Vol. 62.] HALIMEDA AS A REEF-FORMIXG ORGANISM. 703 



In the dredgings across the lagoon at Funafuti the variety macropus 

 occurred in all the samples, excepting Xo. 1 (half a mile from the 

 Mission Church), 10 fathoms, where the genus was represented by 

 the type-form. 1 



An interesting note on the rate of growth of Halimeda is contri- 

 buted by Mr. Finckh. 2 A board used as a support for corals in 

 ascertaining their rate of growth had holes bored through it to 

 increase its buoyancy, and through one of these holes a small branch 

 of Halimeda was found protruding. After six weeks the Halimeda 

 had formed a cluster 55 millimetres high and 80 millimetres in 

 diameter. 3 When dried, this growth represented 14*38 grammes of 

 calcareous matter. 



In the ISTew Hebrides, Halimeda- joints are a conspicuous feature of 

 the recent calm-water beach-deposits, in positions removed from 

 volcanic interference, and especially where volcanic products are 

 absent. The beach-sands in Vila Harbour are notable examples, 

 Halimeda contributing often half of the bulk. The sands from 

 exposed ocean-beaches, where observed, appear to be nearly free 

 from remains of algae. 



II. Previottslt-eecokded Occurrences oe accumulated 

 Halimeda-'Rh'mai^s other than Eecent. 



Solomon Islands. 



A true Halimeda-limestone appears to have been recorded for the 

 first time by Dr. H. B. Guppy. In his description of the calcareous 

 rocks of the Solomon Islands, that author remarks 4 that 



* in the composition of such rocks, corals take only a secondary part. In some 

 instances, the rock is composed for the most part of calcareous alga? ; in others, 

 again, molluscan shells are conspicuous.' 



In a footnote to the foregoing paragraph, Dr. Guppy makes the 

 following interesting observation : — 



' A specimen I obtained at Santa Anna was entirely composed of the joints 

 of '■' Halimeda opuntia " which commonly occur in the soundings off coral-reefs.' 



The Halimeda-limestone, referred to above, evidently occurred in 

 the upraised reef of the elevated island of Santa Anna, described by 

 Dr. Guppy in the before-mentioned work at p. 70. 



Christmas Island (Indian Ocean). 



In the description of the older Tertiary limestones and upraised 

 reefs of Christmas Island, by Prof. T. Rupert Jones and one of the 

 present writers, 5 reference is made to the occurrence of rocks con- 



1 Journ. Linn. Soc. Lond. (Botany) vol. xxxiv (1900) p. 481. 



2 ' The Atoll of Funafuti ' 1904, p. 146. 3 Ibid. p. 180. 



4 'The Solomon Islands: their Geology, General Features, & Suitability for 

 Colonization ' London, 1887, p. 74. 



5 'A Monograph of Christmas Island' London, 1900. See especially 

 pp. 250, 257-64, and also p. 289. 



