SEA-WEEDS. 



99 



to six feet. It may at once be known from the 

 former species by its notched or serrated edges, 

 and by having no air-vessels. It often covers the 

 rocks to the limit of low water. Our engraving 

 represents it in the condition in wh^h w^ often 

 find it, as the place of attachment to various para- 



sitic objects. The thread-like coralline and the 

 rough crust are two zoophytes, which will be 

 described in a future chapter; and the little 

 circular shell-like substances are the structure and 

 dwelling places of that singular and minute worm 

 the spirorbis. They have not, like true shells, 



H2 



