ultimately prove to have an
organic structure, though others would appear to be clearly of
purely inorganic origin. From the Permian of Saxony, Professor
Geinitz has described two species of _Spongillopsis_, which he
believes to be most nearly allied to the existing fresh-water
Sponges (_Spongilla_). This observation has an interest as bearing
upon the mode of deposition and origin of the Permian sediments.

The _Coelenterates_ are represented in the Permian by but a few
Corals. These belong partly to the _Tabulate_ and partly to the
_Rugose_ division; but the latter great group, so abundantly
represented in Silurian, Devonian, and Carboniferous seas, is
now extraordinarily reduced in numbers, the British strata of
this age yielding only species of the single genus _Polycoelia_.
So far, therefore, as at present known, all the characteristic
genera of the Rugose Corals of the Carboniferous had become extinct
before the deposition of the limestones of the Middle Permian.

The _Echinoderms_ are represented by a few _Crinoids_, and by a
Sea-urchin belonging to the genus _Eocidaris_. The latter genus
is nearly allied to the _Archoeocidaris_ of the Carboniferous, so
that this Permian form belongs to a characteristically Palaeozoic
type.

A few _Annelides_ (_Spirorbis, Vermilia_, &c.) have been described,
but are of no special importance. Amongst the _Crustaceans_,
however, we have to note the total absence of the great Palaeozoic
group of the _Trilobites_; whilst the little _Ostracoda_ and
_Phyllopods_ still continue to be represented. We have also to
note the first appearance here of the "Short-tailed" Decapods or
Crabs (_Brachyura_), the highest of all the groups of _Crustacea_,
in the person of _Hemitrochiscus paradoxus_, an extremely minute
Crab from the Permian of Germany.

[Illustration: Fig. 135.--Brachiopods of the Permian formation.
a, _Producta horrida_; b, _Lingula Credneri_; c, _Terebratula
elongata_; d and e, _Camarophoria globulina_. (After King.)]

Amongst the _Mollusca_, the remains of _Polyzoa_ may fairly be
said to be amongst the most abundant of all the fossils of the
Permian formation, The principal forms of these are the fronds
of the Lace-corals (_Fenestella, Retepora_, and _Synocladia_),
which are very abundant in the Magnesian Limestone of the north
of England, and belong to various highly characteristic species
(such as _Fenestella retiformis, Retepora Ehrenbergi_, and
_Synocladia virgulacea_