in natural history, the name of a genus of fossils, of the class of selenite. The word is derived from the Greek "σέλενη thick, σέλε- ten, and πούς a rhombus," and expresses a thick rhom- bohedral body composed of ten planes. The charac- ters of this genus are, that the selenite of it consist of ten planes; but as the top and bottom in the leptoce- rhombes, or most common kind of the selenite, are broader and larger planes than any of the rest, the great thickness of this genus, on the contrary, makes its four longer planes in all the bodies of it, meeting in an obtuse angle from its sides, its largest planes. There are four species of it.