[Illustration: PLATE XXXVI. Prionitis Andersonii. Pikea Californica. Halosaccion ramentaceum. Polyides rotundus.] SUBORDER ~DUMONTIEÆ~ GENUS ^Pikea^ ^P. Californica.^ Divisions of frond thick, narrow, cartilaginous; central axis one eighth of an inch to one inch wide, three to four inches high, thickly set with similar branches irregularly placed; all bordered [pg095] with numerous forward-pointing branchlets, which in turn have spine-like ramuli of various lengths; frond flat, broadly spreading; dark red. It is common at all seasons on the California coast. (Plate XXXVI.) GENUS ^Halosaccion^ ^H. ramentaceum.^ Fronds brownish-purple, six to fourteen inches long, coarse and cartilaginous, cylindrical, hollow, compressed, attenuated at the base; more or less covered with simple or forked hollow branches half the size of the main stem. In exposed pools the plants are short and densely branched; in sheltered places they are larger and more delicate in texture. They are common on the northern New England and northern California coasts. (Plate XXXVI.) SUBORDER ~RHIZOPHYLLIDEÆ~ GENUS ^Polyides^ ^P. rotundus.^ Frond three to six inches high, cylindrical, cartilaginous, repeatedly forked, ends obtuse; spore-masses form numerous lighter-colored excrescences on the upper divisions of the frond; dark red. Common from New York northward, in deep pools and washed ashore. (Plate XXXVI.) SUBORDER ~SQUAMARIEÆ~ GENUS ^Peyssonnelia^ ^P. Dubyi.^ Frond completely adherent to the rock or stone on which it grows; color dark purple; somewhat calcareous; redder and thicker than next species. It is found at low-water mark or in deep water on the northern New England and northern California coasts. GENUS ^Petrocelis^ ^P. cruenta.^ Frond closely adherent, forming dark-purple velvety patches of indefinite outline on rocks and stones. Common north of Cape Cod. GENUS ^Hildenbrandtia^ ^H. rosea.^ Forms continuous pink incrustations of considerable extent on stones and rocks at low-water mark. Common everywhere. SUBORDER ~CORALLINEÆ~ The genera of this suborder are characterized by a calcareous or stony incrustation of the fronds, which gives them the appearance of corals. Most of the species are tropical. [pg096] GENUS ^Corallina^ ("/Coral-like/") ^C. officinalis^, common coralline. Frond grows from a disk in tufts more or less dense. The plant is rigid, and seems like jointed, branched coral. The articulations are cylindrical at the base, wedge-shaped and flattened above. Branches emanate from the top of the articulations. The color varies from reddish-purple to gray-green, and is often bleached white when exposed to the sun. Common in tide-pools and on rocks at low-water mark from New York northward. (Plate XXXVII.) GENUS ^Melobesia^