PAPERS BY MEMBERS 73 



Euglena sanguinea Ehrenberg. 



Appearing at intervals of a year or more in a number 

 of our larger ponds in such quantity as to produce a 

 brick-red or blood red scum on the water. 

 Euglena spirogyra Ehrenberg. 



Rare. Only a few scattered specimens have been 

 recorded. 

 Euglena viridis Ehrenberg. 



Probably the commonest form in polluted streams, ponds, 

 and wet-weather pools. But it is difficult to be certain 

 of the identification when the chromatophore is masked 

 by other cell contents. 

 Phacus longicauda ( Ehrenberg) Duj. 



Rare in ponds. 

 Phacus pleuronectes ( O. F. M.) Duj. 

 Periodically abundant in ponds. 



Peridiniales 

 Peridiniaceae 

 Ceratium hirundinella ( O. F. M.) Schrank. 



Common at times in all the ponds of eastern Illinois from 

 which I have collections. 



Bacillariales 

 Bacillariaceae 



Melosira varians Agardh. 



A periodic constituent of the plankton in the streams of 

 this region. 

 Meridion circulare f Grev.) Ag. 



Occasionally very abundant in small ditches and stream 

 pools. 



Conferyales 

 Confervaceae 

 Ophiocytium arbuscula (A. Braun) Rabenhorst. 



Rare. Recorded from the pond southeast of Lerna, and 

 a pool near Decker. Ind. 

 Ophiocytium cochleare ( Eichwald) A. Braun. 



Common in ponds during the colder months. 

 Ophiocytium gracilipes (A. Braun) Rabenhorst. 



Rather rare in pools during the colder months of the 

 year. 

 Ophiocytium parvulum ( Perty) A. Braun. 



Rather common in ponds and pools during late fall and 

 early spring. 

 Conferva bombycina Agardh. 



\'erv abundant in streams, ponds and pools. The form 

 tenuis frequently occurs with it. 



