112 TEANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



20. Fronds minute, stalked, cells quadrate Frasiola 

 Fronds saccate when young, more or less lacin- 



iate when old, not distinctly stalked, cells 

 irregular in shape Monostroma 



21. Fronds simple 29 



Fronds branched 24 



22. Fronds composed of a double row of elongated 



cells ... ... ...Diploiiema 



Fronds composed of a single row of elongated 

 cells (monosiphonous) ... ... ... ... 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 Ghcetomorpka 



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

 Branches distinct Cladopliora 



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 HimanthaUa 



Fronds forming crusts or expanded pelhcles ... 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 



