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I. Occurrence and Conditions of Growth of Living Halimeda The importance of Halimeda as a reef-forming agent has, until of late years, been greatly overlooked. Many of the earlier records of the occurrence of calcareous seaweeds on coral-reefs were alluded to in a comprehensive manner, as Nullipores and Lithothamnion ; and, although Halimeda was not mentioned, the above terms, convenient but often vague, undoubtedly included growths of that genus. Prof. A. Agassiz has already recorded the fact that ‘immense masses of Nullipores ( Udotea and Halimeda ) . . . grow on the shallowest flats’ of the Florida reefs. With regard to the habitat of Halimeda in the Laccadives, the following interesting note on H. opuntia , Lamx. forma typica , by Mr. J. Stanley Gardiner, has been published in a paper by Miss E. S. Barton (Mrs. Gepp):— ‘Rare everywhere on the Minikoi reef; but small masses may be found by searching under stones or in protected situations of the inner part of the reef, near the beach or boulder-zone. In lagoon, not found in currents, but very luxuriant in moderately-still water where it can find any stones to fix itself upon.’ From the dredging operations of Messrs. David, Halligan, & Finckh around the atoll of Funafuti we learn that Halimeda is found in the outer slope of the atoll, from a foot or so below sea-level down to about 45 fathoms. In the dredgings across the lagoon at Funafuti the variety macropus occurred in all the samples, excepting No. 1 (half a mile |
