174 WISCONSIN PHYTOPLANKTON 



Little Doctor (rr), Mendota (rrr), Palmer (rrr), Pewaukee (rrr), Pine (2) 

 (rr), Pokegama (1) (rr), Poor Farm (rr), Tied Canoe (rrr). 



The four projections in the outer face of marginal cells are due to a 

 deep emargination of the two halves. This, coupled with the deep in- 

 cision of all cells, at once separates the species from others of the genus. 

 The alga does not thrive under plankton conditions although it is com- 

 mon in ditches and ponds of the state. 



var. OBTUSATA Raciborski. 



Akad. Umiej. w. Krakowie 2O: 32. 1889; Printz, Skr. Vidensk. i Kristiana 

 Mat.-Naturv. Kl. 1913 1 , No. 6: 78, pi. 6, fig. 153. 1914. 



Cells larger than typical form, sometimes expanded at base. Halves 

 of outer face of marginal cells entire or very slightly emarginate. 

 ( Ty choplanktont ) . 



Diam. ceUs 14-18 p ; length 18-22 /*. 



Beaverdam (rrr). 



var. TETRAODON (Corda) Hansgirg. PI. 48, Figs. 13-14; PI. 49, Figs. 1-2. 



Prodr. d. Algenfl. v. Bohmen 1: 112. 1888. 



Euastrum tetraodon Corda, Almanach de Carlsbad 9: 238, pi. 2, fig. 9. 1839. 



Coenobia generally 8-celled. Incision of cells deep, and with projec- 

 tions adjacent to incision very pronounced on marginal cells. (Facul- 

 tative Planktont) . 



Diam. marginal cells 8-15 /* ; length 12-18 /x. 



Pine Tree (rr), Travis (r). 



There is no question that my figures of the organism are identical 

 with the one that Nitardy (Beih. Bot. Cent. 32 2 : 123, pi. 5, fig. 8. 1914) 

 has reproduced from Corda. The variety is sharply defined through 

 the greater development of the projections. 



EUASTROPSIS Lagerheim 1894. 



Coenobia free-floating, 2-celled. Cells flattened, approximated at the 

 bases, distal end free and deeply emarginate. Chloroplast single, pari- 

 etal, with one pyrenoid. 



Asexual reproduction by division of cell contents into 2-4-8-16-32 

 zoospores which are extruded in a vesicle and on becoming quiescent 

 join in pairs to form the characteristic coenobe. 



Sexual reproduction unknown. 



