416 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 chthonoplastes 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. RIVULARIACEZ (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, passout 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 and Flahault. 
Dichothrix, Zanardini, 1858, p. 297. 
Dichothrix, Bornet and Flahault, 1886, p. 373. 
Plant mass cespitose, 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, pl. 14, f. 3. 
Dichothrix penicillata, Bornet and Flahault, 1886, p. 379. 
Dichothrix penicillata, Forti, in De Toni, 1907, p. 644. 
Dichothriz penicillata, Tilden, 1910, p. 280. 
P. B.-A. Nos. 62, 1112. 
Plant mass czspitose, 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 ro filaments) on one piece of Chondria littoralis, Bogue Beach, Sep- 
tember 19, 1906. (?) 
The last-mentioned tuft seemed to belong to this species, but contained too few filaments fora posi- 
tive determination. This is the most northern station reported for this species. 
