. 91.--Fragment of _Ceriopora Hamiltonensis_,
of the natural size and enlarged. Devonian, Canada. (Original.)]

[Illustration: Fig. 92.--Fragment of _Fenestella magnifica_, of
the natural size and enlarged. Devonian, Canada. (Original.)]

[Illustration: Fig. 93.--Fragment of _Retepora Phillipsi_, of
the natural size and enlarged. Devonian, Canada. (Original.)]

[Illustration: Fig. 94.--Fragment of _Fenestella cribrosa_, of
the natural size and enlarged. Dovonian, Canada. (Original.)]

The majority of the Devonian _Polyzoa_ belong, however, to the
great and important Palaeozoic group of the Lace-corals (_Fenestella_,
figs. 92 and 94, _Retepora_, fig. 93, _Polypora_, and their allies).
In all these forms there is a horny skeleton, of a fan-like or
funnel-shaped form, which grew attached by its base to some foreign
body. The frond consists of slightly-diverging or nearly parallel
branches, which are either united by delicate cross-bars, or which
bend alternately from side to side, and become directly united
with one another at short intervals--in either case giving origin
to numerous oval or oblong perforations, which communicate to the
whole plant-like colony a characteristic netted and lace-like
appearance. On one of its surfaces--sometimes the internal, sometimes
the external--the frond carries a number of minute chambers or
"cells," which are generally borne in rows on the branches, and
of which each originally contained a minute animal.

[Illustration: Fig. 95.--_Spirifera sculptilis_. Devonian, Canada.
(After Billings.)]

[Illustration: Fig. 96.--_Spirifera mucronata_. Devonian, America.
(After Billings.)]

[Illustration: Fig. 97.--_Atrypa reticularis_. Upper Silurian
and Devonian of Europe and America. (After Billings.)]

The _Brachiopods_ still continue to be represented in great force
through all the Devonian deposits, though not occurring in the
true Old Red Sandstone. Besides such old types as _Orthis,
Strophomena, Lingula, Athyris_, and _Rhynchonella_, we find some
entirely new ones; whilst various types which only commenced their
existence in the Upper Silurian, now undergo a great expansion
and development. This last is especially the case with the two
families of the _Spiriferidoe_ and the _Produclidoe_. The
_Spirifers_, in particular, are especially characteristic of
the Devonian, both in the Old and New Worlds--some of the most
typical forms, such as _Spirifera mucronata_ (fig. 96), having
the s