6. Cells pear-shaped, radiately arranged Marssoniella 



6. Cells some other shape, not radiately arranged 7 



7. Cells cylindrical and strongly curved through % of a circle, 

 often lying parallel and compact within the mucilage of other 



algae; minute, 0.5-1^ in diameter Cyanarcus 



7. Cells ovate or oblong; larger, up to 15fi in diameter— - Synechococcus 



8. Cells 10 or more times their diameter in length; cylindrical, 

 vermiform, reniform, or fusiform ._ 9 



8. Cells round, ovate, or short-cylindric IC 



9. Cells narrowly fusiform, with tapering 



and pointed apices .._ Dactylococcopsis 



9. Cells reniform or vermiform, rounded at the apices Rhabdoderma 



10. Cells oblong or short-cylindric, with rounded ends, many 

 individuals irregularly and densely crowded in copious 



mucilage; individual cell sheaths evident or not -Anacystis ( in part ) 



Including: 



a. Aphanothece ( see p. 465 ) with individual 

 cell sheaths not evident 



b. Gloeothece with individual cell sheaths distinct 



10. Cells spherical or ovate, sometimes ellipsoid, not cyhndrical 11 



11. Cells round, embedded in copious mucilage, and forming 

 shapeless masses on submerged or more 



frequently aerial substrates — - -— Gloeocapsa 



11. Cells of other shapes, or if round not forming 



shapeless masses on substrates ^2 



12. Cells round or ovate, dividing in 2 directions 



to form rectangular plates 13 



12. Cells dividing in 3 planes to form spherical, 



ovate, or shapeless colonial masses 14 



13. Cells regularly arranged in rectiHnear series Merismopedia 



13. Cells irregularly arranged to form 



somewhat rectangular plates __— — - Holopedium 



14. Colony hollow, the cells arranged toward the periphery 15 



14. Colony not hollow; cells distributed throughout 



the colonial mucilage 16 



15. Cells at the ends of branching gelatinous strands which radiate 



from the center of the colony Gomphosphaeria 



15. Colonies without radiating gelatinous strands Coelosphaerium 



16. Cells longer than wide, distributed throughout the colonial muci- 

 lage, with or without evident individual cell sheaths Anacystis (in part) 



Including: 



a. Aphanothece ( see p. 465 ) without evident cell sheaths 



b. Gloeothece with individual cell sheaths evident 



16. Cells globose 17 



17. Cells evenly and remotely distributed within the colonial 



mucilage; pseudovacuoles wanting Aphanocapsa 



17. Celk crowded, usually very densely so, not evenly distributed 

 throughout the colonial mucilage; 

 pseudovacuoles usually present Microcystis 



[445] 



