Remains of these
last-mentioned organisms are extremely abundant in some of the
limestones of the formation, such as the "Coral-rag" and the
Great Oolite; and the former of these may fairly be considered
as an ancient "reef." The _Rugose Corals_ have not hitherto been
detected in the Jurassic rocks; and the "_Tabulate Corals_,"
so-called, are represented only by examples of the modern genus
_Millepora_. With this exception, all the Jurassic Corals belong
to the great group which predominates in recent seas (_Zoantharia
sclerodermata_); and the majority belong to the important
reef-building family of the "Star-corals" (_Astroeidoe_). The
form here figured (_Thecosmilia annularis_, fig. 161) is one
of the characteristic species of the Coral-rag.
[Illustration: Fig. 161.--_Thecosmilia annularis_, Coral-rag,
England.]
[Illustration: Fig. 162.--_Pentacrinus fasciculos_, Lias. The
left-hand figure shows a few or the joints of the column; the
middle figure shows the arms, and the summit of the column with
its side-arms; and the right-hand figure shows the articulating
surface of one of the column-joints.]
The _Echinoderms_ are very numerous and abundant fossils in the
Jurassic series, and are represented by Sea-lilies, Sea-urchins,
Star-fishes, and Brittle-stars. The _Crinoids_ are still common,
and some of the limestones of the series are largely composed
of the _debris_ of these organisms.
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