^C. crispus.^ Frond begins with flattened stem, which divides and subdivides many times in a broad-forked, fan-like manner; varies greatly in length and breadth of divisions, also in size and color, according to conditions of its habitation. In shallow tide-pools it is pale and [pg081] stunted; but under the shelter of rocks, in deep water, it grows in dense masses and is a dark purplish-red or reddish-green. Often it appears iridescent when seen through the water, with the sun shining on it. It is firm and leathery in substance. It is an edible alga, and was formerly very generally used for culinary purposes. At Hingham, Massachusetts, large quantities are gathered as an article of commerce. It is a beautiful and very common plant found from New York northward. (Plate XVII.) GENUS ^Gigartina^ Of the species of this genus but one is found on the eastern coast; on the Pacific coast there are several, and they are large and conspicuous. [Illustration: PLATE XVIII. Gigartina mamillosa. Gigartina radula. Gigartina spinosa. Gigartina microphylla.] ^G. mamillosa.^ Frond three to six inches high, one inch to two inches broad, flat, leathery, gelatinous; forking near the base, then dividing and subdividing in the same plane; segments more or less wedge-shaped and with a tendency to roll inward; covered with numerous small nipple-like protuberances which contain the spores. These projections distinguish this genus from /Chondrus/, which it otherwise resembles, and with which it grows. The color is dark purple. It is found from Boston northward. (Plate XVIII.) ^G. radula.^ Frond flat and thick; rising from a short stem and widening to several inches; sometimes tapering to the top, sometimes blunt or divided, sometimes cleft on the sides, but usually simple; covered with wart-like projections; color dark, livid red. It is found on the Pacific coast at all seasons, growing on rocks between tide-marks. Large specimens are one foot to three feet long and six to ten inches wide. (Plate XVIII.) ^G. spinosa^ ("thorny"). Frond thick, leathery; surface rough and spiny; form variable, the divisions sometimes emanating from a broad, flattened base, or again branching from a main axis; all covered with the protruding processes peculiar to the genus; color dark red, brown, or purple. It is found on the California coast. (Plate XVIII.) ^G. microphylla^ ("small-leaved"). Plant rises from short, flat stem, and rapidly expands into a flat, wide, thin frond which is simple or divided into two or three segments, each of which tapers into a long, pointed apex; thickly covered with long, slender spines, and on its edges bearing small, thin leaflets; color brownish-red. It is abundant on the California coast. (Plate XVIII.) GENUS ^Phyllophora^