TUFTS COLLEGE STUDIES, VOL. IV, No. 7 



17. Fertile cells swollen on one side only. 

 17. Fertile cells swollen on both sides. 



18. Cells less than 25 M diam. 



18. Cells over 30 M diam. 



18. 



21. 



5. gracilis. 

 19- 



19. Cells 40-48 M diam. ; spores marked with a longitudinal line. 



39. S. circumlineata. 



19. Cells under 40 M diam. ; spore without line. 



20. Fertile cells swollen on the tube side. 



20. Fertile cells swollen on the outer side. 

 21. Fertile cell reflexed. 

 21 Fertile cell not reflexed. 



22. Chroniatophore slender. 



22. Chromatophore broad. 

 23. Cells 27-30 M diam., spore 30-33 X 33-45 M. 

 23. Cells 40-45 M diam., spore about 47 M diam 



20. 



5. S. rations. 



40. S. Borgeana. 



57. 5. reftexa. 



22. 



23- 

 24. 



1 8. S. affinis. 

 of varying shape. 



6. S.fusco-atra. 

 20. S. flavescens. 

 25- 



24. Cells under 15 M diam. 



24. Cells over 17 M diam. 

 25. Cells with twochromatophores frequent ; sterile cells often inflated. 



47. S. pratfttsis. 

 25. Chromatophore always single. 26. 



26. No zygospores ; aplanospores 24-26 X 38-50/1. 19. S. tnirabilis. 



26. Zygospores regularly produced. 4. S. catenaeformis. 



27. Chromatophores two, rarely three. 28. 



27. Chromatophores regularly three or more. 30. 



28. Spore membrane scrobiculate. 42. S. velata. 



28. Spore membrane smooth. 29. 



29. "Cells 21-40 ft diam. 66. 



29. Cells 43-50 ft diam. 26. S. dubia. 



30. Spore lenticular. 31. 



30. Spore ovoid, ellipsoid or subglobose. 

 31. Cells 1 20 M diam. or more. 



31. Cells 1 10 /i or less. 



32. Spore membrane pitted. 



32. Spore membrane smooth. 

 33. Fertile cells little or not swollen. 

 33. Fertile cells distinctly swollen. 



34. Spore a>out 72 n diam., 48 M thick. 



31. Spore 70-110 /i diam., 50-75 n thick. 

 35. Cells 90-163/1 diam. 



35. Cells 80 M diam. or less. 



36. Cells over 125 M diam. 



36. Cells 1 10 M diam. or less. 

 37. Spore compressed. 38. 



37. Spore not compressed. 46. S. ellipsospora. 



if.. 



35- 



S. /n \ i >it,i. 



32- 



58. S. kydrodictya. 

 33- 

 34- 



25. 5. bfltis. 



15. S. orthospira. 



45. S. submaxima. 



36- 



41. 



37- 



39- 



