502 BULLETIN OF THE BUREAU OF FISHERIES. 



This species is distinguished from C. dasyphylla by its more slender form, its habit, and its generally 

 lighter color. The branches are borne fairly uniformly throughout and not in clusters in the upper part 

 of the frond; the ultimate branches are more slender and often shorter than in C. dasyphylla, but it lacks 

 the short, top-shaped branchlets frequently found in the latter species, and the apices, so far as has been 

 observed, do not bear short, pointed projections. The species has not been found on Shackleforfl jetties 



or in the harbor. 



Genus 3. Polysiphonia Greville. 



Polysiphonia, Greville, 18243, p. 308. 



Frond erect (or creeping at first, later becoming erect), usually terete, sometimes 

 slightly flattened, laterally and radially or dichotomously branched, usually elongated 

 and delicate, slender and flexible, or bristlelike and rigid ; structure cellular or filamentous- 

 cellular, consisting of a central row of cells surrounded by a circle of 4 to 24 pericentral 

 cells, this primary structure remaining naked or being clothed in the elder parts by a 

 layer of small, cortical cells; sometimes small secondary cells are formed outside of and 

 alternating with the pericentral cells, sometimes the central axis is inclosed by a later- 

 developed layer of rhizoidal filaments; the central cells and inclosing pericentral cells 

 are of the same length, so that the frond has a segmented appearance which is evident 

 throughout or, in the corticated species, only in the younger portions; growth mono- 

 podial, apical cell transversely or obliquely segmented, trichoblasts often borne in 

 regular order, somewhat persistent, but finally evanescent, secondary shoots often borne 

 in regular order; tetrasporangia arising from the pericentral cells of ultimate branchlets, 

 usually singly and in spiral rows, sometimes in straight rows, covered by special 

 cover cells, triangularly divided; antheridia lanceolate or long elliptical, attached by 

 short stalks to trichoblasts near the apices; procarps borne on trichoblasts near the 

 apices; cystocarps becoming secondarily attached to branches, borne on short stalks or 

 sessile, conspicuous, oval or urn-shaped, pericarp thin, opening by prominent carpostome, 

 gonimoblast composed of branched filaments radiating from a basal placenta, bearing 

 single, large, elongated, pear-shaped carpospores in their terminal segments; tetra- 

 sporangia, antheridia, and cystocarps borne on separate plants; sexual and asexual 

 plants alternating with each other in the life cycle. 



About 130 species of varied habit and size, often separated by variable characters, in 

 all seas. The genus is easily recognized, but determinations of the species are usually 

 difficult. This is the central, characteristic genus of the family about which all the 

 others are grouped. 



KEY TO SPECIES. 



a. Frond with four pericentral cells, no cortex b. 



b. Branching somewhat dichotomous, segments about 1.5 diameters long below, 2 to 5 



diameters in branches i. P. havanensis (p. 502) 



bb. Branching pinnate, segments about i diameter long throughout, sometimes up to 2.5 



diameters 2,. P. har-veyi (p. 503). 



00. Frond with more than four pericentral cells, no cortex over most of thallus c. 



c. Frond with 5 to 8 (usually 6) pericentral cells, segments i to 3 diameters long, 



dichotomous 3. P. denudata (p. 503). 



cc. Frond with 8 to 20 (usually 16) pericentral cells, segments i to 4 diameters long, 



branching pinnate 4. P. nigrescent (p. 504). 



1. Polysiphonia havanensis Montagne. PI. CVIII, fig. 3. 



Polysiphonia havanensis, Montagne, 1837, p. 352. 

 Polysiphonia havanensis, Harvey, 1853, p. 34. 

 Polysiphonia havanensis, De Toni, 1903, p. 894. 

 P. B.-A. No. 1043. 



