outer cells lunate, strongly curved, with acute apices; cells 3-6/x in 

 diameter, 16-22/x long. 



Common and widely distributed in many lakes and bogs. Mich., 

 Wis. 



Scenedesmus hystrix Lagerheim 1882, p. 62 

 PI. 63, Fig. 12 



Colony composed of 2-4-8 oblong-cylindric cells arranged in 

 a single series; apices narrowly rounded; wall uniformly beset with 

 short, sharp spines; cells 3-5/x in diameter, 8-18/i, long. 



Rare; in plankton. Wis. 



Scenedesmus incrassatulus Bohlin 1897, p. 24 

 PL 63, Fig. 14 

 Colony composed of (2)-4— 8 fusiform, subacute cells, arranged 

 in either 1 or 2 series (alternating); median cells slightly curved; 

 outer cells definitely curved, with the free walls strongly concave; 

 apices of the cells with a nodular thickening; cells 5-8/a in diameter, 

 17-24^ long. 



Typical plant not reported from our area. 



Scenedesmus incrassatulus var. m,ononae G. M. Smith 1916a, p. 440 



PI. 63, Fig. 13 

 A variety differing from the typical by its smaller, more slender 

 cells, 4.4-5/* in diameter, 11-12/i long. 

 Wis. 



Scenedesmus longus Meyen 1829, p. 774 



PI. 63, Figs. 15, 16 



Colony composed of 2-4-8 oblong-cylindric cells arranged in a 



single series; apices of both inner and outer cells with 1 or 2 sharp 



spines which are longer on the outer cells; cells 4-6/* in diameter, 



8-12/x long. 



Rare in the plankton of several lakes. Mich., Wis. 



Scenedesmus longus var. brevispina G. M. Smith 1916a, p. 471 

 A variety with more slender cells than the typical and with 

 shorter spines; cells 3-5/* in diameter, 9-11/* long. 

 Wis. 



Scenedesmus longus var. ellipticus ( West & West ) 

 G. M. Smith 1916a, p. 472 

 Colony composed of 4 ellipsoid cells arranged in a single series; 

 outer cells bearing 2 outwardly curved spines, the inner cells with 

 a single spine; cells 5/* in diameter, 12/* long. 



Wis. 



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