Aporosa. The calcareous tissue of the corallum is more or less compact and imperforate ; the septa usually constituting complete solid plates, and the theca being as a rule not pierced by any apertures. Dissepiments or synapticulae are usually present, but tabulae are rarely developed. This section includes the most highly developed of existing corals (Tur-binolidae, Oculinidae, Astraeidae, Fungidae, etc.)
Perforata. The calcareous tissue of the corallum is more or less porous, loosely aggregated, spongy, or reticulate, the walls in all being perforated with more or fewer apertures. The septa are generally well developed, but they are also perforated by apertures, and may be simply trabecular. Imperfect dissepiments may be present, and in some cases there are well-developed tabulae ; but the visceral chamber is usually more or less completely open from top to bottom. The three families comprised in this section are the Eupsammidae:, the Madreporidae, and the Foritidae, to which must be added the great and almost extinct family of the Favositidae.
In addition to the above-mentioned groups of the Zoantharia sclerodermata two other groups have been established under the names of the Tabulata and Tubulosa. The former of these included the so-called "Tabulate Corals," distinguished by the imperfect development of the septa, and the fact that the visceral chamber is divided into compartments by horizontal plates or "tabulae" (fig. 76, D). Some of the so-called "Tabulate Corals," however, such as Millepora, have been shown to be Hydrozoa; others, such as Pocillopora (fig. 76) belong to the Aporose division of the Zoantharia sclerodermata ; others, again, such as Favosites and its allies (fig. 79), belong to the Perforate division of the Z. scleroder-mala, and are very nearly related to the Poritidae; others are referable to the Alcyonaria; while others, lastly, are of uncertain affinities. It is clear, therefore, that the section Tabulata can no longer be retained as a division of the Zoantharia sclerodermata, or as a division of the Corals of any zoological value. The section Tubulosa (including only the Palaeozoic genera Aulopora and Cladochonus or Pyrgia) is also of no zoological value, in the present state of our knowledge. The forms included in it are simple or compound, with trumpet-shaped thecae, rudimentary septa, and few or imperfect tabulae; and they are probably referable to the Alcyonaria.
Fig. 79. - A, Portion of the corallum of Favosites favosa, of the natural size. B, Portion of four corallites of Favosites Gothlandica, enlarged, showing the tabulae and the "mural pores " or openings in the walls of the corallites.