Key to the Species 



1. Cells 5-7/x in diameter, spherical C. dubium 



1. Cells smaller, either spherical or ovate 2 



2. Cells round, up to 4/Lt in diameter C. Kuetzingianum 



2. Cells ovate to ellipsoid.— 3 



3. Cells appearing dark and granular because of pseudovacuoles; 



2-Sfj. in diameter, 3.5-6/^ long C. Naegelianum 



3. Cells pale blue-green, without pseudovacuoles, 



1-2. 5yu, in diameter, 2-3.2//, long ____ C. pallidum 



Coelosphaerium dubium Grunow in Rabenhorst 1865, p. 55 



PI. 106, Fig. 1 



Plant a spherical or sometimes irregularly-shaped colony of spher- 

 ical cells, or an aggregate of colonies in a common gelatinous enve- 

 lope; free-floating; cells densely arranged in the colonial mucilage 

 to form a peripheral layer, thus producing a hollow sphere; cell 

 contents blue-green, either homogeneous or with pseudovacuoles; 

 cells 5-7/A in diameter; compound colonies as much as SOOfx in 

 diameter. 



Rare in euplankton. Wis. 



Coelosphaerium Kuetzingianum Naegeli 1849, p. 54 



PI. 106, Fig. 2 



A free-floating spherical, or ovate, gelatinous colony of spherical 

 or subspherical cells arranged at some distance from one another 

 (usually) at the periphery of the colonial envelope; cell contents 

 homogeneous (rarely with pseudovacuoles), light blue-green; cells 

 2.5-4;u, in diameter. 



This species is not quite so common in our collections as C. 

 Naegelianum. It is, however, widely distributed in a variety of lakes, 

 mostly hard or semi-hard water habitats. It seems never to become 

 conspicuous in water blooms as does C. Naegelianum. It is to be 

 differentiated from that species by the shape of the cells and by 

 their lack of the reddish-brown color produced by many pseudo- 

 vacuoles. It also lacks the radiating gelatinous fibrils in the colonial 

 mucilage possessed by C. Naegelianum. 



Mich., Wis. 



Coelosphaerium Naegelianum Unger 1854, p. 196 

 PI. 106, Fig. 4 

 A free-floating, spherical, ovate, or lobed colony of ovate or 

 ellipsoid cells arranged to form a dense peripheral layer in the 



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