144 



THREE CRUISES OF THE " BLAKE. 



branching coral with slender terminal twigs, while the main 

 branches are spirally arranged, with a slender brilliantly irides- 

 cent calcareous axis. The polyps are large, and placed rather 

 far apart. It belongs to the deep-sea family of Chrysogorgida} 

 (Fig. 456), established by Verrill for such gorgonians as have 

 usually an iridescent axis with spiral branches. They are among 



Fig. 456. Chrysogorgia. 



the most beautiful and interesting of the gorgonians. A unique 

 and striking species of the group is Iridogorgia Pourtalesii (Fig. 

 456 a] with its regular upright spiral main stem, and long, flex- 

 ible, undivided branches, arranged in a single row nearly at 

 right angles to the axis ; forming a broad spiral like the skeleton 

 of a spiral staircase. The species are remarkable for their ele- 



