CHORD AT A. 161 



Order 5. Dipnoi, mud fishes ; lead on to the Amphibians. With per- 

 sistent notochord, paired limbs supported by a central jointed axis, 

 branchial and pulmonary respiration, muscular conus arteriosus, spiral 

 valve to the intestine, and a cloaca. 



Monopneumona, with a single lung ; Trias to recent. Cera- 

 todus Forsteri, Queensland. 



Dipneumona, paired lungs. Protopterus annectens, W. Africa 

 (with three pairs of branched external gills). Lepidosiren paradoxa, 

 Brazil. 



