Protologue Description: Hydrocoleum majus, n. sp. Stratum dark aeruginous. Sheaths agglutinated, forming mostly an amorphous, gelatinous, diffluent mass, from which the outer extremities of the trichomes project, naked or enveloped in broad ragged sheaths, or the trichomes escape entirely and become independent. Trichomes aeruginous, not contracted at the nodes, 25-30 µ in diameter; articles 5-10 times shorter than the diameter of the trichome (3-6 µ long) ; dissepiments granulated; apex attenuate-truncate ; apical cell conspicuously calyptrate.
Found in brackish marsh ditches, forming a gelatinous, tubular coating on old stems of Spartina, later floating; occurring at Bridgeport, Connecticut, in late spring and early autumn, disappearing in winter and in the heat of summer. Distributed in Collins, Holden and Setchell, Phycotheca Boreali-Americana, No. 602.