122 WISCONSIN PHYTOPLANKTON 



Tetraedron constrictum nom. nov. PI. 25, Figs. 22-24. 



Tetraedron arthrodesmiforme var. lobulatum Woloszynska, Hedwigia 55: 

 203, pi. 6, fig. 11. 1914. 



Cells medium sized, tetragonal, flattened, two sides straight and two 

 opposite sides concave. Angles produced into narrow slightly taper- 

 ing processes which give the cell a decided H-shape. Ends of proc- 

 esses generally dichotomously branched the branchlets ending in two 

 short spines. (Euplanktont). 



Diam. cells (without processes) 5-8 p.; length 18-25 p.; thickness 8 p.. 

 Length of processes 10-15 p. 



Bone (IT). 



Woloszynska has found these peculiar H-shaped cells in the plankton 

 of Lake Victoria Nyanza, Africa and placed them among other varieties 

 of T. arthrodesmiforme described at the same time. The variety lobu- 

 latum is, however, sufficiently different from the other varieties to war- 

 rant raising it to specific rank. Bone lake is the only station where it 

 has been found but several individuals were seen in the catch from 

 this lake. 



TETRAEDRON GRACILE (Reinsch) Hansgirg. PI. 26, Figs. 1-5. 



Hedwigia 28: 19. 1889. 



Polyedrium gracile Reinsch, Notarisia 3: 502, pi. 7, figs, la-lc. 1888. 



Cells medium size, conspicuously flattened, rectangular, with flattened 

 sides. Angles of cells produced into narrow processes that generally 

 branch twice and end in minute spines. The primary branchings of 

 the processes are at an angle of 90 degrees with one another and always 

 parallel with a side of the cell. Each cell containing several, parietal 

 disciform to laminate chloroplasts without pyrenoids. (Euplanktont). 



Diam. cells (without processes) 15-30 p.; (with processes) 35-80 p.; 

 thickness of cells 6-12 p.. 



Bear (1) (rr), Bear Trap (rrr), Blake (rr), Chain (rr), Elizabeth (rrr), 

 Hillman (sss), Loon (rrr), Pine (2) (rr), Poor Farm (rr), Round (rr), Travis 

 (r), Wapagossett (rr). 



TETRAEDRON LOBULATUM (Nageli) Hansgirg. PI. 26, Figs. 6-7. 



Hedwigia 27: 132. 1888. 



Polyedrium lofoulatum Nageli, Gatt. einz. Algen 84, pi. 4, figs. B4a-B4t>. 1849. 



Cells medium sized, tetragonal, flattened, or pyramidal. Processes 

 of angles with one or two short dichotornous branchings that generally 

 do not end in spines. Sides of cells distinctly concave. Cells contain- 



