The life of the Jurassic has been preserved in wonderful fulness and variety; but with comparatively few exceptions, our knowledge of it has been principally derived from Europe, where a host of eminent geologists have long studied the great wealth of material. The contrast between North America and Europe in regard to the relative abundance of Jurassic marine fossils is seen from the fact that while in Great Britain alone more than 4000 species have been described, in America hardly one-tenth of that number has so far been found.

Plants

The flora of the Jurassic differs little, on the whole, from that of the Trias, and is made up of Ferns, Horsetails, Cycads, Conifers, and Gingkos. Tree ferns flourished in northern Europe in great variety. The Cycads attain their culmination of abundance and diversity in this period, no less than forty species occurring in a single horizon of the English Upper Jura and an extinct order of the Cycadales, the Bennettitece, flourished remarkably. The Conifers are of somewhat more modern aspect than those of the Trias, and, from their resemblance to genera which are still extant, have received such names as Thujites, Tax-ites, Cupressites, Pinites, etc. The Araucarian pines abounded in Europe. The Gingkos, or Maidenhair Trees, continued to be represented by Baiera. Monocotyledons have been reported from the Jurassic, but the evidence for their existence is very doubtful.

Foraminifera

Foraminifera are found in great numbers and variety in the soft Jurassic clays, many of them belonging to genera which still abound in the modern seas. It must not be supposed that these organisms first became so abundant in Jurassic times; it is merely that the conditions for the preservation of these microscopic and exquisite shells had not been so favourable before.

Radiolaria

The beautiful siliceous tests of the Radiolarians are also found in multitudes. In the Alps occur whole strata of red flints and jaspery slates, which are composed almost entirely of these tests.

Plate XIV. - Jurassic Invertebrate Fossils.

Fig. i, Pentacrinus asteriscus M. and H., section of stem, X 2, U. J. 2, Cidaris coronata Goldf., X 1/2,Kimmeridgean, Europe. 3, Antinomia catullz Pictet, X 1/2, Tithon., Alps. 4, Eumicrotis curta Hall, X 3/2, U. J. 5, Tancredia corbuliformis Whitf., x 1, U. J. 6, Gervillia montanaensis Meek, X 1/2, U. J. 7, Volsella subimbricata Meek, X 1/2, U. J. 8, Trigonia americana Meek, X 1/2, U. J. 9, Pholadomya kingi Meek, X 1/2, U. J. 10, Camptonectes bellistriata Meek, X 1/2, U. J. 11, Pleuromya inconstans Aguilera and Costello, x 1/2, U. J. 12, Myacites subconipressus Meek, X 1/2, U. J. 13, Gryphaa arcuata Lam., x 2/5, Lias, France. 14, Ostrea marshi Sowerby, X 3/8, Bajocian, Germany. 15, Lyosoma powelli White, X 1/2, U. J. 16. Pleurotomaria conoidea Deshayes, X 1/2, France. 17, Nerinea dilatata d'Orb, x 1/2, France. 18, Peltoceras of. athleta Phillips, X 1/4, Callovian, Europe. 19, Lytoceras Jimbriatum Sowerby, X 1/4, Lias, England. 20, Crioceras bifurcatum Ouenstedt x 1/2 Bathonian, Germany.

Spongida

Sponges are found in wonderful profusion and diversity and in such perfect preservation that every detail of their beautiful structure may be made out with the microscope. In some localities these sponges are heaped up in such masses that they fill the strata, while other localities of the same horizon are entirely free from them.

Coelenterata

Corals abound, especially in the Upper Jurassic of central Europe. The Anihozoan Corals all belong to the modern Hexacoralla, in decided contrast to the Tetracoralla of the Palaeozoic seas. Isastrcea, Montlivaultia, and Thecosmilia are the dominant genera.

The Echinodermata, especially the Crinoids and Sea-urchins, are of great importance. The Crinoids are vastly more abundant than they had been in the Trias, and although the number of genera and species is not at all comparable to the great assemblage of Carboniferous times, yet for profusion and size of individuals the Jurassic has never been surpassed. Especially characteristic are the superb species of Pentacrinus, a close relative of which still exists in the West Indian seas. Other common genera are Apiocrinus and Eugeniacrinus. These genera all belong to the Articulata, which have a very different type of structure from the Palaeozoic forms, but, like nearly all the latter, they were attached to the sea-bottom by their long stems. In the Jurassic appear the first of the Articulate free-swimming Crinoids, like Co-matula, the commonest of modern genera. These animals possess a stem only in their early stages of development; subsequently they become detached and free. Star-fishes and Brittle Stars are not very common, but have attained a completely modern structure.

The Echinoids have undergone a wonderful expansion and diversification by the time of the Middle Jurassic. In the Lias, as in the Trias, we find only the regular, radially symmetrical sea-urchins, with mouth and anus at the opposite poles of the shell, such as Cidaris (PI. XIV, Fig. 2), but in the Middle and Upper Jura appear the irregular Spatangoids and Clypeastroids. In these the shell is bilaterally symmetrical, rather than radially so, the anus, and even the mouth, losing their polar positions, and the shape of the ambulacral areas being greatly changed. This is another instance of the attainment of modern structure which so many of the Mesozoic Invertebrates display.

Arthropoda

The Crustacea are not found in very many localities, but places like the famous lithographic limestones of Solen-hofen in Bavaria, where the conditions of preservation were favourable, show that this group was very abundant and far advanced in the Jurassic seas. The long-tailed (macrurous) Decapods (of which the lobster is a familiar example) are in the ascendant and are represented by many genera, several of which still exist. The Crabs, or short-tailed Decapods, which are now so very common, make their first known appearance in the Jurassic, but they were still rare, and connecting links between the long-tailed and short-tailed series were more abundant. Isopods and Stomatopods also abounded.

The Xiphosura are reduced to the single genus Limulus, which then occurred in the European seas, while the living horseshoe crabs of that genus are found only on the east coast of the United States and in the Molucca Islands.

Insects are found in multitudes in certain localities, and display a great advance in the number of types over any of the Palaeozoic periods. The Orthopters and Neuropters which we found in the Palaeozoic are enriched by many new forms, such as grasshoppers, while beetles (Coleoptera) become very abundant. The Hy-menopters (ants, bees, wasps, etc.) and the Dipters (flies) date from the Jurassic, and Lepidopters (butterflies) have also been reported, though doubtfully. As the latter insects are dependent upon a flowering vegetation, definite proof of their presence in the Jura will establish the existence of the Angiosperms at that time.

Brachiopoda

These shells are still common in the Jura, but they are simply a profusion of individuals belonging to a few genera, most of which persist in our recent seas; compared even with the Trias, Jurassic brachiopods are much diminished. Tere-bratuloids like Antinomia (XIV, 3), Waldheimia, and Rhynchonella are much the most important genera, and the last strag glers of the long-lived Palaeozoic Spiriferina are here found.