MADREPORES. 



175 



ordinary height, becoming contracted about the middle, hke an hour- 

 glass. When the creature is fully expanded, the tentacula become 

 distended and elongated to about the length of the transverse 

 diameter of the body ; and they are generally darker at their ex- 

 tremities than towards the base. The present species possesses a 

 power of considerably altering its shape ; sometimes the mouth is 

 depressed, and at others it is elevated into an obtuse cone. " This is 

 one of the most inactive of its order," says Mr. A. Couch ; " for, 

 whether in a state of contraction or expansion, it will remain so for 



Fig. 59. — Zoanthus socialis (Cuvier), magnified. 



many days without apparent change. In its expanded state a touch 

 will make it contract, and it will commonly remain so for many 

 days." The trailing connecting-band is flat, thin, narrow, glandular, 

 and of the same texture as the pol}TD, sometimes enlarging into 

 small papillary eminences, which, as they become enlarged, become 

 developed into polyps. 



The genus Caryophillia (Lamarck), from Kapvov, a nut, and (pvA^ov, a 

 leaf, has the polypidom permanently fixed, simple, striated longitudi- 

 nally, and the summit hollowed into a lamellated star-like cup ; the 

 animal, actinia-like, is provided with a simple or double crown of ten- 

 tacula, projecting from the surface of star-lilce, cylindrical, cone-shaped 



