WISCONSIN PHYTOPLANKTON 25 



164. (163) Cells ovoid to reniform Nephrocytium p. 114 



165. (158) Wall lamellated but not expanded Gloeotaenium p. 115 



1C6. (157) Colony not enclosed by old cell wall 167 



167. (176) Length of cell not more than twice the breadth 168 



168. (171) Remains of old cell walls at center of and holding colony 



together 169 



169. (170) Cells spherical Westella p. 106 



170. (169) Cells ovoid to reniform Dimorphococcus p. 106 



171. (168) Colonies without remains of old cell wall at center 172 



172. (173) Outer face of cells with long setae Micractinium p. 125 



173. (172) Outer face of cells with short spines or without ornamenta- 



tion 174 



174. (175) Cells without spines on outer face Coelastrum p. 160 



175. (174) Cells with short spines on outer face Sorastrum p. 162 



176. (167) Length of cells several times the breadth 177 



177. (178) Colony forming a closed hollow sac Hydrodictyon p. 165 



178. (177) Colony not forming a closed hollow sac 179 



179. (180) Cells radiating from a common center Actinastrum p. 164 



180. (179) Cells not radiating from a common center 181 



181. (182) Cells straight or arcuate Ankistrodesmus p. 134 



182. (181) Cells markedly curved Selenastrum p. 132 



183. ( 86) Cells in simple or branched filaments 184 



184. (195) Cells with one to eight chloroplasts, chloroplasts never re- 



ticulate 185 



185. (192) Chloroplasts parietal 186 



186. (191) Chloroplasts laminate to disciform 187 



187. (188) Cells in simple filaments Ulothrix p. 179 



188. (187) Cells in branching filaments 189 



18'9. (190) Setae confined to terminal cells or lacking. . . Stigeoclonium p. 180 



190. (189) Setae occurring on any cell of filament Aphanochaete p. 181 



191. (186) Chloroplast a spiral band Spirogyra p. 185 



192. (185) Chloroplast central 193 



193. (194) Chloroplast an axial plate Mougeotia p. 184 



194. (193) Chloroplasts stellate Zygnema p. 184 



195. (184) Chloroplasts numerous or united to form a single reticulate 



mass Cladophora p. 182 



