CONTENTS Introduction..................................................................................................... 2 Material, methods, acknowledgements .................................................................... 2 Mesogastropoda, Viviparacea............................................................................... 4 Discussion..................................................................................................... 5 Littorinacea...................................................................................................... 8 Discussion..................................................................................................... 13 Rissoacea......................................................................................................... 20 Discussion..................................................................................................... 25 Cerithiacea....................................................................................................... 31 Discussion..................................................................................................... 44 Architectonicacea and Epitoniacea.......................................................................... 62 Discussion..................................................................................................... 63 Strombacea...................................................................................................... 65 Discussion..................................................................................................... 68 Calyptraeacea and Hipponicacea............................................................................ 72 Discussion..................................................................................................... 74 Lamellariacea................................................................................................... 78 Discussion..................................................................................................... 79 Cypraeacea...................................................................................................... 82 Discussion..................................................................................................... 86 Naticacea......................................................................................................... 92 Discussion..................................................................................................... 94 Tonnacea......................................................................................................... 96 Discussion..................................................................................................... 103