143. Filaments growing horizontally or prostrate, forming irregular 

 expansions, or discoid thalli, usually epiphytic or endophytic, not 

 forming erect branches or, if so, very short ones — 144 



143. Filaments not entirely prostrate, sometimes cushion-like or with 

 upright portions predominating; attached, sometimes perforating 



wood and shells; rarely free-floating ._ - 153 



144. Thallus a creeping, freely-branched filament, usually with setae 



or hairs 14o 



144. Thallus not freely branching but forming a disc or a somewhat 

 compact expanse; pseudoparenchymatous (PI. 18, Figs. 3, 10), 



one or more cells thick. 148 



145. Plants creeping in the mucilage of other algae, with very short, 

 upturned branches terminating in a long one-celled hair, the 



base of the hair swollen — - Chaetonema 



145. Filaments not growing in the mucilage of other algae 146 



146. Filaments entirely prostrate, not thalloid, creeping over or en- 

 twined about filamentous algae; some cells bearing 1 to several 



hairs (individual filaments may be unhTanched) —Aphanochaete (in part) 



146. Filaments spreading irregularly; thalloid, and becoming cushion- 

 like in some species; epiphytic or endophytic 147 



147. Filaments bearing setae; both endophytic 



and epiphytic __ Coleochaete (in part) 



147. Filaments not bearing setae, but ends of branches sometimes 

 tapering to fine or blunt points; often epiphytic but not endo- 

 phytic — - - Stigeoclonium (in part) 



148. Thallus a more or less regularly shaped, compact disc, sometimes 

 with an irregular outline, but not irregularly spreading; thallus 

 one-celled in thickness 149 



148. Thallus discoid or cushion-like, more than 1 cell in thickness; 



plan of branching frequently not discernible — 151 



149. Cells without setae Protoderma 



149. Cells bearing setae 1"^0 



150. Setae sheathed at the base, arising from the cell wa\l -Coleochaete (in part) 



150. Setae fine and needle-like, not sheathed at the base, arising from 



a gelatinous envelope which covers the thallus Chaetopeltis 



151. Plants endophytic (rarely epiphytic also), forming irregular 

 parenchymatous masses, or a freely branched thallus in the 



walls of other algae -- - Entocladia 



151. Plants epiphytic, forming somewhat regular discoid cushions - —.152 



152. Thallus pseudoparenchymatous (PI. 15, Fig. 6), with little fila- 

 mentous order apparent; chloroplast a parietal net ''Ulvella 



152. Thallus disc-like, pseudoparenchymatous; filaments radiating 

 from a common center, invested in a gelatinous envelope from 

 which deciduous setae arise (rarely found); chloroplasts numer- 

 ous ovate bodies about a central pyrenoid - Pseudulvella 



153. Filaments without setae, hairs, or bristles 154 



153. Filaments with bristles, or with branches that have setiferous apices... .164 



154. Branches (usually lacking) strictly rhizoidal and short 155 



154. Branches frequent, multicellular 157 



155. Chloroplast a spiral ribbon ._._ Spirogyra (in part) 



155. Chloroplast some other form ___.156 



[ 583 ] 



