By reason of this persistency, the typical form of
such a kind might be called a "persistent type," in contradistinction
to those types which have appeared for but a short time in the course of
the world's history. Examples of these persistent types are abundant
enough in both the vegetable and the animal kingdoms. The oldest group
of plants with which we are well acquainted is that of whose remains
coal is constituted; and as far as they can be identified, the
carboniferous plants are ferns, or club-mosses, or Coniferae, in many
cases generically identical with those now living!
Among animals, instances of the same kind may be found in every
sub-kingdom. The 'Globigerina' of the Atlantic soundings is identical
with that which occurs in the chalk; and the casts of lower silurian
'Foraminifera', which Ehrenberg has recently described, seem to
indicate the existence at that remote period of forms singularly like
those which now exist. Among the corals, the palaeozoic 'Tabulata' are
constructed on precisely the same type as the modern millepores; and if
we turn to molluscs, the most competent malacologists fail to discover
any generic distinction between the 'Craniae', 'Lingulae' and
'Discinae' of the silurian rocks and those which now live. Our
existing 'Nautilus' has its representative species in every great
formation, from the oldest to the newest; and 'Loligo', the squid of
modern seas, appears in the lias, or at the bottom of the mesozoic
series, in a form, at most, specifically different from its living
congeners.
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