The later beds of the island belong to the Jurassic, Cretaceous and Tertiary systems. At the western foot of the Ida massif calcareous beds with corals, brachiopods (Rhvnchonella inconstans, &c.) have been found, the fossils indicating the horizon of the Kimmeridge clay.
Schrenck in the north of the Japanese Sea led to the discovery of no fewer than 256 species (Gasteropods, Brachiopods and Conchifers).
It is a remarkable fact that in Discinisca, although the vessels to the lophophore are arranged as in other Brachiopods, no trace of a heart or of the posterior vessels has as yet been discovered.
The histology of Brachiopods presents some peculiar and many primitive features.
In spite of some assertions to the contrary, all the Brachiopods which have been carefully investigated have been found to be male or female.
By the aid of these cilia the larva swims actively, but owing to its minute size it covers very little distance, and this probably accounts for the fact that where brachiopods occur there are, as a rule, a good many in one spot.
Plankton Expedition, ii., 1897) has described, a few larval brachiopods of undetermined genera, two of which at least were pelagic, or at any rate taken far from the coast.
Brachiopods have been at various times placed with the Mollusca, the Chaetopoda, the Chaetognatha, the Phoronidea, the Polyzoa, the Hemichordata, and the Urochordata.
The suggestion to place Brachiopods with the Polyzoa, Phoronis, Rhabdopleura and Cephalodiscus, in the Phylum Podaxonia made in Ency.
I t may, however, be pointed out that Brachiopods seem to belong to that class of animal which commences life as a larva with three segments, and that tri-segmented larvae have been found now in several of the larger groups.
Brachiopods first appear in the Lower Cambrian, and reached their highest development in the Silurian, from which upwards of 2000 species are known, and were nearly as numerous in the Devonian period; at present they are represented by some 140 recent species.
The former statement is, however, true of animals from other classes at least as highly organized as Brachiopods, e.g.
A full bibliography of Brachiopoda (recent and fossil) is to be found in Davidson's Monograph of British Fossil Brachiopods, Pal.
The slates are interbedded with limestones containing fossil brachiopods, which have led to their determination as Silurian or Devonian; but L.
The brachiopods, generally classed collectively as Spirifer mucronatus, follow at least five distinct lines of evolution in the Middle Devonian of North America, while more than twenty divergent lines have been observed by Grabau among the species of the gastropod genus Fusus in Tertiary and recent times.
The loss of the power to coil, observed in the terminals of many declining series of gastropods from the Cambrian to the present time, and the similar loss of power among Natiloidea and Ammonoidea of many genetic series, as well as the ostraean form assumed by various declining series of pelecypods and by some brachiopods, may be cited as examples.
Among the brachiopods the chief expansion of each type is at a relatively early period in their life-history.
,Among the known fossils are vermes, crustacea and probably brachiopods and pteropods The character of the sediments of the Proterozoic is such as to show that mature weathering affected the older rocks before their material was worked over into the Proterozoic formations.
As in other parts of the world, the system here contains abundant fossils, among which trilobites, brachiopods and worms are the most abundant.
Corals, echinoderms, brachiopods and all groups of molluscs abounded.
The groups of organisms utilized for zoning and correlation by different workers include brachiopods, pelecypods, cephalopods, corals, fishes and plants; and the results of the comparison of the faunas and floras of different areas where Carboniferous rocks occur are generalized in the table below.
Brachiopods occupied an important place; most typical were the Productids, some of which reached a great size and had very thick shells.
Many fish inhabited the Carboniferous seas and most of these were Elasmobranchs, sharks with crushing pavement teeth (Psammodus), adapted for grinding the shells of brachiopods, crustaceans, &c. Other sharks had piercing teeth (Cladoselache and Cladodus); some, the petalodonts, had peculiar cycloid cutting teeth.
The old land area still existed to the north, but doubtless much reduced in height; against this land, detrital deposits still continued to be formed, as in Scotland; while over central Ireland and central and northern England the clearer waters of the sea furnished a suitable home for countless corals, brachiopods and foraminifera and great beds of sea lilies; sponges flourished in many parts of the sea, and their remains contributed largely to the formation of the beds of chert.
The upper divisions consist of bituminous limestones, clay-slates, alum-slate, and contain numerous species of trilobites of the genera Paradoxides, Conocoryphe, Agnostus, Sphaerophthalmus, Peltura, &c. The Ordovician formation occurs in two distinct facies - the one shaley and containing graptolites; the other calcareous, with brachiopods, trilobites, &c. The most constant of the calcareous divisions is the Orthoceras limestone, a red or grey limestone with Megalaspis and Orthoceras.
The typical Silurian rocks are richly fossiliferous, the shales containing trilobites, the sandstones many brachiopods, and the limestones a rich coral and bryozoan fauna.
There is, however, a considerable amount of resemblance between the lophophore of Phoronis australis, with its spirally twisted ends, and that of a typical Brachiopod; nor do the structural details of the adult Brachiopods forbid the view that they may be related to Phoronis.
Spicules of sponges and fragments of other organisms, such as molluscs, polyzoa, foraminifera and brachiopods, often occur in flint, and may be partly or wholly silicified with retention of their original structure.