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134 THE MARINE ALGÆ OF NEW ENGLAND. straight or falcate, sharply serrate, especially on the lower side, and the opposing pinna pinnately divided or compound; pinnæ nearly at right angles to the axis, apices acute; tetraspores borne in dense ellipsoidal cluster either at the ends of the simple pinnæ or on the serrations and tips of the compound pinnæ; tetrasporic masses interspersed with monosiphonous incurved branches; favellæ in similar position to the tetraspores, nearly concealed by the large, incurved, usually serrate divisions of the involucre. On algæ, especially on stems of Laminaria, below low-water mark. Common north of Boston; Thimble Islands, near New Haven, and dredged off Block Island, Prof. Eaton. A common and characteristic alga of our northern coast, extending through Greenland to the northern coast of Europe, and also found in the North Pacific. The present species, together with Euthora cristata and Delesseria sinuosa, form the greater part of the specimens collected for ornamental purposes by ladies on the Northern New England coast. P. serrata, when dried, is usually very dark colored, unless it has previously been soaked for some time in fresh water, and it does not adhere well to paper unless under considerable pressure. It cannot be mistaken for any other species growing on cur coast. Whether it is a variety of P. plumosa is a question about which writers do not agree, but, although in this connection our form has been kept as a distinct species, it is highly probable that it is really nothing more than a coarser northern form of P. plumosa. The typical form of P. plumosa is certainly unknown in New England. The type is more slender, and the pinnæ are pectinate, not serrate. The position of the fruit is the same, the principal difference being in the more strongly marked involucre of the favellæ and in the tetraspores, which are borne on densely fastigiate branches, which have no cortications, and some of which are incurved and project beyond the general sporiferous mass. In P. plumosa the tetraspores are also borne on the tips of monosiphonous branches, but they are not densely conglomerate, nor are the projecting incurved ramuli prominent. The present species is very rare south of Cape Cod, being known in only two localities and in a much reduced form. CERAMIUM, Lyngb. (From κεραµιος [keramios], a small pitcher.) Fronds filiform, dichotomous or occasionally subpinnate, monosiphonous, composed of a series of large ovate or quadrate cells, with bands of small corticating cells at the nodes, and in some species also extending over the internodes; antheridia forming sessile patches on the upper branches; tetraspores tripartite, formed from the corticating cells; cystocarps (favellæ) sessile at the nodes, usually involucrate. A universally diffused and easily recognized genus, of which, however, the species are by no means easily recognized. The genus is distinguished by the monosiphonous, dichotomous frond, with bands of small corticating cells at the nodes, or, in some cases, covering the internodes as well. The tips of the filaments are forked and usually decidedly incurved, whence the generic name is derived. The apical growth and formation of the cortex is fully detailed by Nægeli and Cramer in Pflanzenphysiologische Untersuchugen, Part IV. The procarp in Ceramium is furnished with two trichogynes and a single carpogenic cell formed from the cortical cells on the convex side of the
REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 135 tips of the branches. The genus has been split up into a number of different genera by Kützing, but by most writers his divisions are only accepted as subgenera. Sterile specimens are not easily determined and it is always desirable to have tetrasporic plants. Although we have an abundance of the genus on our coast, the number of species is comparatively small, and the group of species having spines at the nodes is, as far as is known, quite wanting. SECT. I. Fronds without spines, cortical cells decurrent from the nodes and more or less completely covering the internodes. C. RUBRUM, Ag. (C. rubrum, Phyc. Brit., Pl. 181.) Fronds robust, dichotomous, subfastigiate, branches erect, apices incurved or forcipate, nodes contracted below; tetraspores in irregular series at the nodes, immersed; favellæ lateral, solitary, with a short involucre. Var. PROLIFERUM, Ag. (C. botryocarpum, Phyc. Brit., Pl. 215.) Fronds beset on all sides with numerous, lateral, simple or forked branchlets. Var. SECUNDATUM, Ag. Branchlets generally secund. Var. SQUARROSUM, Harv. Fronds small, regularly dichotomous, fastigiate, with very few, short, lateral branchlets, lower divisions distant, spreading, upper divisions close together, widely spreading, apices often revolute. Everywhere common; var. squarrosum on Zostera, Massachusetts Bay. A ubiquitous and variable species, of which we have enumerated only the principal forms. The typical form is easily recognized, and the same is true of most of the varieties. The var. decurrens has the internodes partly naked, especially in the upper part. The var. decurrens of the Nereis is referred by Agardh to the next species, and is distinguished from the true var. decurrens of C. rubrum, which has immersed tetraspores, by the large tetraspores arranged in a regular circle at the nodes and projecting decidedly above the surface. C. circinnatum, Kütz. Fronds setaceous, dichotomous, fastigiate, divisions erect, patent, apices forcipate, internodes partly corticated by the cells which are decurrent from the nodes; tetraspores large, projecting in a ring around the upper nodes. Glencove, L. I., Mr. Young; Dartmouth, Mass., Miss Ingraham; Magnolia, Mass., Mrs. Bray. Agardh, in his Epicrisis, refers to the present species the C. decurrens of Harvey (Phyc. Brit., Pl. 276), which in the Nereis Am. Bor., is made a variety of C. rubrum. There is a var. decurrens of C. rubrum which is admitted by Agardh, which, if we understand correctly, has small immersed tetraspores. This form occurs also with us, but we have no notes as to the locality. To the present species we refer forms in which the upper internodes are scarcely corticated at all and in which the large, projecting tetraspores are in a single ring at the upper nodes.
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