KEY TO THE GENERA. 71 



II. Frond flat, leathery. 



i. Stem long or short, mostly slender. 

 Blade thick, leathery, large' or small, 

 dark olive green or brown. " Kelp." 



Laminaria. 



2. Stem cylindrical, long, stout, winged on 

 each side with long stalked, leathery 

 leaflets. Blade of frond thick, long; 

 midrib at base, which fades out towards 

 the top. Pterygophora. 



3. Stem short, split, blade long, covered 

 with a net-work of prominent nerves. 



Dictyonturon, 



III. Frond flattened. 



1. Frond narrow, thick, tough, forked, from 

 three inches to two feet long. " Rock- 

 weed." Fuch 



2. Frond leafy below, finely divided and 

 filiform above. Air vessels in the swollen 

 bead-like ultimate branchlets. Halidrys. 



3. Frond flat, narrow, thin, pinnately com- 

 pounded, pinnae and pinnulae tapering 

 to top and bottom. Desmarestia. 



4. Frond flat, fen-shaped, small, marked 

 with concentric zones or belts of darker 

 color. /. naria. 



