f the clear Carboniferous seas were the crinoids, corals,
Foraminifera and brachiopods. Each of these groups contributed at one
place or another towards the upbuilding of great masses of limestone.
For the first time in the earth's history we find Foraminifera taking
a prominent part in the marine faunas; the genus _Fusulina_ was
abundant in what is now Russia, China, Japan, North America;
_Valvulina_ had a wide range, as also had _Endothyra_ and
_Archaediscus; Saccammina_ is a form well known in Britain and
Belgium, and many others have been described; some Carboniferous
genera are still extant. Radiolaria are found in cherts in the Culm of
Devonshire and Cornwall, in Russia, Germany and elsewhere. Sponges are
represented by spicules and anchor ropes. Corals, both reef-builders
and others, flourished in the clearer waters; rugose forms are
represented by Amplexoid, Zaphrentid and Cyathophyllid types, and by
_Lithostrotion_ and _Phillipsastraea_; common tabulate forms are
_Chaetetes, Chladochonus, Michelinia_, &c. Amongst the echinoderms
crinoids were the most numerous individually, dense submarine thickets
of the long-stemmed kinds appear to have flourished in many places
where their remains consolidated into thick beds of rock; prominent
genera are _Cyathocrinus, Woodocrinus, Actinocrinus_; sea-urchins,
_Archaeocidaris, Palaeechinus_, &c., were present; while the curious
extinct Blastoids, which included the groups of _Pentremitidae_ and
_Codasteridae_, attained their maximum development.

Annelids (_Spirorbis, Serpulites_, &c.) are common fossils on certain
horizons. The Bryozoa were also abundant in some regions (_Polypora,
Fenestella_), including the remarkable form known as _Archimedes_.

Brachiopods occupied an important place; most typical were the
Productids, some of which reached a great size and had very thick
shells. Other common genera are _Spirifer, Chonetes, Athyris_,
Rhynchonellids and Terebratulids, _Discina_ and _Crania_. Some species
had an almost world-wide range with only minor variations; such are
_Productus semireticulatus, P. cora, P. pustulosus; Orthotetes
(Streptorhynchus) crenistria, Dielasma hastata_, and many others.

Pelecypods among the true mollusca were increasing in numbers and
importance (_Aviculopecten, Posidonomya_); _Nucula, Carbonicola,
Edmondia, Conocardium, Modiola_. Gasteropods also were numerous
(_Murchis