the margins concave; cells 28-36//, in diameter, processes 8fi wide at 

 the base. 



Rare; in plankton. Wis. 



Tetraedron hastatum var. palatinum (Schmidle) 

 Lemmermann 1902, p. (247) 

 PI. 59, Fig. 27 

 Cells pyramidal, the processes longer and more graceful, not 

 tapering, tipped with 3 short spines, the margins of the cell convex; 

 cells 4-14/x in diameter without processes. 

 Euplankter. Wis. 



Tetraedron limneticum Borge 1900, p. 5 



PI. 60, Figs. 2-4 



Cells pyramidal, 4-angled, the angles produced into relatively 



narrow, once or twice furcated processes which are tipped with 



short spines, the margins of the cell concave between the angles; 



cells 3()-55-(85)/>i in diameter including processes. 



Common and generally distributed in many lakes. Mich., Wis. 



Tetraedron limneticum var. gracile Prescott 1944, p. 358 



PI. 60, Fig. 5 

 Cells pyramidal or tetragonal, the angles extended into bifurcate 

 processes which are tipped with 2 or 3 stout spines, the margins of 

 the cell concave between the processes; bases of the processes 

 adjoining so that there is scarcely a cell body; cells 40-46.8/a in 

 diameter; processes 6-8/i. wide. 

 Euplankter. Wis. 



Tetraedron lohulatum ( Naeg. ) Hansgirg 1888a, p. 132 



PL 60, Figs. 6, 7 

 Cells tetragonal, mostly pyramidal ( or flattened ) ; processes short 

 and stout, bifurcate at the apices; cells 35-40/a in diameter. 

 Euplankter. Mich., Wis. 



Tetraedron lohulatum var. crassum Prescott 1944, p. 359 



PI. 60, Fig. 8 

 Cells tetragonal, pyramidal, the angles slightly produced to form 

 relatively wide, short processes which are bilobed, the lobules bi- 

 furcate and ending in short curved spine-like tips; cells 25-30|a in 

 diameter. 



[266] 



