ZOANTHARIA. 149 



ANTIPATHIIXE. 



We need not dwell upon this group, which is comparatively unin- 

 teresting. They correspond with the family of Gorgonidse among 

 the Alcyonarta, which they resemble in having the central axes 

 branching after the manner of a shrub; but the polyps have the 

 mouth surrounded with a crown of six simple tentacula. The axis is 

 of a harder and denser tissue than that of the Gorgons, and presents 

 on its surface small spiniform projections. The polypiferous crust, 

 with which they are covered, is in general very arenaceous, and is so 

 easily detached, that it is rare to see in collections anything but the 

 denuded skeleton of the colony. In A. arborea, the polypidom is fragile 

 and brittle ; when dry, the branches, always slender and delicate, re- 

 semble the barbs of a feather. The colour is of a deep black, or rather 

 bistre and terra de sienna tint. Under a powerful lens, the extremities 

 of the branches appear to be covered with small spines, and the trunk 

 is formed of oval and irregular concentric beds, which are the zones 

 of growth. Its consistence is firm, so that it can be worked up and 

 converted into chaplets for pearls and other bijouterie : it is known in 

 commerce as Uack coral. 



MADRKPOEHXE. 



The Madrepora are better known than their congeners. They are 

 sometimes, but erroneously, designated corals, since the coral forms no 

 part of this group. 



The Madrepores are remarkable for the calcareous crust which always 

 surrounds their tissue, and determines the formation of their polypidom. 

 They are in other respects easily recognized by the star-like structure 

 of their polypidom, in which may always be distinguished a visceral 

 chamber, the circumference of which is furnished with perpendicular 

 laminae or partitions, which are always directed towards the axis of 

 the body. When sufficiently developed they constitute, by their as- 

 semblage, a star-like body formed of a great number of rays. The 

 polypidom is always calcareous. The consolidation of the envelope of 

 each polyp produces at first a kind of sheath, to which Milne Edwards 

 has given the name of the wall. The partitions which proceed from 

 the interior towards the axis of the visceral chamber occupy the sub- 

 tentacular cells ; the terminal and open portion designated the calyx is 



