CALCULUS Tiburtinus, a sort of figured stone, formed in great plenty about the cataracts of the Anio, and other rivers in Italy; of a white colour, and in shape oblong, round, or echinated. They are a species of the stria lapidea, or stalatites, and generated like them; and so like sugar plums, that it is a common jest at Rome to deceive the unexperienced by serving them up as desserts.