Myxophyceae 59 



(2) Apex of trichome spiral, rarely hooked 



A Trichomes 10-17 w'<^- i" diameter, not constricted at joints; apex 

 of trichome not capitate O. curviceps 



B Trichomes 18-23 ™ic. in diameter; apex of trichome slightly taper- 

 ing, obtusely rounded, usually straight O. major 



C Trichomes 9-1 1 mic. in diameter, slightly constricted at joints, 

 here and there interrupted by inflated, refringent cells; apical 

 cell not capitate O. ornata 



D Trichomes 6-8 mic. in diameter, not constricted at joints, here 

 and there interrupted by inflated, refringent cells; apical cell 

 capitate O. anguina 



III Plants living in salt water; trichomes always constricted at joints, 



rarely straight or spiral throughout; apex of trichome scarcely taper- 

 ing, very gradually curved, obtuse. 



1 Trichomes twisted into a regular spiral O. bonnemaisonii 



2 Trichomes not spiral, gradually curved in apical portion, rarely 



straight 

 (i) Plant mass dull red; trichomes 16-24 rnic- in diameter 



O. miniata 



(2) Plant mass olive green; trichomes 17-29 mic. in diameter 



O. margaritifera 



(3) Plant mass dark olive green; trichomes 7-11 mic. in diameter, 



straight, fragile O. nigro-viridis 



(4) Plant mass thin, fragile; trichomes 9.6-1 1.9 mic. in diameter, some- 



times spirally coiled, sometimes curved or even nearly straight 



O. capitata 



(5) Plants epiphytic; trichomes 6-10 mic. in diameter, flexuous, flexible 



O. corallinae 



IV Plants living in fresh water, sometimes in hot water; trichomes 

 straight or curved, not tapering at the apices. 



1 Trichomes 8.5 mic. in diameter, straight or slightly flexuous 



O. nigra 



2 Trichomes 4-10 mic. in diameter, usually slightly constricted at the 



joints, often curved at the apices; transverse walls usually furnished 

 with two rows of granules O. tenuis 



3 Trichomes 2-3 mic. in diameter, not constricted at joints, curved at 



the apices; transverse walls commonly marked by two protoplas- 

 mic granules O. amphibia 



4 Trichomes 1-1.5 mic. in diameter, straight or rolled in a circinate 



manner O. subtilissima 



5 Trichomes 2.3-4 mic. in diameter, curved, very much constricted at 



joints; transverse walls pellucid, not granulated 



O. geminata 



6 Trichomes 2.5 mic. in diameter, especially constricted at joints; trans- 



verse walls pellucid O. minnesotensis 



