CLASS IV. 



GENERA AND SPECIES. 



PoLYPTDOMS of various shapes, formed of a fleshy 

 and animated mass, sometimes inert, sometimes sus- 

 ceptible, and filled with retractile polypi, which ex- 

 pand like blossoms upon its surface. In a state of de- 

 siccation this mass appears composed of interwoven 

 fibres, reticulated at the centre, radiating to the cir- 

 cumference, and enclosed in a firm cellular exterior, 

 leathery and cretaceous. The number of tentacula 

 varies in the different species. 



Alcyonium ; of various shapes, with a smooth sur- 

 face, or slightly tuberculous. 



Palythoa ; with numerous papillae, each one inclo- 

 sing a polypus. 



