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 Paloeontina Oolitica of the Stonesfield slate—­the relationships of which appear to be with some of the living Butterflies of Tropical America.

[Illustration:  Fig. 164.—­Eryon arctiformis, a “Long-tailed Decapod,” from the Middle Oolites (Solenhofen Slate).]

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 Palaeozoic deposits, but they are still individually numerous.  The two ancient genera Leptoena (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 Terebratuloe, in particular, are very abundant, and the species are often confined to special horizons in the series.

[Illustration:  Fig. 165.—­Jurassic Brachiopod. a. Leptoena 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, Fulter’s Earth and Kelloway Rock; e, Terebratula sphoeroidalis, Inferior Oolite; f, Terebratula digona, Bradford Clay, Forest-marble, and Great Oolite. (After Davidson).]

[Illustration:  Fig. 166.—­Ostrea Marshii.  Middle and Lower Oolites.]

[Illustration:  Fig. 167.—­Gryphoea incurva.  Lias.]

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 far the greater portion of the whole formation, the Bivalyes 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,