REVISED LIST OF MABINE AIiGM. 131 



27. Fronds furnished with colourless hairs, pluri- 



locular sporangia formed by the transformation 



of vertical filaments ... ... ... Ascocyclus 



Fronds not provided with colourless hairs, unilo- 

 cular sporangia oval, plurilocular sporangia 

 unknown ... ... ... ... ... Myrionema 



28. Fronds simple, hollow throughout, substance 



thin 29 



Fronds simple, cylindrical, somewhat cartilagin- 

 ous, with numerous diaphragms ... Chorda 



29. Sporangia densely covering the surface Scytosiphon 

 Sporangia external in scattered spots Asperococcus 



30. Fronds capillary, branching, formed of a single 



row of cells (monosiphonous) 31 



Fronds cylindrical, solid or occasionally becoming 

 partially hollow with age... ... ... ... 32 



31. Both unilocular and plurilocular sporangia 



formed by transformation of special branches, 

 plurilocular sporangia in the form of pod-like 

 branches, unilocular sporangia globose, sessile 

 or shortly stalked ... ... ... Ectocarpus 



Both forms of sporangia formed from the cells 

 in the continuity of the branches and not by 

 a transformation of special branches Pylaiella 



Filaments partly polysiphonous, unilocular spor- 

 angia partly immersed in the frond, plurilocular 

 sporangia formed by direct transformation of 

 the cells of the branches ... ... Isthmoplea 



Primary branches creeping in the subtance of 

 other Algae, secondary and fructifying ramuli 

 erect ... ... ... ... ... Streblonema 



32. Fronds slimy, composed of an axial layer of 



elongated filaments and a distinct cortical layer 



of short horizontal filaments ... ... 33 



