WISCONSIN PHYTOPLANKTON 119 



Cells small, length (with processes) slightly greater than the 

 breadth, deeply constricted, sinus acute-angled and with the apex 

 acuminate, isthmus fairly narrow; semicells transversely elliptic- 

 hexagonal, with ventral margin tumid and dorsal margin truncate; 

 cell body with two whorls of processes, the three lower processes aris- 

 ing midway between the isthmus and the apex of the semicell; the 

 six processes of the upper whorl subapical in insertion ; processes of 

 the lower whorl at right angles to the long axis of the cell, with sub- 

 parallel lateral margins and ends deeply bifurcate; processes of the 

 superior whorl similar to those of the lower whorl but lying at an 

 angle of 45 degrees with the long axis of the cell; cell wall smooth. 

 Vertical view triangular, sides of cell body straight and angles con- 

 tinued in very short processes ; sides of cell each with two short intra- 

 marginal processes, one near each angle of the cell. (Tychoplank- 

 tont. ) 



Zygospores spherical, with numerous elongate spines that are bi- 

 furcate at their apices (Rabenhorst). 



Cells 27-30 fj. long with processes, 18-20 fi long without processes ; 

 breadth with processes 22-27 /x, without processes 14 /x; breadth at 

 isthmus 7-8 fi. 



Lindy (rrr). 



The species resembles Staurastrum tohopekaligense Wolle in the 

 double whorl of three inferior and six superior processes. The two 

 are distinguished, however, by the smaller size, relatively shorter 

 processes, different cell shape, and merging of the lower whorl of 

 procsses with the cell body in the vertical view of 8. furcatum. 

 S. senarium (Ehrenberg) Ralfs is a closely related species of the 

 same cell size but with accessory processes in the lower whorl. 



The use of Ralfs' British Desmidieae as the starting point for 

 nomenclature involves certain difficulties in determining the correct 

 name of the species. Ralfs described the species under the name 

 8. spinosum and then in the appendix recognizes the Xanthidium 

 furcatum of Ehrenberg. He suggests that this Xanthidium may be- 

 long to 8taurastrum. Since Ralfs recognizes both names the older 

 one is taken. 



55. Staurastrum brasiliense Nordstedt. 



Vidensk. Medd. f. d. naturhist. Foren. i Kiobenhavn 1869: 227, pi. 4, fig. 39. 

 1870. (non Lundell, Nova Acta Eeg. Soc. Sci. Upsaliae 3 Ser., 8: 73, pi. 5, fig. 2. 

 1871.). 



Cells large, breadth (with spines) one and a third times the length, 

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

 broad, about half the diameter of the cell ; semicells broadly cuneate, 

 with the ventral margins slightly convex and the apex somewhat 

 concave; angles truncate and with three very long stout divergent 

 spines, the two inferior ones lying in the same horizontal plane, the 

 superior one inserted at an angle. Vertical view four- (very rarely 



