ZOANTHARIA. 
151 
Antipathidjs. 
We need not dwell upon this group, which is comparatively unin- 
teresting. They correspond with the family of Gorgonults among 
the Alcyonaria, which they resemble in having the central axes 
branching after the manner of a shrub ; but the polypi 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 
°u 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. arboreci, the polypier is fragile 
a ml 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 
commerco as black coral. 
Madkepokid.*. 
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 polypier. 
They are in other respects easily recognised by the star-like structure 
of their polypier, in which may always be distinguished a visceral 
chamber, the circumference of which is furnished with perpendicular 
lamin;e or partitions, which are always directed towards tho 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 
Polypier is always calcareous. The consolidation of the envelope of 
each polype 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 
