Pediastrum simplex ( Meyen ) Lemmermann 1897, p. 180 



PL 50, Fig. 2 

 Colony entire, composed of 16-32-64 smooth-walled cells; inner 

 cells 5- or 6-sided; peripheral cells with the outer free wall extended 

 to forai a single tapering, horn-like process with concave margins; 

 cells 12-18yu, in diameter. 



Common in the plankton of a number of lakes. Mich., Wis. 



Pediastrum simplex var. duodenarium ( Bailey ) 



Rabenhorst 1868, p. 72 



PI. 50, Figs. 4, 5 



Colony perforate, composed of 36-48-64 cells with their inner 

 margins concave, the outer margin of inner cells forming a long pro- 

 cess, peripheral cells forming a stout process; cells 11-15/i, in dia- 

 meter, 27-28;u, long; 36-celled colony 137/i, in diameter. 



Euplankter. Mich., Wis. 



Pediastrum tetras ( Ehrenb. ) Ralfs 1844, p. 469 



PL 50, Figs. 3, 6 



Colony entire; inner cells (frequently none) with 4-6 stiaight 



sides but with one margin deeply incised; peripheral cells crenate, 



with a deep incision in the outer free margin, their lateral margins 



adjoined along % of their length; cells 8-12- (16) /a in diameter. 



Common and generally distributed in both eu- and tychoplankton. 

 Mich., Wis. 



Pediastrum tetras var. obtusata Raciborski 1889, p. 32 

 Cells larger than in the typical plant, the outer margin of the peri- 

 pheral cells straight, not so emarginate; cells 14-18/* in diameter, 

 18-2^/Lt long. 



Euplankter. Wis. 



Pediastrum tetras var. tetraodon ( Corda ) Rabenhorst 1868, p. 78 



PL 50, Fig.7 

 Colony 4— 8-celled, outer margins of peripheral cells with deep 



incisions; the lobes extended into sharp, horn-like processes; cells 

 12-15/Li in diameter, 16-18/t long. 

 Euplankter. Mich., Wis. 



SORASTRUM Kuetzing 1845, p. 144 

 A spherical colony of either loosely or compactly arranged reni- 

 form, pyriform, cuneate or pyramidate cells, attached by radiating 

 strands to a common polyhedroid central body of mucilage; outer 



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