18 



LEPIDOSIKEMD.E. 



DIPNEUSTI. 



LEPIDOSIRENID^. 



Aberrant Fishes, connected with the early Orossopterygians through a number of 

 forms of which the living Neoceratodus is a survivor. Breathing by both gills and 

 lungs, the latter being a modification of the paired air-bladder characteristic of the 

 preceding family. Nostrils situated under the upper lip and concealed when the 

 mouth is closed. True clavicles present, as in the Orossopterygians, but concealed 

 under the skin. No vertebral centra, notochord persistent throughout life. Limbs 

 consisting of a slender segmented axis with or without a unilateral fringe. No distinct 

 caudal fin. Dentition very remarkable, consisting of sharp ridges of dentine covered 

 with enamel and continuous with the vomerine, palatopterygoid, and splenial bones. 

 Heart with a conus arteriosus with several rows of valves ; intestine with a spiral 

 valve. Lungs paired, elongate, attenuate posteriorly. Young undergoing a larval 

 metamorphosis, the larva with cutaneous external gills and a holder or cement-organ 

 on the gular region. 



Africa and South America. 



Pig. 6. 



■ Upper and lower teeth of Protojpterus mthiopicus. 



For the most recent views on the relationships of these fishes and their nearest 

 allies, the reader is referred to L. Dollo's brilliant memoir, " Sur la Phylogenie des 

 Dipneustes," in Mem. Soc. Beige Geol. ix. 1895, p. 79. 



