DELESSERIA´CEÆ.--In this family, the typical or most highly developed genus of which, _Delesséria_, has beautiful leaf-like rose-red fronds, we shall examine the common _Plocámium coccin´eum_ (Pl. IV. figs. 23 and 22). This is of a fine red colour; the fronds are from 2 to 12 inches long, and consist of numerous branched and bushy filaments. These are compressed, with the branchlets arranged in alternate rows on the two margins of the stem. The end branchlets are acute and pectinate (_pecten_, a comb), or arranged like the teeth of a comb. The cells of which the filaments consist are small and angular, giving the surface the appearance of being elegantly netted under a high power. The fruit (fig. 22) consists of globular capsules, called _coccid´ia_ (κὁκκος, a berry), placed in the axils or forks at which two branches separate, and containing a mass of angular spores. There are also tetraspore-pods (stichidia), as in _Dasya_; and tetraspores (fig. 24) in little leaf-like altered branches (fig. 21), called _spor´ophylles_ (σπορἁ, seed, φὑλλον, leaf), and antheridia are present. RHODYMENIA´CEÆ.--In this family we have _Hyp´nea purpuras´cens_ (Pl. IV. fig. 35). The filamentous pale purple frond of this sea-weed is from 6 inches to a foot or more in length, the branches being alternate and spreading. The fructification consists of capsules or coccidia (fig. 32), immersed in the branches, and containing the spores (fig. 34). Tetraspores also occur in the cells of the surface of the filaments. CERAMIA´CEÆ.--This is the last family to be noticed. _Cerámium nodósum_ (Pl. IV. figs. 10 and 11), which belongs to it, is a most delicate and elegant filamentous sea-weed, commonly found attached to other sea-weeds. The filaments are hair-like or capillary, irregularly dichot´omous; they consist of colourless cells, 3 or 4 times as long as broad, and with thick walls. The junctions of the cells are swollen (fig. 11), and covered with very minute dark red cells, giving them a knotty and jointed appearance to the naked eye or under a low power. The globular capsules, or _favel’læ_ (_favus_, a honeycomb), containing the numerous spores, are situated at the ends of the branchlets, and the tetraspores (fig. 11) in twos or threes on the outer margins of them.