42 CORALS AND CORAL ISLANDS. 



of the species entangles the sand that falls on it, and thus 

 gives a degree of firmness to the mass of the zoophyte. 



3. The Aiitipathus tribe, or Antipathacea. In this tribe 

 the polyps never have locomotion, and, as far as known, always 

 produce compound groups by budding. These groups have 

 the forms of delicate shrubs and long twigs ; and some of 

 them are three feet or more in height. The branches consist 

 of a horny axis, usually spiny or hispid over its surface, sur- 

 rounded by an animal coating, which is made up of united 

 polyps. An example is shown in the following figure of a 

 living species from the Feejees. A view of one of the polyps, 

 much enlarged, is given in the following figure. Its tentacles 

 are closely like those of the Actinia. The height of the entire 



POLYP OF A. AKBOKEA, MUCH ENLARGED. 



shrub, collected by the author, was three feet, and the trunk at 

 base was half an inch thick. The polyps had a brownish- 

 yellow colour, not particularly beautiful, and the tentacles were 

 in general, as in another species described by the author, rather 

 awkwardly handled by the polyp. The number is commonly 

 six ; but in one genus, Gerardia,.it is as great as hventy-fo2ii\ 



2. Polyps having infernal calcareous secretions. Madreporaria 

 of Verrill. i^TJie Cyathophylloid species excluded). 



4. AstrcEa tribe, or Astr^.acea. — In this tribe the polyj)- 

 cells or calicles are distinctly lamello- radiate within, and gener- 

 ally so outside. Moreover, budding is always by division of the 

 disks, or spontaneous fission. The figure of the Caulastraea, on 



