Angelin's _Iconographia crinoideorum_ (1878); the Palaeozoic crinoids and cystids of Bohemia are dealt with in J. Barrande's _Système silurien_ (1887 and 1899); P.H. Carpenter published important papers on fossil crinoids in the _Journal_ of the Geological Society, on Cystidea in that of the Linnean Society, 1891, and, together with R. Etheridge, jun., compiled the large _Catalogue of Blastoidea in the British Museum_, 1886; O. Jaekel, in addition to valuable studies on crinoids and cystids appearing in the _Zeitschrift_ of the German Geological Society, has published the first volume of _Die Stammesgeschichte der Pelmatozoen_ (Berlin, 1899), a richly suggestive work; the Mesozoic Echinoderms of France, Switzerland and Portugal have been made known by P. de Loriol, G.H. Cotteau, J. Lambert, V. Gauthier and others (see _Paléontologie française_, _Mém. Soc. paléontol. de la Suisse_, _Trabalhos Comm. Geol. Portugal_, &c.); a beautiful and interesting Devonian fauna from Bundenbach has been described by O. Follmann, Jaekel, and especially B. Stürtz (see _Verhandl. nat. Vereins preuss. Rheinlande, Paläont. Abhandl._, and _Palaeontographica_); while the multitude of North American palaeozoic crinoids has been attacked by C. Wachsmuth and F. Springer in the _Proceedings_ (1879, 1881, 1885, 1886), of the Philadelphia Academy and the _Memoirs_ (1897) of the Harvard Museum. The vast mass of material made known by these and many other distinguished writers has to be included in our classification, and that classification itself must be controlled by the story it reveals. Thus it is that a change, characteristic of modern systematic zoology, is affecting the subdivisions of the classes. It is not long since the main lines of division corresponded roughly to gaps in geological history: the orders were Palaeocrinoidea and Neocrinoidea, Palechinoidea and Euechinoidea, Palaeasteroidea and Euasteroidea, and so forth. Or divisions were based upon certain modifications of structure which, as we now see, affected assemblages of diverse affinity: thus both Blastoidea and Euechinoidea were divided into Regularia and Irregularia; the Holothuroidea into Pneumophora and Apneumona; and Crinoids were discussed under the heads "stalked" and "unstalked." The barriers between these groups may be regarded as horizontal planes cutting across the branches of the ascending tree of life at levels determined chiefly by our ignorance; as knowledge increases, and as the conception of a genealogical classification gains acceptance, they are being replaced by vertical partitions which separate branch from branch. The changes may be appreciated by comparing the systematic synopses at the end of this article with the classification adopted in 1877 in the 9th edition of the _Ency. Brit._ (vol. vii.), or in any zoological text-book contemporary therewith. In the present stage of our knowledge these minor divisions are the really important ones.