118 WISCONSIN PHYTOPLANKTON 



The ring of bifurcate apical verrucae and ornamentation of the 

 processes is more like that of S. rotula. The curved apices of the 

 cells, smaller number of processes, and most of all the graceful up- 

 ward curvature of the processes shows a greater resemblance to 

 S. Umneticum. The argument for referring this alga to 8. limneticum 

 is much stronger when the variety 'burmense "W. & G. S. West (Ann. 

 Roy. Bot. Garden Calcutta 6: 222, pi. 16, fig. 13. 1907) is taken into 

 consideration. I have found that five- and six-radiate individuals 

 are widely distributed in Ontario (Canada) and that these show a 

 striking resemblance to the variety hurmense, both in shape of the 

 semicells and the curvature of the processes. A comparison of 

 Canadian specimens with type material of the variety 'burmense from 

 the G. S. West collection shows that the two are identical except for 

 the apical verrucae. 



The alga has been found in but one lake in Wisconsin and the cells 

 are almost invariably with seven processes. The apical verrucae are 

 also slightly stouter than those of cells found in the Ontario plankton 

 but it does not seem advisable to separate the two on this account. 



53. Staurastrum radians W. & G. S. West. PI. 82, Figs. 6-7. 



Jour. Linn. Soc. Bot. 33: 318, pi. 18, f,g. 18. 1898. 



Cells fairly large, length (with processes) about half the breadth, 

 fairly deeply constricted, sinus obtuse-angled and with the apex 

 subacute, isthmus broad; semicells trapeziform in outline, with the 

 apex slightly convex and the angles continued in straight short 

 processes with coarsely crenulate margins, ends of processes with 

 three or four stout divergent spines, processes parallel ; body of semi- 

 cell without ornamentation. Vertical view circular, with eight radi- 

 ating processes, processes straight, coarsely crenulate in outline, bases 

 of lateral margins with an elongate emarginate outgrowth on each 

 side ; apex of processes with three or four small stout divergent 

 spines; body of cell without ornamentation. (Tychoplanktont.) 



Zygospores unknown. 



Cells 40 jjL long ; breadth with processes 70 )u, without processes 30 fx ; 

 breadth at isthmus 17.5 ii. 



Des Moines (rrr). Big McKenzie (rrr). 



A distinctive alga which is easily recognized in a vertical view. 



54. Staurastrum furcatum (Ehrenberg) De Brebisson. PI. 83, 



Figs. 1-3. 



'o"- 



Mem. de la soc. imp. d. Sc. nat. de Cherbourg 4: 136. 1856; Eabenhorst, Flora 

 Eur. Algarum 3: 218. 1868; Wolle, Desm. U. S. 150, pi. 40, figs. 40-41; pi. 48, 

 figs. 15-16; pi. 52, fig. 34. 1884; W. West, Jour. Eoy. Micr. Soc. 1890: 292, pi. 5, 

 fig. 11. 1890. 



Xanthidium furcatum Ehrenberg, Abh. Ak. d. Wiss. zu Berlin 1833: 318. 1834; 

 Ealfs, Brit. Desm. 213. 1848. 



