15 158 Proceedings of the Royal Irish Academy. 



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

 nine are inconspicuous species which are probably to be found in England 

 and Scotland if carefully searched for:— 



Phomiidiura persicinum. Ulothrix pseudoflacca. 



P. subuliferum. Dichosporangium Chordariae. 



Lyngbya confervoides. Petroderma maculans. 



Symploca dubia. Chantransia Thuretii. 

 Ulothrix subflaccida. 



Of the remainder : — 



Calothrix endophytic*! sp. nov., is conspicuous on salt-marshes, and should 

 be searched for in Britain. 



Rhizoclonium Keiiieri forma endozoica forms green masses in the sponge 

 Haliehondria, and probably occurs in England. 



Codium mucroiiatum var. atlantievm. — This species is new to Europe. It 

 does not occur in the soutli 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 

 Mesogloin Griffithsio.no. 



Focus cesiculosvs var. muscoides, var. nov. — This variety has never been 

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



Spermotho.mnion Turneri var. svbverticilla&um. — I have not observed var. 

 subcerticillatum 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. 



Ptilotlwmnion lucifugwm. — Caves arc frequently explored by algologists; 

 but this beautiful microscopic species has hitherto escaped detection. It 

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

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

 species. 



Cera mix m Boergesenii. — Doubtless common in England, but passed over 

 as C. decurrens. 



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

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

 Clare Island. 



Lithophyllum incrustans, var. subdichotomvm. — Identified correctly for the 

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



