79. Cells spherical, not bearing spines; subaerial or terrestrial, some- 

 times gregarious and densely clustered 80 



79. Cells aquatic, fusiform, acicular or needle-like, loosely clustered 



or entangled Ankistrodesmus ( in part) 



80. Cells gregarious (although sometimes solitary), but not adjoined, 

 usually in several-celled clusters on damp soil or moist sub- 

 strates; chloroplast not lobed ...Chlorococcum (in part ^ 



80. Cells in dense clumps and adjoined, rarely solitary; spherical, 

 or angular from mutual compression; chloroplast a dense, lobed 



plate nearly filling the cell Protococcus (in part) 



( Pleurococcus ) 



81. Cells bearing spines or setae 82 



81. Cells without spines or setae - 93 



82. Cells bearing a simple, sheathed seta. Chaetosphaeridium (in part) 



82. Cells not bearing a sheathed seta 83 



83. Cells bearing a single dichotomously 



branched hair - ...Dicranochaete ( in part ) 



83. Cells not bearing a dichotomously branched hair. _ 84 



84. Cells ellipsoid or ovate, bearing 1 to 4 teeth or short spines, 

 mostly at the poles; cells usually attached side by side, but 

 sometimes solitary Scenedesmus ( in part ) 



84. Cells fusiform or some other shape than above or, if ellipsoid, 

 bearing long spines over the entire svuface of the wall ....83 



85. Cells triangular, pyramidal, quadrangular, or polygonal 86 



85. Cells ovate, round, fusiform, or acicular 88 



86. Cells pyramidate or tetragonal (rarely pentagonal), with 4 to 6 

 fine, needle-like spines radiating from each angle (see, however, 

 Polyedriopsis qtiadrispina ) Polyedriopsis 



86. Cells pyramidate or polyhedral, without a tuft of needle-like 



spines at each angle - -87 



87. Cells triangular, polygonal, or pyramidal, consisting of a definite 

 body with 3 short, stout spines at the angles or at the apices 



of processes Tetraedron (in part) 



87. Cells pyramidal, each angle extended into a long spine-like pro- 

 cess, the body of the cell small in diameter and not distinguish- 

 able from the bases of the processes Treubaria 



88. Cells acicular or fusiform, the poles extended to form a long, 

 finely-pointed seta, one of which may fork at the tip and serve 



as an attaching organ Schroederia 



88. Cells not acicular or fusiform 89 



89. Cells globose, with radiating spines 90 



89. Cells ovate or elliptical 92 



90. The entire wall beset with long, stout, tapering spines which 



are broad at the base Echinosphaerella 



90. Cells bearing needle-like, slender spines .- 91 



91. Spines needle-like throughout, gradually tapering to a 



fine point Golenkinia (in part) 



91. Spines with basal portion thickened, then tapering abruptly to 



a long, finely pointed tip _._ Acanthosphaer-i 



92. Cells elliptical, with fine, needle-like spines arising from all 



parts of the wall. _... Franceia (in part) 



92. Cells ovate or ellipsoid, with a few long spines at the poles or 



localized at both poles and equator.— .— — - ..-..Lagerheimia 



[578] 



