Marine Algae from Eniwetok — Dawson 
97 
31. Thallus essentially of a single branched 
row of cells 32 
31. Thallus filamentous, membranous or 
massive, consisting of more than a 
single, branched row of cells 51 
32. Filaments prostrate, spreading; plants 
microscopic, epiphytic or endophytic. . 
Entocladia 
32. Not as above; filaments free and more 
or less erect 33 
33. Individual cells mostly essentially cy- 
lindrical and symmetrical except for 
curvature 3 5 
33. Individual cells asymmetrical, mostly 
not cylindrical 34 
34. Cells protruding irregularly on all sides 
from the axes Siphonocladus 
34. Cells inflated, irregularly clavate to sub- 
ovate, in short, more or less repent 
series of only a few cells 
Valonia (in part) 
35. Thallus filaments branched in one plane 
in a fan-, or blade-like manner, at least 
in part. . 36 
35. Thallus filaments variously branched, 
but not forming fan- or blade-like parts 
38 
36. Filaments palmately branched 
Rhipidiphyllon 
36. Filaments not palmately branched; 
blades of net-like form 37 
37. Blades stalked Struvea 
37. Blades without a definite stalk ....... 
Micro dictyon 
38. Branches essentially free, not attached 
to each other 39 
38. Branches attached to each other by 
small, specialized cells Boodlea 
39- Branching opposite or whorled, at least 
on main or lower axes 40 
39. Branching alternate or irregular, multi- 
farious 41 
40. Axes with whorled branchlets; tetra- 
sporangia surrounded by curved fila- 
ments Wrangelia (argus) 
40. Main axes (sometimes prostrate) with 
opposite and distichous or tristichous 
branchlets; tetrasporangia not associ- 
ated with curved filaments 
Antithamnion 
41. Cell wall about as thick as cell cavity, 
at least in lower parts 42 
41. Cell cavity much greater in diameter 
than cell wall thickness 43 
42. Cell cavities oval, longer than broad. . . 
Asterocytis 
42. Cell cavities more or less quadrangular, 
broader than long ..... Goniotrichum 
43. Thalli brownish or reddish, bearing 
specialized external reproductive struc- 
tures 46 
43. Thalli greenish, without specialized ex- 
ternal reproductive structures 44 
44. Filaments bearing septa at base of 
branches 45 
44. Filaments mostly, or commonly, with- 
out septa at base of branches 
Cladophoropsis 
45. Filaments coarse, 1-2 mm. in diameter 
Valonia (fastigiata) 
45. Filaments 0. 3-1.0 mm. in diameter. . . . 
Valoniopsis 
45. Filaments delicate, less than 200 n in 
diameter Cladophora 
46. Thalli brownish, commonly reproduc- 
ing by means of multicellular gametan- 
gia Ectocarpus 
46. Thalli reddish, commonly reproducing 
by means of tetrasporangia or mono- 
sporangia 47 
47. Minute epiphytes with main axes less 
than 15 m in diameter 48 
47. Epiphytic or saxicolous, but main axes 
over 70 in diameter 49 
43. Chromatophores stellate Kylinia 
43. Chromatophores not stellate 
Acrochaetium 
49. Asexual reproduction by tetrasporangia 
50 
49. Asexual reproduction by monosporan- 
gia Neomonospora 
