288 



BRITISH SEA-WEEDS. 



This species has beeu found in Scotlandj and in the 

 sQuth of England J on rocks, on submerged wood^ and on 

 dry bare earth. Kiitzing 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 ; endoehrome 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 ; endoehrome 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 ; endoehrome 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 



