Communities comparable to those figured, together with many others not dealt with here, are found in the limestones which occur in all the regions of the Carboniferous equatorial belt. However, the taxa involved at any age vary in the different regions of the world. Broadly there are three main faunal realms:
1 Eurasia — stretching from China to Western Europe and including North Africa, the Middle East, and possibly Japan and Australia. Here the faunas of the Visean and Namurian are characterized by the large productoids such as Gigantoproductus and Semiplanus. In the Visean the large and stratigraphically very informative chonetoids Delepinea and Daviesiella are widespread. Among corals Lithostrotion and Lonsdaleia are typical, and in the Upper Visean and Namurian Dibunophyllum.
2 The American Cordilleran region. This area contains many of the faunal elements of the Eurasian area, but often in a slightly modified form. For example the large productoids are represented by Titanaria, a rare genus which differs significantly from Giganto-productus, but is assigned to the same family. Among the corals the presence of Lithostrotionella, also common in China and Japan, is notable. There are also, as in all areas, a good many endemic species. The large chonetoids did not reach this region.
3 The mid-western United States, especially the Mississippi valley area. The faunas here contain a larger proportion of local forms than is usual in the Carboniferous. Large productoids and chone-toids are lacking and the coral faunas are to a large extent distinctive. The curious screw-like bryozoan Archimedes is almost restricted to this area.
The reasons for this faunal distribution in the Carboniferous are connected with the contemporary geography (Fig. h, p. 147), which, together with winds, influenced the main oceanic currents. Thus the north-easterly currents in the Ural region caused migrations across the Arctic area to western America, and the generally easterly currents (and easterly winds, of which there is evidence from the distribution of volcanic ashes) caused migrations from China and Russia into western Europe. The mid-west region of the United States was apparently at the end of this chain of migration, and this would account for the high number of local species in that area, and for the later appearance there than elsewhere of the archaediscid foraminiferida.
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