ption, 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. Most of the Jurassic forms
resemble those with which we are already familiar, in having
the body permanently attached to some foreign object by means
of a longer or shorter jointed stalk or "column." One of the
most characteristic Jurassic genera of these "stalked" Crinoids
(though not exclusively confined to this period) is _Pentacrinus_
(fig. 162). In this genus, the column is five-sided, with whorls
of "side-arms;" and the arms are long, slender, and branched.
The genus is represented at the present day by the beautiful
"Medusa-head Pentacrinite" (_Pentacrinus caput-medusoe_). Another
characteristic Oolitic genus is _Apiocrinus_, comprising the
so-called "Pear Encrinites." In this group the column is long
and rounded, with a dilated base, and having its uppermost joints
expanded so as to form, with the cup itself, a pear-shaped mass,
from the summit of which spring the comparatively short arms.
Besides the "stalked" Crinoids, the Jurassic rocks have yielded
the remains of the higher group of the "free" Crinoids, such as
_Saccosoma_. These forms resemble the existing "Feather-stars"
(_Comatula_) in being attached when young to some foreign body by
means of a jointed stem, from which they detach themselves when
fully grown to lead an independent existence. In this later stage
of their life, therefore, they closely resemble the Brittle-stars
in appearance. True Star-fishes (_Asteroids_) and Brittle-stars
(_Ophiuroids_) are abundant in the Jura