MARINE AIvG^E OF BEAUFORT, N. C. 497 



cc. Polysiphonous axis plainly evident, thallus composed of one or more circles of large 

 cells around a row of central cells, apical cell transversely or obliquely divided, 



tetrasporangia produced from pericentral cells d. 



d. Thallus with conspicuous erect branches from a creeping base, distichously 



branched, pericentral cells with secondary transverse divisions 5. Bostrychia (p. 506). 



dd. Thallus erect throughout, radially branched, pericentral cells without second- 

 ary transverse divisions e. 



. Trichoblasts persistent, covering portions of the frond in the form of colored, 



branched, monosiphonous filaments 4. Brongniartella (p. 505). 



ee. Trichoblasts evanescent, occurring only on the younger portions of the frond ./. 



/. Thallus with dense parenchymatous structure, polysiphonous arrangement not 

 conspicuous, covered by a dense cortex, pericarp thick, tetrasporangia occur- 

 ring singly without conspicuous order in spindle-shaped branchlets markedly 



constricted at their bases 2. Chondria(p. 498). 



Jf. Thallus with rather loose structure, polysiphonous arrangement-conspicuous, 

 naked or covered by a thin cortex, pericarp thin, tetrasporangia usually 

 occurring singly in straight or spiral rows in scarcely altered branchlets. 



3. Polysiphonia (p. 502). 



Genus i. Laurencia Lamouroux. 

 I<aurencia, Lamouroux, 1813, p. 130. 



Frond erect, terete or flattened, richly radially or distichously branched; structure 

 cellular, dense, cells large within, becoming smaller toward the surface, situated without 

 conspicuous order, central row of cells not evident except toward apices, apical cell 

 surrounded by evanescent trichoblasts, sunk in a depression, somewhat tetrahedrally 

 divided, pericentral cells not formed; tetrasporangia scattered over the ultimate, fre- 

 quently shortened branchlets among the outer subcortical cells, with no apparent rela- 

 tion to pericentral cells, triangularly divided; antheridia oval to oblong, borne on tufts 

 of branched filaments (trichoblasts) arising from the bases of open, scutellate, apical 

 depressions; procarps borne on trichoblasts within the apical depressions, coming sec- 

 ondarily to lie on the surface as a result of later growth, cystocarps scattered over the 

 smaller branches, prominent, ovate to spherical, pericarp thick, opening by an apical 

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

 bearing single pear-shaped carpospores in their terminal segments. 



About 50 species, often with ill-defined limits and exceedingly difficult to determine, 

 in warm seas. 

 Laurencia tuberculosa J. Agardh. 



Laurencia tuberculosa, J. Agardh, 1852, p. 760. 

 Laurencia tuberculosa, Harvey, 1853, p. 75. 

 Laurencia gemmifera var. 0, Harvey, 1853, p. 73. 

 Laurencia tuberculosa, De Toni, 1903, p. 801. 

 A. A. B. Ex. No. 62. 

 P. B.-A. Nos. 439, 1937- 



Frond subterete or slightly flattened, about i to 2 mm. wide, 5 to 20 cm. tall, branching alternate 

 subdistichous, pinnately decompound, branches spreading, bearing numerous short, simple, blunt, wart- 

 like tubercular branchlets distichously arranged below, naked toward the apices; tetrasporangia in the 

 short, tubercular branchlets; texture rather cartilaginous; color crimson to fleshy purple. 



Florida and West Indies. 



