4! 6 BULLETIN OF THE BUREAU OF FISHERIES. 



somewhat attenuated apices, apical cell rotund, cells up to four times shorter than diameter, cell con- 

 tents homogeneous, pale blue-green. 



Maine; Massachusetts; England; Norway. 



Very abundant with Chroococcus turgidus and Microcoleus chthonop tastes on ocean beach at Ocracoke, 

 N. C., covering many square meters just beyond high-tide line, August, 1907. 



This is the most southern station reported for this species. 



Family 4. RIVULARIACEyE (Meneghini) Kirchner. 



Filaments tapering from base to apex, terminating above in a colorless hair, simple 

 or branched, associated in brushlike or gelatinous layers, rarely solitary; false branches 

 due to development of a new trichome from a cell of the main trichome, usually occurring 

 immediately under an intercalary heterocyst, rarely by the perforation of the sheath 

 between two heterocysts by the trichome, either separating immediately and forming a 

 new sheath, or remaining for some time within the original sheath; heterocysts usually 

 present, usually basal, occasionally intercalary; multiplication by vegetative division 

 and hormogonia, sometimes by gonidia. 



The apical cells always seem nearly empty and are usually colorless; the basal cells 

 show blue-green, violet, red, or brownish cell contents. Sheaths cylindrical, gelatinous 

 or membranaceous, homogeneous or stratose, colorless, yellowish or brownish. The 

 sheaths are often split by apical elongation into superposed lamina; often the inner 

 sheaths, becoming dissolved, pass out from the apex; often incrusted with lime. Hormo- 

 gonia are situated at the apices of the filaments and branches and, the apical hairs being 

 shed, pass out from the apices. To this is due the fact that the older filaments sometimes 

 lack the apical hairs. In some genera Chroococcus-like masses are formed at the base 

 from the vegetative cells and later grow into filaments. 



About 170 species, in fresh and salt water, throughout the world. 



Genus Dichothrix Zanardini, ex Bornet pnd Flahault. 

 Dichothrix, Zanardini, 1858, p. 297. 

 Dichothrix. Bornet and Blahault, 1886, p. 373. 



Plant mass caespitose, penicillate, or pulvinate, filaments more or less dichoto- 

 mously branched; sheaths cylindrical, trichomes often several (2 to 6) inclosed in a com- 

 mon sheath, heterocysts sometimes basal, sometimes intercalary, in one species not 

 present, no gonidia. 



Thirteen species in fresh or salt water, America, Europe, Africa. 

 Dichothrix penicillata Zanardini, ex Bornet and Flahault. 



Dichothrix penicillata, Zanardini, 1858, p. 297, pi. 14, f . 3. 

 Dichothrix penicillata, Bornet and Flahault, 1886, p. 379. 

 Dichothrix penicillata, Ford, in De Toni, 1907, p. 644. 

 Dichothrix penicillata, Tilden, 1910, p. 280. 

 P. B.-A. Nos. 62. iii2. 



Plant mass caespitose, fastigiate-penicillate, scattered or clustered, dark green; filaments short, 

 flexuous, 2 mm. long, 25 to 35 mic. diameter (in ultimate branches); sheaths thick, gelatinous, soft, 

 uniform, colorless; trichomes 15 mic. broad; cells shorter than diameter, cell contents olive, hetero- 

 cysts oblong, solitary. 



Florida; Mexico; West Indies; Guadeloupe; Red Sea. 



Covering a considerable portion of one piece of Sargassum natans, Bogue Beach, Beaufort, N. C., 

 June 29, 1907; one small tuft (8 to 10 filaments) on one piece of Chondria litioralis, Bogue Beach, Sep- 

 tember 19, 1906. (?) 



The last-mentioned tuft seemed to belong to this species, but contained too few filaments for a posi- 

 tive determination. This is the most northern station reported for this species. 



