The numbers of leaflets and structure of the osphradium of 20 species of three subfamilies of Naticidae, viz. Naticinae, Polinicinae and Sininae, were examined in relation to shell form and size. The numbers of leaflets in the Polinicinae is consistently small (50-80) throughout a varied range of sizes of animal (10-60 mm in shell length). All of the Polinicinae under examination except Lunatia are hemispherical in shell shape and have structurally complicated osphradium. The Naticinae are spherical in shell shape and have an osphradium of simpler structure with numbers of leaflets seemingly increasing with shell size. In Cryptonatica wakkanaiensis the numbers of the leaflet are most numerous attaining up to 170. Lunatia has the shell of spherical form and possesses the simple osphradium with about 50 leaflets. This may mean Lunatia stands a transitional situation between the Naticinae and the Polinicinae. Sinum javanicum has a depressed shell and complicated structure with 50 leaflets. Complicated osphradium is consistently found in species which bury deep in the substratum, while simpler one is common among species which either remain shallowly buried or creep on the sand. It is thus suggested that the structural complexity of this organ within the Naticidae is related to the mode of life, particularly degree or depth of burrowing into the soft substratum.
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