BRITISH SEA-WEEDS. 



This species has been found in Scotland, and in the 

 south of England, on rocks, on submerged wood, and on 

 dry bare earth. Kutzing identifies it with his Spirulina 

 tenuissima. 



Oscillatoria nigro-viridis. The dark-green 

 Oscillatoria. 



Threads slender, rigid, blunt and curved at the tip, of a 

 pale green colour, growing in thin, dark olive-green layers 

 at first on the mud, then floating ; endochrome marked with 

 indistinct striae, at intervals of about half the length of the 

 diameter of the threads, not visibly granular. 



Oscillatoria subuliformis. The awl-shaped Oscil- 

 latoria. 



Threads very slender, awl- shaped, attenuated, acute and 

 strongly curved at the tip, of a bright green colour, growing 

 in thin, dark blue, almost black layers at first on the mud, 

 then floating ; endochrome marked with indistinct striae at 

 intervals of about three-fourths the length of the diameter 

 of the threads, not visibly granular. 



Oscillatoria insignis. The remarkable Oscilla- 

 toria. 



Threads robust, somewhat brittle, rounded and adorned 

 with minute, motionless cilia at the tip, of a brown colour, 

 growing in thin dark-brown layers on decaying vegetable 

 matter ; endochrome marked at short intervals with distinct 

 striae, visibly granular. 



The three last species are described in the ' Phycologia 

 Britannica/ from specimens collected by Mr. Thwaites 



