The coral was of various kinds, but a beautiful specimen of Porites clavaria was obtained by one of our people who dived for it in two fathoms' water, within a few yards of the shore.

Upon it we found several varieties of coral, particularly Explanaria mesenterina, Lam.; Caryophylla fastigata, Lam.; and Porites subdigitata, Lam.: the only shell that we observed upon the reef was a Delphinula laciniata, Lam.

Porites subdigitata, Lam. Hist.

Porites clavaria, Lam.

Madrepora porites, Gmel.

These are the Mandrinas, or the so-called Brain-Corals, and the Porites.

The Porites resemble the Astraeans, but the pits are smaller, with fewer partitions and fewer tentacles, and their whole substance is more porous.

. Astraeans, Porites, Maeandrinas, and Madrepores were represented by exactly the same Species seventy thousand years ago as they are now.

The Porites have twelve tentacles only, never more and never less; and in them the whole solid frame presents a complicated system of connected beams.

The Madrepores have also twelve tentacles, but they have a more definite character than those of the Porites, on account of their regular alternation in six smaller and six larger ones; in these also the transverse floors are perfect, but exceedingly delicate.

Porites: twelve tentacles, not alternating in size; system of connected beams.

Eocene, / Cretaceous, \ Porites Jurassic, } and Triassic, } Astraeans.

Such a community increases till its individuals are numbered by millions, and I have myself counted no less than fourteen millions of individuals in a coral mass of Porites measuring not more than twelve feet in diameter.