Until recently, though the master-mind
of Agassiz recognised that these singular bodies were undoubtedly
the teeth of fishes, we were entirely ignorant as to their precise
relation to the animal, or as to the exact affinities of the fish
thus armed. Lately, however, there has been discovered in the
rivers of Queensland (Australia) a living species of _Ceratodus_
(_C. Fosteri_, fig. 147), with teeth precisely similar to those
of its Triassic predecessor; and we thus have become acquainted
with the use of these structures and the manner in which they
were implanted in the mouth. The palate carries two of these
plates, with their longer straight sides turned towards each
other, their sharply-sinuated sides turned outwards, and their
short straight sides or bases directed backwards. Two similar
plates in the lower jaw correspond to the upper, their undulated
surfaces fitting exactly to those of the opposite teeth. There
are also two sharp-edged front teeth, which are placed in the
front of the mouth in the upper jaw; but these have not been
recognised in the fossil specimens. The living _Ceratodus_ feeds
on vegetable matters, which are taken up or tom off from plants
by the sharp front teeth, and then partially crushed between
the undulated surfaces of the back teeth (Guenther); and there
need be little doubt but that the Triassic _Ceratodi_ followed
a similar mode of existence.
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