent, Africa. 

 Lepidosiren. Eecent, South America. 



