15 158 Proceedings of the Royal Irish Academy. 



(«) Additions to the British Isles. — With regard to these, the following 

 nine ai'e inconspicuous species which are probably to be found in England 

 and Scotland if carefully searched for: — 



Phormidium persicinum. Ulothrix pseudoriacca. 



P. subuliferum. Dichosporangium Chordariae. 



Lyngbya confervoides. Petroderma maculans. 



Symploca dubia. Chantransia Thuretii. 

 Ulothrix subflaccida. 



Of the remainder: — ■ 



Calothrix endophytica sp, nov., is conspicuous on salt-marshes, and should 

 be searched for in Britain. 



Rhizoclonium Kemeri forma endozoica forms green masses in the sponge 

 Halichondria, and probably occurs in England. 



Codittm mucronatum var. atlanticum.— This species is new to Europe. It 

 does not occur in the south of England, but is recorded in the present report 

 from south-west Scotland, Isle of Man, and the Orkney Islands, in addition to 

 the north, west, and south-west of Ireland. 



Stictyosiphon adriaticus. — Pare, and only obtained by dredging. It should 

 be found in quiet bays on the south coast of England. 



Acrothrix gracilis. — Probably very rare. Perhaps overlooked as 

 Mesogloia Griffithsiana. 



Fucus vesiculosus var. mv.scoid.es, var. nov. — This variety has never been 

 noted in England. It is probably confined to peaty shores. 



Spermothamnion Turncri var. subrerticillatum. — I have not observed var. 

 snbcerticillatum in England ; but it doubtless occurs in quiet bays on the south 

 coast, since it is known from France. In Clew Bay it is frequent throughout 

 spring and summer. 



Ptilothamnion lucifwjum. — Caves are frequently explored by algologists ; 

 but this beautiful microscopic species has hitherto escaped detection. It 

 is allied to Ptilothamnion micropterwm, which is only known from the 

 Canary Islands and Guethary (Basses Pyrenees). Probably a southern 

 species. 



Ccramium Boergesenii. — Doubtless common in England, but passed over 

 as C. decurrens. 



C. atlanticum. — This pretty and fairly well-marked species probably 

 occurs in England and Scotland. A few specimens only were found on 

 Clare Island. 



Lithophyllam incrv^tans, var. subdichotomum. — Identified correctly for the 

 first time by Dr. Lemoine, in the present report. Only known in the 



