KEY TO THE GENERA. 71 



II. Frond flat, leathery. 



1. Stem long or short, mostly slender. 

 Blade thick, leathery, large or small, 

 dark oKve 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. 



Dictyoneuron. 



III. Frond flattened. 



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

 three inches to two feet long. "Rock- 

 weed." Fucus. 



2. Frond leafy below, finely divided and 

 filiform above. Air vessels in the swollen 

 bead-hke ultimate branchlets. Halidrys. 



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

 pounded, pinnae and pinnulae tapering 

 to top and bottom. Desmarestia. 



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

 with concentric zones or belts of darker 

 color. Zonaria. 



