The _Echinoderms_ of the Devonian period call for little special
notice. Many of the Devonian limestones are "crinoidal;" and
the _Crinoids_ are the most abundant and widely-distributed
representatives of their class in the deposits of this period.
The _Cystideans_, with doubtful exceptions, have not been recognised
in the Devonian; and their place is taken by the allied group of
the "Pentremites," which will be further spoken of as occurring
in the Carboniferous rocks. On the other hand, the Star-fishes,
Brittle-stars, and Sea-urchins are all continued by types more
or less closely allied to those of the preceding Upper Silurian.
Of the remains of Ringed-worms (_Annelides_), the most numerous
and the most interesting are the calcareous envelopes of some
small tube-inhabiting species. No one who has visited the seaside
can have failed to notice the little spiral tubes of the existing
_Spirorbis_ growing attached to shells, or covering the fronds
of the commoner Sea weeds (especially _Fucus serratus_). These
tubes are inhabited by a small Annelide, and structures of a
similar character occur not uncommonly from the Upper Silurian
upwards. In the Devonian rocks, _Spirorbis_ is an extremely common
fossil, growing in hundreds attached to the outer surface of
corals and shells, and appearing in many specific forms (figs.
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