15 130 Proceedings of the Royal Irish Academy. 



Through the growing out of such branches and the decay of the old fronds, 

 colonies of young plants arise, which lack a discoid base, the latter being only 

 produced by sporeling plants. The cylindrical form of the branches, the 

 absence of air-bladders, and the complete sterility are induced, according to 

 Reinke, by the low salt-content of the water ; and he suggests that in less 

 brackish localities such floating shoots of A. nodosum might give rise to 

 A. Mackaii. (See Reinke, '89 and '92.) 



Bifurcaria tuberculata Stackh. 



It appears probable that the Roundstone neighbourhood is the northern 

 limit in the British Isles for this species. It occurs on the coast of southern 

 England, and is known in Ireland from the counties of Cork, Clare, and 

 Galway, being abundant in the last-named at Dog's Bay. The pools of Clare 

 Island, and the more open parts of Clew Bay, which are eminently suited 

 for it, were carefully worked, yet not a single plant was observed. 



Taonia atomaria J. Ag. 



Dredged in Clew Bay, and washed ashore between Old Head and 

 Leckanvy (1909, '10, '11). Frequent on the west coast and known as far north as 

 Bundoran (Johnson) ; on the east coast it has been collected at Wicklow 

 (Harvey). 



Dictyopteris membranacea Batt. (= Haliseris polypodioides Ag.). 

 In contrast to Bifurcaria, an extension of distribution can be recorded for 

 this southern species, Roundstone Bay having hitherto been its northern 

 limit. Several specimens were dredged in Clew Bay by Mr. J. Adams, in 

 August, 1909 ; but the plant was not seen again during the Survey. The 

 specimens were large and strong ; and the species is evidently quite at home 

 as far north as Co. Mayo. 



Erythrotrichia Bertholdii Batters. 



Useful notes on the genus Erythrotrichia will be found in the paper by 

 Batters, in which this species is described ('00, p. 374). The cylindrical 

 filaments resemble those of E. ciliaris (Carm.) Batt. (non Thur.) ; but the plant 

 is distinguished from that species by the absence of a basal disk. 



Achill Sound, October, 1910, on old Zostera leaves. 



E. investiens Born. 

 With slight hesitation I have referred a few odd filaments found at Old 

 Head to this little-known species. The plants fit no other species of the 



