326 L UNG-FISHES. 



mouth, after the manner of the higher Vertebrates. The membrane-bones covering 

 the roof of the skull, which are very few in number, cannot be correlated with 

 those of the bony fishes ; their mode of arrangement being shown in the accom- 

 panying figure. The lung-fishes are at the present day represented only by three 

 genera, with but very few species, but they were formerly a very numerous group, 

 which appears to have been on the wane since a very early epoch. 



The Existing Lung-Fishes. — Family Lepidosirenid^e. 



The three existing genera of lung-fishes may be taken as the typical repre- 

 sentatives of an order including several extinct families, and known as the 

 Sirenoidea. Its essential characters are that the head is covered with membrane- 

 bones ; that the main dentition takes the form of large grinding plates, situated on 







upper palatal teeth OP AN extinct lung-fish (Ceratodus). (From Teller.) 



the pterygoid bones in the upper, and on the splenials in the lower jaw ; that the 

 body is covered externally with overlapping scales ; that the notochord persists 

 throughout life ; that the paired fins are of the fringed type ; and that none of the 

 fins are armed with spines. The existing forms have but few membrane-bones to 

 the skull; no premaxillse, maxillae, marginal teeth, or jugular plates; a fringed 

 tail, furnished with a continuous vertical fin ; and cycloid scales. 



Australian For a great number of years there were known from the Triassic 



Lung-Fish, strata of various parts of Europe fish-teeth of the remarkable type 

 of the specimen represented in the accompanying figure ; and from the fancied 

 resemblance to a deer's antler, presented by these teeth, the name of Ceratodus was 

 suggested for the otherwise unknown fishes to which they pertained. Similar 

 teeth were subsequently obtained from Secondary rocks in India and also in South 

 Africa, but it was not until the year 1870 that a fish was discovered in Queensland 

 having teeth of a similar type. Known to the natives, in common with other large 

 fresh- water species, by the name of barramundi, the Australian lung-fish (C.forsteri) 

 agrees so closely with the extinct forms that it is usually regarded as generically 

 identical. Its mouth is furnished in front with a pair, of chisel-like teeth situated 

 on the vomers, behind which come a pair of palatal teeth of the type of the one 

 shown in the figure, but carrying six complete ridges, and an incomplete seventh ; 



