Some of these,
for which the name of _Onchus_ has been proposed, are in the form
of compressed, slightly-curved spines (fig. 75, A), which would
appear to be of the nature of the strong defensive spines implanted
in front of certain of the fins in many living fishes. Besides
these, have been found fragments of prickly skin or shagreen
(_Sphagodus_), along with minute cushion-shaped bodies (_Thelodus_,
fig. 75, B), which are doubtless the bony scales of some fish
resembling the modern Dog-fishes. As the above mentioned remains
belong to two distinct, and at the same time highly-organised,
groups of the fishes, it is hardly likely that we are really
presented here with the first examples of this great class. On
the contrary, whether the so-called "Conodonts" should prove
to be the teeth of fishes or not, we are justified in expecting
that unequivocal remains of this group of animals will still be
found in the Lower Silurian. It is interesting, also, to note
that the first appearance of fishes--the lowest class of vertebrate
animals--so far as known to us at present, does not take place
until after all the great sub-kingdoms of invertebrates have
been long in existence; and there is no reason for thinking that
future discoveries will materially affect the _relative_ order
of succession thus indicated.
LITERATURE.
Pages:
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217