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PACIFIC SCIENCE, Vol. VIII, October, 1954 
in transverse or longi- section of mid- 
parts 36 
A central axial filament + — obscure or 
not detectable in sections of mid-parts 
47 
36. Thallus essentially cylindrical through- 
out 37 
Thallus flat, at least in part. .Taenioma 
37. Thallus with slender, elongate axes. .38 
Thallus consisting of stipitate, obpyri- 
form branches Acrocystis 
38. Thallus consisting of segments, each 
with a whorl of teeth around the upper 
end Centroceras 
Not as above 39 
39- Filaments consisting of the central axial 
cells and a cortex which is discontinuous 
and in the form of bands, at least in 
young parts or branches 40 
Not as above 41 
40. Cortication continuous in main axes, 
discontinuous in lateral branchlets 
Spyridia 
Cortication essentially the same in 
branches of different orders . . Ceramium 
41. Thallus densely corticated with small 
cells Acanthophora 
Thallus with a single tier of cells sur- 
rounding the central axial filament. . .42 
42. Pericentral cells 3 Falkenbergia 
Pericentral cells 4 or more 43 
43. Axes provided with dense, spirally ar- 
ranged, coarsely spinulose short branch- 
lets Tolypiocladia 
Not as above 44 
44. Pericentral cells equal to the axial cells 
in length 45 
Pericentral cells half the length of axial 
cells Bostrychia 
45. Indeterminate branches alternating with 
groups of determinate branches ....... 
Herposiphonia 
All branches essentially indeterminate. . 
46 
46. Erect filaments arising from extensive 
prostrate, creeping filaments 
Lophosiphonia 
Without extensive, prostrate filaments . . 
Polysiphonia 
47. Apical cell surrounded by short tricho- 
blasts 48 
Apical cell not surrounded by trichoblasts 
52 
48. Apical cell in a terminal depression ... 49 
Apical cell emergent . Chondria (in part) 
49. Thallus cylindrical 50 
Thallus flat 5 1 
50. Ultimate branchlets very short 
Laurencia (in part) 
Ultimate branches not very short 
Chondria (in part) 
51. Branching all in one plane 
Laurencia (in part) 
Branching partly multifarious 
Chondria (in part) 
52. Thallus with slender, rhizoidal filaments 
among the medullary cells 53 
Thallus without rhizoidal filaments. . 54 
53. Cystocarps unilocular Pterocladia 
Cystocarps bilocular. ...... .Gelidium 
54. Axes provided with numerous short 
branchlets equally distributed on all sides 
Hypnea 
