WISCONSIN PHYTOPLANKTON 121 



alga in pure culture with the retention of its distinguishing character 

 shows that the Wests are correct in considering it a distinct species. 

 It resembles T. caudatum in the size, number of corners, character of 

 spines at the corners, and the concave sides ; but differs in having four 

 corners in approximately the same plane and the fifth at an angle with 

 the plane of the other four. There is considerable variation in the 

 angle at which this fifth corner lies but it is never in the same plane as 

 the other corners. The Wests (1. c. fig. 17) also describe a variety 

 minima which, as the name implies, is smaller. I find that the variations 

 in size of cells of the typical form in a pure culture include the dimen- 

 sions set for the variety minima so that this variety cannot be recognized. 



TETEAEDRON HASTATUM (Eeinsch) Hansgirg. PI. 25, Fig. 18. 



Hedwlgia 27: 132. 1888. 



Polyedrium tetraedricum var. Hastatum Reinsch, Die Algenfl. d. mitt. Th. v. 

 Franken 77, pi. 5, figs. 3*-3b. 1867. 



Cells medium sized, pyramidate, with the angles produced into long 

 tapering and somewhat concave processes. Processes unbranched but 

 having 2 or 3 short spines at the tip. (Tychoplanktont). 



Diam. cells (with processes) 28-36 /x; diam. base of process 8 /t. 



Horse (rrr). 



The general shape of the cell is similar to that of T. limneticum but 

 there is no branching of the processes. 



var. PALATINUM (Schmidle) Lemmermann. PI. 25, Figs. 19-21. 



Ber. d. D. bot. Ges. 20: (247). 1902. 



Polyedrium Jiastatum var. palatinum Schmidle, Ber. d. D. bot. Ges. 18: 148, 

 149, pi. 6, figs. 4-5. 1900. 



Cells pyramidal, with convex sides, angles produced into fairly deli- 

 cate non-tapering processes about as long as the diameter of the cells. 

 Processes unbranched but with three short spines at the apex. (Ty- 

 choplanktont). 



Diam. cells (without processes) 4-14 p.; length processes about 10 /t. 



Horse (rr). 



The processes at the angles of the cell do not seem as much a part 

 of the cell as in the typical form. Although both the typical form 

 and the variety palatinum were found at the same station the two seem 

 distinct and without transition forms. 



