124 



WISCONSIN PHYTOPLANKTON 



whorls and continuing nearly to the point of bifurcation. (Faculta- 

 tive planktont.) 



Zygospores unknown. 



Cells 100-110 fi long with processes, 41-45 ja long without processes ; 

 breadth with processes 100-114 jn, without processes 25-28 ju; breadth 

 at isthmus 13 ix ; length of terminal spines 11-14 fi. 



Bass (rrr), Crooked (rrr), Diamond (ss), Dummy (rr), Horseshoe (rr), Lake 

 of the Woods (ss), Mud Hen (rrr), Shell (r), Tank (rrr). 



The species shows a certain resemblance to S. tohopekaligense 

 Wolle in the two whorls of deeply bifurcate processes but the two 

 differ in size of the cells, shape of the cells and number of processes. 

 In Wisconsin specimens the lower whorl always has six and the upper 

 whorl four processes but forms with six lower and six upper, nine 

 lower and six upper, as well as eight lower and four upper have been 

 described, 



59. Staurastrum Arctiscon (Ehrenberg) Lundell. PI. 84, Figs. 1-2. 

 Nova Acta Eeg. Soe. Sci. Upsaliae 3 Ser., 8: 70, pi. 4, fig. 8. 1871. 



Cells large, length slightly greater than the breadth (with proc- 

 esses), fairly deeply constricted, sinus open and acute-angled, isthmus 

 broad; semicells subspherical, with bases obsemicircular and apices 

 strongly tumid to semicircular ; body of semicells without ornamenta- 

 tion, median portion of semicell body with a whorl of nine (five 

 visible in front view) long stout very slightly tapering hollow proc- 

 esses, processes parallel to slightly divergent; apex of semicell with 

 a whorl of six similar processes that are subapical in insertion and 

 lie at an angle of 45 degrees with the lower series; both series of 

 processes with three or four transverse rings of conspicuous conical 

 granules, ends of processes with three stout hollow divergent spines. 

 Vertical view circular, with nine straight marginal processes and an 

 inner whorl of six intramarginal processes, structure of processes as 

 in front view. Cell wall smooth or finely punctate. Chloroplast a 

 central axial mass with a single arm running a short distance into 

 each process; pyrenoid single and central. (Facultative planktont.) 



Zygospores unknown. 



Cells 120 fjL long with processes, 70 fi long without processes ; breadth 

 with processes 114-120 [x, without processes 44-53 fx ; breadth at 

 isthmus 29 fi. 



Bass (rrr), Beaverdam (r), Clear Crooked (rrr), Des Moines (rrr), Diamond 

 (ss), Found (rrr), Horseshoe (rrr), Lake of the Woods (ss), Silver (rrr), South 

 Crab (rrr), Tank (rrr). 



A very distinctive species where the number of processes in the 

 two whorls is quite constant. Aside from differences in the length of 

 the processes, which is generally shorter in American than in Euro- 

 pean individuals, the variation is confined to the number of rings of 

 granules on the processes and the angle of the sinus. 



