t 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.)]

[Illustration: Fig. 80.--_Cystiphyllum vesiculosum_, showing a
succession of cups produces by budding from the original coral.
Of the natural size. Devonian, America and Europe. (Original.)]

[Illustration: Fig. 81--_Zaphrentis cornicula_, of the natural
size. Devonian, America. (Original.)]

[Illustration: Fig. 82--_Heliophyllum exiguum_, viewed from in
front and behind. Of the natural size. Devonian, Canada. (Original.)]

[Illustration: Fig. 83.--Portion of a mass of _Crepidophyllum
Archiaci_, of the natural size. Hamilton Formation, Canada. (After
Billings.)]

No true _Graptolites_ have ever been detected in strata of Devonian
age; and the whole of this group has become extinguished--unless we
refer here the still surviving _Dictyonemoe_. The _Coelenterates_,
however, are represented by a vast number of _Corals_, of beautiful
forms and very varied types. The marbles of Devonshire, the Devonian
limestones of the Eifel and of France, and the calcareous strata
of the Corniferous and Hamilton groups of America, are often
replete with the skeletons of these organisms--so much so as to
sometimes entitle the rock to be considered as representing an
ancient coral-reef. In some instances the Corals have preserved
their primitive calcareous composition; and if they are embedded
in soft shales, they may weather out of the rock in almost all
their original perfection. In other cases, as in the marbles
of Devonshire, the matrix is so compact and crystalline that
the included corals can only be satisfactorily studied by means
of polished sections. In other cases, again, the corals have
been more or less completely converted into flint, as in the
Corniferous limestone of North America. When this is the case,
they often come, by the action of the weather, to stand out from
the enclosing rock in the boldest relief, exhibiting to the observer
the most minute details of their organization. As before, the
principal representatives of the Corals are still referable to
the groups of the _Rugosa_ and _Tabulata_. Amongst the Rugose
group we find a vast number of simple "cup-corals," generally
known by the quarryme