192.')] Setchell-Gardner: Melanophyceae 455 



emended the genus and placed it in the family Chordariaeeae, and in 

 1893 (p. 226) retained it in the same family. Foslie (1890. p. 91) 

 and Rosenvinge (1893, p. 901) and still later, Borgesen (1902, p. 419) 

 placed it in the "Myrionemaceae, " the first two designating the group 

 as a family, and the last as an order. De-Toni (1895, p. 178) retained 

 it in Chordariaeeae. Oltmanns (1904, p. 382) placed it in the group 

 Myrionemeae of the family Ectocarpaceae. In 1922 he arranged it 

 under the "Isogame Ectocarpales" in the family " Myrionemaceae, " 

 along with StrepsithaJia and Ralfsia. 



After a careful study of a large assortment of material belonging 

 to the Ectocarpales, we have limited the genus to include forms 

 possessing the characters mentioned in the foregoing generic diagnosis 

 and placed the genus in the family Myrionemataceae, along with three 

 other very closely related genera; viz., Compsonema, Micraspongium, 

 and Hecatonema. We have, however, included under Myrionema the 

 species formerly assigned to Ascocyclus Magnus and Phycocelis 

 Stroemfelt. 



In working over the members of the genus Myrionema found on 

 the Pacific Coast of North America, we have studied and separated 

 over twenty species or forms. This segregation must be considered 

 as provisional since no attempt at cultural criteria has been possible. 

 We have separated the species into two lines, the one in which only 

 zoosporangial forms are known, and the other in which only game- 

 tangial specimens are known, or those having gametangia and 

 "ascocysts, " the latter problematic structures. Possibly some of the 

 structures we have called "ascocysts" may be young zoosporangia, 

 but probably most or all of such structures, as we have seen them, are 

 hypertrophied gametangia. The possible genetic connection between 

 some of the one series of species and some of the other series cannot 

 be demonstrated except by cultures. 



Key to the Species 



1. With zoosporangia only 2 



1. With gametangia only or with both gametangia and "aspocysts" 3 



2. Plants forming definite circular thalH 21. M. strangulans (p. 471) 



2. Plants forming indefinite rugose thalli 22. M. obscurum (p. 472) 



3. Gametangia sessile 4 



3. Gametangia pedicellate 9 



4. All of the erect filaments transformed into gametangia 5 



4. Part of the erect filaments transformed into gametangia 



10. M. foecundum f. divergens fp. 463) 



5. Plants with subulate rhizoids 7. M. foecundum f. subulatum (p. 462) 



5. Plants without subulate rhizoids 6 



6. Gametangia branched in part 8. M. foecundum f. ramulosum (p. 462) 



6. Gametangia unbranched 7 



