94 WISCONSIN PH7TOPLANKTON 



KEY TO THE GENERA. 



Colony with cells in a flat plate GONIUH 



Colony with cells forming a hollow sphere. 



Cells mutually compressed PANDOBINA 



Cells some distance from one another. 



Asexual reproduction by division of all cells in colony EUDOBINA 



Asexual reproduction by division of special cells. 



At least half of cells capable of forming autocolonies. . .PLEODOBINA 

 Only a few cells capable of forming autocolonies VOLVOX 



GONIUM Mueller 1773. 



Colonies of 4-8-16 cells arranged in a flat quadrangular plate and 

 embedded in a common gelatinous matrix or connected by broad gelat- 

 inous strands. Cells ovoid to pyriform, with a single cup-shaped chlor- 

 oplast containing one pyrenoid. Each cell with two cilia of equal 

 length, contractile vacuoles at the base of the cilia, and an eyespot. 

 Four- and eight-celled colonies with the cilia on the same side ; sixteen- 

 celled colonies with the four central cells having their cilia on the same 

 side and the twelve marginal cells with radially arranged cilia. 



Asexual reproduction by simultaneous division of all cells in the 

 colony to form autocolonies, or by a formation of 2-4 zoospores in each 

 cell. 



Sexual reproduction isogamous, by a fusion of biciliate zoogametes. 



GONIUM PECTORALE Mueller. PI. 16, Figs. 14-15. 



Vermium terrestrium et fluviatilium etc. 1: 60. 1773; Migula, Bot. Cent. 44: 

 72, pi. 2, figs. 1-8. 1890; Harper, Trans. Am. Micr. Soc. 31: 65, pi. 5, figs. 1-19, 

 23. 1912. 



Colonies containing 4816 cells. Usually with 16 cells arranged in 

 two concentric series in a flat plate with truncate corners. Cells con- 

 nected with one another by broad, hyaline, gelatinous processes and 

 with open spaces between the processes; or with processes indistinct 

 and the whole colony embedded in a homogeneous, gelatinous matrix. 

 Outer ring with twelve cells whose long axes lie parallel to the plane 

 of the coenobe. Inner ring of four cells with a large open space at the 

 center and their long axes perpendicular to plane of the coenobe. Cells 

 ovoid to pyriform, with two cilia at the anterior end ; a posterior massive 

 cup-shaped chloroplast ; an anterior eyespot ; and two contractile vacu- 

 cles at the base of the cilia. (Tychoplanktont) . 



Cells 7-11 p. broad, 10-25 /* long. 



Beaver dam (rrr), Clam (rrr), Duck (rr), Fowler (rrr), Island (r), Ke- 

 gonsa (rrr), Long (1) (rrr), Mendota (rrr), Number One (rr), Pike (rrr), 

 Poplar (rrr). 



