LUNG-FISHES. 151 



Nothing more was discovered as to the nature of this j^rob- 

 lematical fish, and it was even doubtful in what position 

 tliese teeth were placed in tlie mouth, or how many of 

 them there were in each jaw. Tlius matters stood till 

 some twenty years ago, when naturalists were startled by 

 hearing that a large fish had been discovered hving in the 

 rivers of Queensland, having teeth like these pi-oblem- 

 atical fossils. This fish was no other than the Australian 

 lung-fish, which, as we have seen, is one of the few living 

 species still retaining the ancient fringed fins. It was 

 found that this fish had one tooth on either side of each 

 jaw, placed in the same jjosition as the figured example ; 

 and it was naturally considered that the living fish belonged 

 to the same genus as the Ceratodus of the Trias. Here, 

 then, we are confronted by the remarkable circumstance 

 that a kind of fish, first made known to us by fossil teeth 

 from the very lowest Secondary strata of Europe, was 

 actually represented by one apparently belonging to the 

 same genus in the rivers of Australia. It is true, indeed, 

 that a recent discovery has shown us that the living lung- 

 fish differs slightly in the structure of its skull from the 

 fossil Ceratodus, and that the teeth of the opjjosite sides 

 of the jaws were not in actual contact with one another, 

 as were those of the latter. Although these points of 

 difference are considered sufiicient to warrant us in regard- 

 ing the living fish as not actually belonging to the same 

 genus as the fossil teeth, yet this does not detract from 

 the extreme interest of the former as being by far the 

 oldest type of back-boned animal now living. This type 

 of fish is, indeed, thus j^roved to have endured throughout 

 the whole of the immense ijeriod during which the entire 

 series of Secondary and Tei-tiary rocks were deposited. 

 And when we reflect that the Secondary rocks include 

 those enormous accumulations of strata known as the trias, 

 lias, oolites, greensands, and chalk, while the Tertiary 

 comprises the threefold divisions termed Eocene, Miocene, 

 and Pliocene, we can scarcely fail to be almost lost in 

 wonder at the prodigious length of time during which 

 lung-fishes have existed, with but comparatively slight 

 structural modification. The fossil lung-fishes occur in the 



