Order 11. Bonnemaisoniaceæ. Bonnemaisonia.
Order 12. Rhodomelaceæ. Rhodomela, Odonthalia; Polysiphonia, of which many species are to be found on the coasts of Great Britain, has a filamentous, richly branched thallus consisting of a central row of cells surrounded by a varying number of cortical cells of similar size—the so-called “siphons.”
Order 13. Ceramiaceæ. Pretty Algæ, often branched dichotomously, or unilaterally pinnate. Spermothamnion, Griffithsia, Callithamnion, Ceramium, Ptilota.
Sub-Family 4. Cryptonemiales. The cells formed by the coalescence of the auxiliary cells and the ooblastema-filaments, produce the gonimoblasts. The carpogonium-filaments and the auxiliary cells are scattered singly in the thallus.
Order 14. Gloiosiphoniaceæ. Gloiopeltis.
Order 15. Grateloupiaceæ. Halymenia, Cryptonemia.
Order 16. Dumontiaceæ. Dumontia, Dudresnaya.
Order 17. Nemastomaceæ. Furcellaria, which has dichotomously branched, round shoots, is common on the coasts of Great Britain.
Order 18. Rhizophyllidaceæ. Polyides, Rhizophyllis.
Order 19. Squamariaceæ. The Algæ belonging to this order form crust-like coverings on stones, mussel-shells, and on other Algæ, but are not themselves incrustated: Petrocelis, Cruoria, Peyssonellia.