15 142 Proceedings of the Royal Irish Academy. 



Callithamnion corymbosum Lyngb. 



Very abundant in spring and early summer, and found probably throughout 

 the whole year. It was plentiful in October, 1910, at Achill Sound; and 

 numerous young plants were dredged in Clew Bay the following February. 



C. granulatum Ag. 

 When Harvey dealt with C. spongiosum in " Phyc. Brit.," he suggested 

 the possibility of its being united with G. granulatv.m Ag. In 1851, J. Agardh 

 carried out this prediction, and his view has been generally accepted. There 

 are, however, two very distinct forms. One, which occurs in the C. arbuscula 

 association, is compact, densely branched, and turns a pale greenish-yellow in 

 summer ; and the other, which hangs from vertical rocks in company with 

 Plvmaria elegans, is larger, less compact, and does not occur in sunny places. 

 The former agrees in habit with the Mediterranean C. granulatum ; and the 

 latter is undoubtedly Harvey's C. spongiosum. The matter requires careful 

 investigation, as it appears possible that Harvey's plant may after all be 

 a good and distinct species. Both forms occur in Clare Island, and no 

 intermediates were seen. 



Ptilota plumosa Ag. 

 This species, which is said to occur all round the Irish coasts, is perhaps 

 the most noteworthy of the boreal algae that are found on the west of Ireland 

 (see pp. 165 and 169). 



Antithamnion crispum Thur. inLe Jolis' "Liste," p. 112. 

 {A. Plumvla var. crispum J. Ag., Batters, Cat., p. 89.) 

 This plant is distinguished from A. Plumvla by its short recurved pinnae 

 and thorn-like pinuulae. It is widely distributed, and often occurs where 

 A. Plumvla is absent (i.e. in the Adriatic; see Krasser in Zahlbruckner, 

 Krypt. Exsicc, No. 648). Batters follows Agardh, who regards it as a variety; 

 but the views of Thuret, Krasser, and others appear warranted. The true 

 A. Plumula was not found in Clew Bay, and the Bantry Bay species in Herb. 

 Kew are also referable to A. crispum. 



Ceramium Boergesenii Petersen. 



Dr. H. Petersen, who is at present investigating this genus, kindly 



undertook to examine my material. To him is clue the discovery of this, and 



the following addition to the ilora of our islands. C. Boergesenii has doubtless 



been passed over as a form of 0. clecurrens, to which it is very closely allied. 



