228 OSCILLATORIA. 



Hyd. Dan. p. 92, t. 22, without having an authentic specimen to guide 

 me. 



VI. OSCILLATORIA. Vauch. [Plate 26, F.] 



Filaments invested by a common, mucous matrix, rigid, 

 elastic, oscillating, simple, continuous. Endochrome divided 

 by close, parallel, transverse striae. Named from the curious 

 motion observed in the filaments, which resembles the oscil- 

 lation of a pendulum. The species of this genus are very 

 numerous, and it is almost impossible to lay down characters 

 by which they may at all times be distinguished. In the 

 following descriptions, the colour of the strata always refers 

 to the appearance presented to the naked eye ; that of the 

 filaments, to what they appear in a dry state. Most of the 

 species are found in fresh water, both stagnant and running : 

 some in thermal springs ; some on damp ground ; very few 

 in salt water, and still fewer in the open sea. The following 

 have more or less claims on the marine flora. 



1. O. littoralis, Carm. ; stratum vivid, aeruginous-green ; 

 filaments thick, deep green, curved ; striae conspicuous, close. 

 Harv. 1. c. p. 375 ; Harv. Phyc. Brit. t. cv. A. 



In pools along the muddy sea-shore, flooded by spring tides. Appin, 

 Capt. Carmichael. " Stratum exceedingly thin, slimy, bullated by the ex- 

 trication of air-bubbles, of a dark green colour, spreading to an indefinite 

 extent over the muddy bottom of the pool. Filaments 1 or 2 lines long, 

 much thicker than those of O. nigra, straight or slightly curved, radiating 

 very irregularly and generally in twisted bundles. Stria strongly marked, 

 at intervals of about one-third the diameter of the filament." Carm. MSS. 

 Most allied to O. limosa. In a dry state it is membranaceous, and scarcely 

 adheres to paper. 



2. O. subsalsa, Ag. ; stratum membranaceous, aeruginous- 

 green, smooth ; filaments slender, densely interwoven ; striae 

 distant, indistinct. Harv. 1. c. p. 376 ; Ag. Syst. Ala. p. 66 ? 



At Brighton, " on a plank between high and low water mark," Mr. Bor- 

 rer. Stratum seruginous or bluish green, smooth, without gloss when dry, 

 peeling off in membranaceous flakes ; filaments hyaline, slender, densely 

 packed, either straight or curved ; stria not very evident. In habit, it 

 somewhat resembles O. littoralis ; but the filaments are much more slender, 

 and the stratum more membranaceous. 



3. O. spiralis, Carm. ; stratum coriaceous, greenish-black, 

 without lubricity ; filaments spirally twisted, radiating in all 

 directions. Harv. 1. c. p. 377 ; Harv. Phyc. Brit. t. cv. B. 



On rocks by the sea-side, where birds are in the habit of resting. Appin, 

 Capt. Carmichael. " It spreads over the dry, naked earth. Stratum seve- 



