CCELENTERATA. 25 



Order 1. Stauromedusse. 



Conical or vase-shaped umbrella. No tentacu- 

 locysts. (Lucernaria, Tessera.) 



Order 2. Peromedusae. 



Conical umbrella with transverse constriction. 

 Four inter-radial tentaculocysts. (Pericolpa.) 



Order 3. Cubomedusse. 



Four-sided umbrella. With per-radial tentacu- 

 locysts. Velum present. (Charybdea.) 



Order 4. Discomedusse. 



Saucer-shaped umbrella. Per-radial and inter- 

 radial tentaculocysts. (Aurelia, Cyanea.) 

 Class 3. Actinozoa. 



With a stomodaeum, and with mesenteries ex- 

 tending into the coelenteron. Fixed forms. 

 Subclass 1. Zoantharia. 



Mesenteries and tentacles usually very numer- 

 ous. 



Order 1. Actiniaria. 



Usually single. No skeleton. (Metridium, Sa- 

 gartia.) 



Order 2. Madreporaria. 



Usually form colonies and always have calcare- 

 ous exoskeleton. (Astrangia, Orbicella, Mean- 

 drina.) 



Order 3. Antipatharia. 



Tree-like. Mesenteries and tentacles compara- 

 tively few. Chitinoid skeleton. (Cirripathes.) 

 Subclass 2. Alcyonaria. 



Mesenteries and tentacles eight in number. 

 Tentacles branched. 



Order 1. Alcyonacea. 



Skeleton in the form of small, irregular bodies, 

 frequently calcareous spicules. (Alyconium, 

 Tubipora.) 



Order 2. Gorgonacea. 



Tree-like, with calcareous or horny exoskeleton. 

 No siphonoglyphes. (Gorgonia.) 



Order 3. Pennatulacea. 



Colony with one end usually embedded in the 

 sea-bottom. (Pennatula, Renilla.) 



