The plants of the Jurassic period consist principally of Ferns, Cycads, and Conifers—­agreeing in this respect, therefore, with those of the preceding Triassic formation.  The Ferns are very abundant, and belong partly to old and partly to new genera.  The Cycads are also very abundant, and, on the whole, constitute the most marked feature of the Jurassic vegetation, many genera of this group being known (Pterophyllum, Otozamites, Zamites, Crossozamia, Williamsonia, Bucklandia, &c.) The so-called “dirt-bed” of the Purbeck series consists of an ancient soil, in which stand erect the trunks of Conifers and the silicified stools of Cycads of the genus Mantellia (fig.160).  The Coniferoe of the Jurassic are represented by various forms more or less nearly allied to the existing Araucarioe; and these are known not only by their stems or branches, but also in some cases by their cones.  We meet, also, with the remains of undoubted Endogenous plants, the most important of which are the fruits of forms allied to the existing Screw-pines (Pandaneoe), such as Podocarya and Kaidacarpum.  So far, however, no remains of Palms have been found; nor are we acquainted with any Jurassic plants which could be certainly referred to the great “Angiospermous” group of the Exogens, including the majority of our ordinary plants and trees.

Amongst animals, the Protozoans are well represented in the Jurassic deposits by numerous Foraminifers and Sponges; as are the Coelenterates by numerous Corals.  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.]