134 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



50. Midrib present Fucus 



Midrib wanting ... ... ... ... ... 51 



51. Fronds destitute of air bladders 52 



Fronds furnished with air bladders 55 



52. Fronds thick and coriaceous, channelled, fruit 



in terminal receptacles ... ... ... Pelvetia 



Fronds thin, membranaceous 53 



53. Sporangia sessile 54 



Sporangia, and antheridia stalked, collected in 



spot-like tufts on the surface of the frond Cutleria 



54. Fronds regularly dichotomous, spores scattered 



irregularly over the surface of the frond Dictyota 

 . Fronds more or less fan-shaped, deeply and 

 irregularly laciniate, sporangia arranged in 

 undulating transverse bands Taonia 



55. Air-bladders simple, immersed in the frond 



Ascophyllum 

 Air-bladders stalked, furnished with numerous 

 diaphragms, fruit terminal ... ... Halidrys 



56. Fronds calcareous .. ... ... ... ... 57 



Fronds not calcareous 59 



57. Fronds erect, filiform, articulated ... Corallina 



Fronds thin, horizontally expanded 58 



Fronds thick, horizontally expanded, but rising 



at intervals in irregular knobs Lithothamnion 



58. Epiphytic Algse Melobesia 



Algae growing on rocks ... ... Litliophyllum 



59. Fronls horizontally expanded or msmbranacsous 60 

 Fronds erect or umbilicate 62 



60. Minute alga endophytic in Cladophora pellucida, 



fruit in hemispherical nemathesia Schmitziella 



Fronds cartilagino-membranaceous 61 



Fronds gelatino-coriaceous, tetraspores cruciate 



Petro cells 



