96 
9. Thalli not minute borers through cal- 
careous material 10 
9. Thalli boring through coral, shell and 
other calcareous material. . Ostreobium 
10. Thalli calcified, either completely so as 
to become hard and stony, or incom- 
pletely so as to appear limy 11 
10. Thalli not calcified 24 
11. Thalli essentially prostrate, crustose; 
if erect branches present, these inflexible 
and stony 20 
11. Thalli erect and flexible, not prostrate 
or crustose 12 
12. Thalli not parasol- shaped 13 
12. Thalli shaped like a small parasol 
Acetabularia 
13. Thallus parts of cylindrical shape. . . 14 
13. Thallus parts flat or flattened 18 
14. Thalli branched 15 
14. Thalli unbranched (as viewed macro- 
scopically) Neomeris 
15. Thalli distinctly jointed 17 
15. Thalli not distinctly jointed. 16 
16. Thalli soft and lubricous Liagora 
16. Thalli firm, not lubricous . . . Galaxaura 
17. Thalli large and coarse, the segments 2 
to several mm. in diameter 
Halimeda (monile forms) 
17. Thalli small and delicate, the segments 
less than Vi mm. in diameter. . . . Jania 
18. Thalli not jointed, fan-shaped 19 
18. Thalli jointed 
. . .Halimeda (except monile forms) 
19. Thalli brownish, with prominent con- 
centric banding Padina 
19. Thalli greenish, not prominently banded 
concentrically Udotea 
20. Thalli forming thin, adherent crusts . 2 1 
20. Thalli forming massive, stony crusts, 
sometimes with erect knobs or branches 
Porolithon 
21. Thalli epiphytic, very delicate 22 
21. Thalli saxicolous, coarser 2 3 
22. Thalli in surface view with frequent 
larger cells (heterocysts) among the 
otherwise uniform cells Fosliella 
PACIFIC SCIENCE, Vol. XI, January, 1957 
22. Thalli in surface view composed of 
uniform cells Heteroderma 
23. Underside of thallus of many fan- 
shaped groups of cells converging and 
diverging irregularly Cruoriella 
23. Underside of thallus of essentially 
parallel cell rows Peyssonelia 
24. Thalli filamentous, membranous, or 
massive, but in any case divided up into 
cells by cross walls 31 
24. Thallus parts not divided up in a cellular 
manner by cross walls 2 5 
25. Filaments composing thalli dichotom- 
ously branched 26 
25. Thalli, or filaments composing thalli, 
not dichtomously branched. .29 
26. Filaments growing together to form a 
flabellate or peltate, spongy plant body 
27 
26. Filaments free, not forming a spongy 
plant body 28 
27. Main forked filaments bearing numer- 
ous terminally pronged lateral branch- 
lets Rhipilia 
27. Main forked filaments without such 
terminally pronged lateral branchlets . . 
Avrainvillea 
28. Filaments over 100 \x in diameter above, 
tending to be larger above than below, 
not attenuated. . Pseudochlorodesmis 
28. Filaments usually under 50 /jl in diameter 
above, attenuated or at least of lesser 
diameter above than below. .Derbesia 
29. Thallus parts spongy, composed of in- 
terlaced filaments forming a surface 
layer of swollen utricles ...... Codium 
29. Thallus parts not spongy, without a 
surface layer of swollen utricles. ... 30 
30. Thalli consisting of basal, cylindrical 
rhizoid-bearing parts and erect, spe- 
cialized branches of distinctive shapes; 
interior of thallus criss-crossed by 
trabeculae Caulerpa 
30. Thalli consisting of erect axes bearing 
pinnate or multifarious branches; in- 
terior without trabeculae. . . . Bryopsis 
