Tetraedron enorme (Ralfs) Hansgirg 1888a, p. 132 



PI. 52, Figs. 6, 7 (var.); PI. 59, Fig. 19 



Cells poly- or tetrahedric, the angles shortly produced and bilobed, 



the lobes bifurcate and tipped with short spines; margins of the cell 



concave between the angles, the processes not all in the same plane; 



cells ( 25 ) -30- ( 45 ) /x in diameter. 



Common in the tychoplankton of several lakes; generally distrib- 

 uted. Mich., Wis. 



Tetraedron enorme var. pentaedricum Prescott 1944, p. 358 



PL 59, Fig. 18 



Cells 5-sided in outUne, the sides straight or slightly convex, with 

 pairs of narrow bifurcated processes extending in all planes, the 

 processes tipped with short spines; cells 50-55/x in diameter, without 

 processes. 



This form difFers from the typical plant by its straight margins 

 and narrow bifurcated processes extending from the angles. It is 

 similar to Borge's figure of T. enorme, which I judge to be typical. 



Rare; in plankton. Wis. 



Tetraedron gigas (Wittr. ) Hansgirg 1888a, p. 131 

 Cells relatively large, irregularly 5- or 6-angled, the processes 

 broadly rounded, with the margins between the angles broadly 

 concave; cells 35-45/a in the short diameter, 65-75/^ lo^g- 

 Typical form not reported in our region. 



Tetraedron gigas var. granulatum Boldt ex Brunnthaler 1915, p. 148 



A variety differing from the typical by the possession of finely 

 punctate walls. 

 Mich. 



Tetraedron gracile ( Reinsch ) Hansgirg 1889, p. 19 

 PI. 60, Fig. 1 



Cells flat, cruciform, rectangular in outline, the angles extended 

 into narrow, twice furcated processes which are tipped with 1 or 2 

 short spines, the margins deeply concave between the processes; 

 cells 15-30;a in diameter, without processes, 35-40ju, wide including 

 processes; 6-12/a thick. 



Rare; in euplankton. Mich., Wis. 



Tetraedron hastatum (Reinsch) Hansgirg 1888a, p. 132 



PI. 59, Fig. 26 

 Cells pyramidal, the angles extended into narrow, slightly taper- 

 ing, unbranched processes which are tipped with 2 or 3 short spines, 



[265 1 



