WISCONSIN PHYTOPLANKTON 23 



70. (71) Cells solitary or in families, divided into two symmetrical 



halves with a chloroplast in each half. Median region 

 generally constricted. .Family Desmidiaceae ('See Part 2) 



71. ( 70) Cells not divided into two symmetrical halves and without 



median constrictions 72 



72. ( 85) Cilia normally present in vegetative cells.. Order Volvocales 73 



73. ( 84) Anterior end of cells with two cilia 74 



74. ( 75 ) Cells solitary Chlamydomonas p. 90 



75. ( 74) Cells in colonies Family Volvocaceae 76 



V6. ( 77) Colony a flat plate Gonium p. 94 



77. ( 76 ) Colony a hollow sphere 78 



78. ( 79 ) Cells mutually compressed Pandorina p. % 



79. ( 78) Cells some distance from one another 80 



80. ( 83) Colony with not more than 256 cells 81 



8.1. ( 82) Asexual reproduction by division of all cells to form daugh- 

 ter colonies Eudorina p. 95 



82. ( 81) Asexual reproduction by division of certain cells to form 



daughter colonies Pleodorina p. 96 



83. ( 80) Colony generally containing many cells Volvox p. 97 



84. ( 73) Anterior end of cells with four cilia Carteria p. 92 



85. ( 72) Cilia not present in vegetative cells 86 



86. (183) Cells solitary or in colonies, never in simple or branched 



filaments Order Protococcales 87 



87. (122) Cells solitary 88 



88. (121) Cells free-floating 89 



89. ( 92 ) Cell shape angular 90 



90. ( 91) Angles simple or with spines, never with long setae 



Tetraedron p. 115 



91. ( 90) Angles with tufts of long setae Polyedriopsis p. 124 



92. (89) Cells spherical, ovoid, or elongate 93 



93. (116) Length of cells not more than three times the diameter 94 



94. ( 109") Cells spherical 95 



95. (102) Cell wall smooth 96 



96. ( 99) Cells embedded in a gelatinous sheath 97 



07. ( 98) Gelatinous sheath lamellated Gloeocystis p. 100 



98. ( 97) Gelatinous sheath not lamellated Planktosphaeria p. 103 



99. ( 96) Cells not embedded in a gelatinous sheath 100 



100. (101) Wall lamellated Gloeotaenium p. 115 



101. (100) Wall not lamellated Chlorella p. 108 



102. ( 95) Wall sculptured, denticulate, or with long spines or setae.. 103 



103. (108) Setae or long spines covering the wall 104 



104. (107) Wall with setae 105 



105. (106) Setae the same thickness throughout, or gradually taper- 



ing Golenkinia p. 127 



106. (105) Setae visibly thickened in the lower third. .Acanthosphaeria p. 128 



107. (104) Walls with long spines Echinosphaerella p. 128 



108. (103) Denticulations or ridges covering the walls Trochiscia 108 



109. ( 94) Cells ovoid to reniform 110 



MO. ( 111 ) Cells reniform Nephrocytium p. 114 



111. (110) Cells ovoid 112 



112. (113) Walls without setae or spines Oocystis p. 110 



113. (112) Walls with spines or setae 114 



