FLUSTRELLA HISPIDA. 507 



quincuncially arranged, the front surface flat, smooth 

 and dense ; orifice somewhat raised, bilabiate, bordered 

 above and below by a thin horny rib, the lower one 

 connected with a movable or extensible lip, which acts 

 as an operculum; a variable number of tall spines 

 surrounding the orifice, and, in many cases, a row of 

 similar appendages along the margins of the cells. 

 Folypide with 30-35 tentacles. 



HABITAT. On various Fuel (Fucus serratus, Gigartina 

 mamillosa, &c.) between tide-marks. 



LOCALITIES. Very common and widely diffused. 



GEOGRAPHICAL DISTRIBUTION. Bahusia, 5-10 fathoms 

 (Smitt) ; Finmark (Goes & Malmgren) : Greenland (Liit- 

 ken) : Heligoland (Kirchenpauer) : Roscoff (Joliet) : 

 France, S.W. (Fischer). 



This is in many ways a remarkable form. Its chief 

 structural peculiarities have already been noticed ; but 

 more remains to be said of it. In the size and beauty of 

 its polypides it is unequalled amongst the Poly/oa. Its 

 rather coarse-looking gelatinous crust, bristling with 

 spines, is to be found on almost every coast where the 

 Fucus serratus grows, and spreads over many other kinds 

 of weed between tide-marks and in the neighbouring 

 shallow water. The multitudes of the large tentacular 

 bells, when expanded, give rise to the appearance which 

 Sir John G. Dalyell has happily likened to a "thin pale- 

 blue cloud," interposed between the dark surface and the 

 spectator's eye. Through the clear still water of the rock- 

 pool on a summer day the blue mist may readily be seen, 

 hovering, as it were, over the masses of Flustrella on the 

 weed. The size of the polypide is remarkable : it has 

 often as many as between 30 and 10 tentacles, and is 

 three or four times as large as that of A/n/ti/ihfintu itn/fi/i. 



