142 University of California Puhlications in Botany [Vol.8 



28. Pseudodictyon (p. 293) 



29. Internoretia (p. 294) 



30. Ulvella (p. 295) 



31. Pseudulvella (p. 296) 



32. Pseudopringsheimia (p. 299) 



33. Gomontia (p. 300) 



Family 13. — Trentepohliaceae (p. 305) 



34. Trentepohlia (p. 305) 



Series 1. ISOKONTAE blackman and tansley 



Unicellular, multicellular and coenocytic Chlorophyceae, repro- 

 ducing by means of zoospores or planogametes provided with two or 

 four equal cilia or, when multinucleate, with the cilia arranged in 

 pairs (Vaucheriaceae) or exceptionally in a circle (Derbesiaceae). 



Isokontae Blackman and Tansley, Revis. Class. Green Algae, 1902, 

 p. 20 ; West, Algae, vol. 1, 1916, p. 156. 



It has seemed best to adopt the classification as outlined by West 

 (1916, p. 153), dividing the Chlorophyceae into four series according 

 to the character and arrangement of the cilia of the zoospores and 

 the planogametes. West adopts four series, viz., Isokontae, Akontae, 

 Stephanokontae and Heterokontae. Of these, our marine flora has to 

 deal only with the first, the Isokontae, where the cilia are equal and 

 arranged in twos or fours. The other groups are not represented. 

 Only two seeming exceptions need explanation. In the Vaucheriaceae 

 the zoospore is large and ' covered with cilia. They are, however, 

 arranged over the surface in pairs. The other, and only real, excep- 

 tion is the Derbesiaceae, where the cilia are arranged in a circle as in 

 the Stephanokontae. It has seemed best to leave the Derbesiaceae 

 with the Isokontae in this account, since this is the usual arrange- 

 ment, but it is done with some reservation of opinion. 



Key to the Orders 



1. Thallus of true cells (uninucleate segments) 2 



1. Thallus coenocytic (of multinucleate segments) fi 



2. Cells solitary or in non-filamentous colonies 1. Protococcales (p. 143) 



2. Cells in filaments or membranes 3 



3. Thallus filamentous 4 



3. Thallus membranaceous 5 



4. Filaments simple or, more often, branched; chromatophore parietal 



6. Ulotrichales (p. 281) 



4. Filaments siiuple; chromatophore axile 5. Schizogoniales (p. 275) 



5. Chromatophores parietal 4. Ulvales (p. 233) 



5. Chromatophores axile 5. Schizogoniales (p. 275) 



6. Thallus septate 3. Siphonocladiales (p. 179) 



6. Thallus non-septate 2. Siphonales (p. 153) 



