77. Oogonia 48-55/lc in diameter; oospores 



46-53m in diameter Oe. oviforme 



77. Oogonia 36-48ja in diameter; oospores 



35-43m in diameter Oe. Richterianum 



78. Pore median 79 



78. Pore supramedian or superior 83 



79. Wall of oospore smooth 80 



79. Wall of oospore spiny or scrobiculate 81 



80. Oogonia 22-24^ in diameter; oospores 



21-23^ in diameter Oe. rufescens 



80. Oogonia 30-38/x in diameter; oospores 



28-35|a in diameter -- Oe. sociale 



81. Outer layer of oospore wall smooth, middle scrobiculate Oe. Magnusii 



81. Outer layer of spore wall echinate 82 



82. Vegetative cells 9-14/x in diameter; oogonia 



32-38^ in diameter Oe. suecicum 



82. Vegetative cells 14-16ai in diameter; oogonia 



40-42^1 in diameter Oe. australe 



83. Wall of oospore smooth. 84 



83. Wall, either outer or median, of oospore 



decorated (scrobiculate or ribbed) 103 



84. Oogonia nearly cylindric, exceeding the diameter of 



the vegetative cells but very little - 85 



84. Oogonia decidedly greater in diameter than the vegetative cells 86 



85. Oospores globose to ovoid, 48-60/i in diameter; 



oogonia subovoid — - Oe. anomalum 



85. Oospores cylindric-globose to oblong, 30-52jn in 



diameter; oogonia cylindric — Oe. capillare 



86. Oospores globose or subglobose 87 



86. Oospores eUipsoid, obovoid, or cylindric-ovoid 96 



87. Vegetative cells 16-30ai in diameter 88 



87. Vegetative cells larger 92 



88. Pore supramedian 89 



88. Pore superior (cf. Oe. lauturnniarum, nearly superior) 90 



89. Vegetative cells 16-22/i in diameter; oogonia 40-49^ in 



diameter; oospores 35-47/u long Oe. lauturnniarum 



89. Vegetative cells and reproductive cells larger throughout; 

 vegetative cells 18-30^ in diameter; oogonia 48-7 0^ in 



diameter; oospores ( 39 ) -42-60/u, long .^....Oe. cardiacum 



90. Vegetative cells 28-30- ( 38 )m in diameter Oe. capilliforme 



90. Vegetative cells smaller 91 



91. Oogonia 36-42/u in diameter; vegetative cells 



20-25^ in diameter Oe. gracilius 



91. Oogonia 42-4 9/^ in diameter; vegetative cells 



22-27 fjL in diameter Oe. plagiostomum 



92. Oospores 58-76ya in diameter Oe. crassum 



92. Oospores smaller 93 



93. Vegetative cells 28-38^ in diameter, 42-120m 



long; oospores 37-45^ in diameter Oe. capilliforme 



93. Vegetative cells and oospores averaging larger 94 



94. Oospores 55-70^1 in diameter, 65-100m long; 



vegetative cells 35-45/^ in diameter Oe. rivulare 



94. Plants smaller throughout 95 



[161] 



