Page:Proceedings of the Royal Society of London Vol 1.djvu/253

Rh the decay of galena, which he suspects to be itself a secondary production, arising from the metallization of white carbonate of lead by hepatic gas. This, our author says, appears evident in a specimen which he means to send to Mr. Greville. In one part of this specimen there is a cluster of large crystals; one of which, upon being broken, was found to be converted into minium, to a considerable thickness, while its centre was still galena.

Mr. Smithson does not say where this native minium was found; but his letter is dated from Cassell in Hesse.

The shells here described were discovered in a small island called Battoo, after a violent earthquake that occurred in the year 1797. Upon the receding of the inundation caused by the earthquake, they were seen protruding from a bank of slightly-indurated mud, in a small sheltered bay, surrounded by coral reefs. They were procured by means of a servant sent by Mr. Grilliths for that purpose, who was very expert in diving, and who stated that he found these shells sticking out of the mud to the extent of ten inches, or even more, and being from one to three fathoms under water. They were in considerable number, standing in diﬂ’erent directions, and separate from each other. Mr. Griffiths was informed that the shells were ﬁlled with a soft gelatinous ﬂesh, and that the animal threw out tentacula, resembling small Actiniw, from the two apertures at the apex. They were easily extracted from their bed, but were all mu- tilated more or less : this, the author thinks, was occasioned by the earthquake.

The longest of these shells that came into the possession of Mr. Grifﬁths was ﬁve feet four inches in length. The circumference at the base was nine inches, tapering upwards to two inches and a half. But others were of very different dimensions. The large end of the shell is completely closed, and has a rounded appearance: at this part it is very thin. The small end, or apex, is very brittle, and is divided by a longitudinal septum, which extends downwards eight or ten inches, into two distinct tubes, from whence protrude the tentacula already mentioned. The substance of the shell has a rediated appearance, and having an outer crust of a pure white colour, and an inside enamel of a yellow tinge. The external surface is often interrupted by a sudden increase of thickness, which probably indicates the different growths of the shells; but these interruptions are merely on the outside shell, and do not extend into the radiated substance. The thickness of these shells varies very much; so also does their shape, some being nearly straight, others crooked and contorted. Their internal surface is generally smooth, but is sometimes