inner walls of the cells; cells in contact only at their inner corners; 

 1 chloroplast, parietal along the outer convex wall; pyrenoid present; 

 cells 4.5-9/i, in diameter, 8-15/a long; quartets of cells adjoined in 

 multiples by remains of old mother cell walls. 



Rare; in the plankton of several lakes. Wis. 



Crucigenia quadrata Morren 1830, pp. 415, 426 

 PI. 65, Fig.lO 

 Colony free-floating, consisting of a circular plate of 4 triangular 

 cells, cruciately arranged about a small central space, the outer free 

 wall of the cells broadly convex, the lateral walls straight, adjoined 

 throughout their length with neighboring cells and converging to- 

 ward the center of the colony; walls sometimes with knob-like 

 projections; chloroplasts parietal discs, as many as 4 in a cell; 

 pyrenoids not always present; cells 2.5-6ju, in diameter, 3.7;u, long; 

 multiple quadrate colonies formed by the close arrangement of 

 component quartets. 



Smith ( 1920, p. 147 ) considers Staurogenia multiseta var. punctata 

 Schmidle and Crucigenia triangularis (Chod.) Schmidle to be 

 synonymous with this species. 



Plankter; found in a large number of lakes in northern counties. 

 Mich., Wis. 



Crucigenia rectangularis (A. Braun) Gay 1891, p. 100 



PI. 65, Figs. 7, 8 

 Colony free-floating, consisting of ovate or oblong cells, very 

 regularly arranged about a rectangular central space in 2 pairs, 

 with the apices adjoining; chloroplasts 1-4, parietal discs, with a 

 pyrenoid in each; cells 4-7/a in diameter, 5-10/x long. 



This species should be compared with C. irregularis Wille. 

 Common in both eu- and tychoplankton of a large number of 

 lakes. Mich., Wis. 



Crucigenia tetrapedia ( Kirch. ) West & West 1902, p. 62 

 PI. 65, Fig. 9; PI. 66, Fig. 1 

 Colony free-floating, consisting of 4 triangular cells cruciately 

 arranged about a minute central space; outer free wall and lateral 

 walls straight, the angles acutely rounded; chloroplast a parietal 

 plate with a single pyrenoid; cells 4.5-9|U, in diameter, frequently 

 forming a rectangular plate of 16 cells (4 quartets). 

 Common in a small lake. Wis. 



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