C(ELENTEE.\TA. 35 



The axis is sulcate, by which it is known, inter alia, from 

 Antipathidae. The branches are frequently anastomosing. In 

 Briareidae there is no horny axis, but the internal parts are com- 

 posed of calcareous spicules. Corallium has a sclerobasic homo- 

 geneous stony axis, and should probably form an order of its own. 

 Its only representative is the red coral of commerce, Corallium 

 rubrum. 



" Heliopora seems to differ from all other Alcyonarians except 

 Corallium" [Moseley.] 



Axis branched, erect, composed of alternate calcareous nodes 

 and horny internodes ; permanently rooted. Polypes embedded 

 in the coenosarc. 



The nodes are larger than the internodes and are generally 

 white and fluted. In Melitk&a the nodes are porous or corky in 

 appearance. 



Isididce. Melithceidce. 



Isis. Melithaea. 



Mopsea. 



Order IV. TUBIPORACE^. 



Corallum sclerodermic, in the form of tubular thecae, bound 

 together by horizontal plates [epithecae] ; no septa. Polypes com- 

 pletely retractile. 



The horizontal plates are confined to the outside of the coral- 

 lum, which is perforated by numerous minute canals. The 

 " organ-pipe coral" (Tubipora musica), forming large hemisphe- 



D 2 



