Corals.—The corals deserve especial notice, as the cup-and-star corals, which have the most massive and stony skeletons, display peculiarities of structure by which they may be distinguished generally, as MM. Milne Edwards and Haime first pointed out, from all species found in strata newer than the Permian. There is, in short, an ancient or Palæozoic, and a modern or Neozoic type, if, by the latter term, we designate (as proposed by Professor E. Forbes) all strata from the triassic to the most modern, inclusive. The accompanying diagrams (Figs. 474, 475) may illustrate these types.

Vertical section of Campophyllum flexuosum, (Cyathophyllum, Goldfuss); from the Devonian of the Eifel. The lamellæ are seen around the inside of the cup; the walls consist of cellular tissue; and large transverse plates, called tubulæ, divide the interior into chambers. Arrangement of the lamellæ in Polycoelia profunda, Germar, sp.; from the Magnesian Limestone, Durham. This diagram shows the quadripartite arrangement of the primary septa, characteristic of palæozoic corals, there being four principal and eight intermediate lamellæ, the whole number in this type being always a multiple of four. Stauria astræiformis, Milne Edwards. Young group, natural size. Upper Silurian, Gothland. The lamellæ or septal system in each cup are divided by four prominent ridges into four groups.
Parasmilia centralis, Mantell, sp. Vertical section. Upper Chalk, Gravesend. In this type the lamellæ are massive, and extend to the axis or columella composed of loose cellular tissue, without any transverse plates like those in Fig. 474, a. Cyathina Bowerbankii, Ed. and H. Transverse section, enlarged. Gault, Folkestone. In this coral the primary septa are a multiple of six. The twelve principal plates reach the columella, and between each pair there are three secondaries, in all forty-eight. The short intermediate plates which proceed from the columella are not counted. They are called pali. Fungia patellaris, Lamarck. Recent; very young state. Diagram of its six primary and six secondary septa, magnified. The sextuple arrangement is always more manifest in the young than in the adult state.
  1. Vertical section of Campophyllum flexuosum, (Cyathophyllum, Goldfuss); from the Devonian of the Eifel. The lamellæ are seen around the inside of the cup; the walls consist of cellular tissue; and large transverse plates, called tubulæ, divide the interior into chambers.
  2. Arrangement of the lamellæ in Polycoelia profunda, Germar, sp.; from the Magnesian Limestone, Durham. This diagram shows the quadripartite arrangement of the primary septa, characteristic of palæozoic corals, there being four principal and eight intermediate lamellæ, the whole number in this type being always a multiple of four.
  3. Stauria astræiformis, Milne Edwards. Young group, natural size. Upper Silurian, Gothland. The lamellæ or septal system in each cup are divided by four prominent ridges into four groups.
  1. Parasmilia centralis, Mantell, sp. Vertical section. Upper Chalk, Gravesend. In this type the lamellæ are massive, and extend to the axis or columella composed of loose cellular tissue, without any transverse plates like those in Fig. 474, a.
  2. Cyathina Bowerbankii, Ed. and H. Transverse section, enlarged. Gault, Folkestone. In this coral the primary septa are a multiple of six. The twelve principal plates reach the columella, and between each pair there are three secondaries, in all forty-eight. The short intermediate plates which proceed from the columella are not counted. They are called pali.
  3. Fungia patellaris, Lamarck. Recent; very young state. Diagram of its six primary and six secondary septa, magnified. The sextuple arrangement is always more manifest in the young than in the adult state.

It will be seen that the more ancient corals have what is called a quadripartite arrangement of the chief plates or lamellæ—parts of the skeleton which support the organs of reproduction. The number of these lamellæ in the Palæozoic type is 4, 8, 16, etc.; while in the Neozoic type the number is 6, 12, 24, or some other multiple of six; and this holds good, whether they be simple forms, as in Figs. 474, a, and 475, a, or aggregate clusters of corallites, as in 474, c. But further investigations have shown in this, as in all similar grand generalisations in natural history, that there are excepions to the rule. Thus in the Lower Greensand Holocystis elegans (Ed. and H.) and other forms have the Palæozoic type, and Dr. Duncan has shown to what extent the Neozoic forms penetrate downward into the Carboniferous and Devonian rocks.

From a great number of lamelliferous corals met with in the Mountain Limestone, two species (Figs. 476, 477) have been selected, as having a very wide range, extending from the eastern borders of Russia to the British Isles, and being found almost everywhere in each country. These fossils, together with numerous species of Zaphrentis, Amplexus, Cyathophyllum, Clisiophyllum, Syringopora, and Michelinia,[[5]] form a group of rugose corals widely different from any that followed them.

Bryozoa and Crinoidea.—Of the Bryozoa, the prevailing forms are Fenestella, Hemitrypa, and Polypora, and these often form considerable beds. Their net-like fronds are easily recognised. Crinoidea are also numerous in the Mountain Limestone (see Figs. 478, 479), two genera, Pentremites and Codonaster, being peculiar to this formation in Europe and North America.