116. Oogonia obovoid to subellipsoid; outer wall internally ribbed; 



median spore wall with 35-45 crenulate ribs Oe. Kjellmanii 



116. Oogonia ellipsoid or ellipsoid-globose; spore wall 



with fewer ribs, not crenulate — 117 



117. Outer spore wall with 13-15 longitudinal ribs Oe. exocostatum 



117. Outer and middle layers of spore wall with 



(22) -27-35 longitudinal ribs Oe. Boscii 



118. Dioecious 119 



118. Monoecious - 145 



119. Operculum median 120 



119. Operculum supramedian or superior. 130 



120. Vegetative cells 2-9m in diameter 121 



120. Vegetative cells larger 127 



121. Oogonia 13-19/li in diameter 122 



121. Oogonia larger — 124 



122. Oogonia subbiconic-ellipsoid, opening wide... Oe. pusillum 



122. Oogonia depressed-globose or subpyriform-globose, 



opening not wide -— - 123 



123. Oospores filling the inflated part of the oogonia; oogonia 1 to 4 in 



series; vegetative cells 3-5/x in diameter.. Oe. inconspicuutn 



123. Oospores not filling the oogonia; oogonia solitary (rarely 2); 



vegetative cells 2-5^ in diameter Oe. tapeinosporum 



124. Vegetative cells capitellate Oe. Howardii 



124. Vegetative cells not capitellate — -.. 125 



125. Vegetative cells 7-9/i in diameter; oogonia 27-30^ in 



diameter, subdepressed-globose ...Oe. calvum 



125. Vegetative cells averaging smaller; oogonia 22-28/t in 



diameter, pyriform or ellipsoid .- —. — 126 



126. Oogonia pyriform with a secondary lateral inflation Oe. Smithii 



126. Oogonia ellipsoid to depressed-globose Oe. poecilosporum 



127. Vegetative cells capitellate Oe. Howardii 



127. Vegetative cells not capitellate - 128 



128. Cell walls with spirally arranged punctations... ..-.Oe. punctatostriatum 



128. Cell walls without punctations 129 



129. Oospores 28-32^1 in diameter; oogonia globose 



or ellipsoid-globose --- - Oe. latiusculum 



129. Oospores 32-38^ in diameter; oogonia depressed 



to broadly pyriform-globose .-. - Oe. pratense 



130. Median wall of oospore with 20 longitudinal striations.-Oe. patwostriatum 



130. Oospore wall smooth - 131 



131. Vegetative cells 4-5/Lt in diameter Oe. trioicum 



131. Vegetative cells larger 132 



132. Oogonia not much greater in diameter than 



the vegetative cells; globular - -Oe. microgonium 



132. Oogonia decidedly greater in diameter than the vegetative cells 133 



133. Opening supramedian 134 



133. Opening superior - 135 



134. Oospores 17-23^ in diameter, 17-23^ long Oe. mitratum 



134. Oospores 23-28/n in diameter, 21-26m long 



( sometimes monoecious ) - - - Oe. spurium 



135. Oogonia 16-20^ in diameter Oe. epiphyticum 



135. Oogonia larger — - 136 



[163] 



