NO. 1 TAYLOR: PACIFIC MARINE ALGAE 257 



4. Branching generally, at least in part, obviously opposite . . 8 



5. Plants less than 1 cm tall 6 



5. Plants moderate to large in size 7 



6. Minute creeping plants, the cystocarps with a pericarplike invest- 

 ment Lejolisia 



6. Plants larger, the cystocarp w^ithout close cellular investment . 

 Spermothamnion 



7. Branching bushy or complanate, the sporangia tetrahedral . . 

 Callithamnion 



7. Branching markedly complanate, reproducing by polysporangia 

 Pleonosporium 



8. Branchlets of tvro types produced, those on the ab- and adaxial 

 sides of the lesser branches differing in form from those on the 

 faces of the branch (so-called "transversal" branchlets) . . . 

 Platythamnion 



8. Branchlets not differentiated 9 



9. Sporangia terminal on the ordinary lateral branchlets . . . 

 Gymnothamnion 



9. Sporangia on the ab- or adaxial sides of the branches or branchlets 

 Antithamnion 



10. Cortex with cells regularly arranged in the larger branches 11 



10. Cortical cells limited to the nodes and not arranged in regular 

 longitudinal rows, or spreading over the internodes and there 

 sometimes in somewhat regular rows Ceramium 



11. Branchlets with cortication limited to the nodes; branches 

 above with cortication in transverse rows, this near the base of 



the plant obscured by rhizoidal overgrowths .... Spyridia 

 11. Branches of all orders with regular longitudinal rows of corti- 

 cating cells, the nodes commonly with a ring of spinelike cells 

 Centroceras 



CALLITHAMNION Lyngbye, 1819 



Plants tufted, the base discoid, fibrous or rhizomatous; of monosipho- 

 nous naked or corticated filaments with dichotomous or alternate branch- 

 ing; cells plurinucleate and with many small chromatophores ; sporangia 

 borne on the upper side of the branches, tetrahedral or more rarely bi- 

 partite ; spermatangia forming small colorless tufts near the bases of the 

 branchlets on the upper side ; cystocarps borne on the axial cells, usually 

 bilobed. 



