1919] Setchell-Gardner : Myxophyceae 59 



Key to the Species. 



1. Trichomes not attenuate at the apex 2 



1. Trichomes phunly attenuate at the apex (Attenuatae) 7 



2. Trichomes thick to very thick, cells very short 



(Principes) 1. O. limosa (p o9) 



2. Trichomes moderately thick to thick, cells short (Margaritiferae) 3 



2. Trichomes slender (not over 11/a) cells at least V:t as long as broad to equally 



long (Aequales) G 



3. Trichomes twisted into a regular spiral 2. O. Bonnemaisonii (p 60) 



3. Trichomes long, arcuate, at times straight 4 



4. Trichomes 17-29/a in diam 3. O. margaritifera (p 61) 



4. Trichomes 6-11/a in diam 5 



5. On mud and rocks; trichomes straight 4. O. nigro-viridis (p 62) 



5. Epiphytic; trichomes flexuous 5. O. Corallinae fp 02) 



6. Trichomes not torulosc, 2-3/a in diam., dissepiments obscure 



6. O. amphibia (p 63) 



6. Trichomes decidedly torulose, 2.3-4/a in diam., dissepiments pellucid 



7. O. geminata (p 63) 



7. Trichomes more or less abruptly attenuate 8 



7. Trichomes long and gradually attenuate 11. O. Okeni (p 66) 



8. Slightly or not at all constricted at the dissepiments 9 



8. Not at all constricted at the dissepiments 10. O. brevis (p 65) 



9. Trichomes very slender, 3-5/a in diam 10 



9. Trichomes coarser (8-13/i in diam.) 12. O. chalybea (p 67) 



10. Cells subquadrate, apical cells obtuse or subacute... 8. O. laetevirens (p 64) 



10. Cells mostly longer than broad, rarely subquadrat(\ apical cell quasi 



mucronate 9. O. acuminata (p 65) 



Section 1. Princij)es Gomont 



Trichomes straight, curved or spiral at or toward the upper end, 

 slightly, if at all, attenuated, apices obtuse ; cells very short. 



Gomont, Monogr. des OscilL, 1892, p. 201 (1893, p. 221 Repr.) 



1. Oscillatoria limosa Ag. 



]. Oscillatoria limosa Ag. 



Trichomes aeruginous or mon; or less olive green, in a blackish- 

 aeruginous layer, on drying often a steel-blue black, straight, on drying 

 rigid and fragile, not at all torulose, 11-20/i., commonly IS-lQfi thick, 

 apices straight, slightly if at all attenuate, not capitate; cells 3-6 

 times shorter than the diameter, 2-5ju, long; dissepiments frequently 

 granulate ; apical cell convex above showing a sliglitly thickened 

 membrane. 



Chiefly in fresli water, but occasionally found floating in pools 

 or ditches in salt marshes where the water is slightly brackish. Whid- 

 bey Island, AVashington. 



