78 
ROOM XI. 
Nat. Hist. 
the Cydonia, in which the bark is hard, and the cen¬ 
tre of the coral almost entirely formed of large radi¬ 
ating spicula. In the other division, containing the 
Zeniae, the coral is light and cellular, especially in the 
dry state, and the outer surface of the stem is scattered 
with small spicula, crowded together, and forming a 
tuft round the mouths of the cells, which are placed 
at the tips of the branches, giving the coral much the 
appearance of the Sea-Pens, from which they differ 
in being attached and irregularly ramose. 
The last family of this order are the Sea-Pens ( Pen- 
natulidcE ), which are peculiar for not being attached by 
a dilated base, like the other corals, but free, living 
partly imbedded in the sand on the sea-coast. They 
have often been called Swimming Corals, but it is now 
generally believed that they never willingly leave their 
situation in the sand. They are all brilliantly phospho¬ 
rescent; the main stem is simple, subcylindrical, and 
fleshy, supported by a linear, fusiform, calcareous bone ; 
the lower part, or that imbedded in the sand, is without 
polypes, which are scattered in various ways over the 
upper half, and the different genera into which the fa¬ 
mily has been divided, depend on their disposition. In 
some, the upper part of the coral is furnished with re¬ 
gular branches placed on one side of the stem, giving 
them very much the appearance of a feather. In the 
common Sea-Pen ( Pennatula ) the branches are again 
similarly divided, and the tubes which have the polypes 
at their tips are surrounded by a bundle of spicula. In 
the Virgularise the branches are simple. In the Pavona- 
riae the polypes are sessile, in a row on each side of the 
front of the stem. In others, as the Umbellariae, the 
branches are united together into a tuft; whilst in the 
remaining two genera the upper part of the coral is 
fleshy, and not branched, the apex of the one ( Renella ) 
being expanded into a kidney-shaped disk, with the po¬ 
lypes on one of its sides, and the other ( Veretillum) 
club shaped, with the polypes scattered over its upper 
part. 
Here 
