NO. 1 DAWSON : MARINE RED ALGAE OF PACIFIC MEXICO 59 



7. Tetrasporangial sori without a heavy sterile 



margin G. pusillum 



7. Tetrasporangial sori with a heavy sterile 



margin G. sclerophyllum 



8. Segments very narrow, 250 /u. in diameter or less . . 9 

 8. Segments broader, 500 /a in diameter or more ... 10 

 9. Rhizoidal filaments scattered through medulla and 



cortex G. crinale var. crinale 



9. Rhizoidal filaments confined to center of 



medulla G. crinale var. luxurians 



10. Plants with few or no lateral branchlets . G. nudifrons 



10. Plants with many lateral branchlets 11 



11. Branching distichous 12 



11. Branching polystichous G. polystichum 



12. Branchlets of ultimate order much reduced in diameter, 



usually densely congested 13 



12. Branchlets of ultimate order not markedly reduced in dia- 

 meter, or if so not particularly densely congested . . 16 

 13. Ultimate branchlets strongly flattened . G. decompositum 

 13. Ultimate branchlets subcylindrical or compressed ... 14 

 14. Tetrasporangial sori markedly elongated, with a sterile 



margin G. coronadense 



14. Tetrasporangial sori occupying clavate ends of ultimate 



branchlets 15 



15. Tetrasporangial branchlets short-stipitate . G. deciduum 

 15. Tetrasporangial branchlets with a long slender "stipe" . . 



G. papenfussii 



16. Main axes provided with more or less uniform, short, 

 distichous, subcylindrical, ascending, determinate branch- 

 lets G. coulteri 



16. Main branches normally only giving rise to indeterminate 



branches 17 



17. Branchlets more or less clearly geniculate at first ... 18 



17. Branchlets not markedly geniculate 19 



18. Tetrasporangial branchlets with cordate apices 



G. cartilagineum var. robustum 



18. Tetrasporangial branchlets blunt or subacute, not cordate 



G. purpurascens 



19. Branching mostly opposite, the ultimate branchlets appearing 

 regular G. johnstonii 



