MEMBRANIPORA MEMBRANACEA. 141 



Colonies forming a delicate network^ often extending to 

 a lei 

 Fuci 



a length of several feet on the fronds of the larger 



Range of Variation. Distinguished for great regularity 

 of growth and constancy of character. 



Habitat. The fronds of Laminaria digitata and other 

 Fuci. 



Localities. Universally distributed on our coasts^ and 

 very abundant. 



Geographical Distribution. Hvidingsoe ; Hougesund 

 (Kirchenpauer) : Roscoff^ on Saccorhiza bulbosa (Joliet) : 

 Adriatic, on sea- weeds (Heller) : LyalPs Bay, New Zealand, 

 on Fucus (F. W. Hutton) : Australia (MacGillivray) . 



Range in Time. Coralline Crag; Palaeolithic (A. Bell). 



This species is one of the commonest of our British 

 Polyzoa, as it is undoubtedly one of the most beautiful. 

 Wherever Laminaria digitata is present its exquisite lace- 

 work is almost sure to be found, lighting up the sombre 

 fronds, and itself appearing all the more delicate in con- 

 trast with the dark surface over which it spreads. 



It possesses a power of free and rapid development cor- 

 responding with the size of the marine plants in which it 

 principally delights ; and the huge fronds of the Laminaria 

 are often swathed in its silvery net. Dr Landsborough 

 mentions a specimen 5 feet in length by 8 inches in 

 breadth ; and probably most tangle-beds of any size would 

 yield a similar growth. 



I have noticed in some cases a remarkable thickening 

 of the membranous front wall of the cells in this species. 

 This is sometimes carried to such an extent that the whole 

 of the free surface of the zoarium seems to be covered by 

 it, except the extremities of the spines. 



