160 HISTORY OF BRITISH ZOOPHYTES. 



2. LAOMEDEA GENICULATA, Knotted-thread Coralline, 

 Doody. (Plate X. fig. 31.) 



Hab. On Laminaria, very often on Halidrys siliquosa, 

 and not unfrequently on Chorda filum. " Some of the finest 

 specimens I have seen were growing on the dorsal and 

 caudal fins of a picked dog-fish." (Couch.} 



It is interesting to observe how indissolubly the fibrous 

 roots of this coralline are twined round the branches 

 of the Halidrys. And though a person would suppose 

 that it would not be able to fasten itself firmly on the 

 smooth frond of Laminaria, he will find, on trial, that it is 

 no easy matter to detach it. The fibres, half-sunk in the 

 frond, " form," as Mr. W. Thompson observes, " a regular 

 piece of network, having meshes of various size, with their 

 junction tied in a knot, as it were by fairy fingers : from 

 each knot, in due time, the zoophyte springs." 



The polypidom is about an inch in height, zigzag, the 

 cells bell-shaped ; the vesicles somewhat resemble an urn in 

 form. Several naturalists have observed that this coralline, 

 like several others, is often tinted with red ; but it has not 

 been ascertained on what the red colouring depends. We 

 think that we have at times observed that it is a slight film 

 of Melobesia. 



