. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. 230 COZLENTERATA. Octactinia and Actinia are distributed in all latitudes. The polyps which build banks and reefs are confined to a zone extending about 28 degrees on either side of the equator, and only here and there extend beyond these bounds. They live for the most part near the coast, and produce there in course of time rocky masses of colossal extent by the accumulations of their stony calcareous frameworks. These masses may form coral reefs (atolls, barrier reefs, fringing reefs), wh
. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. 230 COZLENTERATA. Octactinia and Actinia are distributed in all latitudes. The polyps which build banks and reefs are confined to a zone extending about 28 degrees on either side of the equator, and only here and there extend beyond these bounds. They live for the most part near the coast, and produce there in course of time rocky masses of colossal extent by the accumulations of their stony calcareous frameworks. These masses may form coral reefs (atolls, barrier reefs, fringing reefs), which are perilous to ship- ping, and may also become the foundations of islands. In both cases a gradual alteration of. FIG. 17S.—Astrcca (Goniastrasa) peciinata Elirbg. (after Klunzinger). level, the raising of the bottom of the sea, assists the work of the coral animals. The presence cf the coral banks in the deep sea is, on the other hand, due to a continual sinking of the sea-bottom The part which the Anthozoa take in the alteration of the earth's surface is considerable. In the present time they protect the coast from the consequences of the breaking of the waves and assist in the formation of islands and rocks by producing immense masses of calcareous matter. In earlier geological epochs they have played a still more important part judging from the great thickness of the coral formations of the Palaeozoic period and of the Jurassic formation. Order 1.—HUGOSA == TETRAOORALLA. Palaeozoic Corals with num&rous symmetrically arranged septa, grouped in multiples of four. To these belong the families of the CyitlopJn/Uinrp, Staurido', Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Claus, Carl, 1835-1899; Sedgwick, Adam, 1854-1913; Sinclair, F. G. (Frederick Granville), b. 1858. London, Swan Sonn
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