Lesser Green Algae 131 



Kirchnerella is a loose aggregate of a few blunt- 

 pointed U-shaped cells, enveloped in a thick spherical 

 mass of jelly. It is met with commonly in the plancton 

 of larger lakes. Selenastrum grows in nearly naked 

 clusters of more crescentic, more pointed cells which are 

 found amid shore vegetation. Ankistrodesmns is a 

 related, more slender, less crescentic form of more 

 extensive littoral distribution. The slenderest forms of 

 this genus are free floating, and some of them like A . 

 setigera (fig. 50/) are met with only in the plancton. 



Richteriella is another plancton alga found in free 

 floating masses of a few loosely aggregated cells. The 

 cells are globose and each bears a few long bristles upon 

 its outer face. Kofoid found Richteriella attaining a 

 maximum of 36,000,000 per cubic meter of water in 

 September, while disappearing entirely at temperatures 

 below 6o° F. 



Oocystis grows amid shore vegetation, or the lighter 

 species, in plancton in open water. The ellipsoid cells 

 exist singly, or a few are loosely associated together in a 

 clump of mucus. The cells possess a firm smooth wall 

 which commonly shows a nodular thickening at each 

 pole. 



Ophiocytmm is a curious form with spirally coiled 

 multinucleate cells. The bluntly rounded ends of the 

 cells are sometimes spine-tipped. These cells some- 

 times float free, sometimes are attached singly, some- 

 times in colonies. Kofoid found them of variable 

 occurrence in the Illinois River, where the maximum 

 number noted was 57,000,000 per cubic meter occur- 

 ring in September. The optimum temperature, as 

 attested by the numbers developing, appeared to be 

 about 6o° F. 



Tetraspora — We will conclude this list of miscellanies 

 with citing one that grows in thick convoluted strings 



