Tetraedron caudatum var. longispinwn Lemmermann 1898d, p. 151 



PL 59, Figs. 20-22 

 A variety differing from the typical by having longer spines which 

 are directed at right angles to the flattened surface of the cell, 2 

 turned in one direction, 3 in the opposite; cells 8-18/i, in diameter; 

 spines 3-8/x long. 



Euplankter; in lakes. Wis. 



Tetraedron constrictum G. M. Smith 1920, p. 122 

 PI. 59, Fig. 28 



Cells quadrangular in outline, tetragonal, 2 sides subparallel, the 

 other 2 deeply concave as seen in front view, the angles extended 

 into slightly tapering processes which are dichotomously branched 

 and tipped with a short spine; in side view fusiform, the processes 

 at the superimposed poles of the cell not quite in the same plane 

 but slightly turned at different angles; cells 5-8ju, in diameter, 

 without processes, 8/a thick, 18-25;a in their longest dimension. 



Rare; in euplankton. Wis. 



Tetraedron cruciatum ( Wallich ) West & West 1902a, p. 198 



Cells cruciately 4-lobed, the lobes bifurcate, one division of 2 

 lobes usually again divided; lobes and lobules tipped with 2 short 

 spines; margin of the cell deeply concave between the lobes, more 

 deeply so on 2 sides than on the others; cells (larger forms) 42-54/x 

 or (smaller forms) 17/i, in diameter. 



Typical plant not reported from our region. 



Tetraedron cruciatum var. reductum Prescott 1944, p. 358 



PI. 59, Fig. 23 

 Cell flat, irregularly cruciform or sometimes 3-lobed, the lobes 

 bifurcate, the lobules tipped with a short spine; margins of the cell 

 concave on 2 opposite sides, straight or only slightly concave on the 

 other sides; cells 28-30|U in diameter, up to 54fx in the greatest 

 dimension. 



Tychoplankter; in swamps. Wis. 



Tetraedron duospinum Ackley 1929, p. 304 

 PI. 46, Figs. 22, 23 



This species, described as new from Michigan and illustrated 

 (Ackley, I.e., PI. 35, Fig. 14), appears to be a Cystodinium or some 

 other encysted dinoflagellate. I have not seen type specimens, how- 

 ever. 



Mich. 



[264] 



