[Sidenote: Case A, upright part.] _Alcyonidium gelatinosum_(*) (Fig. 17), so called from its resemblance to the zoophyte Alcyonium, forms fleshy translucent growths occurring in the form of nodulated branched masses, or of long finger-like growths. The species is common round our coasts where it grows attached to stones and shells near low-water mark. [Illustration: Fig. 17. _Alcyonidium gelatinosum._ A, a small piece, natural size; B, the same magnified. ] [Sidenote: Case A, upright part.] _Amathia_ forms bushy growths composed of slender horny branches. The cells, which are cylindrical or squarish, rise from the branches in biserial rows like Pan’s pipes. In _Amathia lendigera_(*) (Fig. 18) the groups of cells are well separated from each other, but in _A. spiralis_(*) and _A. convoluta_(*) the cells form a nearly or entirely continuous series winding in a spiral round the slender stems. In _Bowerbankia imbricata_(*) the cells are clustered on the stems. _Vesicularia spinosa_(*), or the Silk Coralline, forms delicate brown tufts resembling a filamentous alga; the cells arise separately in a single series from the hollow tubular stems and are contracted at their point of attachment. [Illustration: Fig. 18. _Amathia lendigera._ A, natural size; B, magnified. ] Nearly all the Ctenostomata are marine, but a few species live in fresh water. Sub-order 3.—CYCLOSTOMATA. [Sidenote: Case B 2.] In the CYCLOSTOMATA, which are all calcareous, the usually tubular zoœcia have plain circular orifices without a lid or frill closing over the retracted tentacle-sheath. There are two sections in this group, viz., Articulata, in which the cells form branching colonies, the branches being connected by horny joints; and Inarticulata, in which the colonies may be encrusting, or erect and branching, but are without joints. The first section includes the _Crisiidæ_. [Sidenote: Case B 2.] _Crisia denticulata_ (Fig. 19) forms delicate white tufts, in which the flat slender branches are composed of a double row of tubular cells. The horny joints between the branches are black. The Inarticulata occur as crusts or branching growths. In _Tubulipora flabellaris_ (Fig. 20) the colonies form little fan-shaped crusts on seaweeds. _Lichenopora hispida_ forms little white disks, in which rows of tubular cells radiate from the centre. In _Idmonea_, the colony is branched, the tubular cells being arranged in parallel rows on each side of the middle line of the branch. [Illustration: Fig. 19. _Crisia denticulata._ A, natural size; B, branches magnified. ] The Cyclostomata are all marine. [Illustration: Fig. 20. _Tubulipora flabellaris._ _a_, half of an incrusting colony, × 8; _b_, a few cells, × 44; _c_, a colony, natural size. ] Order II.—PHYLACTOLÆMATA. [Sidenote: Table Case A, upright part.]