APPENDIX. 399 



IY. ANKISTRODESMI^E. Cells elongate, entire, small, 

 grouped in fagot-like bundles. 



18. Ankistrodesmus. 



Y. PEDIASTRE.E. Cells grouped in the form of a disk 

 or star, or placed side by side in one or two short rows. 



19. Pediastrum. Cells forming a disk or star, marginal 

 cells bidentate. 



20. Monactinus. Cells as in 19, but marginal cells uni- 

 dentate. 



21. Scenedesmus. Cells placed side by side in one or 

 two rows. 



14. DIATOMACEJE. For genera, see page 142. 



