9. Cells (5)-6-8-(ll)/;i in diameter; contents pale yellow C. pallidus 



9. Cells mostly smaller than above; contents blue-green 10 



10. Cells oblong, 5-7-( 10) fi in diameter; in groups of 2 



inclosed in a homogeneous sheath C. minutus 



10. Cells angular or irregularly globose, 3-4ai in diameter; solitary 

 or 2 together within homogeneous sheaths, sometimes forming 

 small masses on submerged aquatic plants C. minor 



Chroococcus dispersus ( Keissl. ) Lemmermann 1904, p. 102 



PI. 100, Fig. 7 



A free-floating, flattened, ovate or irregularly-shaped colony of 

 4-16 spherical cells which are either single or arranged in small 

 clusters, evenly distributed at some distance from one another in 

 the mucilaginous envelope; individual cell sheaths not evident; cell 

 contents bright blue-green (sometimes gray-green or pale blue- 

 green ) ; cells 3-4.5|U in diameter. 



This species should be compared with C. limneticus, in which the 

 colonies are globular and the cells are larger. 



Euplankter. Found in many lakes of both hard and soft water. 

 Mich., Wis. 



Chroococcus dispersus var. minor G. M. Smith 1920, p. 28 



PI. 100, Figs. 1-3 



A variety differing from the typical in having smaller cells, 1.7- 

 2.5/x in diameter. 



Rare, but has been found in several lakes. Mich., Wis. 



Chroococcus giganteus W. West 1892, p. 741 

 PI. 100, Fig. 16 



Cells hemispherical or ovate, solitary or in groups of 2-5, inclosed 

 by a wide, hyaline, lamellate envelope of mucilage in which indi- 

 vidual cell sheaths are evident; cell contents bright blue-green and 

 densely granular; cells, without sheath, 54-58|u in diameter, 67-70/x 

 including the sheath. 



This species is, by far, the largest of the genus in our region. 

 Except for its greater size it is not unlike C. turgidus with which it 

 should be compared. Specimens of C. giganteus collected in Vilas 

 County, Wisconsin, are so much like a large form of C. turgidus that 

 I am inclined to regard the former as a variety maximum of the latter. 



Tychoplankter. Rare; in mixtures of other algae in shallow water. 

 Mich., Wis. 



[447] 



