116 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 Dictijota 

 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 wdth 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 Litliotliamnion 



58. Epiphytic Algae Melohesia 



Algae growing on rocks Litlioplujllum 



59. Fronds horizontally expanded or membranaceous 60 

 Fronds erect or umbilicate 62 



60. Minute alga endophytic in Cladophora peUiicida, 



fruit in hemispherical nemathecia Schmitziella 



Fronds cartilagino-membranaceous 61 



Fronds gelatino-coriaceous, tetraspores cruciate 



Petrocelis 



