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Allan's magnificent collection by shipwreck, unfortunately prevents its being known to what genera these corals belonged; but from the numbers experimented on, it is certain that all the more conspicuous kinds must have been included. Dr. Allan informs me, in a letter, that he believes it was a Madrepora, which grew most vigorously.

The corals, also, on the margin of Keeling Island occurred in zones; thus the Porites and Millepora complanata grow to a large size only where they are washed by a heavy sea, and are killed by a short exposure to the air; whereas, three species of Nullipora also live amidst the breakers, but are able to survive uncovered for a part of each tide; at greater depths, a strong Madrepora and Millepora alcicornis are the commonest kinds, the former appearing to be confined to this part, beneath the zone of massive corals, minute encrusting corallines and other organic bodies live.

The most frequent coral in the hollows on the reef is Pocillopora verrucosa, which grows in short sinuous plates, or branches, and when alive is of a beautiful pale lake-red: a Madrepora, closely allied or identical with M. pocillifera, is also common.

I examined the rolled fragments cast on the beach during gales, in order further to ascertain what corals grew outside the reef. The fragments consisted of many kinds, of which the Porites already mentioned and a Madrepora, apparently the M. corymbosa, were the most abundant.

It is very unusual to meet with an animal belonging to the family of Lepades in tubular holes made in the coral rocks, as is the case with the Lithonaetta N. Among the twenty kinds of tabular coral here observed, there was not one of those collected at O Tahaiti; there were three new Distichoporæ, Seriatipora, six kinds of Madrepora, two Porites, four Astrea, Pocillopora cærulea, and another kind, forming broad, yellow, leafy masses, the slime of which stings like a nettle; Cariophyllæa glabrescens Cham., and Tubipora, with red animalculæ.

There would be among the Astraeans the different species of Astraea proper, forming the close round heads, the Mussa, growing in smaller stocks, where the mouths coalesce and run into each other as in the Brain-Corals, but in which the depressions formed by the mouths are deeper, and the Caryophyllians, in which the single individuals stand out more distinctly from the stock; among Porites, the P. Astroïdes, with pits resembling those of the Astraeans in form, though smaller in size, and growing also in solid heads, though these masses are covered with club-shaped protrusions, instead of presenting a smooth, even surface like the Astraeans, and the P. Clavaria, in which the stocks are divided in short, stumpy branches, with club-shaped ends, instead of growing in close, compact heads; among the Maeandrinas we should have the round heads we know as Brain-Corals, with their wavy lines over the surface, and the Manacina, differing again from the preceding by certain details of structure; among the Madrepores we should have the Madrepora prolifera, with its small, short branches, broken up by very frequent ramifications, the M. cervicornis, with longer and stouter branches and less frequent ramifications, and the cup-like M. palmata, resembling an open sponge in form.

Of tabular corals already known, there remain to be mentioned, Pavonia boletiformis, Madrepora prolifera abrotanoides, corymbosa, plantaginea, and pocillifera.

Millepora alcicornis lives in from 0 to 12 fathoms, and the genera Madrepora and Seriatopora from 0 to 20 fathoms. Mr. SERTULARIA, 40, Cape Horn 66. CELLARIA, 40, Cape Horn 66. CELLARIA, A minute scarlet encrusting species, found living, 190, Keeling Atoll, 12. CELLARIA, An allied, small stony sub-generic form, 48, St Cruz Riv. 50.

If we compare the external margin of the reef at Keeling atoll with that on the leeward side of Mauritius, which are very differently circumstanced, we shall find a corresponding difference in the appearance of the corals. At the latter place, the genus Madrepora is preponderant over every other kind, and beneath the zone of massive corals there are large beds of Seriatopora.

They rose abruptly from a smooth surface, strewed with worn fragments of coral. They consisted in their lower part of hard calcareous sandstone, and in their upper of great blocks of several species of Astraea and Madrepora, loosely aggregated; they were divided into irregular beds, dipping seaward, in one hillock at an angle of 8 deg., and in the other at 18 deg.