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GENUS I. ZOANTHUS (Cuvier). 



Actinia (Ellis). 

 Zoantlia ) 



Palythoa\^ i0 ™ 0v ^ 

 Zoanthus \ 



Mammilifera > (Lesueur). 

 Corticifera ) 

 Sidisia (J. E. Gray). 



Base permanently attached j spreading over rocks, 

 stones, or shells, in either a linear or incrusting 

 manner. 



Column pillar-like, higher than wide ; margin cut 

 into strongly marked teeth, which are united by a 

 thin membrane. Surface smooth, excreting a mucus, 

 in which occasionally grains of sand become imbedded, 

 constituting an adventitious epidermis. 



Disk slightly concave ; radii inconspicuous. 



Tentacles conical, pointed, similar in structure to 

 those of Astr^acea : wholly retractile. 



Mouth more or less protrusile, simple. 



ANALYSIS OF BRITISH SPECIES. 



Invested with sand ; extension various Couchii. 



Without sand — 



Polypes cylindrical, olive ; several abreast sulcatus. 



Polypes obconic, pellucid white ; in single file . . . . . Alderi. 



