"The maior septa of clisiophyllid corals originate deep down in the calyx and grow upwards, fanning out towards both the axis and the periphery of the coral. The minor septa originate high up near the rim of the calyx and appear in pairs, one septum being inserted on either side of each new major septum. The insertion of minor septa on both sides of a new major septum complicates the development of the subsequent major septum at the fossula." Specimens of corals from various Carboniferous localities in England were used for the investigation.