very slightly so; apical cell truncate, with the outer membrane 

 thickened; cells quadrate, or longer ( sometimes shorter ) than wide, 

 4.5-12ja in diameter, 4.8/u, long, usually not constricted at the cross 

 walls except in the distal end of the trichome; cell contents granular. 

 On submerged aquatics or floating in small tufts in hard water 

 lakes; forming thick, streaming tufts in flowing water; forming a 

 membrane on casing of a spring. Mich., Wis. 



Phormidium Setchellianum Gomont 1892a, p. 156 

 Filaments forming a thin, weft-like, dark purple layer; sheaths 

 thin and generally confluent with the mucilage of the plant mass; 

 tiichomes curved or straight, often hooked at the apex, which is 

 not tapered, or but very slightly so; apical cell capitate with a coni- 

 cal calyptra; cells 4-4.8/a in diameter, 3-6/x long, constricted at the 

 cross walls; cell contents purplish. 

 On muddy shores. Mich. 



Phormidium subfuscum Kuetzing 1843, p. 195 

 PL 107, Fig. 16 



Filaments forming a widely expanded, thin and lamellate plant 

 mass, dark green ( or olive ) in color. Trichomes straight, agglutinated 

 and more or less parallel, relatively short; straight at the apex and 

 briefly tapered; sheath becoming diffluent with the mucilage of 

 the plant mass. Apical cell capitate, with a broadly rounded calyp- 

 tra. Cells 5.5— 11/A in diameter, 2— 4/x long, granular, not constricted 

 at the cross walls. Cell contents sometimes granular and blue- 

 green in color. 



On log near shoreline of lake, Mich. 



Phormidium tenue ( Menegh. ) Gomont 1892a, p. 169 



PI. Ill, Fig. 7 



Filaments forming a blue-green, membranous expanse; sheaths 

 diffluent, mucilaginous and indistinct; trichomes straight except at 

 apices, where they are bent and attenuated; apical cell conical, 

 smooth, neither capitate nor furnished with a calyptra; cells 1.2-3/i 

 in diameter, 2.5-5/i, long, constricted at the cross walls, which are 

 not granulate; cell contents homogeneous. 



Common, forming thin films on submerged aquatics and inter- 

 mingled with decaying vegetation in shallow water. Mich., Wis. 



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



PI. 107, Fig. 18 

 Filaments forming an expanded, thin but firm plant mass, either 



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