Grap"to*lite (?), n. [NL, Graptolithus, from Gr. &?; is engraved, written (gra`fein to write) + &?; stone.] (Paleon.) One of numerous species of slender and delicate fossils, of the genus Graptolites and allied genera, found in the Silurian rocks. They belong to an extinct group (Graptolithina) supposed to be hydroids.