222 RIVULARIA. 



V. MICROCOLEUS. Filaments minute, needle-shaped, en- 



closed, many together, in membranous or gelatinous 

 sheaths. [Plate 26, D.] 



VI. OSCILLATORIA. Filaments needle-shaped, straight, or 

 slightly curved, short, heaped together in gelatinous 

 strata, oscillating. [Plate 26, F.] 



VII. SPIRULINA. Filaments spirally twisted, lying in a 

 mucus stratum. [Plate 27, C.] 



I. RIVULARIA. Roth. [Plate 26, A.] 



Frond globose or lobed, rarely incrusting, green or oliva- 

 ceous, fleshy or gelatinous, firm, composed of continuous, 

 inarticulate filaments, annulated within, and surrounded by, 

 or set in, gelatine. Name, in allusion to the fresh-water ha- 

 bitat of some of the original species. The following are found 

 in the sea. 



1. R. plicata, Carm. ; fronds rather large, densely gre- 

 garious, gelatinous, compresso-plicate, often hollow and 

 ruptured, dark green ; filaments many times dichotomous, at- 

 tenuated. Hare. 1. c. p. 392. Lichen corrugatus, Dicks., 

 according to a specimen given by Dickson himself to Mr. 

 Borrer. 



On the rocky sea-shore, about high-water mark, or in situations where it 

 is only occasionally inundated with salt water. Appin, Capt. Carmichael. 

 Torbay, Mrs. Griffiths. Eyrmouth, Dr. Johnston. Ballantrae, Ayrshire, 

 Mr. W. Thompson. Innischerig Island, Co. Clare; and elsewhere. 

 " Fronds growing from a smooth gelatinous stratum, from a line to half an 

 inch in diameter, mostly confluent and distorted by mutual pressure, gela- 

 tinous, and in their more advanced state often hollow and ruptured. Fi- 

 laments dichotomous, tapering to a fine point, obscurely striated. Globules 

 few in number, pellucid, lodged within the filaments, which at length break 

 oft', leaving the globule attached to the base of the dismembered branch." 

 Carm. 



2. R. atra, Roth ; fronds minute, scattered, globose, 

 smooth, firm, glossy black; filaments deep green, slender, 

 densely packed. Harv. 1. c. p. 392 ; E. Bot. t. 1798 ; Barv. 

 Phyc. Brit. t. ccxxxix. 



In the sea, on rocks, corallines, Algae, &c. Fronds 1 or 2 lines in dia- 

 meter, very hard ; filaments densely packed. 



