49 



Tvhen inhabiting clear waters the fish probably breathes by them 

 alone, the true lungs only coming into action when on the mud 

 flats, or living in turbid waters. The shape of the body, the 

 number, position, and structure of the fins, the elements of the 

 internal skeleton, and above all the co-existence of a lung with 

 gills, show how close is the affinity between the Australian Ceratodus 

 and the mud fishes of Africa and South America, and although the 

 former approach less to the amphibian type than the latter, it is 

 obvious that in a natural classification their place is side by side. 



Fossil Affinities of the Dipnoi. 



Having shown the close connection between the two genera 

 of living dipnoids, let us now consider the relations of the living 

 and fossil Ceratodonts. No remains of this genus have as yet been 

 found in the Tertiary or Cretaceous formations, but the fossil teeth, 

 of which several varieties are recognisable, possibly the relics of 

 numerous species, occur abundantly in the Triassic beds of Aust 

 Cliff", near Bristol, and in the Muschelkalk of Germany. They 

 have also been obtained from strata now determined to be of 

 Triassic age at Maledi, South of Nagpur, in India, and associated, 

 as in Europe, with the reptihan remains Ilyperodapedon. 



Many of these fossil teeth are much larger than those of the 

 existing species (specimens of one Triassic form measure over two 

 inches in length), and must necessarily have belonged to 

 individuals of a gigantic race. The dental plates only have been 

 found fossil, but the structure of Ceratodus Fosterl indicates that 

 they alone of a like constructed animal would be susceptible of 

 preservation in sedimentary strata, and the classification of the 

 xecent forms with those of the Mesozoic rocks, separated by so 

 wide a gulf of geological time, though founded on the similarity of 

 dentition alone, is the only reasonable one, as there is no evidence 

 that the hving and fossil Ceratodonts, difi"ered from each other. 

 The teeth of this genus resemble in general shape and structuie 

 those of Ctenodiis which are widely distributed in Carboniferous 



