Rugosa

Rugosa, a group of Corals, including most, of those of the Palaeozoic period, and therefore of much interest to geologists. The value of the order is, however, very uncertain, and some zoologists are inclined to merge it in the "Aporosa" group of ordinary Corals. It differs from this by the fact that the septa are arranged in multiples of four and not of six, and that there is usually one or more fossulae, or gaps left by the sqppression of one or more of the septa. The Rugosa are divided into three groups :-

(1) Cyanthophylloidea, in which there is a zone of vesicular tissue around the margin of the coral.
(2) Zaphrentoidea, in which this zone is absent, and the spaces or "loculi" between the septa are open.
(3) Cystiphylloidea, in which the whole coral is full of vesicular tissue, while the septa are reduced to mere, marginal striae. The members of this group occur only in the Silurian and Devonian.