^R. subfusca.^ Frond six to eighteen inches long; main stem cylindrical, and branching widely on all sides; branches longest at base and gradually shortening to the top of the stem; branches naked below, but at the ends profusely branched, forming tufts of branchlets. It is a perennial plant, and changes in aspect with the season. When mature it is stiff and coarse, and when dry it is quite black. Common from New York northward. ^R. Rochei.^ This species resembles in form /R. subfusca/, but is much finer and more delicate. In spring it is a soft, fine, feathery, and beautiful [pg090] alga of a red-brown color. It is found washed ashore, or in deep tide-pools, south of Cape Cod. (Plate XXIX.) ^R. larix.^ Frond cylindrical, robust, six to fourteen inches high; branches of unequal length standing out horizontally all around the main stem; clusters of branchlets growing spirally around stem and branches. Found on the northern California coast. (Plate XXIX.) ^R. floccosa.^ Frond four to ten inches high; less robust than /R. larix/; stem and branches flat and divided in one plane; branches alternate; ultimate branchlets somewhat incurved; color black. In fertile plants the terminal branchlets are gathered in a mass. Found on the California coast. (Plate XXIX.) GENUS ^Chondria^ Plants of this genus are distinguished by having the ultimate branches attenuated at the base. ^C. dasyphylla.^ Frond four to eight inches high; general outline pyramidal; branches alternate on main stem; stem and branches covered with short, club-shaped (blunt at top, attenuated at base) branchlets; cystocarps, or spore-cases, adherent to branchlets or on short stalks; color light or dull brown. It grows in tufts, and is common from New York to Cape Cod. (Plate XXX.) ^C. tenuissima.^ This species is similar to /C. dasyphylla/, but is more slender, and the branchlets taper at both ends instead of being club-shaped. ^C. striolata.^ A species similar to /C. tenuissima/. The branchlets bear secondary branchlets, and the cystocarps are on short stalks. It is plentiful in Long Island Sound. SUBORDER ~CERAMIEÆ~ GENUS ^Callithamnion^ These are very beautiful and delicate plants, growing in small, soft, silky tufts, bright red in color, with darker dots along the much-branched filaments. There are many species, and they are common on the northern shores of both oceans; but the different species are not easy to distinguish with the naked eye, and so but a few of them are described below. The special characteristics by which the genus may be recognized are: fronds filamentous, of cobweb fineness, one inch to six inches long, much branched, and closely crowded at the top; brilliant red color. [Illustration: PLATE XXIX. Bostrychia rivularis. Rhodomela Rochei. Rhodomela larix. Rhodomela floccosa.]