Zoarium, always encrusting.

Zoœcia pyriform, average length, and breadth ·43 mm. and ·28 mm.; aperture semicircular, with a small tubercle at each side; front wall normally formed of five pairs of spines, the space between the lowest pair being filled by a triangular plate perforated at the apex and possibly tubular, as when it is broken off its base proves to be perforated; when there is a preceding zoœcium with an oœcium the fifth pair of spines and the triangular plate disappear, and the space so left is filled by the preceding oœcium, which always carries a small avicularium, possibly a relic of the triangular plate; the spines are not always strictly paired; the backbone is often depressed and pierced by irregular pores.