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IOWA ACADEMY OF SCIENCE 
Filaments 5. 5-6.5 u in diameter O. tenuis 
Filaments 6.5-8.5 u in diameter O. limosa 
Filaments 9-10 u in diameter O. nigra 
Articulations less than half as long as broad. 
Filaments 12-18 u in diameter. 
Forming greenish stratum O. froelichii 
Forming dark olive brown stratum O. froelichii fusca 
Filaments broader than 18 u. 
Filaments 30-45 u in diameter, 4-5 articulations to the width 
O. princeps 
Filaments 38-56 u in diameter, 9 articulations to a diameter 
O. imperator 
33. 0. angustissima W&G. S. West. 
Ontario, la. In pond with other algae. Buchanan. 
3U. O. tenerrima Kuetz. 
A common species in stagnant water, and on soil. 
Fayette. Fink. 
Ames. Effluent of the filter beds of the College Sewage disposal plant. 
Buchanan. 
Ames. On the soil in greenhouse. Buchanan. 
Eagle Grove. Pond. Buchanan. 
35. O. tenuis. Ag. 
This is the most common of the Oscillarias, being almost universally 
present in stagnant water, and in slow running streams, where water 
drops upon the soil, on boards, etc. 
Iowa City. Hobby. 
Grinnell. Fink. 
Allamakee Co. Spring. Pammel. 
Eagle Grove. Hewitt’s Pond. Amid Utricularia. Buchanan. 
Eagle Grove. From a watering trough. Buchanan. 
Eagle Grove. Stone under a water drop, very dense mat. Buchanan. 
Ames. Board from a spring. Buchanan. 
Ames. Effluent of the filter beds. Buchanan. 
And many similar localities. 
36. O. limosa. Vauch. 
Next to the tenuis this is probably the commonest species in the state. 
Iowa City. Hobby. 
Ames. Bessey. 
Fayette. Fink. 
Ames. On damp earth, forming a thin coating. Buchanan. 
Eagle Grove. Moist earth. Buchanan. 
31. 0. nigra Vauch. 
Usually floating free in stagnant water. 
Iowa City. Hobby. 
Ames. Bessey. 
Ames, stagnant ditch. Buchanan. 
38. O. froelichii Kuetz. 
Floating among other algae in ponds. 
Iowa City. Hobby. 
