of the columella. The secondary septa are furnished with laminæ of the same description, which join those of the first set, at an acute angle, without reaching the columella; and the tertiary septa pass into this point of union, having no supplementary laminæ of their own. The two sets of plates, just noticed, present a rounded shoulder internally (more prominent in the primary ones) giving them the character of lateral pali, or dismemberments of the septa.
The columella is composed of a spongy tissue, with an oval and slightly convex summit.
All the plates of the disk are spongy, or minutely granular, on the surface, but compact within. The body of the corallum is spongy at the axis, in continuity with the columella, more compact below and around this, and again more porous towards the exterior, especially above.
The loculi are circumscribed, but not crossed by synapticulæ or interseptal dissepiments. They are just double the number of the septa, lying one on either side of the later, and are thus arranged by pairs in three distinct circles; the internal corresponding with the primary, and the external with the tertiary rays.
In the species taken at the Bellona Shoals the oral disk was distorted, with a central constriction, as though the process of fission had been going forward. In one specimen indeed the opposite margins of the disk had actually coalesced. The primary septa were twelve in number, and all the plates are so much compressed that the loculi are exceedingly narrow. The external surface of the corallum is beset with minute granulations disposed in broke latitudinal lines with porous channels between them; on the other hand, in the Feegean species the disk is regular, with six primary rays and wider loculi, and the external surface of the corallum, is coarsely granulated, without any very obvious linear disposition, as the first rudiments of costæ.
In a recent visit to Moreton Bay we dredged (in a few fathoms depth) two beautiful specimens of another species of this genus, differing from the foregoing in having well marked longitudinal costæ, exactly forty-eight in number, and corresponding, each for each, with all the radiating septa and laminæ, with which they are directly continuous at the margin of the disk. The principal laminæ are falcate towards the hollow of the cup and deeply notched, toothed and echinate, as they pass into the spongy coiumells, whose actual limit is thus rendered less definite than in the other species described.
Of the soft core parts of this polyps, I can say but little. They appear to be very scanty, from the fact, that when the animals are immediately taken from the water there is scarcely anything to be seen but a brown, soft and tenacious matter, filling up the crevices of the skeleton above described, and all the prominent points and ridges become quite bare. The whole surface of the corallum is covered over with a thin ectodermic layer, which however is much worn at the
