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



2. Dissepiments plane. 3. 



2. Dissepiments replicate. 27. 



3. Chromatophore single. 4. 



3. Chroniatophores two or more. 16. 



4. Spore membrane punctate. 27. S. punctata. 



4. Spore membrane smooth. 5. 



5. Fertile cells not distinctly swollen. 6. 



5. Fertile cells distinctly swollen. 10. 



6. Cells less than 30 M diam. 7. 



6. Cells 30 M diam. or more. 9. 



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



9. 5. snbsalsa. 

 7. Spore ellipsoid, 2-3 times as long as the diam. 8. 



8. Chromatophore slender, with inconspicuous pyrenoids. 



7. 5. communis. 



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



3. 5". Jnergensii. 



8. Chromatophore broad. \. S. longata. 



9. Cells 30-48 //, diam. 2. 5. porticalis. 



9. Cells 48-70 fj. diam. 8 6". condensata. 



10. Fertile cells swollen on one side only. n. 



10. Fertile cells swollen on both sides. 12. 



n. Cells 18-22 /j. diam. 21. 5. gracilis. 



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



12. Chromatophore slender. 13. 



12. Chromatophore broad. 14. 



13. Cells 27-30 /A diam. ; spore 30-33x33-45 M- 18. 5. affinis. 



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



6. 5. fusco-atra. 



14. Cells 11-13 M diam. ; spore about 20X30 /a. 20. S. flavesccns. 



14. Cells 24-27 M diam. 15. 



14. Cells 30-43 ft. diam. ; spore 30-42X70-120 /j.. 22. S. lutctiana. 



15. Spore 30X60-75 fj.. 4. S. catenaeformis. 



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



19. S. mirabilis. 



16. Chroniatophores two, rarely three. 17. 



16. Chromatophores regularly three or more. 18. 



17. Cells 27-40 /u. diam. . 10. S. decimina. 



17. Cells 43-50 M diam. 26. S. dubia. 



18. Spore lenticular. 19. 



18. Spore ovoid, ellipsoid or subglobose. 21. 



19. Cells 100 /j. diam. or more. 16. .9. maxima. 



19. Cells less than 100 /u diam. 20. 



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



20. Fertile cells distinctly swollen. 25. 5. bellis. 



21. Cells 90-160 M diam. 22. 



