Key to the Species 



1. Cells spindle-shaped, numerous and scattered within a gelatinous 



investment but with the longitudinal axes parallel Q. lacustris 



1. Cells arcuate, lunate, or straight, arranged in bundles of 4 



within the gelatinous investment, fewer in number than above 2 



2. Cells straight, margins subparallel in the 



median portion; poles rounded Q. closterioides 



2. Cells arcuate or lunate; poles pointed Q. Chodatii 



Quadrigula Chodatii (Tan.-Ful.) G. M. Smith 1920, p. 138 



[Ankistrodesmus Chodati ( Tan.-Ful. ) Brunnthaler] 



PI. 59, Figs. 1-3 



Free-floating; cells long, fusiform to slightly lunate or arcuate, 



tapering to subacute points, longitudinally arranged within a 



broadly fusiform colonial envelope; chloroplast a parietal plate with 



a median notch, containing 2 pyrenoids; cells 3.5-7/a in diameter, 



30-80/A long; colony as much as 250|U, long. 



Rare; in euplankton of a few lakes as well as in the tychoplankton 

 of shallow water. Mich., Wis. 



Quadrigula closterioides (Bohlin) Printz 1915, p. 49 

 PI. 58, Figs. 9, 10 

 Cells long, straight, but with one margin slightly curved, cylin- 

 drical in the mid-region, tapering to sharply rounded apices, 

 arranged in longitudinal bundles of 4 within a fusiform colonial 

 envelope; chloroplast parietal, covering almost the entire cell wall, 

 with a median notch; 1 pyrenoid; cells 4-6/x in diameter, 22-35-(45)/x 

 long. 



Common in many soft water lakes. Mich., Wis. 



Quadrigula lacustris (Chod.) G. M. Smith 1920, p. 139 



[Ankistrodesmus lacustris ( Chod. ) Ostenf eld] 



PI. 59, Figs. 4, 5 



A free-floating, fusiform-shaped colony containing many short, 



fusiform cells, mostly arranged in pairs; cells straight, but with 



slightly convex margins, tapering to blunt points; chloroplast a 



parietal plate, sometimes twisted in the cell, without a median 



notch, with 1 pyrenoid; cells 3-5;u, in diameter, 20-25ja long. 



Rare; in the plankton of many lakes, mostly soft water. Mich., Wis. 



TETRAEDRON Kuetzing 1845, p. 129 

 Cells solitary and unattached; of various shapes, triangular and 

 flat, pyramidal, polyhedric; the angles entire, with or without spines, 



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