106 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



2. Dissepiments plane. 3- 



2. Dissepiments replicate. 

 3. Chromatophore single. 

 3. Chromatophores two or more. 



4. Spore membrane punctate. 27. S. pundata. 



4. Spore membrane smooth. 5- 



5. Fertile cells not distinctly swollen. 

 5. Fertile cells distinctly swollen. 

 6. Cells less than 30 /x diam. 



6. Cells 30 fj- diam. or more. 9- 



7. Spore ovoid, slightly longer than the diam. ; cells 22-25 M diam. 



9. S. subsalsa. 



7. Spore ellipsoid, 2-3 times as long as the diam. 

 8. Chromatophore slender, with inconspicuous pyrenoids. 



7. S. communis. 

 8. Chromatophore slender, with many large, distinct pyrenoids. 



3. 5". Juergensii. 



8. Chromatophore broad. f- $" longata. 



9. Cells 30-48 fj. diam. 2 - S. porticalis. 



9. Cells 48-70 M diam. 8. 5. condensata. 



10. Fertile cells swollen on one side only. 

 10. Fertile cells swollen on both sides. 



ii. Cells 18-22 /x diam. 21. S. gracilis. 



ii. Cells 33-40 M diam. 5- S. varians. 



12. Chromatophore slender. 

 12. Chromatophore broad. 



13. Cells 27-30 n diam. ; spore 30-33x33-45 M- l8 - S. affinis. 



13. Cells 40-45 /x diam. ; spore about 47 /x diam., of varying shape. 



6. S. fusco-atra. 



14. Cells 11-13 M diam.; spore about 20X30 M. 2O ' S. flavescens. 

 14. Cells 24-27 /x diam. 



14. Cells 30-43 /x diam. ; spore 30-42X70-120 n. 22. 5. lutetiana. 



15. Spore 30X60-75 M. 4- 5. catenaeformis. 



15. Spore 24-26X38-50 M, formed without conjugation. 



19. 5. mirabilis. 



16. Chromatophores two, rarely three. 



16. Chromatophores regularly three or more. 18. 



17. Cells 27-40 /a diam. 10. 5. dedmina. 



17. Cells 43-50 M diam. 26 - ^ rf*- 



18. Spore lenticular. I 9- 



18. Spore ovoid, ellipsoid or subglobose. 



19. Cells 100 /x diam. or more. 16. S. maxima. 



19. Cells less than 100 M diam. 



20. Fertile cells little or not swollen. 15- S- orthospira. 



20. Fertile cells distinctly swollen. 25. S. bellis. 



21. Cells 90-160 /x diam. 



