In _Cerámium rúbrum_, which is also very common, being found attached to stones, rocks, and the larger Algæ, the filaments (Pl. IV. fig. 12) are stouter than in _C. nodosum_, branched so as to form tufts from 2 to 10 inches long, and their ends forked, with the tips hooked inwards (fig. 14). The central cells of the filaments are large and rounded, and their walls are entirely covered with a layer of very small angular red cells. The globular capsules (fig. 15), or _favellæ_, are situated on the suter surface of the branches, stalked, and supported by 3 or 4 short branchlets. The tetraspores (fig. 13) are imbedded in the branches, towards the ends. The capsules called favellæ differ from the coccidia in the walls being simply membranous, while the walls of the coccidia, like those of the ceramidia, are composed of cells. The tetraspores are usually imbedded, among the cells of the superficial layer of the filaments, and are not very easily recognized by an unpractised eye; it will be observed in the figures that they are sometimes cleft horizontally, at others obliquely. CONFERVOID´EÆ.--This Order consists principally of the green freshwater Algæ, although some of them are yellowish brown, purple, or red, and some are marine. Their general structure may be best illustrated by selecting certain common examples from the families composing the order. The families are 13 in number. The species which are figured in the plates are found in fresh water, except when otherwise stated. PLATE V. [PAGE 70.] FRESHWATER ALGÆ. Fig. 1. _Conferva floccosa_, single filament. 2. _Lyngbya muralis_, single filament. 3. _Ulothrix mucosa_ (?), filament. 4. _Synedra radians_, prepared frustules. 5. _Synedra radians_, tuft of natural frustules. 6. _Cladophora crispata_, with zoospores (_a_). 7. _Batrachospermum moniliforme_, portion of filament. 8. _Batrachospermum moniliforme_, filament. 9. _Closterium acerosum._ 10. _Draparnaldia glomerata._ 11. _Spirogyra quinina._ 12. _Spirogyra nitida_, filaments conjugating. 13. _Zygnema cruciata._ 14. _Coleochæte scutata._ 15. _Xanthidia_ in flint. 16. _Micrasterias rotata._ 17. _Gomphonema acuminatum._ 18. _Gomphonema acuminatum_, prepared frustules. 19. _Ankistrodesmus falcatus._ 20. _Pediastrum Boryanum._ 21. _Hyalotheca dissiliens._ 22. _Pinnularia viridis._ 23. _Fragilaria capucina._ 24. _Fragilaria capucina_, prepared frustules; _s_* side view of _F. virescens_. 25. _Scenedesmus quadricauda._ 26. _Schizogonium_, probably a form of _Lyngbya_. 27. _Campylodiscus costatus._ 28. _Nitzschia minutissima_, front view. 29. _Nitzschia minutissima_, valves. 30. _Epithemia turgida._ 31. _Diatoma elongatum_, natural frustules. 32. _Diatoma elongatum_, prepared frustules. 33. _Cocconeis placentula._ [Illustration: Plate V. _W Bagg sculp_ _London: John Van Voorst._]