WISCONSIN PHYTOPLANKTON 121 



of the cell, ends of processes -with two (seldom three) long divergent 

 hollow spines. Cell wall smooth. Vertical view triangular, with 

 sides straight but frequently bending in the vicinity of the angles to 

 form a sharply pointed angle ; angles prolonged into processes, each 

 lateral margin of cell with two perpendicular processes arising one 

 near each angle but inside the margin of the cell. 



Zygospores unknown. 



Cells 70-83 fi long with processes 32-39 //, long without processes ; 

 breadth with processes 67-75 fi, without processes 28-32 [x ; breadth 

 at isthmus 15 fx ; length of terminal spines 4.5-6.5 fi. 



Not found in the plankton of Wisconsin lakes. 



This is a well defined species but one which is subject to consider- 

 able variation and one where, owing to the incomplete original de- 

 scription and poor figures, there is some doubt as to the type. The 

 varieties trifurcatum and quadrangulare were described by W. & 

 G. S. West in 1895 (Trans. Linn. Soc. 2nd. Ser. Bot. 5: 80, pi. 9, figs. 

 8-9) and the variety has been observed by them again in Ceylon in 

 1902 (I. c.) and in the Scottish plankton in 1905 (Trans. Roy. Soc. 

 Edinburhg 41: 503, pi. 7, fig. 7). Two years later in discussing the 

 plankton of the Central African lakes G. S. West (Jour. Linn. Soc. 

 Bot. 38: 130, 1907) mentions quadrangular and triangular forms 

 that "were typical as regards proportions and length of processes." 



After ^a careful comparison of specimens from Burma and from 

 the plankton of Victoria Nyanza (Africa), Scotland, New York, 

 Ontario and Wisconsin I have reached the conclusion that text figure 

 16 is that of the type. It is characterized by processes which are 

 about as long as the diameter of the cell, a flat cell apex, triangular 

 body and long divergent spines at the ends of the processes. The 

 figure of an American specimen from Wolle given by W. & G. S. 

 West in 1902 (I. c), which shows two supplementary processes on 

 each face of the cell, has not been observed. This shows that the 

 number of processes is no sure criterion in determining varieties in 

 this species. In my opinion the ends of the processes in the West 

 drawing are too rounded. The number of spines at the ends of the 

 processes is generally two but I have found that occasionally the 

 processes on either the superior or the inferior whorls may be tris- 

 pinate. 



The varieties trifurcatum and quadrangulare which have been 

 found in Madagascar, Burma, and the African plankton should be 

 considered synonyms of S. tohopekaligense var. nonanum (Turner) 

 Schmidle. 



var. brevispinum nom. nov. PI. 82, Figs. 8-11. 



Staurastrum tohopekaligense var. trifurcatum W. & G. S. West, Trans. Roy. 

 Soc. Edinburgh 41: 503, vl. 7, fig. 7. 1905 (non Trans. Linn. Soc. 2nd. Ser. Bot. 

 5: 80, pi. 9, fig. 8. 1895). 



