702 MESSES. F. CHAPMAN AND D. MAWSON ON [Nov. 1906, 



30. On the Importance of Halimeda as a Beef-forming Organism : 

 ivitli a Description of the Halimeda-Lihibsto^hs of the 

 New Hebeides. By Frederick Chapman, A.L.S., F.R.M.S. r 

 National Museum, Melbourne, and Douglas Mawson, B.E. r 

 B.Sc., Adelaide University. (Communicated by Prof. T. W. 

 Edgeworth David, B.A., F.B.S., F.G.S. Read May 23rd, 

 1906.) 



[Plates XLIX-LL] 



Contents. 



Page 

 I. Occurrence and Conditions of Growth of Living 



Halimeda 702 



II. Previously-recorded Occurrences of accumulated 

 Halimeda-~R,emdi\ns other than Eecent : — frora tbe 

 Solomon Islands, Christmas Island, Funafuti, 



Fiji, Niue, and the Tonga Islands 703 



III. Description of the Halimeda -Limestones of the New 



Hebrides 706 



IV. Concluding Observations 709 



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, con- 

 venient 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. 1 



With regard to the habitat of .Halimeda in the Laccadives, the 

 following interesting note on H. oj)untia, Lamx. forma typica, by 

 Mr. J. Stanley Gardiner, has been published in a paper by Miss E. S. 

 Barton (Mrs. Gepp) 2 : — 



' Hare 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 ruodei-ately-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 Halimedais found 

 in the outer slope of the atoll, from a foot or so below sea-level down 

 to about 45 fathoms. 3 



1 ' Three Cruises of the LT.S. Coast & Geodetic-Survey Steamer Blake '' 

 vol. i (1888) p. 82 (Bull. Mus. Comp. Zool. vol. xiv). 



2 Journ. Linn. Soc. Lond. (Botany) vol. xxxv (1903) p. 476. 



3 ' The Atoll of Funafuti ' London, 1904, p. 158. 



