MADREPORES. 175 
ordinary height, becoming contracted about the middle, like 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 polyp, sometimes enlarging into 
small papillary eminences, which, as they become enlarged, become 
developed into polyps. 
The genus Caryophillia (Lamarck), from xapior, a nut, and pirrov, 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-like, cylindrical, cone-shaped 
