286 BRITISH SEA-WEEDS. 



the surface of all kinds of rocks with dull green, slip- 

 pery layers of its tiny fronds. It is common in most 

 localities, but too insignificant to attract attention. Its 

 characters are of course microscopic. 



Calothrix pannosa. The ragged Calothrix. 



Threads from a quarter to half an inch long, rigid, 

 strongly curled, hlunt, of the same diameter throughout, 

 closely woven into thin laminae, which are arranged in a 

 compact layer, the surface of which is sometimes irregular 

 and ragged, sometimes divided into round or angular spaces, 

 like a honeycomb ; tube filled with strongly annulated, dark 

 green endochrome. 



This plant grows in pools near high-water mark, and 

 is perennial. The tvpo forms described above appear to 

 depend on the position occupied by the specimens, — those 

 which are parasitic on CorallirnE, etc., being irregular 

 and ragged on the surface, while those which grow on 

 rocks are honeycombed. 



Calothrix semiplena. The variegated Calothrix. 



Threads from half an inch to an inch or more long, very 

 slender, tough, bent, blunt at the tip; closely woven into 

 flat tufts, which are broad at the base, gradually tapered to 

 a point at the top, stand erect, and are either loosely 

 bundled together or piled one above another ; tube par- 

 tially filled with dense, verdigris-green endochrome, a long 

 space of empty transparent tube alternating with a similar 

 length of endochrome. 



This species grows on Corallinee and algse in rock- 



