1), 
14. 
15. 
16. 
17a 
8. 
IQ. 
20. 
132 
Filamentous algae, not gelatinous or vermiform, with branches 
all opposite or whorled, or some alternate and some opposite 
Filamentous algae, not gelatinous or vermiform, with branches 
alternate 
13 
17 | 
19 
Branches whorled sig Sc ai nee wns > 
Branches opposite or occasionally in threes, or main branches 
alternate and ultimate branches opposite 16 
Thallus small, delicate, pinnately divided ; main branches in 
whorls, sometimes in threes ; tetraspores cruciately divided ... 
Antithamnion ...p.98 
Plants 2-6 inches long, densely covered by branches in whorls or 
coming off irregularly all round the main axes 15 
Cells of main filaments very large and uncorticated ; whorls of 
branches overlapping one another giving a bottle-brush 
effect 306 ese : ea SB. . Halurus ...p.94 
Whorls of branches en from one anette showing main 
filament in between ; cells of main branches may be corticated 
Spondylothamnion ...p.93 
Small plants forming dense cushions or tufts of filaments, 
quarter to three-eighths inch long ; main branches alternate, 
ultimate branches anes ; oa eal or in groups on 
lateral branches 
Plants with definitely eee or sone Hanae 18 
Cells of the filament cee here and there small interpolated 
colourless cells... : $36 500 Trailiella ...p.93 
Cells of the filament enone small colourless cells 
Spermothamnion  ...Pp. 93 
Delicate pinnately divided plants, less than three-quarters inch 
long, with tetrahedrally divided tetraspores on the ends of the 
pinnules.... ee ; ats ... Ptilothamnion ...p.93 
Pinnately divided or ute plants, three-quarters to two 
inches long; cruciately divided tetraspores as _ lateral 
appendages, stalked or sessile... ... Antithamnon ...p.98 
Plants in small tufts or forming a dense fluffy covering to other 
algae or to the substratum (especially where a thin coating of 
sand covers the rock) ; plants half-inch long, or less ... 
Plants three-quarters to 5 inches in length, forming tufts of 
branched filaments 
One chromatophore in each cell, usually with a conspicuous 
pyrenoid ; monospores or (occasionally) cruciately divided 
tetraspores Jo so A ...  <Acrochaetium ...p.77 | 
Several Berea or spirally twisted chromatophores in 
20 
2I | 
each cell; cruciately divided tetraspores  Rhodochorton ...p.95 
