130. Filaments creeping on large filamentous algae, cells in continuous 



series -- Aphanochaete (in part) 



130. Filaments free-floating, or with basal attachment; if prostrate, 



with cells in interrupted series 131 



131. Filaments short, up to 20 cells in length; series of cells often 

 interrupted — 132 



131. Filaments longer than 20 cells; series continuous 133 



132. Chloroplast a parietal plate covering but a small part of 

 the wall; filaments composed of few cells, frequently inter- 

 rupted - Stichococcus 



132. Chloroplast a broad parietal plate covering most of the cell wall; 

 filaments continuous Hormidiopsis 



133. Filaments composed of cylindrical units inclosing 2 protoplasts, 

 arranged in pairs, with the space between the protoplasts and the 



end walls filled with lamellated, gelatinous material— — - Binuclearia 



133. Cells not in pairs as above - - 134 



134. Filaments inclosed by a gelatinous sheath _ 133 



134. Filaments not inclosed by a gelatinous sheath 139 



135. Cells oblong, broadly elliptic or quadrate, rather loosely arranged 

 in a narrow or wide gelatinous sheath in which the individual 



cell sheaths are conspicuous and lamellate Cylindrocapsa 



135. Cells without conspicuously lamellated sheaths — 136 



136. Cells cylindrical, subcylindrical, or globose; adjoined at the 



cross walls 137 



136. Cells oblong, not adjoined at the cross walls Geminella (in part) 



137. Cells quadrate, short- or long-cylindric 138 



137. Cells subglobose or elHptical; wall usually composed of 2 parts 



which overlap or adjoin in the midregion of the cell Radiofilum 



138. Chloroplast a parietal ring or band that encircles the wall or 



nearly so -- -- -- Ulothrix (in part) 



138. Chloroplast a laminate plate covering but a small portion of the 



wall and not encircling it Geminella (in part) 



139. Filaments without basal-distal differentiation; chloroplast a par- 

 ietal plate encircling one-half the wall or less Hormidium 



139. Filaments with basal-distal differentiation, often attached by 



a basal hold-fast — 140 



140. Cells long-cylindric, the terminal cell tapering unsymmetrically 



to form a blunt point Uronema 



140. Cells short-cyhndric or quadrate, the terminal cell not tapering 



to a point Ulothrix (in part) 



141. Plants orange- or brick-red from an abundance of haematochrome 

 which often masks the chlorophyll; chloroplasts discoid or band- 

 hke; walls usually roughened externally; plants of aerial habitats, 

 usually branching Trentepohlia (in part) 



141. Plants without haematochrome; wall usually composed of 2 por- 

 tions which overlap or adjoin in the midregion (PI. 8, Figs. 1, 5), 

 forming H-shaped pieces upon fragmentation; chloroplast mas- 

 sive, a branched band or a thick, parietal plate, or a cushion Microspora 



(cf. Tribonema) 



142. Filaments branched, coenocytic and tubular, without cross walls 



except where reproductive cells are cut off 168 



142. Filaments not coenocytic and tubular, but having cross walls — - 143 



[582 ] 



