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 _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 Palæozoic 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.]