Helioporidse, a family of Alcyonarian (q.v.) corals popularly known as the "Blue Corals" from their fine azure blue colour. The skeleton is calcareous, and is formed of a series of tubes of two sizes. Each set are inhabited by polypes of different structure, so that the colony is dimorphic. The larger tubes especially are crossed by tabulte or horizontal plates, and have septal plates running along them. The latter are usually twelve in number in each tube, and have no relation to the mesenteries. They are really foldings of the walls, and are known as pseudo-septa. The smaller or "ccenenchymal" tubes contain rudimentary sexless polypes. The only genus in the family is Heliolites, which forms round lobed masses. It lives in the Indian and Pacific Oceans. The Silurian genera Heliolites, Plasmopora, etc., are probably also members of this family. They are tabulate, and consist in the same way of masses of large and small ccenenchymal tubes.