^T. atomaria.^ Spreading, fan-shaped frond; clefts irregular and not extending to the basal stem; spores arranged in dark wavy lines and spots on the frond, giving it a mottled appearance and beautiful gradation of color. Found in tropical seas. (Plate XIII.)
^P. pavonia^, the peacock's-tail. Frond broadly fan-shaped; substance between membranaceous and leathery; powdery on the outer surface; deeply and variously cleft or entire; several laminæ emanating from a stalk-like base; each lamina fan-shaped; concentric lines numerous; variegated in zones. This beautiful alga is always regarded as a prize. It is found on stones at low-water mark, and is not uncommon south of Charleston, South Carolina, but is more luxuriant in tropical seas. (Plate XIII.)
^H. polypodioides.^ Fronds flat, forked, notched on lower part; divisions about one quarter of an inch wide; distinct midrib; olive-green; grows in tufts. It is found in North and South Carolina, and is abundant on the Florida Keys. (Plate XIV.)
^C. multifida.^ Frond erect, flat; branches in a forking manner; ultimate branches fine and short, and with branchlets on the tips. This species resembles /Taonia/. It is found in Southern waters. (Plate XIV.)
^H. lorea^, the sea-thong. A cup-shaped base, from the center of which arises a flat, strap-like frond one fourth to one half of an inch wide and two to twenty feet long, branching dichotomously (or by forking), and dotted with pits, or conceptacles, in which the spores are formed. Found in the extreme North. [pg072]
The rockweeds. The plants of this genus grow in thick bunches, and are found in great abundance between tide-marks. The plants are attached by sucker-like disks to the rocks, from which they hang like fringe when the tide recedes; when it rises they float and sway in the water in beautiful bouquet-like forms. In color they are brown or olive-green, in texture thick and leathery, but they sometimes expand into thin membranes. They are many times forked in the same plane, which produces a flat thallus. They often have a distinct midrib. The air-vessels, whose function it is to float the plant, are disposed along the midrib, usually in pairs.
The species are named according to the divisions of the frond, and the disposition, or presence, of the air-bladders and the /conceptacles/, or spore-chambers.