in Natural History, fossil shells, called also serpent-stones or snake-stones. They are found of all sizes, from the breadth of a sixpence to more than two feet in diameter, and a few even larger; some of them rounded, others greatly compressed, and lodged in different strata of stones and clays; some again are smooth, and others variously ridged, their striae and ridges being either straight, irregularly-crooked, or undulated.