410 BULLETIN OF THE BUREAU OF FISHERIES. 



inous, so that they adhere together very easily. Propagation occurs by hormogonia 

 longer or shorter fragments of trichomes, breaking out the sheaths and moving of them- 

 selves by circumnutation in the water, then, the movement ceasing, sheaths are formed 

 and cell division commences. In the genera without sheaths e. g., Oscillatoria, Spiru- 

 lina the movements persist throughout their life. 



The Oscillatoriacese inhabit principally moist, aerated places; many live in water 

 containing decaying organic matter; some are incrusted with calcium carbonate; some 

 thrive in temperatures as high as 85 C. 



About 550 species throughout the world. 



The members of this family are usually easily distinguished in that they do not taper 

 to long hairs at the apices, they lack heterocysts, and in the majority of cases are un- 

 branched. The only species found in this region that is likely to be wrongly identified as 

 belonging to this family is Plectonema battersii, one of the Scytonemaceae. This species 

 lacks hairlike apices and heterocysts and might easily be taken for one of the branching 

 Oscillatoriaceae. From these it can be easily distinguished by the fact that it has only 

 one trichome within a sheath, while both Hydrocoleum and Microcoleus have several or 

 many trichomes within each sheath. 



KEY TO GENERA. 



a. Sheaths absent 6. 



6. Trichomes straight or nearly so, multicellular i. Oscillatoria (p. 410). 



bb. Trichomes forming a regular spiral, unicellular 2. Spirulina (p. 411). 



aa. Sheaths present c. 



c. Filaments consisting of one trichome within each sheath, simple d. 



d. Sheaths swollen, gelatinous, filaments more or less .agglutinated 3. Phormidium (p. 411). 



dd. Sheaths not swollen, firm, filaments free or forming a tangled mat, not agglutinated 



4- Lyngbya (p. 411). 



cc. Filaments consisting of several trichomes within a single sheath, simple or branched . e. 



e. Filaments consisting of few trichome swi thin a single sheath, trichomes of ten loosely 



aggregated .5. Hydrocoleum (p. 413). 



ee. Filaments consisting of numerous trichomes within a single sheath, trichomes 



densely aggregated, often twisted into ropelike bundles 6. Microcoleus (p. 413). 



Genus i. Oscillatoria Vaucher, ex Gomont. 



Oscillatoria, Vaucher, 1803, p. 165. 

 Oscillaria, Farlow, 1882, p. 32. 

 Oscillatoria, Gomont, 1892, tome 16, p. 198. 



Trichomes cylindrical, free, usually motile, without a sheath or rarely inclosed in a 

 very thin, fragile, mucous sheath, sometimes constricted at the joints, not moniliform, 

 often attenuated at the apices, straight or curved or more or less regularly corkscrew- 

 shaped in some species, but not constantly spiral ; outer wall of apical cejl thickened in 

 some species, forming a calyptra. 



About 100 species in fresh or salt water, sometimes in hot springs or on moist earth, 

 throughout the world. 



Oscillatoria nigro-viridis Thwaites, ex Gomont. 



Oscillatoria nigro-viridis, Thwaites, in Harvey, 1851, pi. 2sia. 



Oscillaria limosa var. chalybea, Farlow, 1882 p. 33. 



Oscillatoria nigro-viridis, Gomont, 1892, tome 16, p. 217, pi. 6, f. 20. 



Oscillatoria nigro-viridis , Forti, in De Toni, 1907, p. 161. 



Oscillatoria nigro-viridis, Tilden, 1910, p. 69. 



P. B.-A. No. 1056. 



