15 132 Proceedings of the Royal Irish Academy. 



develop directly into broad frondose tlialli. I fully agree, however, with 

 Thuret and with Rosenvinge, who regard P. Uncarts as a young and winter 

 form of P. umbilicnlis. Observations made at Swanage, though not BO 

 extensive as tliose of Rosenvinge, led to that conclusion. On exposed coasts 

 a very large proportion of the growth does not survive the spring. On the 

 more sheltered shores of Clew Bay the plant doubtless develops, as it does at 

 Swanage, into var. laeiniata. A typical band of P. linearis was. however, only 

 observed on the exposed parts of the Clare Island district. 



CHANTRANSIA. 



The species of this genus have been very erroneously named in the past ; 

 and it is highly satisfactory to have had the Survey material named by 

 Dr. Rosenvinge. The following account is derived from his report : — 



The epiphytic covering of Chantransia, which is conspicuous on many 

 algae on Clare Island, appears to consist almost entirely of various varieties 

 of C. viryaiula. In sheltered localities (e.g. Clew Bay and Achill Sound) 

 the same species is abundant; and C. Thvretii also is exceedingly common. 

 It will be noted that in his work on the Danish species ('09) Rosenvinge 

 places C. sccundata and C. luxuriam (which are given specific rank by Batters 

 ('02)) as varieties of C. virgatula. 



C. virgatula Thur. 



Var. luxurians (J. Ag.) Rosenv. — Common and very conspicuous on 

 Ceramium spp. in rock-pools at Khmacorra and Portlea (Clare Island). On 

 the mainland it was found on Gracilaria and Zostera dredged in shallow 

 water. New to Ireland. 



Var. tetrica Rosenv. — This variety, which is also new to Ireland, occurred 

 on Cod iu Di tomentoswa on Clare Island, and on Gracilaria at Old Head. It is 

 distinguished by the presence of tetraspores on short opposite branches. 



Var. secundata (Lyngb.) Rosenv. — Exceedingly abundant in all parts of 

 the Survey area. On Clare Island it is the form which gives the pink colour 

 to the growth of Porphyra on exposed rocks; and it is also found on the 

 Rhodymenia and the Laurcncia pinnaiifida communities. The plant moreover 

 covers Codium and Ceramium spp. in pools, and can endure a certain amount 

 of fresh water, being found in the spray of the waterfall at Portlea. On the 

 sheltered mainland it is common on many algae, both in the littoral and 

 sub-littoral regions. 



C. Thuretii (Horn.) Kylin. 



Though a new record for the British Isles, this species is common in 

 Britain, ami has doubtless been passed over as C. JDaviesii. It is distinguished 



