f. Membrane of polygonal plates (fig. i8). Peridinium. 



ff. Membrane of plates with long horn-like processes (fig. 17). 



Ceratiiini. 

 ee. With one or more flagella, no collar, no transverse furrow. 

 f. With an armor with a pointed posterior end ; colonies formed by 

 growth from rim (fig. 5). Dinobryon. 



ff. Colonies of numerous individuals in a gelatinous sphere (fig. 9). 



Uroglena. 



fff. Spherical colonies of radialh^ arranged individuals each with two 



brown chromatophores (fig. 15). Synura. 



Desmidiaceae.* 



a. Cell wall apparently not divided into two parts, and without pores, 

 b. Cells elongate, cylindrical and not constricted, forming loose filaments. 

 Cell wall with a differentiated outer layer, of which the small rough- 

 nesses and spines form a part, 

 c. Chloroplasts axile (fig. i). Gofiatozygon. 



cc. Chloroplasts parietal and spirally twisted (fig. 16). Genicularia. 



bb. Cells solitary, relatively short, and mostly unconstricted ; cell wall a 

 simple sac, without a differentiated outer layer. 

 c. One chloroplast in each cell, 

 d. Chloroplast spirally twisted, axile, or parietal (fig. 2). Spirotccnia. 

 dd. Chloroplast plane, axile; cells solitary (fig. 10). Mesotccninin. 



cc. Two chloroplasts in each cell, 

 d. Chloroplasts star-shaped, radiating from a central pyrenoid (fig. 25). 



Cylindrocystis . 

 dd. Chloroplasts ridged with longitudinal serrated ridges (fig. 12). 



Netriu})i. 

 aa. Cell wall showing two segments, and with a differentiated outer porous 

 layer, 

 b. After division the cells remain free and solitary. 

 c. Cells not constricted, 

 d. Cells of moderate length, straight, cylindrical (figs. 17, 23). Peniiini. 

 dd. Cells elongate, generally curved and attenuated, 

 e. Cells almost cylindrical, scarcely attenuated ; chloroplasts single, 

 without apical moving granules. K'oya. 



ee. Cells strongly attenuated towards each extremity ; two chloroplasts 

 in each cell, with apical moving granules (figs. 5, 6, 7, 8). 



Closteriiim . 

 cc. Cells more or less constricted at the middle, 

 d. Cells elongated and cylindrical, constriction slight. 

 e. Apices of cells truncate or round, entire, 

 f. Base of semi-cells plicate (figs. 3, 4). DoiidiiDii. 



ff. Base of semi-cells plane (fig. 20). Pleurotcrniuiii. 



ee. Apices of cells cleft, apical incision narrow (fig. 19). Tetmevioriis. 

 dd. Cells relatively short ; deeph' constricted. 



* Adapted from Conn and Bessey. 



