WISCONSIN PHYTOPLANKTON 175 



EUASTROPSIS RICHTERI (Schmidle) Lagerheim. PI. 49, Fig. 3. 

 Tromso Museums Aarshefter 17: 20, pi. 1, figs. 8-27. 1894. 



Cells trapezoidal, outer face deeply emarginate. (Tyehoplanktont). 

 Cells 4.5-25 /* broad, 5-20 /* long. Coenobia 4.5-25 ^ broad, 10-40 

 jt long. 



Kegonsa (rrr). 



It is quite possible to mistake 2-celled Pediastrum colonies for 

 E. Richteri, but since such Pediastrum colonies are of very rare occur- 

 rence the similarity of the two is not apt to lead to confusion. 



Family PLANOSPORACEAE. 



Cells solitary or gregarious; ovoid, pyriform, fusiform, cylindrical, 

 or hemispherical ; epiphytic, endophytic, or epizootic. Cells capable of 

 growth but incapable of division after their formation. Generally with 

 a single chloroplast with one or more pyrenoids. 



Asexual reproduction by division of cell contents to form many zoo- 

 spores. 



Only one genus, Characium, is found in the plankton of the state. 



CHARACIUM A. Braun 1849. 



Cells sub-spherical, ovoid, pyriform, fusiform, or cylindrical; soli- 

 tary or gregarious; epiphytic or epizootic; generally attached to sub- 

 stratum by a more or less elongate stipe, rarely sub-sessile. Chloroplast 

 parietal and laminate to cup-shaped in young cells; later expanded to 

 fill entire cell : with one or more pyrenoids. Cells at times with several 

 ehloroplasts. 



Asexual reproduction by repeated division of cell contents into 8-16- 

 32-64-128 zoospores that are liberated through a lateral or apical pore. 

 Zoospores swarming but a short time and then coming to rest on sub- 

 stratum and developing into vegetative cells. 



Microgametes reported but doubtful. 



KEY TO THE SPECIES. 



Epiphytic upon other algae. 



Cells ovoid C. STIPITATUM 



Cells lunate C. CUBVATUM 



Epizootic upon crustaceans. 



Apices of cells rounded C. CYLTNDBICFM 



Apices of cells produced into a fine seta. 



Stipe simple C. LIMNETICUM 



Stipe ending in filiform rhizoids C. GBACILIPB 



