NO. 1 TAYLOR: PACIFIC MARINE ALGAE 87 



1. Thallus with a distinct, if delicate, percurrent midrib Dictyopteris 



2. Thallus not composed of fan-shaped segments 3 



2. Thallus broad, divided into fan-shaped segments .... 5 



3. Segments of the thallus strap shaped; growth from one distinct 

 apical cell 4 



3. Segments broad and somewhat foliose; growth from a group of 

 initial cells Spatoglossum 



4. Thallus generally smooth Dictyota 



4. Thallus in the older and darker parts constantly beset with small 

 appendages Glossophora 



5. Growing margin plane; blade never calcified 6 



5. Growing margin of the blade inrolled ; blade sometimes lightly 

 calcified Padina 



6. Plant thin and with the reproductive structures slightly im- 

 mersed Taonia 



6. Plant thicker and with the reproductive structures eventually 

 superficial 7 



7. Tetrasporangial sori with paraphyses ; median cell layer in trans- 

 verse section not distinctive Zonaria 



7. Tetrasporangial sori lacking paraphyses ; cells of the median layer 

 larger than those contiguous to it Pocockiella 



DICTYOTA Lamouroux, 1809 



Plant bushy, not markedly stalked, the base generally naked ; dichot- 

 omously or alternately branching, the segments flat, narrow or mod- 

 erately broad, with entire to dentate edges; growth of each branch from 

 a large, broad apical cell; structurally showing a single-layered cortex on 

 each face and a generally single medullary layer of much larger cuboidal 

 cells with few chromatophores ; tetrasporangia scattered; gametangia in 

 scattered sori. 



KEY TO SPECIES 



1. Margin of the blade closely toothed D. crenulata 



1. Margin of the blade entire 2 



2. Plants large, when vegetatively mature exceeding 1.5 dm in 



height ^ 



2. Plants small, less than 1.5 dm tall when mature .... 5 



3. Sparingly branched, light in color D. major 



3. More closely branched 4 



