ABSTRACT
Although the morphology of the radulae of molluscs have been extensively studied, but little is known of their composition ; it is generally stated to be of a chitinous nature. There are two exceptions to this statement: Troschel (1856) and Sollas (1907). The former reported that calcium, phosphorus and iron were present in the enamel which covered the teeth and that the organ contained both organic and inorganic constituents. Sollas found that the radulae of the Docoglossa contained up to 27 per cent, of ash of which silica was the chief constituent: from microdeterminations of specific gravity she suggested that the silica was in the form of a hydrate or opal ; the marginal teeth were found to contain no silica. She recognised the presence of iron and stated that “the ash contained (in addition to silica) a noticeable quantity of calcium, iron, magnesium and phosphoric acid.” No other groups of molluscs were found to have siliceous teeth in their radulae, but to have chitinous teeth hardened by deposits of iron, calcium and phosphorus. The Chitonidae were somewhat exceptional, for the most important constituent of their teeth was ferric oxide.
