130 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



20. Fronds minute, stalked, cells quadrate Prasiola 

 Fronds saccate when young, more or less lacin- 



iate when old, not distinctly stalked, cells 

 irregular in shape Mono stroma 



21. Fronds simple 29 



Fronds branched ... ... ... ... ... 24 



22. Fronds composed of a double row of elongated 



cells Diplonema, 



Fronds composed of a single row of elongated 

 cells (inonosiphonous) ... ... ... ... 23 



23. Small algae, filaments soft and flaccid, mega- 



zoospores, not tailed Ulothrix 



Megazoospores tailed Urospora 



Rather coarse algae, filaments more or less rigid, 



often twisted together Chcetomorpha 



24. Branches small and root-like ... ffliizoclonium 

 Branches distinct ... ... ... Claclophora 



25. Fronds irregularly globose, hollow, gelatinous, 



sporangia at the base of the coloured cortical 

 filaments ... ... ... ... ... Leathesia 



Fronds cup shaped, fruit on very long strap- 

 shaped receptacles Himanthalia 



Fronds forming crusts or expanded pellicles ... 26 

 Fronds small, tufted, composed of a dense basal 

 portion and an outer portion composed by free 



filaments Elachista 



Fronds tubular 28 



Fronds filamentous ... ... ... 30 



Fronds membranaceous, expanded 42 



26. Fronds densely parenchymatous throughout, fruit 



in external spots ... ... ... ... Balfsia 



Fronds minute, thin, formed of a basal horizon- 

 tal layer of cells with short vertical filaments, 

 between which the sporangia are borne ... 27 



