224 THE OCEAN WORLD. 
IsIDINA. 
The Jstdine constitute an intermediate group between the Gor- 
goning and Coraline. Their polypidom is arborescent, but its axis is 
> i: 
Gn 
fi iH) iG 
wo 
v 
1S, 
Fig. 82,—Isis hippuris. 
formed of articulations alternately calcareous and horny. The prin- 
cipal genus is that called /s¢s, which is met with in the Indian Ocean, 
on some parts of the American coast, and in the Pacific Ocean. 
