^P. fastigiata.^ This species grows on /Ascophyllum nodosum/ in a globular tuft, and appears like a dark-brown ball, one inch to three inches in diameter. The frond is a dense mass of rigid filaments branching many times in a forking manner and at broad angles. The ends are of nearly equal length, giving the plant a spherical shape. It is common from New York northward at all seasons, and is easily recognized by its general form and place of growth. Egg-shaped cystocarps, or spore-cases, occur in the ends of the terminal filaments. (Plate XXV.)
^P. nigrescens.^ Frond three to twelve inches long, rigid below, soft above; main stem thick as a bristle, but not always easy to distinguish; branches alternate and densely branched at the ends; siphons twelve to sixteen in number; filaments banded; color black or very dark brown. (Plate XXVII.)
^P. parasitica.^ Frond one inch to three inches long; branched in a pinnate or feather-like manner; filaments flat; all branches and branchlets emanating from the edges and on the same plane, giving a flat frond; color reddish-brown; resembles a fine /Ptilota plumosa/; cystocarps on short stalks. It is found on the California coast. (Plate XXV.)
^P. dendroidea.^ This is a variety of the species /P. parasitica/. Frond four to five inches long; main branches placed at irregular intervals, but the secondary branches at regular intervals and alternate; branches [pg088] set at acute angles, giving the plant a slender appearance; color black or dark brown. It is common on the California coast. (Plate XXVI.)
^P. Baileyi.^ Frond three to six inches high, flat; branches emanate from edges of the flat stems; main branches wide-spreading and irregularly placed, secondary branches regular and alternate; branchlets one eighth to one half of an inch long, covered on the edges and around the top with incurved ramuli; branchlets broken off near the base of the branches in mature plants; branchlets usually uniform in length, but occasionally one is longer and branches like the primary stem; color black. Common on the California coast.
^P. Harveyi.^ Frond two to six inches high; grows in globose tufts, and has a bushy aspect; branches stiff and wide-spreading; stems and branches beset with simple or branched spine-like branchlets; color dark brown, or black when dry; does not collapse when taken from the water; cystocarps on short stalks; siphons four in number. It grows on eel-grass and algæ, and is common in Long Island Sound and northward. Called locally /niggerhair/. (Plate XXVI.)