Clare Island Survey — Marine Algae. 15 163 



Nearly all the above species are confined in England to the southern 

 counties. Several have been found only in south Devon and south Cornwall ; 

 others reach as far as the Isle of Wight ; whilst a small number extend 

 through the Straits of Dover as far north as Norfolk. All are known to occur 

 in Normandy or Brittany, and with few exceptions they have been recorded 

 by Sauvageau from the Bay of Biscay and north Spain. Though their head- 

 quarters are in a southerly direction, a few extend up the Irish Channel to 

 Auglesea and the Isle of Man ; and several have been noted in the Clyde area 

 and in the Orkney Islands. The Clyde has been thoroughly worked (see 

 Batters, '91); hence numerous outliers have been detected. The Orkney 

 records are distinctly interesting, and tend to show that some of the southern 

 forms in the west Irish flora extend northwards by way of the Hebrides. For 

 this the Gulf Stream drift is doubtless responsible. 



The plants listed above grow luxuriantly in Ireland, and are evidently at 

 home in their surroundings. The much-indented coast supplies great variety of 

 conditions ; and the lack of intense insolation in summer permits the presence 

 of a better littoral and shallow sub-littoral vegetation than in the south of 

 England. Several of the species are only found sparingly, as in other parts of 

 our islands ; but others occur in great profusion — e.g., Petrospongium Berkeleyi, 

 Dasya arbuscnla, Polysiphonia subidifera (local), and Corallina squamata ; 

 whilst Codium adhaerens, Cutleria multifida, Bifurcaria (at Roundstone), 

 Cystoseira fibrosa, Halurus, Monospora 2^dicellata are very frequent. The 

 abundance of Dasya arbuscula at low- water mark on Clare Island is very 

 remarkable (see Phyc. Brit., tab. 274). 



(b) Northern element. — With regard to northern forms we find that there 

 occur in oar area a large number of the species which Borgesen and Jonsson 

 place in their sub-arctic and boreal-arctic groups. Many of these hav r e, how- 

 ever, a very wide distribution, being abundant in all parts of the British Isles 

 and extending to France and even Spain. Of the most noticeable boreal 

 species (selecting from well-known plants only) we may pick out seven for 

 notice. The first four are annuals, 1 and occur chiefly in spring ; the last two 

 are found all the year round, and are important constituents of the flora. 



Stictyosiphon tortilis. — Very common in Clew Bay during spring, also in 

 Scotland. It occurs in Northumberland, Cheshire, and Carnarvon. Batters 

 gives a Cornwall record ; but if it occurs on the south English coast, it must 

 be extremely rare. 



Desmotriclmm undidatum. — Common in Clew Bay. Not known from 

 England, but recorded from several localities in Scotland. It is rather small, 



1 The distribution of many of the smaller and inconspicuous species is so imperfectly known that 

 they are best omitted. 



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