284 BRITISH SEA-WEEDS. 



near low-water mark, and at greater depths. It is 

 annual, and may be found during summer and autumn 

 in many localities round our coast. The colour of the 

 tufts is a very dark green, almost black. 



Lyngbya ferruginea. The dark-blue Lyngbya. 



Threads slender, soft, curved, growing on mud, in thin 

 layers of considerable extent, or floating on the surface of 

 stagnant pools of salt or brackish water; tube very thin, 

 containing strongly annulated, bluish-green eudochrome, 

 with empty spaces at intervals. 



This species is much smaller, and less conspicuous 

 than L. majuscula, and in consequence is, no doubt, 

 frequently overlooked. It grows on mud, in pools of 

 brackish water, and is probably abundant in many loca- 

 lities, although but few habitats are recorded. 



Genus CXVIII. CALOTHRIX. 



Erond a separate, free, somewhat rigid, erect, stationary, 

 non-mucilaginous thread, composed of a continuous tube, 

 filled with densely annulated, green eudochrome, from 

 which lens-shaped sporidia are developed. — Calotheix, 

 from the Greek kalos, beautiful, and tJirix, a hair. 



This genus contains a large number of species, some 

 of which are found in salt water, and some in fresh. They 

 are all minute, and grow in tufts or patches on rocks, 

 mud, or sea- weeds. 



Calothrix Confervicola. The Conferva Calothrix. 



Threads about one-tenth of an inch long, rigid, straiglit 

 or slightly curved, blimt, opake, of a verdigris-green colour, 



