12. Chloroplasts numerous irregular plates arranged in a reticulum 

 or in strands of cytoplasm radiating from the center of the cell; 

 wall thin - Eremosphaera 



12. Chloroplasts cone-shaped, arranged at the periphery and 



projecting inward; wall thick and lamellate. — Excentrosphaera 



13. Cell wall with reticular markings or with short spines - Trochiscia 



13. Cell wall with several long, sometimes stout, spines Echinosphaerella 



14. Cells ellipsoid - - -15 



14. Cells lunate, straight and fusiform, or acicular 17 



15. Cells without spines or setae — Oocystis (part) 



15. Cells bearing spines or setae 16 



16. Setae distributed over the entire cell wall Franceia 



16. Setae arising from the poles only, or from the poles 



and the equator - - Lagerheimia 



17. Cells lunate, distinctly curved 18 



17. Cells straight, acicular, or fusiform 19 



18. Cells invested by a gelatinous sheath Kirchneriella (part) 



18. Cells not inclosed by a sheath Ankistrodesmxis (part) 



19. With a fine, needle-like spine at one or both poles of the cell Schroederia 



19. Poles of the cell without a spine, although apices may taper 



to a fine point 20 



20. Chloroplast an elongate plate with a row of pyrenoids; 



cell up to 530/Li long -— -Closteriopsis 



20. Chloroplast without pyrenOids, or with but 1; 



cell much shorter than above Ankistrodesmus (part) 



21. Cells with a gelatinous investment -— 22 



21. Cells without a gelatinous investment- 26 



22. Cells spherical or broadly ovate. 23 



22. Cells not spherical, but elongate, at least twice as long as wide - 24 



23. Cells arranged in clusters at the ends of radiating strands ..Dictyosphaerium 



23. Cells not adjoined by radiating strands Planktosphaeria (part) 



24. Cells straight, with long axes parallel in the colony. ._. _ ..Quadrigula 



24. Cells curved -- 25 



25. Cells invested by a firm sheath (gelatinized mother cell wall); 



cells sUghtly curved or reniform Nephrocytium 



25. Cells in a homogeneous, thin mucilage; sharply 



curved, lunate or sickle-shaped Kirchneriella (part) 



26. Cells adjoined by remains of old mother cell walls 



at the center of the colony — 27 



26. Cells held together by other means; fragments of old mother cell 



walls not present at center of colony — 28 



27. Cells spherical; cell wall fragments curved and unbranched— ..-.Westella 



27. Cells reniform or ovoid; cell wall fragments forming 



straight, branching strands. ...Dimorphococcus 



28. Cells spindle-shaped; adjoined end to end to form 



a chain which may branch Dactylococcus 



28. Cells not spindle-shaped and not adjoined end to end 



in a chain-like series. 29 



29. Cells ovate or spherical, inclosed by enlarged mother cell walls — 30 



29. Cells' elongate, acicular, or spindle-shaped — .- -31 



30. Cells separated from one another by a deposit of semi-opaque 

 mucilage which forms cruciately arranged bands 



about the colony - — - Gloeotaenium 



[234] 



