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emerald green. A very satisfactory photographic picture of this 

 coral, in its living and fully extended state, was obtained, and is 

 herewith submitted. It is worthy of note that the organ pipe 

 coral belongs to a separate order, as compared with the ordinary 

 reef -forming corals. In the corals last named, the tentacles are 

 invariably a multiple of six, and are simple in structure, while in 

 the organ pipe coral, and all allies of it, there are always eight 

 tentacles only, which are feathered or pinnately branched. This 

 peculiarity of structure is well shown in the jihotograph exhibited. 

 One other coral, that is not unfrequently obtained in the 

 neighbourhood of Thursday Island, invites brief notice. This is 

 the blue coral, Heliopora cerulea, remarkable for the circum- 

 stance that its interior substance, when broken through, is 

 coloured a deep indigo blue. The true affinity of the coral was, 

 to within a recent date, a matter of conjecture, and even up to 

 the present time I have not been able to discover that the polyps 

 have been observed in their expanded state. Professor H. N. 

 Moseley obtained the species in connection with the Challenger 

 expedition, and determined, from an investigation of preserved 

 and retracted examples, that the organism was i*eferable to the 

 same order as the organ pipe coral, Tulipora, it possessing in a 

 similar manner eight tentacles, upon which there were evidences 

 of short, stout, lateral tubercles. This species was obtained by 

 myself last year, in the neighbourhood of AVarrior Island, in 

 Torres Straits ; but, though preserved in constantly-changed sea- 

 water, and carefully watched for many da^s, the polyps i*efused 

 to expand. Dui'ing my recent visit to Torres Straits, I was 

 accorded a passage to Thursday Island in H.M.S. '" Eambler," 

 and stopped for some days on the way in the vicinity of Adolphus 

 Island, near the scene of the terrible catastrophe that befel the 

 " Quetta." This ground the "Eambler" had been deputed to 

 survey, and the opportunity was consequently afforded me of 

 exploring the neighbouring coral reefs. On one of these, near 

 the Mid-brother Rock, I again obtained specimens of the blue 

 coral, Heliopora, and its investigation on this occasion pi'oduced 

 some totally unexpected results. The surface of the corallum in 



