334 BRITISH SEA-WEEDS. \_Diatomacea . 



it covers the rocks, almost at liigli-water mark, witli a dense 

 fleece of dark-green filaments, lying flat during ebb, but 

 waving gracefully in the water when the tide returns. See 

 Pliyc. Brit., PI. clxxxvi. A. 



Genus C. STRIATELLA, Agardh. 



Gen. Char. Stipes very short, filaments curved, pellucid at the 

 articulations, striated transversely. — It takes its name from the 

 striated joints. 



1. Striatella arcuata, Agardli. 



Hab. On marine filiform Algae ; on the coast of Ayrshire 

 this is very common, especially in spring, almost covering 

 the plant on which it grows, and often giving it a greenish 

 tint. AThen dry, this parasitic coat has a glistering metallic 

 cast. 



Genus CI. ISTHMIxV, Agardh. 



1. IsTHMiA OBLIQUA, Agardh. 



Ilab. On filiform Alga?. Frequent on the shores of 

 England and Ireland ; we know not that it has been found 

 in Scotland. AYe have numerous fine specimens of it from 

 Mrs. Lyon, gathered by her on the shore at Glcnarm, 



