238 SCYTONEME^E. 



1. PETALONEMA ALATUM. 

 Plate LXVIII. Fig. 6. 

 Char. Filaments broadly membranaceous. 



P. alatum Berk., Glean, of Alg., p. 23. t. 7. fig. 2. Oscilla- 

 toria alata Carm. Grev. Crypt. Fl. 222. ; Harv. in 

 Hook. Br. Fl. 378. ; Harv. in Manual, p. 168. 



Hab. On wet calcareous cliffs, Appin : Capt. Carmichael. 

 Oban : Rev. M. J. Berkeley* Aberdeen : Dr. Dickie. 



This highly curious plant forms a brownish or chestnut- 

 coloured stratum, subgelatinous. The filaments, which are 

 irregularly branched, central, consist of a coloured thread, 

 Avhich is distinctly annulated, and a broad colourless striated 

 sheath, obtuse at its extremity. The contrast between the 

 coloured and uncoloured portions of the filaments, and the 

 delicate stria) on the sheath, render this a very beautiful 

 object. 



26. ARTHRONEMA Hass. 



Char. Filaments simple, rarely branched ? of equal diameter, 

 divided into successive portions. 



Derivation. From apOpov, a joint, and w)/j,a, a thread. 



It is not without some hesitation that I have ventured to 

 constitute a new genus for the reception of this curious pro- 

 duction, which could not consistently I think be allowed to 

 remain with either Scytonema or Hassallia. 



1. ARTHRONEMA CIRRHOSUM Hass. 

 Plate LXVIII. Fig. 7. 



Char. Filaments of considerable size, stria close and evident. 

 Scytonema cirrhosum Carm. Tufts widely spreading, ^/a- 

 ments floating in bundles, spuriously ? branched ; 

 branches beset with fragments towards the top." - 

 Carm. MS. 



