THE JURASSIC (PERIOD. 231 
tion, 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” (Astre@ide). The form here figured (Zhecos- 
milia annularis, fig. 161) is one of the characteristic species 
of the Coral-rag. 
«& 
qT AY 
UNS \ WEZE 
Lg= = 
Fig. 161.—Thecosmilia annularis. Coral-rag, England. 
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 Cyvzwoids are still 
common, and some of the limestones of the series are largely 
composed of the déris 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 Pentacrin- 
ite” (Pentacrinus caput-meduse). 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. 
