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 Cystiphyllum, Lonsdale (Silurian and Devonian). Goniophyllum, M. Edw. and H. (In this Silurian genus the calyx is provided with a movable operculum, consisting of four paired triangular pieces, the bases of each being attached to the sides of the calyx, and their apices meeting in the middle when the operculum is closed). Calcecla, Lam. (In this Devonian genus there is a single semicircular operculum furnished with a stout median septum and numerous feebly developed secondary septa. The calyx is triangular in section, pointed below, and the operculum is attached to it by hinge-like teeth.)

.—The following list contains only the names of the more important and more general works on the structure and classification of corals and on coral reefs. For a fuller bibliography the works marked with an asterisk should be consulted: * A. Andres, Fauna und Flora des Golfes von Neapel, ix. (1884); H. M. Bernard, “Catalogue of Madreporarian Corals” in Brit. Museum, ii. (1896), iii. (1897); * G. C. Bourne, “Anthozoa,” in E. Ray Lankester’s Treatise on Zoology, vol. ii. (London, 1900); G. Brook, “Challenger Reports,” Zoology, xxxii. (1899) (Antipatharia); “Cat. Madrep. Corals,” Brit. Museum, i. (1893); D. C. Danielssen, “Report Norwegian North Atlantic Exploring Expedition,” Zoology, xix. (1890); J. E. Duerden, “Some Results on the Morphology and Development of Recent and Fossil Corals,” ''Rep. Brit. Association, 1903, pp. 684-685; “The Morphology of the Madreporaria,” Biol. Bullet'', vii. pp. 79-104; P. M. Duncan, ''Journ. Linnean Soc''. xviii. (1885); P. H. Gosse, Actinologia britannica (London, 1860); O. and R. Hertwig, Die Actinien (Jena, 1879); R. Hertwig, “Challenger Reports,” Zoology, vi. (1882) and xxvi. (1888); * C. B. Klunzinger, Die Korallthiere des Rothen Meeres (Berlin, 1877); * G. von Koch, Fauna und Flora des Golfes van Neapel, xv. (1887); ''Mitth. Zool. Stat. Neapel'', ii. (1882) and xii. (1897); Palaeontographica, xxix. (1883); (also many papers in the Morphol. Jahrbuch from 1878 to 1898); F. Koby, “Polypiers jurassiques de la Suisse,” ''Mem. Soc. Palaeont. Suisse'', vii.-xvi. (1880–1889); A. von Kölliker, “Die Pennatuliden,” ''Abh. d. Senck. Naturf. Gesell''. vii.; * “Challenger Reports,” Zoology, i. Pennatulidae (1880); Koren and Danielssen, Norske Nordhaus Exped., Alcyonida (1887); H. de Lacaze-Duthiers, ''Hist. nat. du corail (Paris, 1864); H. Milne-Edwards and J. Haime, Hist. nat. des coralliaires (Paris, 1857); H. N. Moseley, “Challenger Reports,” Zoology'', ii. (1881); H. A. Nicholson, Palaeozoic Tabulate Corals (Edinburgh, 1879); M. M. Ogilvie, ''Phil. Transactions'', clxxxvii. (1896); E. Pratz, Palaeontographica, xxix. (1882); J. J. Quelch, “Challenger Reports,” Zoology, xvi. (1886); * P. S. Wright and Th. Studer, “Challenger Reports,” Zoology, xxxi. (1889).

ANTHRACENE (from the Greek , coal), C14H10, a hydrocarbon obtained from the fraction of the coal-tar distillate boiling between 270° and 400° C. This high boiling fraction is allowed to stand for some days, when it partially solidifies. It is then separated in a centrifugal machine, the low melting-point impurities are removed by means of hot water, and the residue is finally hot-pressed. The crude anthracene cake is purified by treatment with the higher pyridine bases, the operation being carried out in large steam-jacketed boilers. The whole mass dissolves on heating, and the anthracene crystallizes out on cooling. The crystallized anthracene is then removed by a centrifugal separator and the process of solution in the pyridine bases is repeated. Finally the anthracene is purified by sublimation.

Many synthetical processes for the preparation of anthracene and its derivatives are known. It is formed by the condensation of acetylene tetrabromide with benzene in the presence of aluminium chloride:—

and similarly from methylene dibromide and benzene, and also when benzyl chloride is heated with aluminium chloride to 200° C. By condensing ortho-brombenzyl bromide with sodium, C. L. Jackson and J. F. White (Ber., 1879, 12, p. 1965) obtained dihydro-anthracene

Anthracene has also been obtained by heating ortho-tolylphenyl ketone with zinc dust

Anthracene crystallizes in colourless monoclinic tables which show a fine blue fluorescence. It melts at 213° C. and boils at 351° C. It is insoluble in water, sparingly soluble in alcohol and ether, but readily soluble in hot benzene. It unites with picric acid to form a picrate, C14H10·C6H2(NO2)3·OH, which crystallizes in needles, melting at 138° C. On exposure to sunlight a solution of anthracene in benzene or xylene deposits para-anthracene (C14H10)2, which melts at 244° C. and passes back into the ordinary form. Chlorine and bromine form both addition and substitution products with anthracene; the addition product, anthracene dichloride, C14H10Cl2, being formed when chlorine is passed into a cold solution of anthracene in carbon bisulphide. On treatment with potash, it forms the substitution product, monochlor-anthracene, C14H9Cl. Nitro-anthracenes are not as yet known. The mono-oxyanthracenes (anthrols), C14H9OH or  and  resemble the phenols, whilst   (anthranol) is a reduction product of anthraquinone. β-anthrol and anthranol give the corresponding amino compounds (anthramines) when heated with ammonia.

Numerous sulphonic acids of anthracene are known, a monosulphonic acid being obtained with dilute sulphuric acid, whilst concentrated sulphuric acid produces mixtures of the anthracene disulphonic acids. By the action of sodium amalgam on an alcoholic solution of anthracene, an anthracene dihydride, C14H12, is obtained, whilst by the use of stronger reducing agents, such as hydriodic acid and amorphous phosphorus, hydrides of composition C14H16 and C14H24 are produced.

Methyl and phenyl anthracenes are known; phenyl anthranol (phthalidin) being somewhat closely related to the s (q.v.). Oxidizing agents convert anthracene into (q.v.); the production of this substance by oxidizing anthracene in glacial acetic acid solution, with chromic acid, is the usual method employed for the estimation of anthracene. ANTHRACITE (Gr. , coal), a term applied to those varieties of coal which do not give off tarry or other hydrocarbon vapours when heated below their point of ignition; or, in other words, which burn with a smokeless and nearly non-luminous flame. Other terms having the same meaning are, “stone coal” (not to be confounded with the German Steinkohle) or “blind coal” in Scotland, and “Kilkenny coal” in Ireland. The imperfect anthracite of north Devon, which however is only used as a pigment, is known as culm, the same term being used in geological classification to distinguish the strata in which it is found, and similar strata in the Rhenish hill countries which are known as the Culm Measures. In America, culm is used as an equivalent for waste or slack in anthracite mining.

Physically, anthracite differs from ordinary bituminous coal by its greater hardness, higher density, 1·3–1·4, and lustre, the latter being often semi-metallic with a somewhat brownish reflection. It is also free from included soft or fibrous notches and does not soil the fingers when rubbed. Structurally it shows some alteration by the development of secondary divisional planes and fissures so that the original stratification lines are not always easily seen. The thermal conductivity is also higher, a lump of anthracite feeling perceptibly colder when held in the warm hand than a similar lump of bituminous coal at the same temperature. The chemical composition of some typical anthracites is given in the article.

Anthracite may be considered to be a transition stage between ordinary bituminous coal and graphite, produced by the more or less complete elimination of the volatile constituents of the former; and it is found most abundantly in areas that have been subjected to considerable earth-movements, such as the flanks of great mountain ranges. The largest and most important anthracite region, that of the north-eastern portion of the Pennsylvania coal-field, is a good example of this; the highly contorted strata of the Appalachian region produce anthracite exclusively, while in the western portion of the same basin on the Ohio and its tributaries, where the strata are undisturbed, free-burning and coking coals, rich in volatile matter, prevail. In the same way the anthracite region of South Wales is confined to the contorted portion west of Swansea and Llanelly, the