De Blainville gave the name of MADREPORÆA to the second group of his stony _Zoantharia_, placing them after the _Madrephylliæ_. The products of this section are generally arborescent, with small, partially lamelliform cells, which are constantly porous in the interstices of the walls of the cells, this being its most important characteristic. Thus the visceral apparatus constitutes the essential part of the polypus, presenting no side plates, the visceral chamber being open from the base to the summit, and neither filled with dissepiments, pulpy matter, nor with plates. The history of these inhabitants of the deep is extremely obscure, and will probably always remain so; the most beautiful of their productions are intertropical, and consequently beyond the reach of discriminating observers during the life of the animal. Solander proposed to divide the genus according to certain characteristics in the growth of the coral, and De Blainville has rearranged the groups formed by Lamarck, Lamouroux, and Goldfuss, with special reference to the soft parts of the animals figured by Lesueur, Quoy, Gaimard, and others, who have observed them in their native state. The perforated _Zoantharia_ form three very natural families: the _Eupsammidæ_, the _Madreporidæ_, and the _Poritidæ_. The first have the solid parts of the polyps, simple or complex, with well-developed lamellar portions, the central column spongious, walls granular, semi-ribbed, and perforated. The second are composite, increasing by gemmation; walls spongy and porous; septa lamellous, and well developed. In the third the visceral chambers are divided into two equal parts by the principal septa, which are more developed than the others, meeting by their inner edge. The _Dendrophylliæ_ (Fig. 74) are conspicuous among the _Eupsammidæ_. We shall describe three genera, the two first of which belong to the MADREPORÆA, and the last of the family of the _Porides_. [Illustration: Fig. 74. Dendrophyllia ramea, half natural size (De Blainville).]