Tetraedron muticum fa. punctulatum ( Reinsch ) 



DeToni 1889, p. 600 



PI. 60, Fig. 18 



Cells flattened, triangular, the angles sharp but without spines; 



margins slightly convex; wall granular; cells 15-20/a in diameter, 



8-lOix thick. 



Euplankter. Wis. 



Tetraedron obesum (West & West) Wille ex Brunnthaler 1915, p. 154 



PI. 60, Figs. 19, 20 



Cells ovate or broadly elliptic in outline, but with 3 lobes 

 which are scarcely produced, one lobe lateral to the long axis of 

 the cell, all lobes tipped with a short sharp spine; cells 15jli in 

 diameter, Sl-SS/t long. 



Plankter; in lakes and ponds. Mich., Wis. 



Tetraedron pentaedricum West & West 1895, p. 84 

 PI. 60, Figs. 21-23 

 Cells irregularly 5-lobed, with 1 lobe extended in a different 

 plane from the others; angles sharply rounded, the apex of each 

 lobe furnished with a sharp spine; diameter of cells 18-21/x. 

 Rare; in euplankton. Mich., Wis. 



Tetraedron planctonicum C. M. Smith 1916, p. 479 

 PI. 60, Figs. 27, 28 

 Cells polyhedral-pyramidate, 4- or 5-angled, with convex sides, 

 the angles produced into once- or twice-furcate processes, becoming 

 narrower in the furcations, the lobes tipped with 2 or 3 spines; 

 cells 18-30/x in diameter without processes, 45-60/i, including the 

 processes. 



Common in the plankton of many lakes. Mich., Wis. 



Tetraedron pusillum ( Wallich) West & West 1897, p. 237 



PI. 60, Fig. 29 

 Cells cruciform, deeply 4-lobed, concave between the lobes, the 

 lobes bifurcate at the apices, all in one plane; cells elongate-elliptic 

 in side view; lOfi in diameter, 25/a long. 



Plankter; found in several lakes; common. Mich., Wis. 



Tetraedron quadratum (Reinsch) Hansgirg 1889, p. 18 

 PI. 46, Figs. 21, 21a 

 Cells quadrangular in front view, the lateral margins straight 

 with sharp angles which are furnished with a short spine; membrane 

 2-layered, up to 4.5/a thick; cells 17-34/x in diameter. 

 Mich. 



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