in natural history, a genus of fossils of the order of the selenite; consisting of ten planes, each so nearly equal to that opposite to it as very much to approach to a decahedral parallelopiped, though never truly or regularly so.

Of this genus there are only five known species:

1. A thin, fine, pellucid, and slender streaked one, with transverse striae, found in considerable quantities in the strata of clay in most parts of England, particularly near Hedgington in Oxfordshire.

2. A thin, dull-looking opake, and slender streaked one, more scarce than the former, and found principally in Leicestershire and Staffordshire.

3. A thin fine streaked one, with longitudinal striae, found in the clay-pits at Richmond, and generally lying at great depths. This has often on its top and bottom a very elegant smaller rhomboide, described by four regular lines.

4. A rough kind, with thick transverse striae, and a scabrous surface, very common in Leicestershire and Yorkshire.

And, 5. a very short kind, with thick plates, common in the clay-pits of Northamptonshire and Yorkshire.