Honeycomb corals consist of masses of small, close-set prismatic cells, each crossed by horizontal partitions, or tabulæ, while the septa are rudimentary, being represented by faintly projecting ridges or rows of spines.
Fig. 290. Honeycomb Corals
| Fig. 291. A Chain Coral | Fig. 292. A Syringopora Coral |
Chain corals are also marked by tabulæ. Their cells form elliptical tubes, touching each other at the edges, and appearing in cross section like the links of a chain. They became extinct at the end of the Silurian.
The corals of the Syringopora family are similar in structure to chain corals, but the tubular columns are connected only in places.
| Fig. 293. A Blastoid: A, side view, showing portion of the stem; B, summit of calyx (species Carboniferous) | Fig. 294. A Silurian Scorpion |
To the echinoderms there is now added the blastoid (bud-shaped). The blastoid is stemmed and armless, and its globular “head” or “calyx,” with its five petal-like divisions, resembles a flower bud. The blastoids became more abundant in the Devonian, culminated in the Carboniferous, and disappeared at the end of the Paleozoic.
The great eurypterids—some of which were five or six feet in length—and the cephalopods were still masters of the seas. Fishes were as yet few and small; trilobites and graptolites had now passed their prime and had diminished greatly in numbers. Scorpions are found in this period both in Europe and in America. The limestone-making seas of the Silurian swarmed with corals, crinoids, and brachiopods.