SERTULAKIA ABIETINA. 71 



receptacles are tubular and are arranged 

 oppositely on each side of the stem ; the outer 

 lip of the margin being very sharp and pointed. 

 The capsule is somewhat balloon-shaped, with 

 a plain aperture. It is often symbiotic on 

 Laminarian stems and Mussel valves. It 

 would hardly be venturing too far to say, that 

 the colony here shown on the Laminarian 

 stem (see plate VI.) probably equals innumber 

 the population of London. The previous 

 species might be regarded as a dwarfed form 

 of the present; S. operculata, however, is vastly 

 more profuse in its growth. It is common in 

 the trawl. 



Sertularia abietina, Linnaeus. 



4 dry specimens, and 1 specimen in box. 



SPECIMENS This species has been 



54, 55, 56, 57, 58. popularly called the 

 " Sea-fir." The main stem grows to a 

 considerable height, and throws out alternate 

 lateral branches which in some specimens 

 branch again. The receptacles are 



sub-opposite ; the capsules are ovate, 



