True Sponges (such as _Astrtoeospongia, Sphoerospongia_, &c.)
are not unknown; but by far the commonest representatives of
this sub-kingdom in the Devonian strata are _Stromatopora_ and
its allies. These singular organisms (fig. 79) are not only very
abundant in some of the Devonian limestones--both in the Old World
and the New--but they often attain very large dimensions. However
much they may differ in minor details, the general structure of
these bodies is that of numerous, concentrically-arranged, thin,
calcareous laminae, separated by narrow interspaces, which in turn
are crossed by numerous delicate vertical pillars, giving the whole
mass a cellular structure, and dividing it into innumerable minute
quadrangular compartments. Many of the Devonian _Stromatoporoe_
also exhibit on their surface the rounded openings of canals,
which can hardly have served any other purpose than that of
permitting the sea-water to gain ready access to every part of
the organism.
[Illustration: Fig. 79.--a, Part of the under surface of
_Stromatopora tuberculata_, showing the wrinkled basement membrane
and the openings of water-canals, of the natural size; b, Portion
of the upper surface of the same, enlarged; c, Vertical section of
a fragment, magnified to show the internal structure. Corniferous
Limestone, Canada. (Original.
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