124 WISCONSIN PHYTOPLANKTON 



Diam. cells (without processes) 18-30 /x; (with processes) 45-60 /*. 



Cranberry (rr), Cochrane (rr), Devils (2) (sss), Granite (rr), Horseshoe 

 (1) (rr), Lindy (rrr), Lost (rr), No Mans (rr), Prairie (rr), Rock (rr), Ver- 

 milion (r). 



The chief difference between this species and T. limneticum is the 

 greater size of the cells in proportion to the length of the processes. 



TETRAEDRON ENORME (Ralfs) Hansgirg. PI. 27, Fig. 6. 

 Hedwigia 27: 132. 1888; G. S. West, Brit. Freshw. Algae 231, flg. lOlo. 1904. 



Cells irregularly tetrahedric, angles produced into short processes 

 and sides emarginate. Processes generally bilobed and ending in short 

 spines. (Tychoplanktont). 



Diam. cells 25-45 /*,. 



Carson (rr), Cochrane (rr), Devils (2) (r), Horse (rrr), Horseshoe (2) 

 (rrr), Lake of the Woods (rrr), Okauchee (rrr), Pine (2) (rr). 



POLYEDRIOPSIS Schmidle 1899. 



Cells solitary, generally tetragonal, flattened; rarely pyramidal cr 

 with sides cruciate. Corners truncate and with 3-10 long, hyaline, 

 slightly tapering setae. Chloroplast parietal or entirely filling the 

 cell, pyrenoid single. 



Reproduction by the formation of 2-4-8 autospores through the divi- 

 sion of the cell contents. 



POLYEDRIOPSIS SPINULOSA Schmidle. PI. 27, Figs. 7-8. 



Allg. Bot Zeitschr. 5: 17. 1899. 



Tetraedron spinulosum Schmidle, ibid. 2: 193, fig. 2. 1896. 



Characters the same as those of the genus. (Euplanktont). 

 Greatest diameter of cells 12-25 n ; length of setae about 40 /*. 



Horse (rr), Prairie (rrr). 



The general tendency among phycologists is to follow Wille's prac- 

 tice and place the alga in a special sub-genus of Tetraedron. The 

 setae on the cell angles are of the same type as those found on Lager- 

 Jieimia and Micractinium so that Polyedriopsis forms, in my opinion, 

 a genus parallel with Tetraedron just as Lagerheimia does with Oocystis. 



