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" (Astræida). 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, Seaurchins, 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-medusa). 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

Fig. 162.-Pentacrinus fasciculosus, Lias. The left-hand figure shows a few of 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.

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 Starfishes (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 Ŏolites (Hemicidaris crenularis, fig. 163) is here figured.

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 Palæontina Oolitica of the Stonesfield slate-the rela

tionships of which appear to be with some of the living Butterflies of Tropical America.

Coming to the Mollusca, the Polyzoans, numerous and

beautiful as they are, must be at once dismissed; but the Brachiopods deserve a moment's attention. The Jurassic Lamp-shells (fig. 165) do not fill by any means such a predominant place in the marine fauna of the period, as in many Palæozoic deposits, but they are still individually numerous. The two ancient genera Leptana (fig. 165, a) and Spirifera (fig. 165, b), dating the one from the Lower and the other from the Upper Silurian, appear here for the last time upon the scene, but they have not hitherto been recognised in deposits later than the Lias. The great majority of the Jurassic Brachiopods, however, belong to the genera Terebratula (fig. 165, c, e, f) and Rhynchonella (fig. 165, d), both of which are represented by living forms at the present day. The Terebratulæ, in particular, are very abundant, and the species are often confined to special horizons in the series.

Remains of Bivalves (Lamellibranchiata) are very numerous

in the Jurassic deposits, and in many cases highly characteristic. In the marine beds of the Oolites, which constitute by

Fig. 165.-Jurassic Brachiopods. a, Leptana Liassica, enlarged, the small cross below the figure indicating the true size of the shell-Lias; b, Spirifera rostrata, Lias; c, Terebratula quadrifida, Lias; d, d', Rhynchonella varians, Fuller's Earth and Kelloway Rock; e, Terebratula sphæroidalis, Inferior Oolite; f, Terebratula digona, Bradford Clay, Forest-marble, and Great Oolite. (After Davidson).

far the greater portion of the whole formation, the Bivalves are of course marine, and belong to such genera as Trigonia, Lima, Pholadomya, Cardinia, Avicula, Hippopodium, &c.; but in the Purbeck beds, at the summit of the series, we find bands of Oysters alternating with strata containing fresh-water or brackish-water Bivalves, such as Cyrena and Corbula. The predominant Bivalves of the Jurassic, however, are the Oysters, which occur under many forms, and often in vast numbers, particular species being commonly restricted to particular horizons. Thus of the true Oysters, Ostrea distorta is characteristic of the Purbeck series, where it forms a bed twelve feet in thickness, known locally as the "Cinder-bed;" Ostrea expansa abounds in the Portland beds; Ostrea deltoidea is characteristic of the Kimmeridge clay; Ostrea gregaria predominates in the Coral-rag; Ostrea acuminata characterises the small group of the Fuller's Earth; whilst the plaited Ostrea Marshii (fig. 166) is a common shell in the Lower and Middle Oolites. Besides the more typical Oysters, the Oolitic rocks abound in examples of the singularly unsymmetrical forms