Order 2. =Helminthocladiaceæ.= Tetraspores are generally wanting (_e.g._ in _Nemalion_) or arise one in each tetrasporangium (_e.g. Batrachospermum_) and it is only in _Liagora_ that four cruciate tetraspores are formed. _Chantransia corymbifera_ consists of simple, branched cell-rows, and is an independent species. Several other _Chantransia-forms_, living in fresh water, are “proembryos” of species of the genus _Batrachospermum_. The germinating carpospore grows out into filaments and forms a so-called proembryo which, if not shaded, attains only a small size, but when growing in shady situations presents a much greater development. These highly developed proembryos have been described as species of _Chantransia_. The proembryo can reproduce by division, or by tetraspores which are developed singly in the sporangia; in _B. vagum_ and _B. sporulans_ which do not possess fully developed female reproductive organs, the proembryos serve almost entirely to reproduce the species. The young _Batrachospermum_-plant arises from the end of an upright filament of the proembryo. The proembryo is generally persistent, and continually produces new _Batrachospermums_. These latter bear the sexual reproductive organs and also whorls of branches: the central row of cells is enclosed by cells growing from the base of the whorls of branches, and from these cortical cells secondary proembryos are developed. In this alternation of shoots there is really no alternation of generations, since the proembryo and the shoots with the sexual reproductive organs are parts of the same thallus. Several species of _Batrachospermum_ have a bluish green or verdigris colour. _Nemalion multifidum_ has a brown-red thallus, slightly branched, which is attached to rocks near the water’s edge. Order 3. =Chætangiaceæ.= _Galaxaura_ has a thallus thickly incrusted with lime. Order 4. =Gelidiaceæ.= _Naccaria, Gelidium._ Sub-Family 2. =Gigartinales.= The fertilised auxiliary cell grows towards the thallus, to produce the gonimoblasts. Procarpia generally present. Order 5. =Acrotylaceæ.= _Acrotylus._ Order 6. =Gigartinaceæ.= _Gigartina_, _Phyllophora_, _Ahnfeltia_; _Chondrus crispus_, with dark red, dichotomously branched thallus, is common on the coasts of Scandinavia and Great Britain. Order 7. =Rhodophyllidaceæ.= _Rhodophyllis_, _Euthora_; _Cystoclonium purpurascens_ is common, and sometimes the ends of its branches may be modified into tendril-like haptera. Sub-Family 3. =Rhodymeniales.= The fertilised auxiliary cell forms the gonimoblast on the side away from the thallus. Procarpia are abundantly produced. Order 8. =Sphærococcaceæ.= _Gracilaria._ Order 9. =Rhodymeniaceæ.= _Rhodymenia palmata_ is a common species. _Lomentaria_, _Chylocladia_, _Plocamium_.