Rivularia.} ALG^ CHLOROSPERME^. 235 



SECT. 1. (Rivularia, Roth. Linkia, Lyngb.) Frond verru- 

 ctEform, rarely incrusting. Filaments close set, sparingly annu- 

 lated within, mostly dichotomously branched, radiating from a 

 common fixed base. 



1. R. atra, Roth. Black Rivularia. Fronds minute, scat- 

 tered, globose, smooth, firm, glossy black ; filaments deep 

 green, slender dichotomous. Harv. in Hook. Br. Fl. v. ii. 

 p. 392. E. Bot. t. 1798. 



On marine rocks, Algse, &c. very common. 



2. R. Pisum, Ag. Spherical Rivularia. Frond globose, 

 smooth, soft, shining, dark-green; filaments dichotomous. 

 Berk. Alg, t. 2. /. 2. Harv. in Hook. Br. Fl. v. ii. p. 392. 



On aquatic plants, in sub-alpine streamlets. 



3. R. applanata, Carm. Flattened Rivularia. Fronds mi- 

 nute, gregarious, orbicular, depressed, black ; filaments simple, 

 attenuated ; the apices free (protruded beyond the gelatine.) 

 Carm. Harv. in Hook. Br. Fl. v. ii. p. 392. 



On rocks and stones in the sea ; first observed by Captain Car- 

 michael on the Coast of Scotland. 



4. R. plicata, Carm. Wrinkled Rivularia. Fronds rather 

 large, densely gregarious, gelatinous, compresso-plicate, often 

 hollow and ruptured, dark green ; filaments many times dicho- 

 tomous, attenuated. Harv. in Hook. Br. Fl. v. ii. p. 392. 



On the sea-shore, near high-water mark. Innischerrig Island, 

 Clare. 



SECT. 2. (Scytochloria, Harv.) Frond gelatinoso-coriaceous, 

 lobed and bullated or incrusting. Filaments close, densely and 

 conspicuously annulated, set in a firm gelatine t and pointing 

 towards the periphery (not radiating.) 



5. R. nitida, Ag. Shining bullated Rivularia. Frond large, 

 gelatinoso-coriaceous, lobed and plaited, often bullated, lubri- 

 cous, shining, deep green ; filaments simple or pseudo-branched. 

 Harv. in Hook. Br. Fl. v. ii. p. 393. R. bullata, Berk. Alg. 

 t. 2.f. 1. 



On rocks in the sea. Miltown Malbay ; W. H. Harvey. 



6. R. plana, Harv. Green crustaceous Rivularia. Frond 

 crustaceous, plane, widely spreading, dull-green, lubricous, 

 darker towards the centre; filaments erect, straight, tufted, 

 pale green, subsimple. Harv. in Hook. Br. Fl v. ii. p. 394. 

 Chcetophora plana, Ag. Syst. p. 28. ? 



On marine rocks. Miltown Malbay. 



