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The Atoll of Funafuti, Ellice group : its zoology, botany, ethnology and general structure based on collections made by Charles Hedley of the Australian Museum, Sydney, N.S.W.

[XV.] — The Madreporaria

page 349

The Madreporaria.

Mr. C. Hedley furnishes the following note:—

"For one who has surveyed the wealth of life as developed on the great coral reefs of Queensland, New Guinea, or New Caledonia, the chief impression of the coral reef of Funafuti is its poverty. In a single tide one could collect more genera and species on any of the former reefs than an industrious search of several weeks would yield from the latter. Neither is the poverty of species compensated for by an abundance of individuals.

"At the first glance over the windward reef flat, no living corals would probably be seen, but an exploration of the deep cracks and pools near the outer edge would usually reveal a few Astrœa, Porites, and others, sheltered from the blows of the surf.

"A better field for observation is provided by the small reefs which stud the lagoon. Two or three of these, just in front of the village, and from a quarter to half a mile from the shore, yielded much of the material now dealt with.

"On approaching a coral reef the first glimpse a naturalist usually has of his quest are the great hemispherical masses of some Astrean coral, dimly seen through the shoaling water, studding the sea floor. If the boat passes a submarine ledge, from its face are sure to project the large basin or bracket-shaped corallia of Montipora, sometimes in clusters like a group of huge sea mushrooms. Jumping overboard in shallow water he is likely to step on a flat tabular mass of pale purple, whose corallites are too small to be distinguished in the water. Applying hammer and chisel, he will find that at his first venture he has struck the hardest, toughest, and most unbreakable thing on the whole reef, a Porites block. From the Madrepora bush beside it his difficulty, on the contrary, is to convey his samples ashore intact. The stout limbs of red, yellow, or green Pocillopora or Stylophora snap easily; while a skull-shaped mass of Astrœa will split along the grain. A fragile little coral is the Pocillopora cæspitosa, which grows in dainty little pink tufts here and there among the stones. Fungidœ were very uncommon on Funafuti; I only picked up one alive and saw a few others dead on the western side of the atoll.

page 350

Where the soft Alcyonaria luxuriate, hard corals do not occur: the latter are perhaps smothered by their rivals.

"Dead corals thrown up on the outer beach suggested a distinct deep-water fauna that was beyond my reach. One of these is Mussa. Another much battered species of which I preserved no examples was frequently seen on the outer beach of both Funafuti and Nukulailai, I suppose to be a Tridacophyllia.

"Noticeable for their absence were the genera Galaxea, Turbinaria, Merulina and Dendrophyllia.

"The usual method of collecting was to anchor a boat or canoe on a reef, wade round in water from knee to waist deep and break off with a hammer and chisel any attractive specimens. Size and colour, the least stable of characters, chiefly guided me in such selection. With many genera a specialist in his study separates with difficulty the species by microscopic characters. When a non-specialist in the field views specimens through several feet of water, it is obvious that he must often confound together distinct species, and therefore fail to collect what he ought to take. Mr. Whitelegge has so frequently recognised two species in material that had been chosen as illustrating one, that I am not now as confident of the completeness of the collection as I was on my departure from Funafuti."

The Madreporarian corals obtained by Mr C. Hedley at Funafuti consist of one hundred and seventy specimens, referred to forty-seven species, and include representatives of nineteen genera.

The larger portion of the collection comprises the usual forms common throughout the coral regions; there are, however, a few rare or little known species not hitherto recorded from the Pacific, and also two species and one variety apparently new to science.

In the following pages, a few of the rarer forms have been described at some length, and in many cases, when dealing with the surface echinulations, I have given micrometric measurements of the average distance apart at the apex. It appears to me that the echinulations, if carefully measured in each species, would afford a fairly constant specific character which has hitherto been neglected.

The measurements given herein have been taken from the younger portions of the corallum. The echinulæ are generally a little compressed, at least at the base, and the micrometre lines have been brought parallel with the compression, but the measurements have been taken from the apices.

Of course there is a considerable amount of variation in the distance apart at the apex, owing to the bending of the echinulæ, page 351or to secondary spinular growths at the summits, but the average distances, when numerous measurements are taken, prove to be pretty constant and equally as reliable in corals as in other organisms determined by micrometric measurements.

The species described as new are Madrepora spinulifera and M. impressa. The former is referable to the subgenus Odontocya-thus and the latter to the subgenus Isopora.