and confluent with the mucilage of the plant mass; apex slightly 

 tapering, either straight or somewhat curved and capitate, with a 

 calyptra; cell contents blue-green; cells 4-7/1, in diameter, 2-5/x long, 

 not constricted at the cross walls, which are granular. 

 Mich. 



Phormidium Corium (C. A. Ag. ) Gomont 1890, p. 355 



Filaments compactly intertwined and entangled to form a soft 

 but tough membranous layer, dark bluish-green to black; sheaths 

 thin and becoming confluent with the mucilage of the plant mass, 

 trichomes curved (or sti'aight) and slightly tapering at the apex, 

 but not capitate and without a calyptra; cells 3-4.5/x in diameter, 

 3.4-8/t long, not constricted at the cross walls; cell contents granular. 



Mich. 



Phormidium favosum (Bory) Gomont 1892a, p. 180 



PI. Ill, Fig. 2 



Filaments forming a dark green expanded, thin or thick plant 

 mass; individual sheaths not clearly evident; trichomes straight or 

 flexuous and sometimes coiled in the distal region which tapers 

 slightly; apical cell capitate, with a conical or hemispherical calyp- 

 tra; cells 4.5-9/x in diameter, 3-7/i, long, not constiicted at the cross 

 walls but with a double row of granules at the partitions; cell con- 

 tents blue-green. 



In tiough, at Osceola, Wisconsin. 



Phormidium incrustatum ( Naeg. ) Gomont in Bornet & 

 Flahault 1889, p. CLIV 

 Filaments forming a dark red or violet stratum, encrusted with 

 lime. Trichomes parallel, or curved and entangled in thin mucous 

 sheaths; straight at the apex and tapering slightly, not capitate. 

 Apical cell obtuse-conical. Cells quadrate or slightly longer than 

 wide; not constricted at the cross walls, which are sometimes gran- 

 ular; 4-5/x in diameter, 3.5-5.2/i long. 

 In a stream at Osceola, Wisconsin. 



Phormidium inundatum Kuetzing 1849, p. 251 

 PI. Ill, Fig. 3; PL 107, Fig. 15 

 Filaments forming a blue-green, gelatinous, membranous expan- 

 sion; individual sheaths scarcely discernible, diffluent. Trichome 

 straight and parallel, tapering at the apices to form a conical apical 

 cell, which is not capitate. Cells quadrate or short-cylindric, 3-5//. 



[494] 



