OSCILLATORIA. 249 



meter, coated with a frequently interrupted covering of a 

 dull glaucous green hue, under which the thread itself ap- 

 pears of a lighter glaucous bluish colour, very even in thick- 

 ness and surface, consisting of scarcely distinguishable joints, 

 about as broad as they are long." Sm. 



6. OSCILLATORIA ^RUGESCENS Drum. 

 Plate LXXII. Fig. 2. 



Char. Stratum of a fine deep green, highly gelatinous ; when 

 dried, czruginous blue, and glossy. Filaments slender, 

 opaque green. Striae evident. 



Drummond, in Ann. Nat. Hist. vol. i. p. 1. ; Manual of 

 Brit. Alg. p. 163. 



Hob. Lakes of Glaslough, co. Monaghan, Ireland: Dr. 

 Drummond. Farnham: Mr. Jenner. Bottom of pools 

 near Stocket, Aberdeen : Dr. Dickie. 



" Filaments exceedingly slender, opaque green ; conglom- 

 erated in large toughish glutinous masses, in sheltered, calm 

 situations, and rarely floating on the surface ; in more open 

 exposures, broken into innumerable fragments, and suspended 

 like cloudy flocculi in the water. Stria numerous, at dis- 

 tances of about half a diameter from each other. Oscillatory 

 movement often lively. Colour when dried, a beautiful 

 aeruginous blue ; adheres strongly to paper, exhibiting a glossy 

 surface. Filaments expanded by moisture so as to seem re- 

 cent, and sometimes resuming the oscillatory motion."- 

 Dr. Drummond. 



This species may at once be distinguished when dried from 

 all others by the peculiarly dense and waxen appearance of 

 the stratum, which also exhibits numerous fissures. The fila- 

 ments are smaller than those of O. tenuis, and the striae closer. 

 They are likewise brittle, and when dried break up into very 

 short pieces, which are not of uniform diameter. 



