Pediastrum muticum var. crenulatum Prescott 1944, p. 356 



PI. 49, Fig. 9 



A variety differing from the typical in having crenulate or ir- 

 regularly wavy walls on both the adjoining and the outer free 

 surfaces; colony large, as many as 134 cells (in concentric rows of 

 34, 31, 27, 21, 15, 6); cells 18-24.5^ in diameter, colony up to 167/x 

 wide; 340/A long. 



Rare; in plankton. Wis. 



Pediastrum obtusum Lucks 1907 (reprint), p. 13 



[Pediastrum quadricornutum Prescott 1944, p. 3561 



PI. 49, Figs. 6, 7 



Colony nearly entire, with minute interstices formed by the 

 retuse margins of some cells; colony oblong, rarely subcircular (the 

 rows of cells arranged: 7-1; 16-11-5; 16-9-7), composed of from 

 8-32 cells which have a deep narrow sinus forming 2 major lobes, 

 the lobes incised to form bluntly rounded lobules, the two central 

 lobules in contact or nearly so, thus closing the sinus outwardly, 

 the two lateral lobules in contact with the lateral lobules of the 

 adjoining cells; interior cells about the same shape as the peripheral 

 cells but with the lobules less prominent, sometimes wanting, with 

 the wall merely emarginate or nearly straight; cells 10.5-18ju, in 

 diameter; 8-celled colony up to 144/x wide. 



Euplankter. Wis. 



According to Bigeard (1935) such a form as this would be included 

 with P. tetras, a species which has many variations. Pediastrum 

 obtusum is here regarded as separable from P. tetras on the basis 

 of the narrow, closed incisions of the cells and the obtuse apices. 

 The form was described by Prescott (1944) as P. quadricornutum 

 because it seemed to be separable from the forms included in 

 Bigeard's monograph (1935). It had been described earlier, how- 

 ever, as P. obtusum by Lucks (1907). 



Pediastrum sculptatum G. M. Smith 1916, p. 475 

 PI. 49, Fig. 5 



Colony entire or with narrow perforations; internal cells 4-6-sided; 

 peripheral cells with 2 lobes having subparallel margins; cell wall 

 covered with a fine reticulum of ridges; cells 10-15/x in diameter; 

 colony 150-180/A wide. 



Euplankter. Wis. 



[226] 



