WISCONSIN PHYTOPLANKTON 149 



Coenobia joined in multiple coenobia of at least sixteen cells by the re- 

 mains of old cell walls and a gelatinous envelope. Cells flattened, sub- 

 hemispherical in front view with the flattened side towards the center 

 of the coenobe. Chloroplast single, parietal, on the outer face of the 

 cell; with one pyrenoid. (Euplanktont). 



Cells 4.5-9 /A broad, 8-15 /* long. Coenobia 15-25 /* in diam ; multiple 

 coenobia up to 150 /* in diam. 



Kegonsa (r), Fokegama (rr), Rice (1) (r), Upper Turtle (r). 



A very distinct species and one that is readily recognized by the large 

 opening at the center of the colony. C. fenestrata also has a large, rec- 

 tangular open space at the center of the coenobe but the two species 

 have quite differently shaped cells ; those of C. Lauterbomei being semi- 

 circular in front view, and those of C. fenestrata trapezoidal. 



TETEASTRUM Chodat 1895. 



Coenobia four-celled, with cells cruciately arranged in a flat plate; 

 at times embedded in a thin gelatinous envelope. Cells triangular to 

 ovoid, with several spines or setae on the free face. Chloroplasts 1-4, 

 parietal, disciform, with or without pyrenoids. 



Reproduction by autocolony formation in any cell. 



The genus is closely related to Crucigenia, differing only in the spines 

 on the margins of the cells and an absence of an association in multiple 

 coenobia. 



TETRASTRUM STAUROGENIAEFORME (Schroder) Lemmermann. PI. 37, 



Figs. 5-6. 



Ber. d. D. bot. Ges. 18: 95. 1900. 



Cohniella Staurogeniaeformis Schroder, Ber. d. D. bot. Ges. 15: 373, pi. 17, 

 fig. 5. 1897. 



Coenobia four-celled, with a very minute open space at the center 

 of the colony. Coenobe embedded in a very delicate gelatinous envelope. 

 Cells cruciately arranged, triangular, with 5-6 very delicate setae on 

 the free surface. Chloroplasts 1-4, parietal, disciform, with or without 

 pyrenoids. ( Euplanktont ) . 



Diam. cells (without setae) 3-6 /*; diam. coenobia (without setae) 

 7-15 fi. Setae 4-8 /* long. 



Horse (rr), Mendota (rrr). 



The setae on the outer face of the cells are very delicate and easily 

 overlooked. If the setae are not taken into consideration the alga looks 

 exactly like Crucigenia quadrata. 



