^P. capitatus.^ Holdfast a dense mass of fibers two or more inches long; stipe one to five inches long, one fourth to one third of an inch in diameter, usually cylindrical, sometimes wider at top than at base, sometimes flattened; thickly incrusted with lime, which is smooth and often polished; top a dense, spherical mass of filaments one to two inches in diameter; filaments branching dichotomously, and rigid from incrustation of lime. ^P. Phœnix.^ Stipe cylindrical, one to three inches long, one fourth of an inch in diameter, thickly incrusted with lime, smooth; capitulum or head ovoid, and composed of filaments which are incrusted with lime and coherent, forming many distinct, flat, wedge-shaped, level-topped, spreading laminæ. This species is found at Key West. GENUS ^Udotea^ ^U. flabellata.^ Short, flattened stem, expanding into a broad, fan-shaped, smooth frond, concentrically zoned; margin wavy; thickly incrusted with lime. Abundant at Key West. ^U. conglutinata.^ Deeply descending root; stem expanding into fan-shaped frond; entire, lobed, or irregularly torn; slightly incrusted with lime. The frond is composed of longitudinally parallel, adherent filaments, which are visible, giving a striated, rough surface. (Plate VI.) GENUS ^Halimeda^ This genus resembles the corallines externally, and is abundant on coral reefs. It appears as if formed of separate parts, resembling a series of heart- or kidney-shaped segments strung together. The plants are more or less incrusted with lime. The branching holdfast grasps particles of sand, and with them forms a solid ball. ^H. tuna.^ Articulations roundish or half kidney-shaped, one half to three quarters of an inch broad; frond flat, smooth, and thinner than most species; bright green; somewhat flexible. (Plate VII.) [Illustration: PLATE VII. Halimeda tuna. Halimeda tridens. Bryopsis plumosa. Codium tomentosum.] [Illustration: PLATE VIII. Caulerpa Mexicana. Caulerpa Wurdemanii. Caulerpa plumaris. Caulerpa paspaloides.] ^H. tridens.^ Fronds solitary, erect; base composed of confluent articulations; above divided into numerous branches of articulations, which are all flat, and in one plane giving a fan-shaped outline; middle joints wedge-shaped; upper ones divided into three lobes, frequently bearing articulations at the summit of each lobe; thinly incrusted with lime; color bright green. (Plate VII.) ^H. opuntia.^ Articulations kidney-shaped, flat, rather thin; margins scalloped; irregularly branched and spreading; dense tufts. ORDER =CODIACEÆ= GENUS ^Bryopsis^ ("/Moss-like/") There are said to be about twenty species of this genus. They are distinguished by the manner of branching, but are not very definitely marked. All are erect, one-celled, branching stalks, and are feather-like in appearance.