PSEUDAXONIA, AXIFERA, STELECHOTOKEA, and
CORNOTHECALIA.

[Illustration: FIG. 5.

A. Skeleton of a young colony of _Tubipora purpurea_. st, Stolon; p,
platform.

B. Diagrammatic longitudinal section of a corallite, showing two
platforms, p and cup-shaped tabulae, t. (After S.J. Hickson.)]

In the order STOLONIRERA the zooids spring at intervals from branching
or lamellar stolons, and are usually free from one another, except at
their bases, but in some cases horizontal solenia arising at various
heights from the body-wall may place the more distal portions of the
zooids in communication with one another. In the genus _Tubipora_
these horizontal solenia unite to form a series of horizontal
platforms (fig. 5). The order comprises the families _Cornulamdae,
Syringopordae, Tubipondae_, and _Favositidae_. In the first-named, the
zooids are united only by their bases and the skeleton consists of
loose spicules. In the _Tubipondae_ the spicules of the proximal part
of the body-wall are fused together to form a firm tube, the
corallite, into which the distal part of the zooid can be retracted.
The corallites are connected at intervals by horizontal platforms
containing solenia, and at the level of each platform the cavity of
the corallite is divided by a transverse calcareous partition, either
flat or cup-shaped, called a _tabula_. Formerly all corals in which
tabulae are present were classed together as Tabulata, but Tubipora is
an undoubted Alcyonarian with a lamellar stolon, and the structure of
the fossil genus Syringopora, which has vertical corallites united by
horizontal solenia, clearly shows its affinity to Tubipora. The
Favositidae, a fossil family from the Silurian and Devonian, have a
massive corallum composed of numerous polygonal corallites closely
packed together. The cavities of adjacent corallites communicate by
means of numerous perforations, which appear to represent solenia, and
numerous transverse tabulae are also present. In _Favosites
hemisphaerica_ a number of radial spines, projecting into the cavity
of the corallite, give it the appearance of a madreporarian coral.

[Illustration: FIG. 6.--Portion of a colony of _Coralinum rubrum_,
showing expanded and contracted zooids. In the lower part of the
figure the cortex has been cut away to show the _axis_, ax, and the
longitudinal canals, lc, surrounding it.]

In the order ALC