CORNU ammonis, 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; some of them rounded, others greatly compressed, and lodged in different strata of stones and clays; some again are smooth, and others ridged in different manners, their striæ and ridges being either straight, irregularly crooked, or undulated.
CORNU cerui. See HARTSHORN.