24 WISCONSIN PHYTOPLANKTON 



114. (115) Setae somewhat tapering Lagerheimia p. 129 



115. (114) Setae not tapering Franceia p. 131 



3 16. ( 93) Length of cells several times the diameter 117 



117. (118) Ends of cells produced into setae Schroederia p. 136 



118. (117) Ends of cells not produced into setae 119 



119. (120) Chloroplast with an axial row of pyrenoids Closteriopsis p. 136 



120. (119) Chloroplast without or with one pyrenoid. . Ankistrodesmus p. 134 



121. ( 88) Cells epiphytic or epizootic Characium p. 175 



122. ( 87) Cells in colonies 123 



123. (142) Colonies enclosed by a conspicuous gelatinous sheath 124 



124. (125) Cells connected by branching remains of old cell walls 



Dictyosphaerium p. 104 



125. (124) Cells not connected by branching remains of old cell walls.. 126 



126. (137) Cells spherical to ovoid or reniform 127 



127. (136) Chloroplast cup to disc-shaped and parietal 128 



128. (129) Cells with pseudocilia Tetraspora p. 102 



129. (128) Cells without pseudocilia - 130 



130. (131) Colonies never containing more than eight cells. .Gloeocystis p. 100 



131. (130) Colonies always with at least eight cells 132 



132. (133) Cells ovoid to reniform Gloeocystopsis p. 102 



133. (132) Cells spherical 134 



134. (135) Chloroplasts of old cells cup-shaped Sphaerocystis p. 101 



1T>5. (134) Chloroplasts of old cells disciform Planktosphaeria p. 103 



136. (127) Chloroplasts star-shaped and central Asterococcus p. 103 



1ST. (126) Cells elongate 138 



Io8. ( 141) Cells straight 139 



139. (140) Colonies with cells in groups of two Elaktothrix p. 139 



140. (139) Colonies with cells in groups of 2-4-8 Quadrigula p. 137 



141. (138) Cells curved Kirchneriella p. 140 



112. (123) Cells not enclosed by a gelatinous sheath 143 



143. (156) Colonies always forming a flat plate 144 



144. (155) Number of cells, except in rare cases, greater than two 145 



145. ( 152 ) Cells quadrately arranged 146 



146. (147) Quadrate arrangement apparent in end view of colony 



Tetradesmus p. 150 



147. (146) Quadrate arrangement apparent in front view of colony.... 148 



148. (149) Cells without setae or spines Crucigenia p. 144 



1 *9. (148) Cells with spines or setae 150 



150. (151) Long setae or spines on outer face of cells. . . .Micractinium p. 125 



151. (150) Short spines on outer face of cells Tetrastrum p. 149 



152. (145) Cells not quadrately arranged 153 



153. (154) Colony a flat circular or oval disc Pediastrum p. 166 



154. (153) Colony a single or double row of cells Scenedesmus p. 150 



155. (144) Number of cells in colony always two Euastropsis p. 174 



156. (143) Colony not forming a flat plate 157 



157. (166) Colony enclosed by old cell wall 158 



1B8. (165) Wall enclosing colony greatly expanded and homogeneous.. 159 



159. (162) Wall with spines or setae 160 



160. (161) Setae somewhat tapering Lagerheimia p. 129 



161. (160) Setae not tapering Franceia p. 131 



162. (159) Wall without spines or setae 163 



163. (164) Cells ovoid Oocystis p. 110 



