116 WISCONSIN PHYTOPLANKTON 



51. Saurastrum rotula Nordstedt. PL 81, Figs. 5-8. 



Videusk. Medd. f. d. naturh. Foren. i Kiobenliavn 1869: 227, pi. 4, fig. 38. 1870; 

 WoUe, Desm. U. S. 135, pi. 44, figs. 13-14. 1884; W. & G. S. West, Trans. Linn. 

 Soc. 2nd. Ser. Bot. 5: 268, pi. 18, fig. 11. 1896. 



Cells fairly large, length about twice the breadth (without proc- 

 esses), deeply constricted, sinus widely open and with a subacuminate 

 apex, isthmus narrow ; semicells subhexagonal, with portion below 

 the processes straight-sided and that above truncate ; body of semi- 

 cells with a transverse row of subapical bidenticulate verrucae ; proc- 

 esses arising midway between the apex and isthmus of semicells, 

 subparallel, slightly attenuated and terminating in three short di- 

 vergent spines, body of processes with three or four rings of sharp 

 denticulations. Vertical view nine-rayed (very rarely eight-rayed), 

 with the processes straight and slightly attenuated, ends of proc- 

 esses trispinate; body of cells with a single bidenticulate verruca at 

 the base of each process, the verrucae forming an intramarginal ring. 

 Cell wall smooth or finely punctate. (Tychoplanktont.) 



Zygospores unknown. 



Cells 40-45 jx. long ; breadth with processes 92-102 ju,, without proc- 

 esses 22-30 /i, ; breadth at isthmus 10.5-12 ju,. 



Little Butternut (rrr), Des Moines (rrr), George (rrr). Bound (rrr). 



W. & G. S. West's criticism of Wolle's drawing which shows rec- 

 tangular instead of conical apical papillae is, at least as far as Wis- 

 consin specimens are concerned, without justification; the apical 

 verrucae are distinctly bifid and not conical as their drawing shows. 

 The species should be compared with S. limncticum var. cornutum 

 G. M. Smith which appears closely related but is not, for reasons 

 stated below, placed as a variety of S. rotula. 



52. Staurastrum limneticum Sehmidle. 



Engl. Bot. Jahrb. 26: 52, pi. 4, fig. 5. 1899; G. S. West, Jour. Linn. Soc. Bot. 38: 

 129. 1907. 



Cells large, length (without processes) about twice the breadth, 

 deeply constricted, sinus widely open and with an acute apex, isthmus 

 fairly narrow ; semicells elliptic-obsemicircular, with the ventral mar- 

 gin more rounded than the dorsal (almost semicircular) ; processes 

 arising at a point about a third of the distance from the apex to the 

 isthmus, fairly delicate and very gracefully upwardly curved; lower 

 margin of processes always crenulate and upper surface smooth or 

 very shallowly crenulate, ends with three or four short divergent 

 spines ; body of semicells without ornamentation. Vertical view pen- 

 tagonal or hexagonal, with sides slightly retuse and angles continued 

 in long slightly tapering processes, lateral margins smooth, ends of 

 processes trispinate to quadrispinate, processes of one semicell oppo- 

 site those of the other semicell; central portion of cell body without 

 ornamentation. 



