CLASS IV. 
GENERA AND SPECIES. 
Polypidoms 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. 
