visible to the unaided eye; trichomes very slightly and briefly taper- 

 ing at the apex. Apical cell usually not capitate, sometimes very 

 slightly so, the outer membrane broadly convex and smooth. Cells 

 32-55- ( 80 )/x in diameter, 4-8.7 fx long; not constricted at the cross 

 walls, which are not granular; cell contents densely granular. 



Common in tychoplankton of a variety of lakes and small ponds; 

 in marshes. Mich., Wis. 



Oscillatoria prolifica (Grev. ) Gomont 1892a, p. 205 

 PL 110, Figs. 2, 3 

 Trichomes aggregated to form a floating, purple-black expanded 

 mass; straight, but flexible, slightly tapering toward the apex. Apical 

 cell capitate, with a broadly flattened calyptra. Cells 2.5-5/i, in 

 diameter, 4-6/x long, without constrictions at the cross walls, which 

 are sometimes granular; cell contents densely granular. Plant 

 described as becoming lilac-colored upon drying. 

 Tychoplanktonic and euplanktonic. Mich., Wis. 



Oscillatoria rubescens De Candolle 1825, Mem. Soc. Phys. 



Nat. Geneve, 2, p. 29 



PI. 107, Fig. 21 



Trichomes solitary or forming small fascicles, appearing red or 

 purple in the plankton; very slightly if at all tapering toward the 

 apex. Apical cell often capitate, with a calyptra, but (in our speci- 

 mens ) as often broadly rounded and smooth. Cells 6-8/a in diameter, 

 2-4/x long; not constricted at the cross walls, which are usually 

 granular; cell contents with pseudovacuoles. 



Our specimens definitely appear to belong to this species, but 

 the lack of capitate apical cells in most plants observed, and the 

 non-tapering trichomes are in disagreement with the original de- 

 scription. 



Euplanktonic and tychoplanktonic. In hard water lakes of south- 

 ern Michigan; forming blooms during late winter immediately after 

 the disappearance of ice. 



Oscillatoria sancta ( Kuetz. ) Gomont 1892a, p. 209 

 PI. 110, Fig. 4 



Trichomes aggregated to form a dark gray-green plant mass (in 

 our collections), usually on submerged vegetation; straight, not at 

 all or scarcely tapering toward the apex. Apical cell somewhat 

 capitate, with a calyptra, and with a much thickened outer mem- 

 brane. Cells 11— 13— (20) /x in diameter, 4— 5yu long; sHghtly con- 

 stricted at the cross walls, which are conspicuously granular; cell 

 contents coarsely granular, olive- or gray-green in color. 



On submerged aquatics. Mich., Wis. 



[490] 



