NO. 1 DAWSON: MARINE RED ALGAE OF PACIFIC MEXICO 11 



7. A main indeterminate branch usually without an opposite 



determinate branch 8 



7. A main indeterminate branch usually with an opposite deter- 

 minate branch 11 



8. Terminal cells of ultimate branchlets pointed 9 



8. Terminal cells of ultimate branchlets rounded 10 



9. Tetrasporangia sessile A. pygmaeum Gardner 



9. Tetrasporangia pedicellate A. setaceum Gardner 



10. Length of cells of main axes 2-3 times the breadth 



A. defectum Kylin 



10. Length of cells of main axes 3.5-6 times the breadth 



A. sparsum Tokida 



11. Terminal cells always blunt, or at least not distinctly acute .... 12 



11. Terminal cells distinctly acute 13 



12. Determinate lateral branches simple or with secund 



branchlets A. miharai Tokida (in part) 



12. Determinate lateral branches with pinnate branchlets .... 



A. nipponicum Yamada & Inagaki 



13. Gland cells resting laterally on 2-3 cells .... A. kylinii Gardner 

 13. Gland cells resting on a single cell 



A. plumulum (Ellis) Thur. var. plumulum 



14. Terminal cells blunt 15 



14. Terminal cells pointed 18 



15. Plants over 1 cm tall, becoming corticated by lateral branchlets 

 A. corticatum Tokida 



15. Plants under 1 cm in length (except A. thouarsii), completely 



uncorticated 16 



16. Plants with erect, percurrent axes from a prostrate 



stolon A. percurrens Dawson 



16. Main axis of plant ± branched, not conspicuously per- 

 current 17 



17. Primary lateral branches straight 



A. pteroton (Schousb.) Born. 



17. Primary lateral branches adaxially curved 



A. thouarsii (Mont) DeToni 



18. Tetrasporangia always pedicellate 



A. shimamuranum Nagai 



18. Tetrasporangia sessile, or sometimes pedicellate 19 



19. Determinate branchlets mostly incurved 



A. alternans Gardner 



19. Determinate branchlets mostly recurved 



A. secundatum Gardner 



20. Gland cells present 21 



