[Illustration:  Fig. 142.—­Head and upper part of the column of Encrinus liliiformis.  The lower figure shows the articulating surface of one of the joints of the column.  Muschelkalk, Germany.]

[Illustration:  Fig. 143.—­Aspidura loricata, a Triassic Ophiuroid.  Muschelkalk, Germany.]

The remains of Articulate Animals are not very abundant in the Trias, if we except the bivalved cases of the little Water-fleas (Ostracoda), which are occasionally very plentiful.  There are also many species of the horny, concentrically-striated valves of the Estherioe (see fig. 122, b), which might easily be taken for small Bivalve Molluscs.  The “Long-tailed” Decapods of the type of the Lobster, are not without examples but they become much more numerous in the succeeding Jurassic period.  Remains of insects have also been discovered.

Amongst the Mollusca we have to note the disappearance, amongst the lower groups, of many characteristic Palaeozoic types.  Amongst the Polyzoans, the characteristic “Lace-corals,” Fenestella, Retepora,[22] Synocladia, Polypora, &c., have become apparently extinct.  The same is true of many of the ancient types of Brachiopods, and conspicuously so of the great family of the Productidoe, which played such an important part in the seas of the Carboniferous and Permian periods.

[Footnote 22:  The genus Retefora is really a recent one, represented by living forms; and the so-called Reteporoe of the Palaeozoic rocks should properly receive another name (Phyllopora), as being of a different nature.  The name Retepora has been here retained for these old forms simply in accordance with general usage.]

[Illustraton:  Fig. 144.  Triassic Lamellibranchs. a, Daonella (Halobia) Lommelli; b, Pecten Valoniensis; c, Myophoria lineata; d. Cardium Rhoeticum; e. Avicula contorta; f. Avicula socialis.]

Bivalves (Lamellibranchiata) and Univalves (Gasteropoda) are well represented in the marine beds of the Trias, and some of the former are particularly characteristic either of the formation as a whole or of minor subdivisions of it.  A few of these characteristic species are figured in the accompanying illustration (fig. 144).  Bivalve shells of the genera Daonella (fig. 144, a) and Halobia (Monotis) are very abundant, and are found in the Triassic strata of almost all regions.  These groups belong to the family of the Pearl-oysters (Aviculidoe), and are singular from the striking resemblance borne by some of their included forms to the Strophomenoe amongst the Lamp-shells, though, of course, no real relation exists between the two.  The little Pearl-oyster, Avicula socialis_ (fig. 144, f), is found throughout the greater part of the Triassic series, and is especially