[Illustration: PLATE XXXIII. Ptilota densa. Ptilota hypnoides. Ptilota hypnoides, magnified. Spyridia filamentosa.] ^C. rubrum^, red ceramium. This is a very common and robust species, found everywhere, and growing on everything. It is variable in appearance, becoming quite coarse when old, the incurving, claw-like ends, which are characteristic of the genus, being less pronounced. It branches by repeated forking, and, under the microscope, shows a bark-like [pg093] layer of cells over the whole surface, which make the ring-like bands on the filaments less conspicuous. [Illustration: PLATE XXXIV. Ceramium rubrum, var. proliferum. Ceramium rubrum, top of frond magnified. Ceramium diaphanum. Ceramium tenuissimum, var. patentissimum.] Variety ^proliferum^. Fronds beset on all sides with simple or forked branchlets. (Plate XXXIV.) Variety ^secundatum^. Branchlets generally arranged on one side of the filaments, or secund. ^C. strictum^ ("straight"). Brown or purplish-red filaments of hair-like fineness, growing in tufts two to six inches high, branching in narrow forks more and more closely as they reach the top of the frond. There are no principal branches, the filaments being of about the same diameter and regularly dividing in a forking manner throughout. The filaments are banded, the red rings being relatively very narrow. The white interstices at the base are several times longer than broad, but shorten gradually until at the top they are of equal length with the red bands. This species is common from Cape Cod to New York. ^C. diaphanum.^ This species has comparatively stout leading branches, with secondary alternate branches which are finer than the main stems and divide in a forking manner throughout, and ultimately become very fine. The color is brown or purplish-red, distinctly banded. It grows on eel-grass and algæ, and is found from Cape Cod to New York. (Plate XXXIV.) ^C. fastigiatum.^ Filaments of hair-like fineness and of about same size throughout; branched in regular forking manner throughout, the divisions being wide and distant at the base, but gradually becoming closer and narrower as they reach the top; the upper segments about equal, giving a level top and regular outline in mounted specimens; the terminal forks erect, or less incurved than in other species; small points or branchlets emanate from some of the nodes or joints between the bands of color; tufts globe-shaped, two to five inches high; color lake-red. This species grows on mud-flats and mud-covered rocks as well as on algæ and eel-grass. ^C. tenuissimum.^ Fronds two to four inches high, densely tufted; the forked divisions very wide or open; color rose-pink. Variety ^patentissimum^. Fronds small; the forked divisions distant and very wide open. A mounted specimen appears somewhat like network. The species is common in Long Island Sound. (Plate XXXIV.)