The genus ^Oscillaria^ is so named from an oscillating movement which these filamentous plants show when viewed under the microscope. They are very delicate blue-green threads occurring singly, or in loose or felt-like floating masses, or like slime or scum, on mud or woodwork. In ^Spirulina^ the filaments are spirally twisted like a corkscrew and also have a vibrating movement. /Spirulina/ is often found growing with /Oscillaria/, and forms purple patches on wharves. GENUS ^Calothrix^ ("/Beautiful hair/") Filaments one tenth of an inch long, terminating in transparent hair-like points, occasionally branching. The plant grows in fine tufts or like a fringe on algæ or in patches on rocks. Sometimes it forms a spongy layer, again a velvety stratum. The color varies in different species; it may be bright green, brownish-green, [pg050] or dark bluish-purple. The genus is very common, and the plants are often found on the bottoms of boats. GENUS ^Lyngbya^ (/Named for Hans Christian Lyngbye, a Danish botanist/) ^L. majuscula^, mermaid's-hair. The filaments are curled or crisped, long, thick, and tenacious, matted together at the base, and blackish-green. The species grows in tufts on eel-grass and algæ, and is often found floating free. It is common in summer everywhere south of Cape Cod and on the Pacific coast. ^L. ferruginea^ or ^æstuarii^. In this species the filaments are thin, soft, and without stability (flaccid), so that they lie flat like a thin stratum. They are verdigris-green in color, and are found in brackish pools and ditches and on muddy shores near the sea. [pg051] TABLE SHOWING THE CLASSIFICATION OF THE GRASS-GREEN SEAWEEDS DESCRIBED IN THIS CHAPTER Class =ALGÆ= Subclass =Chlorophyceæ= (/Grass-Green Seaweeds/) Order Genus Species =CONFERVACEÆ= ^Ulothrix^ ^Chætomorpha^ ^C. melagonium^ ^C. ærea^ ^C. linum^ ^Cladophora^ ^C. arcta^ ^C. rupestris^ ^C. gracilis^ =ULVACEÆ= ^Ulva^ ^U. lactuca^ ^U. latissima^ ^Enteromorpha^ ^E. clathrata^ ^E. compressa^ ^E. intestinalis^ ^E. lanceolata^ ^Monostroma^ Group =Siphoneæ= =VALONIACEÆ= ^Chamædoris^ ^C. annulata^ ^Anadyomene^ ^A. flabellata^ =DASYCLADACEÆ= ^Acetabularia^ ^A. crenulata^ ^Dasycladus^ ^D. occidentalis^ ^Cymopolia^ ^C. barbata^