15. Oospores with one spiral ridge; vegetative cells 30-33/i in 



diameter; oogonia 63-67/Lt in diameter Oe. Sawyerii 



15. Oospores with 4-7 spiral ribs; vegetative cells 15-35/i in 



diameter; oogonia 51-64^1 in diameter Oe. stellatum 



16. Oogonia with longitudinal ribs on the inner surface; outer spore 



wall with 35-40 longitudinal ribs Oe. striatum 



16. Oogonia wall smooth; oospores with fewer longitudinal ribs 17 



17. Ribs of oospore wall 16-24, anastomosing — - 18 



17. Ribs of oospore wall 25-35, not anastomosing Oe. Wolleanum 



18. Oogonia 65-85^ in diameter; oospores 



61-80m in diameter - Oe. perfectum 



18. Oogonia smaller, 57-66/i in diameter; 



oospores 51-62/^ in diameter Oe. cyathigerum 



19. Oospore wall layers smooth ... . - 20 



19. Oospore wall decorated - 25 



20. Oogonia sexangular-ellipsoid — -- — 21 



20. Oogonia globose or subglobose — - 22 



21. Oogonia 36— 48/i in diameter; oospores 34-40/ii 



in diameter Oe. subsexangulare 



21. Oogonia 29-33/x in diameter; oospores 27-31/ti 



in diameter Oe. sexangulare 



22. Vegetative cells 8-9^ in diameter Oe. depressum 



22. Vegetative cells larger 23 



23. Oospores 27-33^ in diameter - Oe. Braunii 



23. Oospores larger 24 



24. Pore supramedian ( sometimes median ), vegetative 



cells 14-18^1 in diameter - -- - Oe. magnum 



24. Pore median; vegetative cells averaging larger, 



17-22^ in diameter „ Oe. gallicum 



25. Oospore wall spiny — 26 



25. Oospore wall with 4-7 spiral ridges Oe. spiralidens 



26. Vegetative cells 18-30/x in diameter Oe. echinospermum 



26. Vegetative cells smaller 27 



27. Oogonia terminal, subellipsoid Oe. hispidum 



27. Oogonia intercalary, globose or obovoid Oe. hystricinum 



28. Opening of oogonium inferior or inframedian... 29 



28. Opening of oogonium median, supramedian, or superior... 31 



29. Walls of vegetative cells undulate 30 



29. Walls of vegetative cells not undulate, but capitellate Oe. ambiceps 



30. Oogonia 56-68ai in diameter Oe. sinuatum 



30. Oogonia 48-55ai in diameter Oe. undulatum 



31. Opening median or supramedian 32 



31. Opening clearly superior or supreme 40 



32. Oogonia (46)-48-63m in diameter - --- 33 



32. Oogonia smaller — 34 



33. Vegetative cells 14-16/ci in diameter; oogonia 46-52/i 



in diameter, opening supramedian Oe. Kozminskii 



33. Vegetative cells 16-22^1 in diameter; oogonia 



53-63m in diameter Oe. brasiliense 



34. Opening supramedian ^'^ 



34. Opening median *-"" 



35. Oogonia depressed-globose, 25-32^14 long, wdth 



12-16 longitudinal ridges - -- -- Oe. oelandicum 



[158 1 



