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Show 752 MR. J. STANLEY GARDINER ON [June 6, below by a more or less developed columella, formed by trabeculaB from the septal edges. Interseptal loculi deep, closed below by transverse endothecal dissepiments. Septa usually somewhat exsert and well-developed, commonly at least two cycles fusing with the columella. Paliform lobes* generally present and well-developed, usually recognizable at least in some parts of a colony. Costae varying in development, generally distinct, but sometimes not recognizable in surface view. Exotheca usually well-developed, often completely filling in the space between the theca of neighbouring corallites. Increase by intercalicular gemmation over the costae, where three or more calices meet, sometimes also by fissiparity. 1. ORBICELLA ACROPORA Linnaeus. Madrepora acropora, Linnaeus, Syst. Nat., edit. 12, p. 1276 (1767). Madrepora acropora, Esper, Forts. Pflanz. i. p. 21, pl. xxxviii. (1797). ' Heliastrcea acropora, Milne-Edwards & Haime, Cor. n. p. 47/ (1857). There are two specimens, both incrusting masses, which correspond closely to the above descriptions. The edges of the calices are free for about 1 m m . in height, while the calices are about 2 m m . deep to the top of the columella and in diameter vary up to 5 m m . The costae and septa are as described by Milne- Edwards and Haime, but the smaller costae are not usually present, and the septa which reach the columella-generally 9-12-have commonly a very distinct paliform lobe. Increase is usually by intercalicular gemmation, but in three calices of the larger specimen-10 by 6 cm.-fissiparity is occurring. There are two specimens, the first as described above, but the second differing in having rather smaller calices, more delicate septa, and less distinct pali. Rotuma; outer reef. The appearance represented by Esper in the lower right calice of fig. 2 is due to a worm boring in the columella. It commonly occurs in many corals, and ultimately results in killing the polyp into which it grows. 2. ORBICELLA ORION Dana. Orbicella orion, Dana, Zooph. p. 720, pl. xiii. fig. 14 (1848). A single lobe from the surface of a colony, which agrees closely with Dana's figures and descriptions so far as they go. The calices are more or less rounded, with distinct free edges, very little raised. There are three complete cycles of septa and a few septa of a fourth cycle are often distinguishable. Of these the primary septa are usually markedly larger and broader than the rest and have well-developed, blunt paliform lobes, which may be simulated by two or three septa of the second cycle. The |
