Fig. 160.—Mantellia (Cycadeoidea) megalophylla, a Cycad from the Purbeck "dirt-bed." Upper Oolites, England. forms more or less nearly allied to the existing Araucariœ; 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 (Pandaneœ), 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 Cœlenterates 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" (Astrœidoe). The form here figured (Thecosmilia annularis, fig. 161) is one of the characteristic species of the Coral-rag.
| 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 Crinoids are still common, and some of the limestones of the series are largely composed of the débris 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-medusœ). 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
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. "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 Jurassic rocks, and the Sea-urchins (Echinoids) are so numerous and so well preserved as to constitute quite a marked feature of some beds of the series. All the Oolitic urchins agree with the modern Echinoids in having the shell composed of no more than twenty rows of plates. Many different genera are known, and a characteristic species of the Middle Oolites (Hemicidaris crenularis, fig. 163) is here figured.
| Fig. 163.—Hemicidaris crenularis, showing the great tubercles on which the spines were supported. Middle Oolites. |
Passing over the Annelides, which, though not uncommon, are of little special interest, we come to the Articulates, which also require little notice. Amongst the Crustaceans, whilst the little Water-fleas (Ostracoda) are still abundant, the most marked feature is the predominance which is now assumed by the Decapods—the highest of the known groups of the class. True Crabs (Brachyura) are by no means unknown; but the principal Oolitic Decapods belonged to the "Long-tailed" group (Macrura), of which the existing Lobsters, Prawns, and Shrimps are members. The fine-grained lithographic slates of Solenhofen are especially famous as a depot for the remains of these Crustaceans, and a characteristic species from this locality (Eryon arctiformis, fig. 164) is here represented. Amongst the air-breathing Articulates, we meet in the Oolitic rocks with the remains of Spiders (Arachnida), Centipedes (Myriapoda), and numerous true Insects (Insecta). In connection with the last-mentioned of these groups, it is of interest to note the occurrence of the oldest known fossil Butterfly—the Palœontina Oolitica of the Stonesfield slate—the relationships of which appear to be with some of the living Butterflies of Tropical America.
Coming to the Mollusca, the Polyzoans, numerous
