Clare Island Survey — Marine Algae. 15 69 



the size of the plant is more dependent on the nature of the bottom than on 

 the depth in which it grows. He shows that the form with short, narrow 

 leaves is found on firm sand, and that the long, broad-leafed form is 

 characteristic of soft mud, rich in food substances. A slight difference 

 between the algal vegetation of the sand and mud Zostera was 

 observed in Clew Bay, but not with sufficient care to warrant comment, 

 except to note that the latter proved the most productive in the way of 

 algae. 



In spring, masses of Ectocarpi occur, together with innumerable tufts of 

 Cladophora lanosa; whilst in summer and autumn species of Bangia and 

 Chantransia are more abundant. Ascocyclus orbicularis is almost always 

 present, being noted in quantity in spring, summer, and autumn. At 

 the margins of the Zostera-rneadows, and in spots where largest ones exist 

 other plants, such as Halidrys, Laminaria saccharina, and Cystoseira 

 granulata, are met with ; and the association then tends to approach that 

 which Ostenfeld has termed the "mixed Zostera vegetation " (I.e., p. 33). Of 

 the larger epiphytes the following are usually frequent in their respective 

 seasons : — 



Cladophora lanosa. Myriotricha densa. 



Castagnea Zosterae. Scytosiphon lom. var. zostericola. 



Punctaria tenuissima. Laurencia obtusa var. crucifera. 



Desmotrichum undulatum. Polysiphonia violacea. 



Ectocarpus confervoides. Ceramium striatum. 



E. siliculosus. Giraudiasphacelarioides, r. 



E. sp. Leptonema fasciculatum, r. 



Litosiphon pusillus. Mesogloia lanosa, r. 



Whilst among microscopic species may be mentioned : — 



Calothrix confervieola. Melobesia farinosa. 



Chantransia virgatula. Bivularia atra. 



C. Thuretii. Isactis plana, r. 



Ascocyclus orbicularis. Erythrotrichia Bertholdii, r. 

 Pthodophysema Georgii. 



The Fruticulose Lithothamnium Association. 



Probably no group of seaweeds is more generally recognized as forming 

 extensive colonies or associations than the Lithothamnia. Submerged beds, 

 often known as " coral-banks," occur in the arctic, temperate and tropical 

 regions. In the latter they are frequently exposed at low water, and play 



